Caterpillartrack-type tractor

Caterpillar D6D

Maintenance schedule, common problems & OEM parts breakdown

The Caterpillar D6D is a mid-size track-type tractor (crawler dozer) in Caterpillar's medium-dozer class, built from 1977 into the mid-1980s. It replaced the D6C and was itself replaced by the D6H in 1986, the first D6 to switch to Caterpillar's elevated-sprocket, high-drive undercarriage. Every D6D configuration runs the Cat 3306 turbocharged inline-six diesel, roughly 10.5 L displacement. Standard and LGP (wide-track, low-ground-pressure) dozer versions are rated near 104 kW (140 hp) gross with a 3-speed powershift transmission (a direct-drive gearbox was also offered); the D6D SA agricultural/drawbar version used a different tune, commonly cited near 93 kW (125 hp) at the drawbar. Operating weight varies widely by configuration and source, landing roughly in a 12-17 t (26,000-38,000 lb) band, so treat the machine's own data plate as the final word over any published chart.

Across its production run Caterpillar kept the D6D's 3306 engine and steering-clutch/brake steering layout largely unchanged, offering it as standard, LGP, and SA variants with either direct-drive or powershift transmissions rather than a major mechanical redesign - that leap came with the D6H's elevated sprocket, which lifted the final drive off the ground to cut the undercarriage wear that the D6D's conventional low-drive layout could not avoid. That gap is exactly why the D6D still holds a place in the used and parts market today: it is a simple, pre-electronic machine with no ECM to diagnose, generally cheaper to buy than later models, and still backed by a healthy aftermarket for undercarriage, final drive, and transmission components, even as factory dealer stock keeps thinning as these units age out of common inventory.

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 D6D specifications

Engine

Engine model	Cat 3306, inline 6-cylinder diesel, turbocharged, direct injection, liquid-cooled
Displacement	10.5 L (638-641 cu in, rounding varies by source)
Bore x stroke	121 mm x 152 mm (4.75 in x 6.00 in)
Rated speed	approx. 1,900-2,000 rpm depending on source
Gross power, Standard/LGP configuration	104 kW (140 hp); some spec sheets round to 139.5 hp
Gross/net power, SA (Special Application) configuration	123 kW (165 hp)
Drawbar power rating, SA configuration	93 kW (125 hp), quoted for agricultural drawbar use
Emissions	Pre-emissions-regulation design; built mid-1970s to mid-1980s, no EPA/EU emissions tier applies
Electrical system	24V, electric start; alternator rated 35-50A depending on configuration; SA configuration uses two 12V batteries

Weights (by configuration)

Standard configuration, operating weight	Reported inconsistently across sources: one widely-mirrored spec sheet lists 9,235 kg (20,360 lb); another source (with dozer blade and ROPS) lists 14,288 kg (31,500 lb), with 11,820 kg (26,060 lb) bare shipping weight. The higher figures are more consistent with the LGP weight relationship below - verify against the machine nameplate.
LGP configuration, operating weight	17,373 kg (38,301 lb)
SA (Special Application) configuration, operating weight	approx. 12,930-13,150 kg (28,500-29,000 lb)

Dimensions

Standard config, length without blade	3.20-3.73 m (10.5-12.25 ft) - varies by source/measurement point
Standard config, length with 6S (straight) blade	approx. 4.72 m (186 in)
Standard config, length with 6A (angle) blade	approx. 4.77 m (188 in)
Standard config, width over tracks	1.98-2.36 m (6.5-7.75 ft) - varies by source
Standard config, height to top of cab	2.90 m (9.52 ft)
Standard config, height to ROPS canopy	approx. 2.87 m (113 in)
Standard config, height to exhaust stack	approx. 3.05 m (120 in)
Standard config, ground clearance	0.36 m (1.19-1.2 ft)
Standard config, track gauge	1.52 m (4.99 ft)
Standard config, standard shoe width	406-457 mm (16-18 in) - varies by source
Standard config, track rollers per side	5
Standard config, track length on ground	1.83-2.36 m (6.01-7.75 ft) depending on source
LGP config, length with blade	5.18 m (17.0 ft)
LGP config, length without blade	3.96 m (13.0 ft)
LGP config, width over tracks	3.05 m (10.0 ft)
LGP config, height to top of cab	2.93 m (9.6 ft)
LGP config, ground clearance	0.34 m (1.1 ft)
LGP config, track gauge	2.13 m (7.0 ft)
LGP config, standard shoe width	912 mm (35.9 in)
LGP config, track rollers per side	7
SA config, width over tracks	2.39 m (7.85 ft)
SA config, height to top of cab	2.87 m (9.42 ft)
SA config, length without blade	3.96 m (13.0 ft)
SA config, track length on ground	2.36 m (7.75 ft)
SA config, ground clearance	0.31 m (1.02 ft)
SA config, track gauge	1.88 m (6.17 ft)
SA config, standard shoe width	510 mm (20.08 in)
SA config, track rollers per side	6

