Caterpillarwheel tractor-scraperwheel scraper
Caterpillar 639D
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar 639D is a twin-engine elevating wheel tractor-scraper, the largest elevating scraper Caterpillar ever built. A front-mounted Cat 3408T V8 (336 kW / 450 hp) drives the tractor and wheels, while a second, rear-mounted Cat 3306T inline-six (187 kW / 250 hp) sits on the scraper unit and powers only the elevator and bowl-loading system, for roughly 522 kW (700 hp) combined at the flywheels. An eight-speed powershift transmission with a variable-capacity torque converter handles propulsion. Empty operating weight runs 55-56 tonnes (121,825-123,900 lb), with a heaped bowl capacity near 26 cubic meters (34 cu yd). Built only as a D-series machine from 1979 to 1984, it shares its tractor unit with the single-engine 633D and rides on 37.25-35 E-3 tires, with radial tires offered as an option.
No 639C came before it and no 639E followed it — the 639D was a single-generation model, a twin-engine version built onto the existing 633D tractor to out-lift Wabco's large elevating scrapers. Its launch coincided with a steep downturn in large earthmoving projects, and Caterpillar dropped it from the lineup after roughly five and a half years, with total production well under 300 units. Caterpillar's later big scrapers moved away from the twin-engine elevator format entirely, continuing instead as single-engine E-series elevating scrapers and eventually as open-bowl, twin-power machines. Most surviving 639Ds worked mining and quarry sites, heavily concentrated in Western Australia. That rarity, combined with two distinct mechanical-era engines and drivelines in one machine, makes parts sourcing and finding shops with direct 639D experience a real challenge for owners today.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar 639D specifications
Engine
| Configuration | Twin-engine layout: front engine drives the tractor/wheels, rear engine (mounted on the scraper unit) powers the elevator and bowl functions. |
| Tractor engine | Cat 3408, 4-stroke-cycle V8 diesel, 137 mm x 152 mm (5.4 in x 6.0 in) bore and stroke, 18.0 L (1,099 cu in) displacement, 8 cylinders. |
| Tractor engine gross (flywheel) power | 336 kW (450 hp) at 2,000 rpm. |
| Scraper engine | Cat 3306, 4-stroke-cycle inline-6 diesel, 121 mm x 152 mm (4.75 in x 6.0 in) bore and stroke, 10.5 L (638 cu in) displacement, 6 cylinders. |
| Scraper engine gross (flywheel) power | 187 kW (250 hp) at 2,200 rpm. |
| Combined flywheel power | 522 kW (700 hp) total from both engines. |
| Net power | Not published separately from flywheel/gross ratings on available spec sheets for this model. |
| Emissions tier | Not applicable. Mechanical diesel engines, produced 1979-1984, predate modern emissions tier regulation. |
Weights
| Operating weight, tractor unit (empty) | 31,870 kg (70,260 lb) per factory spec sheet. |
| Operating weight, scraper unit (empty) | 22,070 kg (48,660 lb) per factory spec sheet. |
| Total operating weight (empty) | 55,260-56,200 kg (121,825-123,900 lb); figure varies slightly by source/market configuration. |
| Total operating weight (loaded) | approx. 90,200 kg (198,857 lb), as listed in equipment spec databases; not confirmed on the factory sheet reviewed. |
| Shipping weight | 45,620 kg (100,570 lb) per factory spec sheet. |
| Ground pressure | Not published in available sources. |
Dimensions
| Overall length | 14.5-14.6 m (47 ft 8 in - 47 ft 9 in); minor variance between sources. |
| Overall width | 3.96 m (13 ft 0 in). |
| Overall height | 4.42-4.45 m (14 ft 6 in - 14 ft 7 in); minor variance between sources. |
| Wheelbase | 8.99 m (29 ft 6 in), per equipment spec databases; not listed on the factory sheet reviewed. |
| Ground clearance (cutting edge, cushion hitch mid-position) | 381 mm (15 in). |
| Tire size | 37.25-35, E-3 tread. Ply rating listed as 36PR on the factory Europe sheet and as 42PR in North American equipment databases; radial tires offered as an option. |
Performance
| Maximum travel speed | 48-56 km/h (30-35 mph); figure varies by source, factory sheet lists 30 mph (48.3 km/h) with eight forward speeds. |
| Transmission | Cat eight-speed semi-automatic powershift with variable-capacity torque converter, plus two special loading ranges in addition to standard 1st and 2nd gears. |
| Elevator speed | Two speeds forward: 91 m/min and 61 m/min (300 fpm and 200 fpm); one reverse speed at 61 m/min (200 fpm). |
| Maximum depth of cut | 381 mm (15 in). |
| Maximum width of cut | 3.5 m (11 ft 6 in). |
| Heaped bowl capacity | 26 m3 (34 cu yd). |
| Turning circle (curb-to-curb) | 12.4 m (40 ft 7 in). |
| Gradeability | Published only as a combined rimpull/speed/gradeability performance chart on the factory sheet; not reducible to a single percentage figure. |
Service capacities (summary)
| Fuel tank, tractor unit | 946 L (250 US gal) per factory spec sheet. |
| Fuel tank, scraper unit | 643 L (170 US gal) per factory spec sheet. |
| Fuel tank, combined | approx. 1,589 L (420 US gal) per factory sheet; some equipment databases list a combined total of 1,403 L (370.7 US gal) instead - varies by source. |
| Engine oil (crankcase), tractor engine | 45 L (12 US gal). |
| Engine oil (crankcase), scraper engine | 27 L (7.2 US gal). |
| Hydraulic system reservoir | 340 L (90 US gal). |
| Cooling system, tractor engine | 140 L (37 US gal). |
| Cooling system, scraper engine | Not published in available sources. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
639D fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Tractor engine crankcase (Cat 3408T V8, with filter) | 45 L (12 US gal) | Cat Diesel Engine Oil (Cat DEO). Multigrade diesel engine oil selected off Cat's ambient-temperature chart: roughly SAE 15W-40 or 10W-30 for temperate ranges, straight SAE 30 in sustained hot climates, SAE 10W for cold-weather starts. |
| Scraper engine crankcase (Cat 3306T inline-six, with filter) | 27 L (7.2 US gal) | Cat Diesel Engine Oil (Cat DEO), same viscosity-by-climate selection as the tractor engine. |
| Tractor cooling system | 140 L (37 US gal) | Cat Diesel Engine Antifreeze/Coolant (Cat DEAC), full-strength permanent-type ethylene-glycol coolant, mixed to the freeze-protection level needed for the region and topped up with the correct supplemental coolant additive on schedule. |
| Scraper cooling system | 76 L (20 US gal) | Cat DEAC coolant, same mix and additive treatment as the tractor engine. |
| Tractor fuel tank | 946 L (250 US gal) | No. 2-D diesel fuel meeting Cat's fuel specification (rated power quoted at 35 API gravity fuel). |
| Scraper fuel tank | 643 L (170 US gal) | Same diesel fuel specification as the tractor tank. |
| Tractor transmission (8-speed power shift, variable-capacity torque converter) | 126 L (33.5 US gal) | Cat Transmission/Drive Train Oil (Cat TDTO). Period Cat charts call for SAE 30 in warm ambient ranges and SAE 10W for cold starts. |
| Scraper transmission (4-speed planetary, torque converter, electronically synchronized to tractor) | 72 L (19 US gal) | Cat TDTO, same viscosity-by-climate selection as the tractor transmission. |
| Tractor differential (operator-controlled lock) | 136 L (36 US gal) | Cat TDTO. |
| Scraper differential (NoSPIN) | 17 L (4.5 US gal) | Cat TDTO. |
