Caterpillar D8N
Caterpillartrack-type tractor

Caterpillar D8N

Maintenance schedule, common problems & OEM parts breakdown

The D8N is a mid-large Caterpillar track-type tractor in the D8 size class, built from 1987 through 1996. It runs the Cat 3406 turbocharged, aftercooled inline-six diesel: early production used the mechanical 3406 and 3406B, later builds moved to the electronically-assisted 3406C, rated around 228 kW (306 hp) gross and 213 kW (285 hp) net at 2100 rpm. Bare shipping weight runs roughly 26,400 kg (58,300 lb); operating weight with a standard S-blade and full fluids lands near 37,500 kg (82,600 lb), and a dozer-plus-ripper configuration runs closer to 36,000 kg (79,400 lb) - the exact figure varies by blade, ripper, and undercarriage choice. It followed the larger, more powerful D8L (1982-1987) and was replaced by the D8R starting in 1996. Factory configurations included straight (S) and semi-U (SU) dozer blades with PAT hydraulic control, single- or multi-shank rippers, a waste-disposal application package, and a choice of rigid or bogie-suspended undercarriage.

The D8N's signature change was differential steering, the first time Caterpillar built that system into a track-type tractor, replacing the clutch-and-brake steering used on the D8L and earlier D8s; it carried differential steer forward into the D8R and D8T that followed. Within the D8N run itself, the biggest split is undercarriage: some serial groups carry a bogie-suspended (oscillating) track frame while a separate rigid-frame group was built alongside them, so undercarriage parts should be matched by serial prefix rather than by year alone. Engine control moved from purely mechanical fuel systems early in the run to the electronically-assisted 3406C later, though core service capacities stayed the same across that change. In the used and parts market the D8N holds up well: it predates emissions aftertreatment entirely, its 3406-family engine and TO-4 drivetrain fluids are common across a wide range of Cat iron, and used units and take-off parts remain plentiful compared to the tighter-supply D8R and D8T that followed it.

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 D8N specifications

Engine

Engine modelCat 3406, inline-6 diesel. Early production tractors (from 1987 launch) used the mechanical 3406B; later production years used the electronically-assisted 3406C. Spec sheets most commonly cite the 3406C rating.
AspirationTurbocharged and aftercooled
Displacement14.6 L (891 cu in)
Gross power228 kW (306 hp) at 2100 rpm
Net power213 kW (285 hp) at 2100 rpm
EmissionsPre-emissions-regulation mechanical/PEEC diesel; no EPA Tier certification applies to this production era
Cylinders6

Weights

Shipping weight (bare tractor)26,427 kg (58,261 lb)
Operating weight, dozer + ripper configuration36,007 kg (79,381 lb)
Operating weight, standard S-blade configuration37,462 kg (82,590 lb) — figure most widely published for the standard dozer configuration; exact figure varies by blade type, ripper, and other attachments
NoteA dedicated factory LGP (Low Ground Pressure) trim is not clearly documented for the D8N in available spec sheets, unlike later D8T/D8R generations. Weight varies with track shoe width and attachment package

Dimensions

Overall length with S-blade6.27 m (20 ft 6-7 in)
Length without blade4.95 m (16 ft 3 in)
Overall width over tracks2.65-2.66 m (8 ft 8-9 in)
Height to top of cab3.43-3.44 m (11 ft 3 in)
Ground clearance0.55 m (1 ft 9-10 in)
Track gauge (centerline to centerline)2.08-2.10 m (6 ft 10 in)
Standard track shoe width560 mm (22 in); wider shoes available for softer ground conditions
Ground contact length3.20 m (126 in)
Ground contact areaapprox. 3.6 sq m (5,580 sq in) per track pair, standard shoe

Performance

Travel speed, forward (top gear)10.8-10.9 km/h (6.8 mph)
Travel speed, reverse (top gear)13.9-14.0 km/h (8.7 mph)
Number of speeds3 forward, 3 reverse
Transmission typePlanetary powershift, with differential steering — the D8N was the first Cat track-type tractor fitted with differential steer as standard
Final driveDouble-reduction planetary
Ground pressure, standard shoe100.6 kPa (14.6 psi)
Drawbar pullNot published in available spec sheets for this model; consult a dealer or the operator's manual drawbar-pull performance chart for gear-by-gear figures
GradeabilityNot documented in available spec sheets for this exact configuration

Blades

Blade types offeredStraight (S), Semi-Universal (SU), and Universal (U) blades were offered across the D8 platform this tractor belongs to; the S-blade is the configuration most consistently tied to published D8N spec sheets
Standard S-blade width3.96 m (13 ft)
Standard S-blade capacity8.7 cu m (11.4 cu yd)
Other blade capacitiesSU and U blade capacity figures specific to the D8N are not consistently documented across spec sources; SU/U blade hardware sold for this platform is shared with the later D8R/D8T chassis, so figures for those should not be assumed identical for the D8N without direct confirmation