Performance

Transmission options	Powershift (3 forward / 3 reverse) offered on Standard and LGP configurations; direct-drive gear transmission offered as an alternative, reported as either 5F/4R (industrial listing) or 6F/4R-5R depending on source, likely tied to the SA (Special Application) configuration
Max travel speed, powershift (Standard/LGP)	Forward approx. 10.8-10.9 km/h (6.7-6.8 mph); reverse approx. 12.9-13.0 km/h (8.0-8.1 mph)
Max travel speed, direct-drive (SA config)	Lower top speed than powershift; direct-drive gear transmission with multiple ratios, exact per-gear chart not consistently published across sources - verify with dealer or operator's manual
Ground pressure, Standard configuration	approx. 65 kPa (9.4-9.5 psi)
Ground pressure, LGP configuration	approx. 32 kPa (4.7 psi)
Ground pressure, SA configuration	Not separately published; approximate value derived from published weight and ground-contact-area figures is roughly 54 kPa (7.8 psi) - treat as an estimate, not a factory-quoted figure
Ground contact area, Standard configuration	approx. 1.48 sq m (2,294 sq in)
Ground contact area, LGP configuration	approx. 5.25 sq m (8,138 sq in)
Ground contact area, SA configuration	approx. 2.40 sq m (3,720 sq in)
Drawbar pull	Not documented in available spec sheets for the Standard/LGP configurations. Only a drawbar horsepower rating (125 hp / 93 kW) is published, for the SA configuration - verify actual drawbar pull force with dealer or operator's manual
Gradeability	Not documented in available spec sheets for this model - verify with dealer or operator's manual
Hydraulic relief valve pressure	15,500 kPa (2,250 psi), consistent across Standard/LGP sources
Hydraulic pump flow, Standard/LGP configuration	approx. 166 L/min (43.9 US gpm)
Hydraulic system type/flow, SA configuration	Open-center system, approx. 91 L/min (24 US gpm)

Blades

Standard (6S straight) blade - width	3.20 m (10.5 ft)
Standard (6S straight) blade - height	1.13 m (44.5 in)
Standard (6S straight) blade - capacity	3.3 cu m (4.3 cu yd)
Standard (6S straight) blade - max angle each direction	12 degrees
Standard (6S straight) blade - cutting depth	approx. 472 mm (18.6 in)
6A angle blade	Referenced in overall-length dimension data (adds approx. 51 mm / 2 in vs 6S blade to overall machine length); width and capacity not consistently published across sources
LGP blade - width	3.72 m (12.2 ft)
LGP blade - capacity	3.13 cu m (4.1 cu yd)
SA configuration blade	Cutting depth approx. 231 mm (9.1 in) documented; width/capacity not separately published - confirm blade fitment for the specific unit

Service capacities

Fuel tank, Standard/LGP configuration	Reported inconsistently: 295 L (78 US gal) from one source family, 238 L (62.9 US gal) from another - verify tank size against serial/configuration
Fuel tank, SA configuration	436 L (115 US gal)
Hydraulic system fluid	45.8-49.2 L (12.1-13 US gal) depending on source
Engine oil (crankcase, with filter)	approx. 27.4 L (29 qt)
Cooling system	approx. 37-39 L (39 qt) on direct-drive-equipped machines; approx. 38.8 L (41 qt) on powershift-equipped machines
Power train/transmission oil, direct-drive configuration	approx. 98.4 L (104 qt)
Power train/transmission oil, powershift configuration	approx. 92.7 L (98 qt)