| Tractor final drives, each side (compact planetary, full-floating axle) | 24.6 L (6.5 US gal) per side | Cat TDTO. |
| Scraper final drives, each side | 26 L (7 US gal) per side | Cat TDTO. |
| Hydraulic reservoir (steering, cushion hitch, elevator, bowl and ejector circuits; single tank mounted ahead of the tractor fuel tank, serves both power units) | 340 L (90 US gal) — no separate scraper hydraulic reservoir | Cat wheel tractor-scrapers of this era commonly run Cat TDTO through shared transmission/hydraulic compartments; some fluid guides instead call for Cat HYDO in standalone hydraulic tanks. Confirm the exact spec against the 639D lubricant chart before fill — not fully verified for this tank. |
| Grease points (chassis pins, hitch, gooseneck, elevator, steering linkage) | spec only, no reservoir capacity listed | Cat Multipurpose Grease (Cat MPGM). NLGI grade 2 for normal ambient temperatures, dropping to NLGI grade 1 for sustained sub-freezing cold. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 639D maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 6,000 h |
|
Servicing the 639D beyond the schedule
Predictive Maintenance & Fluid Analysis
Run separate oil sampling programs for the 3408T tractor engine and the 3306T scraper engine — they wear on different schedules and mixing trend data hides problems. Track cushion hitch accumulator nitrogen precharge; a slow bleed shows up as a harsher ride before it becomes stress cracking. Watch elevator chain tension and sprocket wear on a fixed schedule since a jumped chain accelerates flight wear fast. Monitor charging output and connector condition on both engines' electrical systems given their age.
Corrective & Common Repairs
A rear engine that lags or hunts on throttle usually traces to the air/electric sync link between the two engines, not the 3306T itself. On the tractor's 3408T, chase persistent black smoke to the turbo or fuel system rather than treating it as normal. Hard-starting on the 3306T often comes from limited travel in the injection pump governor linkage or contaminated fuel scoring the pump. Leaking cylinder rod seals on bowl, apron, and ejector circuits, plus worn ejector wear strips, are routine open-center hydraulic wear items.
Overhaul & Rebuild Points
Any 3408T that's been through a top-end rebuild needs liner protrusion and head-bolt torque verified before it goes back to heavy pulling — incorrect protrusion is the recurring cause of head gasket failure on this engine family. Elevator chain, sprockets, and flights wear as a set; inspect and plan replacement together rather than piecemeal. Cushion hitch mounting structure needs a close look for stress cracking, with accumulator reseal on the same interval. Powershift clutch packs and torque converter condition deserve evaluation at extended hours given the loads this machine pulls.
Seasonal & Environment Servicing
Two separate crankcases and two cooling systems mean cold-weather prep doubles: switch engine oil viscosity and confirm coolant freeze protection on both the tractor and scraper power units before winter work. Most 639Ds worked abrasive mining and quarry ground, so sand and rock accelerate wear on tires and rims, bowl wear plates, and elevator wear shoes faster than dirt-only sites. Dust-heavy ground demands more frequent air cleaner service on both engines. Any unit coming out of long-term storage needs a full harness, connector, and hose inspection before returning to service.
639D common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 1P-2299 | Filter As-Fuel | Fuel system service | Check fitment → |
| 5P-9141 | Transmission Filter | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
639D fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| Engine Oil Pressure lamp (red) | Low oil pressure warning on either power unit — the 3408T V8 tractor engine or the 3306T inline-six scraper engine — triggered by a pressure switch on the main oil gallery. | Low crankcase oil level, worn oil pump, plugged oil filter, or a faulty pressure switch. | Idle down immediately, check crankcase level, and stop the engine if the lamp stays lit; inspect filter and pump before restarting. |
| Coolant Temperature lamp (red) | Engine coolant on the tractor or scraper engine has exceeded safe operating temperature. | Low coolant level, plugged radiator core or fins, slipping/failed fan drive, or a stuck thermostat. | Reduce load, idle to cool, then check coolant level, radiator core, and fan drive belt or clutch once safe to inspect. |
| Torque Converter Oil Temperature lamp | Powershift transmission torque converter oil is running above safe temperature. | Low converter/transmission oil level, restricted converter oil cooler, or prolonged lugging/stall under load. | Bring throttle back and let the converter cool in neutral; check oil level and cooler for restriction before resuming work. |
| Alternator / Charging System lamp | Charging circuit output is inadequate and the battery is discharging. | Worn or broken drive belt, failed alternator, or loose/corroded wiring connection. | Check belt tension and battery terminal condition, test alternator output, repair or replace as needed. |
| Air Cleaner Restriction indicator | Intake air filter restriction on the tractor or scraper engine has reached the service limit. | Dust-loaded primary element, plugged precleaner, or a damaged filter element. | Service or replace the air filter element and reset the restriction indicator. |
| Parking Brake lamp | Parking or secondary brake is applied, or brake system hydraulic pressure is low. | Brake lever left engaged, low brake system charge pressure, or worn brake components. | Confirm brake lever position, then check brake system pressure and fluid level. |
| Hydraulic Oil Temperature lamp | Implement hydraulic oil for the bowl, apron, elevator, and cushion hitch circuits has exceeded safe operating temperature. | Low hydraulic oil level, restricted hydraulic oil cooler, or a relief valve stuck open causing continuous high-pressure bypass. | Reduce hydraulic demand, idle to cool, then check oil level, cooler core, and relief valve operation. |
| Fuel Level Low lamp | Fuel tank level has dropped below the reserve threshold. | Normal fuel consumption approaching empty, or a faulty fuel level sender/gauge. | Refuel, and verify sender/gauge accuracy if the lamp stays on after refueling. |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
639D attachments & work tools
Bowl cutting edge
Standard bowl fitted with a fixed cutting edge sized to the 3.51 m (11.5 ft) cut width and 38 cm (15 in) max depth of cut. Center section could be built with a 5 cm (2 in) drop-center edge, or fitted with bolt-on teeth for aggressive penetration in hard or rocky soils.
Elevator loading system
Self-loading elevator with 20 flights driven by a single hydraulic motor giving two forward speeds and one reverse, around 60-90 m/min (200-300 fpm). This is the core loading mechanism for the 639D class and removes the need for a separate push-tractor to load the bowl.
Bowl ejection / tilting floor
Unique tilting-floor ejection system shared with the related 633D: the floor pivots back and up in an arc away from the fixed cutting edge to dump, with the leading floor edge acting as a strike-off blade. This replaces the conventional flat ejector-wall found on non-elevating scrapers.