Service capacities

Fuel tank481-488 L (127-129 gal)
Cooling system74 L (19.6 gal)
Engine oil (with filter)37 L (9.8 gal)
Hydraulic/implement system57-70 L (15-18.5 gal), figure varies by source — likely reservoir-only vs total system fluid volume
Transmission/final drive oilapprox. 129 L (136 qt) combined powershift/steering system, per factory service data
Hydraulic system operating pressureapprox. 24 MPa (3,500 psi)
Hydraulic pump outputapprox. 280 L/min (74 gpm)

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

D8N fluids & capacities

SystemCapacityRecommended fluid
Engine crankcase (with filter)37 L (9.8 US gal)Cat Diesel Engine Oil (DEO). D8N ran the Cat 3406-family inline-six across its production run (3406, then 3406B, then 3406C depending on build year), gross rating up to about 306 hp (228 kW) / net 285 hp (213 kW) at 2100 rpm; crankcase fill stays the same across those engine variants. Use SAE 15W-40 for general service; drop to SAE 10W-30 in cooler climates and straight SAE 30 or 40 only where ambient stays warm and multigrade isn't available. Match oil to the coldest expected start-up temperature, not the daytime high.
Cooling system73.9 L (19.6 US gal)Cat heavy-duty diesel engine antifreeze/coolant (glycol-based, factory-era equivalent of Cat DEAC) treated with Cat SCA (supplemental coolant additive). Full-strength mix protects to roughly -37°C (-34°F); adjust glycol/water ratio for local climate, minimum recommended concentration around 30-50% glycol. Check and maintain SCA level at scheduled intervals rather than a one-time fill. This machine's era predates Cat's long-life ELC as factory fill.
Fuel tank488 L (129 US gal)No. 2-D diesel fuel for normal operation; blend with No. 1-D or use a winter-grade No. 2-D in cold weather to keep pour/cloud point below ambient. Keep tank topped at end of shift to limit condensation.
Power train - transmission and bevel gear/differential-steering compartment129 L (34.1 US gal) combinedCat TDTO (Transmission/Drive Train Oil), TO-4 specification. SAE 30 covers most moderate ambient ranges; step down to SAE 10W in sustained cold and up to SAE 50 in sustained high heat, per the OMM's viscosity-by-temperature guidance. The D8N was Caterpillar's first track-type tractor with a differential-steer transmission, so the powershift transmission and the bevel-gear/steering section share one oil system and one combined refill figure in the OMM rather than the separate steering-clutch compartment used on earlier D8-family machines; a further sub-compartment split is not confirmed in available sources.
Final drives (each side)14 L (3.7 US gal) per sideCat TDTO, TO-4 specification, same grade selection as the power train: SAE 30 for moderate climates, SAE 50 for sustained hot ambient, SAE 10W for sustained cold. Service both sides equally.
Hydraulic system/tank70 L (18.5 US gal)Cat TDTO-class hydraulic-compatible oil (this era of track-type tractor commonly shares drivetrain-oil viscosity grades with the hydraulic reservoir rather than a separate dedicated hydraulic-only product line). Grade selection follows the same cold/moderate/hot viscosity pattern as the power train and final drives. System relief valve is set at roughly 24 130 kPa (3500 psi); pump flow is roughly 240 L/min (63.5 US gpm). Useful for cross-checking system health, not a fluid spec.
Pivot shaft / equalizer barGrease point, not a measured fluid-fill reservoirLubricate through the grease fitting on the documented interval; not part of the OMM's refill-capacity chart. Use the same multipurpose grease specified for the rest of the chassis.
Grease (all chassis/track/linkage points)Per-fitting service, no single system capacityCat Multipurpose Grease (MPG), NLGI 2, lithium-complex base, effective roughly -30°C to 40°C (-22°F to 104°F) ambient. For sustained extreme heat or heavy shock-load pin joints, Cat's higher-temperature Prime/Extreme-duty grease lines are the climate-driven step-up; pick the grade for the expected ambient and duty cycle rather than defaulting to standard MPG in extreme conditions.