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

D6D fluids & capacities

System	Capacity	Recommended fluid
Engine crankcase (with filter)	Approx. 27-29 L (7.1-7.7 US gal); exact figure varies by sump/filter configuration. Engine is the Cat 3306 turbocharged diesel, 10.5 L displacement, direct injection, 6-cylinder.	Cat diesel engine oil (Cat DEO), API CD/CE service class. SAE 10W below 0°C (32°F), SAE 30 from 0-40°C (32-104°F), SAE 15W-40 multigrade where ambient swings across a wide range through the season.
Cooling system	Not firmly documented for the D6D machine installation specifically. Cat 3306 engine-only cooling system figures in available references span roughly 15-18 L, but with radiator and machine cooling circuit included the full system likely runs closer to 30-50 L (8-13 US gal). Treat as a range only - confirm against the OMM's own refill chart or dealer.	Ethylene-glycol based antifreeze/water mixture per Cat cooling system spec of the period. Current-generation cross-reference is Cat ELC (Extended Life Coolant).
Fuel tank	238 L (62.9 US gal) reported for one tank configuration; 295 L (78 US gal) reported for another. Varies by configuration/series (standard vs. LGP and other tank options).	No. 2-D diesel fuel for normal ambient use; No. 1-D diesel recommended in cold-climate operation.
Powershift transmission (power train)	Not consistently documented for the D6D specifically in available sources. Figures for other Cat dozer power-train systems of similar frame size run roughly 90-150 L (24-40 US gal), but this is NOT confirmed for the D6D - confirm against the OMM refill chart or dealer before servicing. Note: the D6D was also offered with a direct-drive (5-speed) transmission option instead of the 3-speed powershift; capacities differ between the two.	Cat TO-2 transmission/drive-train oil, historically SAE 30 for general service, adjusted by ambient temperature per the OMM's viscosity chart. Current cross-reference is Cat TDTO meeting Cat TO-4 spec.
Bevel gear & steering clutch compartment	No separate refill figure confirmed in available sources for the D6D. This compartment draws from the same oil family as the transmission on this model generation; the steering clutch side should read dry/no oil present in normal operation (oil here signals a bevel gear housing seal leak). Confirm exact quantity against the OMM/dealer.	Cat TO-2 gear oil, same fluid family as the transmission; current cross-reference is Cat TDTO meeting TO-4 spec.
Final drives (each)	Roughly 13-14 L per side reported in some secondary specification tables, but not cross-verified against an authoritative D6D-specific source. Treat as unconfirmed and check the OMM/dealer refill chart before servicing.	Cat TO-2 gear oil, SAE 30 or SAE 50 depending on ambient temperature per the OMM's viscosity chart; current cross-reference is Cat TDTO meeting TO-4 spec.
Hydraulic system/tank	45.8 L (12.1 US gal) hydraulic tank/reservoir; this figure repeats across multiple independent spec listings for the D6D.	Cat TO-2 hydraulic/transmission-type oil, the same fluid family used across transmission and hydraulic circuits on this machine generation. Current cross-reference is Cat HYDO Advanced or an equivalent anti-wear hydraulic oil.
Pivot shaft (track roller frame compartment)	No specific refill quantity documented for the D6D. General practice on this era of Cat dozer is to keep the pivot-shaft reservoir at half-full on the sight/expansion bottle, not filled to full, to avoid pressure buildup and seal leaks.	Cat pivot-compartment oil for normal service; Cat arctic-grade oil where the machine runs in sustained sub-zero ambient conditions.
Grease (chassis and track lubrication points)	Applied per fitting during scheduled lubrication - not a bulk refill quantity.	Cat Multipurpose Grease, NLGI 2, service range approx. -30°C to 40°C (-22°F to 104°F). Cat Arctic Platinum grease for extreme cold climates; Cat Desert Gold / Extreme Application grease for high ambient heat and heavy-load track/pin service.

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Caterpillar D6D maintenance schedule