Cushion hitch (drawbar)
Caterpillar oil/nitrogen cushion hitch is the standard drawbar connection between tractor and scraper unit, damping shock loads from haul roads to permit higher travel speeds and faster cycle times. No alternate rigid or push-pull tandem hitch is documented for this model.
Tires
Standard fitment is 37.25-35, 42-ply rating, E-3 tread pattern on all four wheels. Other tire sizes and ply ratings were offered to suit ground conditions, though exact alternate sizes are not documented for this series - verify with your dealer.
Operator cab / ROPS
Open ROPS structure was listed as base equipment, one of Cat's first integrated ROPS designs for this scraper family, but most production 639D units left the factory with a fully enclosed ROPS cab rather than the open frame.
Cab comfort and sound package
Factory options included air conditioning and additional sound-suppressing material in the cab, aimed at operator comfort on long haul cycles typical of scraper work.
Fenders
Bolt-on fenders were offered as a factory option for wheel and tire guarding, typical for scrapers running on public or shared haul roads.
Fast-fuel system
Quick-fill fueling system supplied by either Wiggins or Buckeye was available as a factory option to cut refueling downtime on high-utilization fleets.
Twin-engine drivetrain configuration
Base machine configuration (not a swappable attachment) pairs a front-mounted 450 hp Caterpillar 3408T V8 tractor engine with a rear-mounted 250 hp Caterpillar 3306T inline-six booster engine, driving an 8-speed powershift transmission with variable-input torque converter for elevator loading. Noted here because it defines which hydraulic and cooling capacity is available for any bowl/elevator work-tool options.
All 639D assemblies by section
Every catalogued assembly group for the Caterpillar 639D. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Basic Engine
2p6202 Camshaft Group
| 2P***02 | Camshaft Group-Single; Single Camshaft Group | 1 |
7n1292 Cylinder Block Cover Group
| 7N***92 | Cover Group-Cylinder Block; Cylinder Block Cover Group | 1 |
2p6517 Cylinder Block Cover Group
| 2P***17 | Cover Group-Cylinder Block; Cylinder Block Covers Group | 1 |
2p6530 Cylinder Head Cover Group
| 2P***30 | Cover Group-Cylinder Head; Cylinder Head Cover Group | 1 |
2p6528 Front Housing Cover Group--Timing Gear
| 2P***28 | Cover Group-Front Housing; Front Housing Cover Group | 1 |
2p6516 Valve Mechanism Cover Group
| 2P***16 | Cover Group-Valve Mechanism; Valve Mechanism Cover Group | 1 |
4n7693 Crankshaft Assembly--Field Installation
| 4N***93 | Crankshaft As | 1 |
Crankshaft Bearing Replacements
| 4S***81 | Bearing (.010 In. Undersize); Bearing (0.25 mm Undersize) | 7 |
| 4S***83 | Bearing (.020 Undersize); Bearing (.020 Undersize) | 7 |
| 4S***85 | Bearing (.030 In. Undersize); Bearing (0.76 mm Undersize) | 7 |
6n8079 Crankshaft Group
| 6N***79 | Crankshaft Group; Crankshaft Group | 1 |
2p6222 Crankshaft Group
| 2P***22 | Crankshaft Group; Crankshaft Group | 1 |
Crankshaft Service Thrust Plate--Field Installation
| 7N***43 | Thrust Plate | 1 |
7n6550 Cylinder Block Assembly
| 7N***50 | Cylinder Block As | 1 |
2p8776 Cylinder Block Assembly
| 2P***76 | Cylinder Block As | 1 |
2p6560 Cylinder Block Group
| 2P***60 | Cylinder Block Group; Cylinder Block Group | 1 |
7n8016 Cylinder Block Group
| 7N***16 | Cylinder Block Group; Cylinder Block Group | 1 |
6n8124 Cylinder Block Assembly
| 6N***24 | Cylinder Block Group | 1 |
1n3576 Cylinder Block Group
| 1N***76 | Cylinder Block Group | 1 |
9n3561 Cylinder Head Group
| 9N***61 | Cylinder Head Group; Cylinder Head Group | 1 |
8n1187 Cylinder Head Group
| 8N***87 | Cylinder Head Group | 1 |
9n2382 Cylinder Head Group
| 9N***82 | Cylinder Head Group; Cylinder Head Group | 1 |
2p7838 Damper Group
| 2P***38 | Damper Group; Damper Group | 1 |
2p7831 Fan Drive Group
| 2P***31 | Drive Group-Fan; Fan Drive Group | 1 |
2p6546 Cylinder Head Fastener Group
| 2P***46 | Fastener Group-Cylinder Head; Cylinder Head Fastener Group | 1 |
7n9536 Cylinder Head Fastener Group
| 7N***36 | Fastener Group-Cylinder Head; Cylindetr Head Fastener Group | 1 |
2p6498 Front Housing Fastener Group--Timing Gear
| 2P***98 | Fastener Group-Front Housing; Front Housing Fastener Group | 1 |
2p6206 Oil Pan Fastener Group
| 2P***06 | Fastener Group-Oil Pan; Oil Pan Fastener Group | 1 |
7s7877 Flywheel Group
| 7S***77 | Flywheel Group; Flywheel Group | 1 |
2p9559 Oil Level Gauge Group
| 2P***59 | Gauge Group-Oil Level (Dipstick) | 1 |
9l6675 Front Timing Gear Group
| 9L***75 | Gear Group-Front; Front Timing Gear Group | 1 |
2p6166 Flywheel Housing Group
| 2P***66 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
8n5014 Flywheel Housing Group
| 8N***14 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
2p9641 Front Housing Group
| 2P***41 | Housing Group-Front; Front Housing Group | 1 |
6n8326 Engine Lifting Group
| 6N***26 | Lifting Group; Lifting Eye Gp-Engine | 1 |
2p6152 Oil Pan Group
| 2P***52 | Pan Group-Oil; Oil Pan Group | 1 |
9n1291 Connecting Rod And Piston Group--6 Required
| 9N***91 | Piston & Rod Group | 1 |
6n1612 Protection Cover Group--Oil Level Gauge
| 6N***12 | Protection Group-Vandalism; Protection Cover Group--Oil Level Gauge | 1 |
7n2879 Crankshaft Pulley Group
| 7N***79 | Pulley Group-Crankshaft; Crankshaft Pulley Group | 1 |
7n3990 Fan Pulley Group
| 7N***90 | Pulley Group-Fan | 1 |
8j6273 Cylinder Block Hardware Kit--Field Installation
| 03***80 | Bolt 4.128 cm(1.625 In.) Long | 2 |
| 0S***85 | Bolt; 12.7 mm (1/2") Diameter X 38.1 mm (1 1/2") Length Generator To Engine | 2 |
| 0T***65 | Bolt--3/8" X 3 1/2"--Use As Required; Bolt 5t***56 Plate To Cover Gp 4n***72 | 3 |
2p6226 Crankshaft Seal Group
| 2P***26 | Seal Group-Crankshaft; Seal Group-Crankshaft | 1 |
2p7745 Support Group--Front
| 2P***45 | Support Group-Engine; Engine Support Group | 1 |
2p6246 Trunnion Group
| 2P***46 | Trunnion Group-Engine | 1 |
7n9589 Trunnion Group
| 7N***89 | Trunnion Group-Engine | 1 |
7n8026 Valve Mechanism Group
| 7N***26 | Valve Mechanism Group; Valve Mechanism Group | 1 |
2p6526 Valve Mechanism Group
| 2P***26 | Valve-Mechanism Group; Valve Mechanism Group | 1 |
Braking System
3g3806 Brake Control Group--Top View--Part 1 Of 3
| 3G***06 | Brake Control Group | 1 |
3g3806 Brake Control Group--Side View--Part 3 Of 3
| 3G***06 | Brake Control Group | 1 |
3g3806 Brake Control Group--Side View--Part 2 Of 3
| 3G***06 | Brake Control Group | 1 |
9d2010 Service Brake Group
| 9D***10 | Brake Group | 1 |
4n8272 Brake Oil Cooler Group
| 4N***72 | Cooler Group-Brake Oil; Brake Oil Cooler Group | 1 |
9j5337 Rotochamber Assembly
| 9J***37 | Rotochamber As | 1 |
6d6355 Brake Shield Group
| 6D***55 | Shield Group-Brake | 1 |
5d5754 Slack Adjuster Assembly--L.H.