Service interval	Tasks
Every 50 h	Check engine oil level and look for milky or foamy oil on the 3306 dipstick before startup. Check coolant level and scan the radiator core and oil cooler fins for mud or debris packing that leads to chronic overheating. Drain sediment and water from the fuel tank and check the fuel/water separator. Walk the undercarriage: check track sag over several links, and inspect both final drive hubs (especially the left side) for oil seepage around the bearing/seal area. Check the recoil spring/track adjuster cylinder at each side for grease weeping past the barrel seal. Start cold and watch exhaust color and listen near the manifold for leaks pointing to broken manifold bolts.
Every 250 h	Change engine oil and filter and pull an oil sample from the 3306 crankcase. Check and adjust fan belt and alternator belt tension. Check battery condition and, in cold weather, watch the ammeter needle drop during cranking to confirm the glow plug circuit is pulling current. Clear the ether starting-aid injection orifice if the machine uses one, especially after fitting a new bottle. Check transmission/hydraulic oil level and top off with the correct fluid family for this machine generation. Inspect the crankcase breather and clean if restricted.
Every 500 h	Change the transmission/hydraulic filter. Pressure-test the transmission and torque converter circuit at low and high idle to catch a weak scavenge pump, plugged oil cooler, or leaking valve-feed tube early. Check final drive oil level on both sides and run a magnet through a drained sample looking for metal fines. Inspect and adjust the steering clutch and brake bands under the triangle covers. Check the driveshaft-to-torque-converter yoke coupling for play or a spongy feel under load; treat any looseness there as a stop-work item. Clean or replace the air cleaner element depending on service indicator readings.
Every 1,000 h	Change powershift transmission oil, bevel gear/steering clutch compartment oil, and final drive oil on both sides. Pull oil samples from each final drive as part of the fluid-change service. Check turbocharger shaft play and inspect for oil leakage at the compressor and turbine housings. Inspect oil cooler core for rust-scale restriction and rod out if flow is reduced. Check charging system output and inspect wiring grounds if any no-charge complaints have occurred. Re-torque exhaust manifold bolts and check for leaks at the head-to-manifold joint.
Every 2,000 h	Adjust engine valve lash on the 3306. Inspect the fuel injection pump and nozzles for wear or uneven spray pattern. Check torque converter stall speed against factory reference to gauge internal wear. Measure track chain wear across multiple links and pins rather than judging by eye, and inspect sprocket segments, rollers, and idlers for play or wear. Inspect recoil spring cylinder barrels for seal wear at each track adjuster. Check steering clutch lining wear and cover-plate flatness if any shift hesitation has been noted.
Every 4,000 h	Rebuild or replace final drive hub bearings and seals; if one side has failed, inspect the opposite side closely since a second failure within months is common on this machine. Rebuild the powershift transmission clutch packs, retorquing replacement through-bolts to spec and rechecking cover-plate flatness. Overhaul or replace the fuel injection pump and turbocharger as a set if wear findings from the 2000-hour inspection warrant it. Replace undercarriage wear components as a set - track chain, rollers, idlers, and sprocket segments - since the D6D's conventional low-drive layout carries full machine weight through these parts. Change engine coolant and flush the cooling system. Confirm driveshaft and yoke alignment through the torque converter coupling after any major powertrain rebuild.

Servicing the D6D beyond the schedule

Predictive Maintenance & Fluid Analysis

Pull an engine oil sample from the 3306 at every oil change and track trends for rust-scale contamination, a known driver of chronic overheating on this machine. Sample final drive oil from both hubs and run a magnet through it looking for metal fines - the left-side hub is a documented early-wear point. Measure track sag across several links rather than eyeballing it, and pressure-test the transmission/torque converter at low and high idle to catch a weak scavenge pump before it causes overheating or slipping.

Corrective & Common Repairs

Recurring D6D fixes center on the steering clutch/brake linkage, clutch-pack through-bolts that back out and leak oil while warping cover plates, and final drive hub leaks from the inner bearing spinning in its bore. A driveshaft-to-torque-converter yoke that walks partway out of engagement can cause partial or total loss of drive and should stop work immediately. Exhaust manifold bolt failures and oil-cooler rust-scale blockages are common causes of overheating and smoke on higher-hour units.

Overhaul & Rebuild Points

Major D6D rebuild work concentrates on the powershift clutch packs (retorque through-bolts and recheck cover-plate flatness), full final drive teardowns for new bearings and seals, and 3306 injection pump/nozzle overhaul. Because the D6D uses a conventional low-drive undercarriage - unlike the elevated-sprocket layout that followed on the D6H - track chain, rollers, idlers, and sprocket segments carry the full machine weight and typically represent the largest share of lifetime rebuild cost.

Seasonal & Environment Servicing

In cold weather, watch the ammeter for a glow-plug current draw during cranking and keep the ether starting-aid orifice clear; relying on ether to mask weak glow plugs risks cracked rings and blown intake gaskets. In muddy or dusty conditions, keep the radiator core and oil cooler clear of packed debris and check final drive hubs for debris intrusion around the seals, since a clogged cooling package is this era's most common overheating cause.

D6D common service parts

Part number	Part	Notes
8T-6765	Plug-Pipe	Scheduled service item	Check fitment →

Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.

D6D fault codes & troubleshooting

Code	Meaning	Likely cause	What to do
OIL PRESSURE (red warning lamp / gauge below normal)	Engine lubricating oil pressure has dropped below the safe operating range on the D6D's Cat 3306 diesel engine.	Low oil level, plugged oil filter, worn oil pump, or a failed pressure sending unit.	Stop the machine and shut down the engine immediately. Check oil level and filter condition before restarting.
WATER TEMPERATURE (red warning lamp / gauge in red zone)	Engine coolant temperature has exceeded the normal operating range on the D6D's 3306 diesel.	Low coolant level, failed thermostat, plugged radiator core, slipping fan drive, or worn water pump.	Reduce load and let the engine idle to cool gradually. Do not shut off hot. Check coolant level and radiator once safe, then inspect thermostat and fan drive.
ALTERNATOR / CHARGING (red warning lamp, ammeter shows discharge)	Charging system is not supplying adequate voltage to the D6D's 24-volt battery and electrical system.	Worn or broken alternator belt, failed alternator, or loose/corroded battery and alternator connections. Charging capacity varies by configuration (commonly a lower-amp or higher-amp internally regulated alternator depending on build), but the fault logic is the same.	Check belt tension and condition first. Inspect wiring and battery terminals, then test alternator output.
AIR FILTER RESTRICTION (indicator flag on air cleaner housing)	Intake air restriction across the air cleaner has reached the service limit.	Clogged primary or secondary air filter element, or a collapsed/damaged intake hose.	Service or replace the air filter element, reset the restriction indicator, and inspect intake piping for damage.
TRANSMISSION / TORQUE CONVERTER OIL TEMPERATURE (gauge in red range)	Powershift transmission and torque converter oil temperature is above the normal operating range. The D6D uses a powershift transmission with a torque converter and an oil-to-air cooler; the exact red-line temperature varies by configuration.	Low transmission oil level, sustained lugging or overload, plugged oil cooler, or a failing torque converter.	Reduce load and check transmission oil level. Inspect the oil cooler for blockage before returning to full duty.
PARKING BRAKE / STEERING CLUTCH-BRAKE (mechanical lever/pedal lock; brake circuit checked at service test port, not a continuous dash warning)	Parking brake is mechanically engaged through the lever/pedal lock and will not release, or the hydraulically actuated steering clutch/brake system is not performing normally. The D6D has no electronic parking-brake or steering-clutch-brake warning lamp; clutch and brake band pressure is verified with a gauge at the hydraulic test ports during service, not displayed continuously on the dash.	Parking brake linkage worn, misadjusted, or over-center so it will not release; low or contaminated brake-compartment oil; or worn/out-of-adjustment brake bands.	Check parking brake lever/pedal free travel and linkage condition. Check brake compartment oil level and condition, and have a technician verify steering clutch and brake band pressure at the test ports and adjust per the service manual.
FUEL PRESSURE / FUEL LEVEL (gauge reading low)	Fuel delivery pressure from the transfer pump, or fuel level, is below normal, risking fuel starvation. The 3306 engine's instrument panel carries a fuel pressure gauge alongside the tank fuel level gauge.	Clogged fuel filter, air in the fuel system, or a failing fuel transfer pump.	Replace the fuel filter and bleed the fuel system. Inspect the transfer pump if the condition persists.

Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.

D6D attachments & work tools

Blades

Standard dozer blade (straight/angling type) is 3.2 m (10.5 ft) wide, 1.13 m (44.5 in) tall, 3.3 m3 (4.3 yd3) capacity, angles 12 degrees each direction, max cutting depth 472 mm (18.6 in). The LGP undercarriage variant carries a wider blade, about 3.7 m (12.2 ft) wide with roughly 3.1 m3 (4.1 yd3) capacity, matched to the LGP track gauge and shoes for flotation work. Semi-U and full-U blade shapes were offered across this dozer class for mixed-material and land-clearing work, though S (straight) and A (angling) are the two configurations most consistently documented for this model; VPAT (variable-pitch angle-tilt) blades are not a D6D option, that blade type arrived on later D6N/D6R/D6T/D6 XE generations.

Rippers

Rear-mounted parallelogram ripper, available as single-shank or multi-shank (commonly three shanks/tips), hydraulically raised and pitched from the tractor's own hydraulic system. A three-shank ripper assembly weighs approximately 1,600 kg (about 3,500 lb) complete with tips. Single-shank setups suit deep production ripping in hard, frozen, or rocky ground and root removal; multi-shank setups suit lighter, more variable ripping conditions with higher production per pass.

Winches

A rear cable winch (Cat #56 class, also catalogued under PA55/PA56 designations for this size machine) fits the D6D in place of, or alongside, the ripper mount. Bare-drum line pull is rated in the range of roughly 31 to 40 metric tons (about 69,000 to 90,000 lb) depending on the specific winch and gearing, using wire rope around 26-29 mm (1 to 1-1/8 in) diameter. This class of winch on the D6D saw common use in pipeline, oilfield, and logging service for pulling in equipment; figures vary by specific winch build and gear-reduction option.

Winches - forestry note

For forestry brush-clearing work the winch is typically paired with a lighter straight blade rather than the full LGP or U blade, so the machine can push and drag felled material as well as winch it, rather than running ripper and winch together.