| 5D***54 | Slack Adjuster Assembly | 1 |
9d390 Slack Adjuster Group--R.H.
| 9D***00 | Slack Adjuster Group-Lh | 1 |
Cooling System
6n3447 Water Aftercooler Group
| 6N***47 | Aftercooler Group-Water | 1 |
2p7738 Engine Oil Cooler Group
| 2P***38 | Cooler Group-Engine Oil; Engine Oil Cooler Group | 1 |
4n8268 Transmission Oil Cooler Group
| 4N***68 | Cooler Group-Transmission Oil; Transmission Oil Cooler Group | 1 |
2s6096 Protection Cover Group--Radiator Cap
| 2S***96 | Cover Group-Protection; Protection Cover Group-- Radiator Cap | 1 |
1n3599 Protection Cover Group--Radiator Cap
| 1N***99 | Cover Group-Protection; Radiator Cap Protection Cover Group | 1 |
4n3586 Jacket Water Heater Group--Type 2
| 4N***86 | Heater Group-Jacket Water; (120v) | 1 |
4n3586 Jacket Water Heater Group--Type 1
| 4N***86 | Heater Group-Jacket Water; (120v) | 1 |
4n8271 Housing And Regulator Group
| 4N***71 | Housing & Regulator Group; Housing & Regulator Group | 1 |
4n8270 Aftercooler Water Lines Group
| 4N***70 | Lines Group-Aftercooler Water | 1 |
9n1246 Water Lines Group
| 9N***46 | Lines Group-Water; Water Lines Group | 1 |
7n6587 Water Lines Group
| 7N***87 | Lines Group-Water; Water Lines Group | 1 |
7n5909 Water Pump Group
| 7N***09 | Pump Group-Water; Water Pump Group | 1 |
2p662 Water Pump Group
| 2P***62 | Pump Group-Water; Water Pump Group | 1 |
4n8263 Radiator Group--Side View--Part 2 Of 2
| 4N***63 | Radiator Group; Radiator Group | 1 |
4n8263 Radiator Group--End View-Part 1 Of 2
| 4N***63 | Radiator Group; Radiator Group | 1 |
4n8263 Radiator Group--End View--Part 1 Of 2
| 4N***63 | Radiator Group; Radiator Group | 1 |
Engine Arrangement
7n1547 Engine Arrangement--Part 1 Of 2
| 2P***52 | Pan Group-Oil; Oil Pan Group | 1 |
| 2P***66 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
| 2P***02 | Camshaft Group-Single; Single Camshaft Group | 1 |
7n1547 Engine Arrangement--Part 2 Of 2
| 1P***99 | Filter As-Fuel; (Advanced Efficiency)(Secondary) | 1 |
| 1P***44 | Breather Group | 1 |
| 2P***62 | Pump Group-Water; Water Pump Group | 1 |
Frame And Bowl
9j1071 End Bit And Cutting Edge Group
| 2J***07 | Nut-Full; (1-8 X38.1 Thd) | 33 |
| 4F***42 | Bolt 7.62 cm(3 In.) Long | 33 |
| 4J***65 | Bit (Routing) | 2 |
3g3227 Bowl Group--Part 1 Of 2
| 3G***27 | Bowl Group | 1 |
3g3227 Bowl Group--Part 2 Of 2
| 3G***27 | Bowl Group | 1 |
1u4379 Shipping Bracket Group
| 1U***79 | Bracket Group | 1 |
3g3624 Floor Carriage Group
| 3G***24 | Carriage Group-Floor | 1 |
3g2514 Chain And Flight Group
| 3G***14 | Chain & Flight Group | 1 |
3g6093 Floor Cleaner Group
| 3G***93 | Cleaner Group-Floor | 1 |
8j1599 Chain Adjuster Cylinder Group--(Changes 1 & 2)--76 Mm
| 8J***99 | Cylinder Group | 1 |
1u3365 Chain Adjuster Cylinder Group--(Change 0)--76 Mm (3.00 In.)