Drawbars/counterweights

A rear drawbar/hitch is fitted for towing implements or loads, sized to the tractor's engine class (about 104-123 kW / 140-165 hp gross depending on source and tune). The D6D SA (special application) variant is tuned to roughly 93 kW (125 hp) at the drawbar specifically for balanced pull and lower fuel burn in agricultural towing duty. Rear counterweight ballast can be fitted at the drawbar location when no ripper or winch is installed, to help retain rear stability and traction during straight dozing.

Cab/ROPS guarding

Standard protection is a four-post ROPS frame, offered as an open canopy or an enclosed cab with optional air conditioning. Forestry and waste-duty builds on dozers of this size and era commonly add FOPS-rated screening over the canopy/cab glass, brush guards, a hinged belly guard, and extra screening ahead of the radiator and engine compartment to keep debris out; these are documented broadly for Cat dozers in this class rather than as a distinct factory-named waste-handler package on the D6D itself - the named "WH" waste-handler package designation appears on later D6N/D6T generations, not the D6D.

Hydraulic arrangement

Standard dozer hydraulic system is open-center, delivering about 166 L/min (43.9 gpm) at roughly 155 bar (2250 psi) relief pressure, with about 45.8 L (12.1 gal) system fluid capacity; the D6D SA agricultural variant runs a lower-flow circuit at about 91 L/min (24 gpm) for its lighter-duty use. Blade lift, tilt, and angle functions run off the main valve bank; a rear ripper or winch ties into an added control valve and lever sharing the same pump, so ripper and winch are generally alternative rear attachments rather than both installed and run at once.

All D6D assemblies by section

Every catalogued assembly group for the Caterpillar D6D. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Basic Engine

284-7808 Kit-Hardware

0L***43	Bolt 63.5 mm (3/8" X 2 1/2" -Cover Assembly To Fender	1
0S***71	Screw,Cap,Hexagon; Tube Assembly To Turbocharger And Elbow Mounting	3
0S***91	Screw,Cap,Hexagon Bearing Retainer; Part Of Kit P/N 1w***82	1
0S***94	Bolt (1 In. Long 3/8 In. Dia.); Plate Assembly To Support Assembly	2

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Engine Arrangement

284-3285 Conversion Ar-Engine

0R***14	Rod As-Connecting	1
0R***24	Nozzle As-Fuel Injection	6
0R***88	Cylinder Pack Group	6
0S***16	Screw,Cap,Hexagon H Receptacle Mtg; Bolt Brackets To Firewall Assembly	2

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Fuel System

7c-8993 Fastener Gp-Fuel Inj Pump

0S***14	Bolt (.25" Diameter-.50" Long)	3
2S***83	Bolt (3.25" Long-Drilled Head)	1
4F***57	Screw,Cap,Hexagon H Shock Mount To Bracket	8
4N***61	Bolt 165.1 mm(6.5 In.) Long	4

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1w-3597 Torque Control Gp

1P***52	Insulator,Bushing Governor	1
1W***97	Torque Control Group	1
2P***85	Spacer (.635 mm Thk); (0.635-mm Thk)	1
2W***34	Bar-Load Stop; (4.0mm Thk)	1

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2w-6559 Governor Gp

03***16	Bolt-Self Locking; (1/4unc X 3/4)	3
0S***16	Screw,Cap,Hexagon H Receptacle Mtg; Bolt Brackets To Firewall Assembly	6
15***28	Gasket-Governor	1
15***30	Gasket-Governor	1

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111-3769 Pump Gp-Fuel Injection

0S***15	Bolt 19 mm (.75 In.) Long Return Air Console To Enclosed Rops	4
11***69	Pump Group-Fuel Injection	1
11***70	Camshaft Group	1
11***71	Camshaft-Fuel Pump	1

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4p-9827 Pump Gp-Fuel Injection

1W***87	Valve As-Check; (Fuel Injection Pump)	1
4P***27	Pump Group-Fuel Injection	1
4P***30	Plunger & Barrel Assem.	1
6I***27	Bonnet-Valve	1

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7c-8992 Seal Gp-Pump

03***79	Seal-O-Ring (Id=10.82mm)	1
14***77	Gasket	1
15***26	Gasket	1
15***27	Gasket-Fuel	1

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Service Equipment And Supplies

284-3296 Kit-Engine Parts

10***27	Coupling-Exhaust	1
11***28	Elbow; (90-Deg)	1
28***96	Kit-Engine Parts	1
28***08	Kit-Hardware	1

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D6D serial number reference

On the D6D the PIN/serial plate is a metal tag on the rear of the machine, upper left side, high on the end of the left frame rail; it can be hidden behind a rear-mounted ripper. The engine carries its own separate serial plate on the block - don't confuse the two. Pre-2001 Cat serials run 8 characters total: the first 3 (two digits plus a letter, e.g. 20X, 31X, 33X) are the prefix identifying the model and production block, and the remaining 5 digits are the sequential unit number within that block.