| 1U***65 | Cylinder Group-Chain Adjuster | 1 |
3g2511 Elevator Drive Group
| 3G***11 | Drive Group-Elevator | 1 |
3g3587 Floor Group
| 3G***87 | Floor Group | 1 |
1u1484 Draft Frame Group
| 1U***84 | Frame Group-Draft | 1 |
3g7804 Elevator Frame Group--Part 2 Of 2
| 3G***04 | Frame Group-Elevator | 1 |
3g7804 Elevator Frame Group--Part 1 Of 2
| 3G***04 | Frame Group-Elevator | 1 |
7g1383 Planetary Reduction Gear Group--Part 1 Of 2
| 7G***83 | Gear Group-Reduction | 1 |
7g1383 Planetary Reduction Gear Group--Part 2 Of 2
| 7G***83 | Gear Group-Reduction | 1 |
9d8870 Axle Shaft Guard Group
| 9D***70 | Guard Group-Axle | 1 |
9j1067 Elevator Guard Group
| 9J***67 | Guard Group-Elevator | 1 |
2g9025 Hood Group
| 2G***25 | Hood Group | 1 |
9j1035 Idler Group
| 9J***35 | Idler Group | 1 |
1u982 Positioner And Kickout Group
| 1U***82 | Kickout & Positioner Group | 1 |
3g3394 Link Group
| 3G***94 | Link Group | 1 |
1u817 Elevator Linkage Group
| 1U***17 | Linkage Group-Elevator | 1 |
3g7822 Overflow Guard Group
| 3G***22 | Overflow Guard Group | 1 |
9d5575 Platform Group
| 9D***75 | Platform Group | 1 |
6g2280 Sound Suppression Group--Vehicle Parts
| 6G***80 | Sound Suppression Group | 1 |
6g1390 Radiator Guard And Support Group
| 6G***90 | Support & Radiator Guard Group | 1 |
5j9256 Support Group
| 5J***56 | Support Group | 1 |
2g7740 Engine And Transmission Support Group
| 2G***40 | Support Group-Engine & Tmsn | 1 |
9j1070 Scraper Tooth Group
| 9J***70 | Tooth Group-Scraper | 1 |
6g1420 Safety Tread Group
| 6G***20 | Tread Group-Safety | 1 |
Fuel System And Governor
1n4440 Fuel Heater Changeover Group--Field Installation
| 1N***40 | Changeover Group | 1 |
6n4654 Fuel Ratio Control Group
| 6N***54 | Control Group-Fuel Ratio | 1 |
2g9270 Governor Control Group--Part 1 Of 2
| 2G***70 | Control Group-Governor | 1 |
2g9270 Governor Control Group--Part 2 Of 2
| 2G***70 | Control Group-Governor | 1 |
4n4510 Governor Cover Group
| 4N***10 | Cover Group-Governor; Governor Cover Group | 1 |
9d630 Dust Cover Group
| 9D***30 | Cover-Dust | 1 |
8n601 Electric Shut-Off Group--24 Volt
| 8N***01 | Electric Shut-Off Group | 1 |
6g3255 Fast Fill Fuel Adapter Group--Type 2
| 6G***55 | Fast Fill Fuel Adapter Group | 1 |
6g3255 Fast Fill Fuel Adapter Group--Type 1
| 6G***55 | Fast Fill Fuel Adapter Group | 1 |
4n9586 Exhaust Manifold Fastener Group
| 4N***86 | Fastener Group-Exhaust Manifold; Exhaust Manifold Fastener Group | 1 |
1p2299 Fuel Filter Assembly
| 1P***99 | Filter As-Fuel; (Advanced Efficiency)(Secondary) | 1 |
6n5359 Governor And Fuel Injection Pump Group--Part 4 Of 4
| 6N***59 | Gov & Fuel Inj Pump Group | 1 |
6n2981 Governor And Fuel Injection Pump Group--Part 1 Of 2
| 6N***81 | Gov & Fuel Inj Pump Group | 1 |
6n5359 Governor And Fuel Injection Pump Group--Part 2 Of 4
| 6N***59 | Gov & Fuel Inj Pump Group | 1 |
6n5359 Governor And Fuel Injection Pump Group--Part 1 Of 4
| 6N***59 | Gov & Fuel Inj Pump Group | 1 |
6n3072 Governor And Fuel Injection Pump Group
| 6N***72 | Gov & Fuel Inj Pump Group; Governor & Fuel Injection Pump Group | 1 |
6n5359 Governor And Fuel Injection Pump Group--Part 3 Of 4
| 6N***59 | Gov & Fuel Inj Pump Group | 1 |
6n2981 Governor And Fuel Injection Pump Group--Part 2 Of 2
| 6N***81 | Gov & Fuel Inj Pump Group | 1 |
7n3616 Drain Lines Group
| 7N***16 | Lines Group-Drain; Drain Lines Group | 1 |
6g1640 Fuel Lines Group--Part 1 Of 2
| 6G***40 | Lines Group-Fuel | 1 |
6g1640 Fuel Lines Group--Part 2 Of 2
| 6G***40 | Lines Group-Fuel | 1 |
8n9617 Fuel Injection Lines Group
| 8N***17 | Lines Group-Fuel Injection | 1 |
7n5588 Fuel Injection Lines Group
| 7N***88 | Lines Group-Fuel Injection; Fuel Injection Lines Group | 1 |
2p6574 Exhaust Manifold Group
| 2P***74 | Manifold Group-Exhaust; Exhaust Manifold Group | 1 |
4n4314 Fuel Priming Pump Group
| 4N***14 | Pump Group-Fuel Priming; Fuel Priming Pump Group | 1 |
6d4397 Rotochamber Group
| 6D***97 | Rotochamber Group | 1 |
6n581 Torque Control Group
| 6N***81 | Torque Control Group | 1 |
2g9000 Fast Fill Adapter Group
| 2G***00 | Valve As-Tank | 1 |
Gauges And Accessories
2g9220 Warning And Gauge Group--Rear View--Part 2 Of 2
| 2G***20 | Gauge & Warning Group | 1 |
2g9220 Warning And Gauge Group--Side View--Part 1 Of 2
| 2G***20 | Gauge & Warning Group | 1 |
Hydraulic System
9j8675 Accumulator Group
| 9J***75 | Accumulator Group | 1 |
3g9677 Bowl Lift Cylinder Group--(Change 0)--2 Required--184.2 Mm (7.25 In.) Bore X 635 Mm (25 In.) Stroke
| 3G***77 | Cylinder Group | 1 |
3g2949 Ejector Cylinder Group--(Change 2)--2 Required--114.3 Mm (4.50 In.) Bore X 1308 Mm (51.50 In.) Stroke
| 3G***49 | Cylinder Group-Ejector | 1 |
6d8490 Power Pack Lift Group
| 6D***90 | Lifting Group-Power Pack | 1 |
3g7157 Draft Frame Lines Group--Part 2 Of 4
| 3G***57 | Lines Group-Draft Frame | 1 |
3g7157 Draft Frame Lines Group--Part 1 Of 4
| 3G***57 | Lines Group-Draft Frame | 1 |
3g7157 Draft Frame Lines Group--Part 3 Of 4
| 3G***57 | Lines Group-Draft Frame | 1 |
3g7157 Draft Frame Lines Group--Part 4 Of 4
| 3G***57 | Lines Group-Draft Frame | 1 |
3g3794 Ejector Lines Group--Rear View - Part 2 Of 2
| 3G***94 | Lines Group-Ejector | 1 |
3g3794 Ejector Lines Group--Side View - Part 1 Of 2
| 3G***94 | Lines Group-Ejector | 1 |
3g7021 Motor Lines Group--Part 2 Of 3
| 3G***21 | Lines Group-Motor | 1 |
3g7021 Motor Lines Group--Part 3 Of 3
| 3G***21 | Lines Group-Motor | 1 |
3g7021 Motor Lines Group--Part 1 Of 3
| 3G***21 | Lines Group-Motor | 1 |
9j2392 Hydraulic Vane Motor Group
| 9J***92 | Motor Group-Vane | 1 |
6g2195 Hydraulic Tank Group--Part 2 Of 2
| 6G***95 | Tank Group-Transmission Oil | 1 |
6g2195 Hydraulic Tank Group--Part 1 Of 2
| 6G***95 | Tank Group-Transmission Oil | 1 |
7j7524 Ejector Check Valve Group
| 7J***24 | Valve Group-Check | 1 |
9j3479 Control Valve Group
| 9J***79 | Valve Group-Control | 1 |
9j3477 Pilot Valve Group
| 9J***77 | Valve Group-Pilot | 1 |
9j8096 Relief Valve Group
| 9J***96 | Valve Group-Relief | 1 |
1u1110 Relief Valve Group
| 1U***10 | Valve Group-Relief | 1 |
9j830 Check Valve Group
| 9J***30 | Valve Group-Vent | 1 |
Intake And Exhaust System
4n8261 Air Cleaner Group
| 4N***61 | Air Cleaner Group | 1 |
6n6612 Cartridge Group
| 6N***12 | Cartridge Group | 1 |
4n8262 Dust Ejector Group
| 4N***62 | Dust Ejector Group | 1 |
4n8274 Suction Fan Group
| 4N***74 | Fan Group-Suction | 1 |
7n3991 Air Lines Group
| 7N***91 | Lines Group-Air | 1 |
7n3992 Air Lines Group
| 7N***92 | Lines Group-Air; Air Lines Group | 1 |
4n9175 Air Lines Group
| 4N***75 | Lines Group-Air | 1 |
6n1305 Turbocharger Oil Lines Group
| 6N***05 | Lines Group-Turbocharger Oil; Turbocharger Oil Lines Group | 1 |
4n8260 Muffler Group
| 4N***60 | Muffler Group | 1 |
6n3477 Turbocharger Group
| 6N***77 | Turbocharger Group; Turbocharger Group | 1 |
6n3678 Turbocharger Group
| 6N***78 | Turbocharger Group | 1 |
Lubrication System
1p4244 Breather Group
2p6854 Oil Filler Group
| 2P***54 | Filler Group-Oil; Protection Cover Group Oil Filler Cap | 1 |
2p6475 Oil Filter Group
| 2P***75 | Filter Group-Engine Oil; Oil Filter Group (10z1 ~ 10z7023) | 1 |
4n3325 Fumes Disposal Group
| 4N***25 | Fumes Disposal Group; Fumes Disposal Group | 1 |
2p6105 Oil Lines Group
| 2P***05 | Lines Group-Engine Oil; Engine Oil Lines Group | 1 |
2g5890 High Speed Oil Change Group
| 2G***90 | Oil Change Group-High Speed | 1 |
2p1784 Oil Pump Group
| 2P***84 | Pump Group-Engine Oil; Engine Oil Pump Group | 1 |
2p1785 Gear Pump Group
| 2P***85 | Pump Group-Engine Oil | 1 |
2p1785 Oil Pump Group
| 2P***85 | Pump Group-Engine Oil | 1 |
Power Train-Power Transmission Unit
9d8875 Power Train Breather Group
| 9D***75 | Breather Group-Power Train | 1 |
7g2992 Transmission Hydraulic Control Group--Part 1 Of 2
| 7G***92 | Control Group-Transmission Hydraulic | 1 |
7g2992 Transmission Hydraulic Control Group--Part 2 Of 2
| 7G***92 | Control Group-Transmission Hydraulic | 1 |
2p9217 Shift Cylinder Group
| 2P***17 | Cylinder Group-Shift | 1 |
9d2020 Differential And Bevel Gear Group--Part 1 Of 2
| 9D***20 | Differential & Bevel Gear Group | 1 |
9d2020 Differential And Bevel Gear Group--Part 2 Of 2
| 9D***20 | Differential & Bevel Gear Group | 1 |
2g4880 Differential Group
| 2G***80 | Differential Group | 1 |
6d7820 Drive Shaft Group
| 6D***20 | Drive Shaft Group | 1 |
8p6192 Transmission Fastener Group
| 1A***29 | Bolt (1-1/8") Tube Assembly To Transfer Drive Case | 12 |
| 3B***06 | Washer,Lock; Flange,Elbow,Clamp Assembly,Tube To Pump,Tube Assembly To Screen,Clip Mounting,And Tube Assembly To Transmission | 12 |
| 8P***92 | Fastener Group-Transmission | 1 |
2s6457 Transmission Filter Group
| 2S***57 | Filter Group-Transmission; (Transmission) | 1 |
2g6905 Power Train Oil Lines Group--Part 2 Of 2
| 2G***05 | Lines Group-Power Train Oil | 1 |
2g6905 Power Train Oil Lines Group--Part 1 Of 2
| 2G***05 | Lines Group-Power Train Oil | 1 |
2g9250 Retarder Lines Group--Part 2 Of 2--Type 2
| 2G***50 | Lines Group-Retarder; Retarder Lines Group | 1 |
2g9250 Retarder Lines Group--Part 2 Of 2--Type 1
| 2G***50 | Lines Group-Retarder; Retarder Lines Group | 1 |
2g9250 Retarder Lines Group--Part 1 Of 2--Type 2
| 2G***50 | Lines Group-Retarder; Retarder Lines Group | 1 |
2g9250 Retarder Lines Group--Part 1 Of 2--Type 1
| 2G***50 | Lines Group-Retarder; Retarder Lines Group | 1 |
6p3151 Planetary Transmission Group--Part 2 Of 3
| 6P***51 | Planetary Group | 1 |
6p3151 Planetary Transmission Group--Part 1 Of 3
| 6P***51 | Planetary Group | 1 |
6p3151 Planetary Transmission Group--Part 3 Of 3
| 6P***51 | Planetary Group | 1 |
7s2983 Transmission And Scavenge Pump Group
| 7S***83 | Pump Group-Tmsn & Scavenge | 1 |
6p3158 Retarder And Torque Converter Group--Part 1 Of 2--Type 2
| 6P***58 | Retarder & Torque Converter | 1 |
6p3158 Retarder And Torque Converter Group--Part 2 Of 2--Type 1
| 6P***58 | Retarder & Torque Converter | 1 |
6p3158 Retarder And Torque Converter Group--Part 2 Of 2--Type 2
| 6P***58 | Retarder & Torque Converter | 1 |
6p3158 Retarder And Torque Converter Group--Part 1 Of 2--Type 1
| 6P***58 | Retarder & Torque Converter | 1 |
9m8669 Magnetic Screen Group
| 9M***69 | Screen Group-Magnetic; -Differential Lock | 1 |
6p3759 Torque Converter Group--Part 2 Of 2
| 6P***59 | Torque Converter Group | 1 |
1t1210 Torque Converter Group
| 1T***10 | Torque Converter Group | 1 |
6p3759 Torque Converter Group--Part 1 Of 2
| 6P***59 | Torque Converter Group | 1 |
1t1325 Torque Converter Group
| 1T***25 | Torque Converter Group | 1 |
7g3199 Transfer Gear Group--Part 1 Of 2
| 7G***99 | Transfer Case & Gear Group | 1 |
7g3199 Transfer Gear Group--Part 2 Of 2
| 7G***99 | Transfer Case & Gear Group | 1 |
7g3341 Powershift Transmission Arrangement
| 7G***41 | Transmission Ar; Transmission Arrangement | 1 |
7g2993 Power Shift Transmission Arrangement
| 7G***93 | Transmission Ar | 1 |
5s7937 Priority Valve Group
| 5S***37 | Valve Group; -Transmission Control | 1 |