Prefix	Identifies	Notes
03X	D6D Std, Direct Drive	Machine serial 03X00001-01008, continuing as 03X01009-and-up. Introduced 1977. Cat 3306 diesel engine. Steering clutch and brake system (no differential steering on this generation).
04X	D6D Std, Power Shift	Machine serial 04X00001-06607, continuing as 04X06608-and-up. Introduced 1977. Cat 3306 diesel engine, power shift transmission, steering clutch/brake system.
06X	D6D LGP, Power Shift	Machine serial 06X00001-01114, continuing 06X01115-and-up. Introduced 1977. LGP (Low Ground Pressure) undercarriage, power shift transmission, Cat 3306 engine. Some parts-catalog scans render this prefix as '6X' with the leading zero dropped; same production block.
20X	D6D Std, Power Shift	First parts manual covers machine serial 20X00001-03041; a second manual picks up at 20X03042-and-up, so the block continues well past the first manual's stated ceiling into the early 1980s. Power shift transmission, Cat 3306 engine, steering clutch/brake system. Exact split versus 04X (also Power Shift, same era) is not documented in available sources - may reflect a track-gauge or blade-class split; confirm with dealer.
30X	D6D Std, Direct Drive	Machine serial 30X00001-02069. Dated to around 1981, a later continuation of the Direct Drive line started under 03X. Cat 3306 engine.
31X	D6D Std, Power Shift	Machine serial 31X00001-01496. Cat 3306 engine, power shift transmission.
32X	D6D LGP, Direct Drive	Machine serial 32X00001-01180. Dated to around 1980. Cat 3306 engine, Direct Drive transmission, LGP undercarriage.
33X	D6D LGP	Machine serial 33X00001-and-up. Cat 3306 engine, LGP undercarriage. Transmission type (Direct Drive vs Power Shift) not confirmed. A market-specific split from the 32X block has been suggested but not corroborated - confirm with dealer.
6HC	D6D (configuration not confirmed)	Machine serial 6HC00001-and-up. Cat 3306 engine confirmed via parts-catalog listing. Undercarriage (Std/LGP) and transmission (Direct Drive/Power Shift) not confirmed - confirm with dealer.

Frequently asked questions

What engine does the Caterpillar D6D use?

All D6D configurations use the Cat 3306 turbocharged inline six-cylinder diesel, about 10.5 L displacement. Standard and LGP dozer versions are rated near 104 kW (140 hp) gross; the SA agricultural/drawbar version used a different tune, commonly cited near 93 kW (125 hp) at the drawbar. Output varies by configuration and serial block, so match the rating on the machine's own data plate rather than assuming from the model name alone.

What is the Caterpillar D6D's operating weight?

Operating weight varies by configuration. Published figures run from roughly 12 t (26,000 lb) for a base standard unit up to about 17.4 t (38,300 lb) for the wider-track LGP version, with the SA farm-tractor version landing near 13 t (28,500-29,000 lb). Sources disagree even within the same configuration, so weigh the actual machine or check its nameplate before hauling or trailer-rating it.

What replaced the Caterpillar D6D?

The D6H, introduced in 1986, replaced the D6D. It was the first D6 built with Caterpillar's elevated-sprocket, high-drive undercarriage, which lifts the final drive above the track frame instead of carrying it at ground level like the D6D's conventional layout - a change aimed at cutting final-drive and undercarriage wear.

What D6D owners discuss

What engine does the D6D use, and how do owners rate it?

The D6D runs Caterpillar's 3306 inline six, turbocharged in the standard and LGP configurations for roughly 104 kW (140 hp) at the flywheel. The agricultural D6D SA variant used a lower-output, naturally aspirated tune rated near 93 kW (125 hp) at the drawbar, and some special long-frame direct-drive and power-shift variants are cited near 119 kW (160 hp) - output varies by configuration and series, so match the rating to the data plate rather than the model name alone. Owners and mechanics generally call the 3306 tough and torquey, but on high-hour units expect head-to-manifold exhaust leaks from broken manifold bolts, pre-combustion-chamber O-ring seepage onto the head, and oil coolers clogged with rust scale that need rodding out to restore flow. A fan mounted backward or a collapsed fan/alternator pulley is a surprisingly common, easily-missed cause of chronic overheating on these machines.

Is the D6D power-shift transmission reliable, and what fails on it?