5s7936 Selector Valve Group
| 5S***36 | Valve Group; -Transmission Control | 1 |
5s7941 Lock-Up Clutch And Synchronizing Valve Group--Type 1
| 5S***41 | Valve Group | 1 |
5s7941 Lock-Up Clutch And Synchronizing Valve Group--Type 2
| 5S***41 | Valve Group | 1 |
6p9487 Lock-Up Clutch And Synchronizing Valve Group
| 6P***87 | Valve Group-Lockup Clch & Sync | 1 |
6p5033 Pressure Control Valve Group
| 6P***33 | Valve Group-Pressure Control; -Transmission | 1 |
8m8551 Relief Valve Group
| 8M***51 | Valve Group-Relief; -Transmission Lubrication | 1 |
2p5802 Retarder Control Valve Group
| 2P***02 | Valve Group-Retarder Control | 1 |
9d4410 Final Drive And Wheel Group--37.25 X 35 Tubeless Tires--Part 1 Of 2
| 9D***10 | Wheel & Final Drive Group | 1 |
9d4410 Final Drive And Wheel Group--37.25 X 35 Tubeless Tires--Part 2 Of 2
| 9D***10 | Wheel & Final Drive Group | 1 |
Service Equipment And Supplies
Gasket Kits
| 5P***66 | All Other Arrangements | 0 |
| 5P***68 | Kit-Gasket; (Single Cylinder Liner)(Single Cylinder Liner) | 0 |
| 5P***72 | 1n***14, 7n***16, 7n***17, 8n***21, 8n***22,; 1w***66, 1w***67, 1w***36, 1w***05, 2w***57, | 0 |
8f9866 Grease Gun
| 8F***66 | Grease Gun As | 1 |
Name Plates And Films
| 1H***68 | Plate-Serial Number-Scraper On Left | 1 |
| 1P***80 | Film; (Cat)(Cat) | 2 |
| 1S***88 | Film-- Drain Valve; --On Each Side Of Radiator Support | 1 |
9s7978 Hand Tool Group
| 9S***78 | Tool Group-Hand | 1 |
Starting And Electrical System
6n9294 Alternator Group--24 Volt, 35 Ampere--Type 2
| 3T***52 | Alternator Group-Charging | 1 |
| 6N***94 | Alternator Group; (24-Volt, 35-Ampere) | 1 |
| 7N***20 | Alternator Group; Alternator Group (Robert Bosch) | 1 |
6n9294 Alternator Group--24 Volt, 35 Ampere--Part 1 Of 2--Type 1
| 6N***94 | Alternator Group; (24-Volt, 35-Ampere) | 1 |
6n9294 Alternator Group--24 Volt, 35 Ampere--Type 1
| 6N***94 | Alternator Group; (24-Volt, 35-Ampere) | 1 |
| 7N***20 | Alternator Group; Alternator Group (Robert Bosch) | 1 |
| 9G***55 | Alternator Group-Charging | 1 |
7n9720 Alternator Group--24 Volt, 35 Ampere
| 7N***20 | Alternator Group; Alternator Group (Robert Bosch) | 1 |
6n9294 Alternator Group--24 Volt, 35 Ampere--Part 2 Of 2--Type 2
| 6N***94 | Alternator Group; (24-Volt, 35-Ampere) | 1 |
7n6224 Alternator Group--24 Volt, 35 Ampere
| 7N***24 | Alternator Group-Charging | 1 |
3t6352 Alternator Group--24 Volt, 35 Ampere--Part 2 Of 2
| 3T***52 | Alternator Group-Charging | 1 |
9g8255 Alternator Group--24 Volt, 35 Ampere--Delco-Remy--Part 2 Of 2
| 9G***55 | Alternator Group-Charging | 1 |
9g8255 Alternator Group--24 Volt, 35 Ampere--Delco-Remy--Part 1 Of 2
| 9G***55 | Alternator Group-Charging | 1 |
3t6352 Alternator Group--24 Volt, 35 Ampere--Part 1 Of 2
| 3T***52 | Alternator Group-Charging | 1 |
6g1380 Fuel Tank Group--Type 2
| 6G***80 | Fuel Tank Group | 1 |
6g1380 Fuel Tank Group--Type 1
| 6G***80 | Fuel Tank Group | 1 |
5s8501 Glow Plug Group--24 Volt
| 5S***01 | Glow Plug Group; Glow Plug And Wiring Group | 1 |
2g9251 Harness Assembly
| 2G***51 | Harness As | 1 |
1m3387 Dash Lamp Group--24 Volt
| 1M***87 | Lamp Group | 1 |
2g9275 Retarder Arrangement
| 2G***50 | Lines Group-Retarder; Retarder Lines Group | 1 |
| 2G***75 | Retarder Arrangement | 1 |
| 4N***72 | Cooler Group-Brake Oil; Brake Oil Cooler Group | 1 |
7s5410 Electric Starting Motor Group--24 Volt
| 7S***10 | Starting Motor Group-Electric; Electric Starting Motor Group | 1 |
2p3926 Electric Starting Motor Group--24 Volt--Part 2 Of 3
| 2P***26 | Starting Motor Group-Electric | 1 |
2p3926 Electric Starting Motor Group--24 Volt--Part 3 Of 3
| 2P***26 | Starting Motor Group-Electric | 1 |
2p3926 Electric Starting Motor Group--24 Volt--Part 1 Of 3
| 2P***26 | Starting Motor Group-Electric | 1 |
6g40 Starting Receptacle Group
| 6G***40 | Starting Receptacle Group | 1 |
7n718 Disconnect Switch Assembly
| 7N***18 | Switch As-Disconnect; -Battery-Ground Level | 1 |
6n5123 Solenoid Switch Assembly--24 Volt
| 6N***23 | Switch As-Solenoid | 1 |
4m1812 Solenoid Switch Assembly--24 Volt
| 4M***12 | Switch As-Solenoid | 1 |
4n8985 Coolant Flow Switch Group
| 4N***85 | Switch Group | 1 |
6g1500 Back-Up Warning Group
| 6G***00 | Warning Group-Back-Up | 1 |
2g9290 Wiring Group--Top View--Part 4 Of 4
| 2G***90 | Wiring Group-Scraper | 1 |
2g9290 Wiring Group--Side View--Part 2 Of 4
| 2G***90 | Wiring Group-Scraper | 1 |
2g9290 Wiring Group--Side View--Part 3 Of 4
| 2G***90 | Wiring Group-Scraper | 1 |
2g9290 Wiring Group--Side View--Part 1 Of 4
| 2G***90 | Wiring Group-Scraper | 1 |
639D serial number reference
The 639D is built as two separately serialized units (tractor and elevating-scraper trailer), so look for two riveted PIN plates: one on the tractor frame near the operator's station/steering console, and one on the trailing scraper unit's frame. Each plate shows a 3-character prefix followed by a sequential build number (99Xnnnnn on the tractor, 88Xnnnnn on the scraper); the prefix ties the unit to its engine and build series, and the digits after it are the sequential unit number. Exact plate position is not documented for this model in the sources checked - treat the operator's-station/frame location as general Cat wheel-tractor-scraper practice and confirm with a dealer or the OMM. When ordering parts, match the correct plate (tractor vs. scraper) to the group you're working on, since fuel, drivetrain, and hitch components are split between the two prefixes.
| Prefix | Identifies | Notes |
|---|---|---|
| 99X | 639D Tractor unit, power shift, front-engine half of the twin-unit elevating scraper | Covers the tractor (front) unit of the 639D, serial range 99X00001-UP. This half carries the turbocharged, jacket-water-aftercooled Cat 3408T V8 rated 336 kW (450 hp) at 2000 rpm, the machine's primary tractive power source. Control-group and cushion-hitch listings for this prefix run through at least serial 99X712-up, showing running production changes within the range. Pair unit is the trailing scraper, carrying its own 88X-prefixed PIN. |
| 88X | 639D Scraper (trailing/elevating) unit, rear-engine half of the twin-unit machine | Covers the elevating scraper (rear) unit of the 639D, serial range 88X00001 through at least 88X00699, continuing under the same prefix from 88X00700-UP. This half carries the turbocharged, aftercooled Cat 3306T inline-six rated 186 kW (250 hp) at 2200 rpm, which drives the elevator and assists propulsion. Combined with the tractor engine the machine produces roughly 522 kW (700 hp) at the flywheel. Sold and cataloged as a separate machine PIN from the 99X tractor unit, since the 639D is a two-frame, two-engine articulated machine. |
Frequently asked questions
What engine does the Caterpillar 639D use?
Two of them. A front-mounted Cat 3408T V8 rated at 336 kW (450 hp) drives the tractor and wheels, and a second, rear-mounted Cat 3306T inline-six rated at 187 kW (250 hp) sits on the scraper unit to power the elevator and bowl-loading system. Combined flywheel output runs close to 522 kW (700 hp).
What is the operating weight of the 639D?
Empty operating weight runs 55-56 tonnes (121,825-123,900 lb), split roughly 32 tonnes (70,260 lb) on the tractor unit and 22 tonnes (48,660 lb) on the scraper unit; the exact figure varies slightly by source and configuration. Loaded weight climbs to around 90 tonnes (198,857 lb) with a heaped bowl.
What replaced the Caterpillar 639D?
Nothing directly. No 639E followed it — the 639D was Caterpillar's only twin-engine elevating scraper, built for a single run of roughly five and a half years from 1979 to 1984 before the format was dropped. Caterpillar's elevating scrapers continued afterward as single-engine E-series machines like the 633E and 637E, and today Caterpillar's largest scrapers are open-bowl, twin-power machines rather than elevators.
What 639D owners discuss
How do the two engines on a 639D work together, and what commonly goes wrong with the setup?
Twin-engine tractor-scrapers of this era link the front and rear engines through an air-actuated throttle circuit: a pedal-operated air valve feeds a small air-brake-style actuator at each engine to hold both throttles in step. Owners of these twin-engine scrapers report the linkage as the usual weak point - leaking air lines, a sticking actuator diaphragm, or a maladjusted rod let one engine idle low while the other revs, producing an unbalanced or lurching pull under load. Cleaning and lubricating the linkage and checking air lines for leaks clears most cases. If RPM mismatch persists after that, look at fuel delivery or governor setting on the lagging engine rather than the sync hardware itself.
What are the known quirks of the front 3408T V8 that powers the 639D tractor?
The turbocharged, aftercooled 3408T (rated 336 kW / 450 hp at 2000 rpm in this application) has a reputation as a durable, long-life engine - many are run 16,000+ hours before major work. Its recurring weak points sit in the fuel system: injector tips fouling and running lean from any water or dirt in the fuel, and worn transfer-pump O-rings that let fuel bleed back to tank instead of reaching the injection pump, causing hard starting or a gradual power loss. Boost that reads low at idle is usually a symptom of one of these fueling faults rather than a turbo problem by itself - check fuel delivery before condemning the turbo.
The rear 3306T runs the scraper unit - what should owners expect from it?
The turbocharged, aftercooled 3306T (rated 186 kW / 250 hp at 2200 rpm in this application) is generally regarded as one of Cat's more over-built mid-range diesels, commonly reaching 20,000 hours between overhauls with routine care. Known wear items: wet cylinder liners that pit from cavitation if coolant additive isn't kept up, letting coolant migrate into the oil over time; pencil-style injector tips that erode quickly on contaminated fuel; and turbo bearing wear that shows up as an unusual whine or vibration, worth listening for at every service interval. The water-to-air aftercooler on these engines is also prone to internal blockage from mineral scale when coolant quality is neglected, showing up as a slow loss of boost and creeping fuel consumption.
What wears out on the elevator and bowl, and how does that affect uptime?
On any elevating scraper, the elevator chain, flights, sprockets, and idlers are the highest-turnover wear parts because they run in direct contact with abrasive material on every pass. Loose chain tension accelerates sprocket and flight wear and can lead to chain jumping, so keeping tension in spec is the single biggest lever on elevator life. The bowl cutting edge and apron wear steadily too and are treated as routine consumables rather than failures. On a machine this size (roughly 34 cubic meters / 34 cu yd heaped capacity), tire condition is a major factor in used-machine economics - weathered, cracked, or worn tires can mean a five-figure replacement bill given the tire size needed to carry a loaded operating weight near 90 tonnes (99.5 tons).
What issues show up on the cushion hitch and gooseneck system?
The nitrogen-over-oil cushion hitch, fitted to smooth road shock between the tractor and the loaded bowl, relies on a hydraulic load cylinder, a leveling valve, and free-floating pistons inside the nitrogen accumulators. A hitch that won't raise, or that rides hard and bottoms out, is commonly traced to a leveling valve out of adjustment, a leaking load-cylinder seal, or an accumulator that has lost its nitrogen pre-charge. Because this is a pressurized system supporting the scraper end and capable of releasing stored energy under a fault, have your dealer verify accumulator charge and cylinder condition before anyone works on it.
What electrical issues are typical on a machine of this vintage?
The 639D predates electronic engine controls, so its wiring is simple mechanical-era circuitry covering charging, starting, lighting, and gauges only - there is no engine ECM or sensor network to chase. On machines this old, the recurring complaints are generic to any legacy Cat: corroded or loose battery terminals and ground straps causing charging faults, brittle or cracked harness insulation after decades of heat and UV exposure, and gauge senders that read erratically once connectors corrode. None of this is specific to the 639D, it is the same punch list any 40-plus-year-old Cat with mechanical engines will show, and a full continuity and ground check is standard practice before chasing an intermittent no-start or gauge complaint.
What should a buyer check before purchasing a used 639D?
Production was limited to well under a few hundred units across 1979-1984, and a large share went to export markets such as Australia, so parts availability and dealer familiarity vary a lot by region - confirm parts support in your area before buying. Review both engines' service records separately since they wear independently: hours, injector and turbo work, and any liner or head history on the 3306T in particular. Check the cushion hitch for smooth operation with no bottoming-out, inspect elevator chain tension and flight/sprocket wear, and look hard at tire condition given the replacement cost at this tire size. Have your dealer verify the cushion hitch accumulator charge, the twin-engine throttle synchronization, and overall hydraulic and steering function on a test run before finalizing a purchase - these are the systems most likely to hide an expensive fault behind a clean walk-around.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Serial-range & configuration variants
This page covers the Caterpillar 639D. Related factory variants of the same model family:
639D
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