Community consensus rates the D6C/D6D power-shift transmission as one of the best Cat ever built, and it rarely gives serious trouble if serviced properly. The recurring failure point is the long through-bolts holding the clutch packs together; when they break, oil leaks out and cover plates can warp, so any rebuild should recheck plate flatness and retorque replacement bolts to about 115 Nm (85 ft-lb). Older brass-impregnated clutch linings shed material as they age, and that debris migrates past the filters into valve spools, causing erratic or hesitant shifts. A less common but reported failure is the transmission pinion gear, with at least one owner's unit failing around 6,000 hours. Torque converter overheating is usually traced to the scavenge pump not keeping the converter case empty, a plugged oil cooler, a dirty radiator, or a leaking seal on the tube feeding the transmission valve - checking filter pressure at both low and high idle is the standard way operators localize it.

What undercarriage and final drive wear patterns show up on the D6D?

Final drive hub leaks, especially on the left side, are a recognized weak spot on this machine: the inner bearing mounting surface wears from the bearing spinning in its bore, the dead-axle nut works loose, and no amount of heavier gear oil or added grease keeps it sealed once that starts. At that stage the fix is a full teardown for new bearings and seals, or a complete final drive assembly swap, not just a seal replacement. If one side's final drive is failing, treat the other side as suspect too - owners commonly report the second side following within months. Recoil spring/track-adjuster cylinders on aging units are also reported weeping grease past the barrel seal, usually solved by replacing the cylinder and barrel rather than repacking it. For general track wear, use the standard measure-over-multiple-links-and-pins method rather than judging by eye, and budget undercarriage as the largest share of this machine's upkeep cost.

Does the D6D have electrical or sensor problems like newer machines?

The D6D predates electronic engine controls, so there is no ECM or sensor network to chase - issues are old-school mechanical/electrical: sending units, glow plug circuits, and the ether starting aid. Watch the ammeter while cranking in cold weather: the needle should drop about halfway across the gauge as the glow plugs draw current, and a weak drop points to one or more burnt-out plugs. The ether injection orifice is prone to plugging and needs to be pulled and cleared whenever a new bottle is fitted; leaning on ether to compensate for weak glow plugs risks cracked rings and blown intake gaskets over time. Alternator/regulator no-charge complaints on these older machines trace to the same generic causes as any charging system - bad grounds, worn brushes, or a failed field circuit - nothing unique to the D6D design itself.

Is a driveshaft yoke or steering-drive fault on a D6D a do-it-yourself fix?

One owner's shop quoted a very large repair bill for what turned out to be a driveshaft-to-torque-converter yoke that had walked partway out of engagement, compounded by missing transmission hoses and both the magnetic and transmission filters missing from a prior repair. The community fix was working the yoke by hand - light outward pressure while slowly rotating the torque output shaft lets the seal ring clear the seal bore, and the yoke seats with an audible pop. Because this joint sits between the engine, torque converter, and final drives, a partially engaged yoke can mean partial or total loss of drive or steering response under load. Treat any play, gap, or "spongy" feel at this coupling as a stop-work item, and have your dealer verify proper yoke engagement and driveshaft alignment before returning the machine to service.

What do experienced operators say about how the D6D handles?

Run as a bare dozer with no rear attachment, several long-time operators describe the D6D as poorly balanced and among the harder Cats to work with - light in the back, which affects blade control and ripping feel. Fitting a rear ripper or winch is widely reported to correct the balance and make it feel like a different machine to run. Opinion is split on serviceability: some mechanics call it one of the more difficult Cat dozers of its era to wrench on, while others say it is no harder than any comparable D-series once you know the machine. Both camps agree parts availability keeps getting tighter as these units age out of common dealer stock, worth factoring in for anyone planning long-term ownership.

What should I check before buying a used D6D?

Start with the undercarriage since it drives most of the ownership cost: measure track wear over multiple links and pins rather than trusting a visual look, and pry on the sprockets to check for play that suggests bearing wear. Run a magnet through the final drive oil on both sides looking for metal fines, and inspect the left final drive housing specifically for seepage around the hub - a known weak point on this model. Start the engine cold and watch for white or blue smoke, blow-by at the oil fill tube, and listen around the exhaust manifold for leaks that hint at broken manifold bolts. Cycle the transmission through forward, reverse, and all gears feeling for hesitation, and pressure-test the transmission/torque converter at low and high idle if a gauge is available. Check the recoil spring cylinder at each track adjuster for grease weeping past the seal. Ask for maintenance records and find out whether the machine has run an implement off the rear, since balance and wear patterns differ between bare-blade and rigged configurations. Finally, confirm exactly which D6D configuration is in front of you - standard, LGP, SA agricultural, direct-drive versus power-shift - since horsepower, gearing, and available parts differ across them.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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