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

Caterpillar D8N maintenance schedule

Service intervalTasks
Every 50 h
  • Check engine oil level before starting and top off as needed.
  • Check coolant level at the sight glass and inspect the radiator core for debris.
  • Drain water and sediment from the primary fuel filter/water separator.
  • Walk around and check the final drives, the differential-steer compartment, and hydraulic lines for leaks.
  • Grease the blade PAT lift and tilt pins and the rear ripper pivot points.
  • Check track sag visually and check shoe and master-link bolts for looseness.
Every 250 h
  • Change engine oil and filter using the seasonally correct viscosity grade.
  • Grease all chassis, track-frame, and equalizer-bar pivot points.
  • Inspect the primary air filter element and clean or replace it.
  • Check fan belt tension and condition.
  • Check battery terminals and electrolyte level.
  • Inspect the blade cutting edge and end bits for wear.
Every 500 h
  • Pull an oil sample from the differential-steer/power-train compartment for TO-4 analysis.
  • Adjust track sag through the track adjustment valve on each side.
  • Clean the radiator core and oil cooler fins.
  • Check coolant SCA concentration and add supplemental coolant additive if low.
  • Inspect the ripper shank, tip, and protector for wear, if fitted.
  • Check alternator output and starter wiring connections.
Every 1,000 h
  • Change the differential-steer transmission/bevel-gear compartment oil and filter.
  • Change final drive oil on each side.
  • Change hydraulic system oil and filter.
  • Replace primary and secondary fuel filters.
  • Check turbocharger shaft play and inspect for boost leaks.
  • Inspect undercarriage bushings, sprockets, and rollers for wear pattern, and torque track shoe bolts.
Every 2,000 h
  • Test coolant freeze protection and SCA level, and change coolant if condition warrants (this pre-extended-life-coolant engine needs periodic renewal, not a one-time fill).
  • Check and adjust engine valve lash on the 3406/3406C top end.
  • Pressure-test the cooling system and inspect hoses for age cracking.
  • Inspect the differential-steer clutch and brake packs for wear and sample oil for metal content.
  • Check ROPS/cab mounting bolts and isolators.
  • Inspect PAT blade and ripper hydraulic cylinders for seal leakage.
Every 4,000 h
  • Inspect the differential-steer clutch and brake packs and rebuild if wear limits are reached.
  • Send the turbocharger out for inspection or rebuild if shaft play or boost leakage is out of spec.
  • Inspect final drive planetary gear sets for wear.
  • Deep-clean the fuel tank and check for internal sediment or water contamination.
  • Inspect PAT blade lift arms, trunnions, and tilt cylinder mounts for wear.
Every 12,000 h
  • Plan for a 3406/3406C top-end or in-frame engine overhaul; well-maintained units often run beyond this before it's needed.
  • Rebuild or replace undercarriage components (rollers, idlers, sprockets, track chain) as wear dictates; the interval is application-dependent, not a fixed hour count.
  • Rebuild the differential-steer transmission if oil analysis and clutch wear indicate.
  • Overhaul final drives on both sides.
  • Inspect and rebuild the implement hydraulic pump if flow or pressure has dropped from spec.

Servicing the D8N beyond the schedule

Predictive Maintenance & Fluid Analysis

Sample oil from each drivetrain system on a schedule: the combined differential-steer/power-train compartment, each final drive separately, and the engine crankcase. Because the D8N's steering clutches and transmission share one oil system, a single sample flags wear in either before it shows up as a steering complaint. Track coolant SCA/glycol concentration on this pre-extended-life-coolant machine rather than assuming a one-time fill lasts the whole interval. Pull hydraulic oil samples too, since the PAT blade and rear ripper draw off the same implement pump.

Corrective & Common Repairs

Watch the differential-steer clutch and brake packs for slipping or uneven turning response. This was Caterpillar's first application of that system on a track-type tractor, and early units see the most wear complaints. Turbocharger seal leaks and boost loss are common on both the 3406 and 3406C. Expect PAT blade lift/tilt cylinder seal replacement and rear ripper auxiliary-valve hydraulic leaks with age. Track sag drifts faster on bogie-suspended frames working rough ground than on rigid-frame units.

Overhaul & Rebuild Points

The 3406-family engine typically runs well past 10,000 hours before a top-end or in-frame overhaul under a disciplined oil-sample program. Undercarriage wear (rollers, idlers, sprockets, chain) is application-driven rather than fixed-hour: bogie-suspended frames working abrasive or rocky ground wear faster than rigid frames on stable underfoot conditions. Rebuild the differential-steer clutch packs and final drive planetaries when oil analysis or shift and turn quality signal wear, not on a blind calendar.

Seasonal & Environment Servicing

Adjust coolant glycol ratio and confirm SCA level before cold weather, since this era predates long-life coolant and depends on periodic additive top-up. Switch engine and TDTO viscosity grades for winter versus summer per the OMM chart, and blend winter-grade diesel to keep the pour point below ambient. Machines running a waste-disposal package need extra attention to cab sealing and air filtration in dusty landfill duty; forestry-guarded units need PAT cylinder and hose inspection for debris packing.

D8N common service parts

Part numberPart
8T-6765Plug-PipeCheck fitment →
9S-8752Nut-FullCheck fitment →

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

D8N fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
Engine Coolant Temperature warning lamp (gauge red zone / blinking indicator)Coolant temperature has exceeded the machine's normal operating range on the mechanical 3406/3406B engine used in the D8N.Low coolant level, plugged or debris-packed radiator core, slipping or damaged fan drive, bad thermostat, or (if the gauge disagrees with actual engine temp) a faulty coolant-temperature sender or wiring.Idle down and shut off safely, check coolant level and radiator fins for blockage, check fan drive belt condition/tension, and verify the sender circuit before condemning the engine.
Engine Oil Pressure warning lamp (flashing) with audible alarmOil pressure has dropped below the switch point monitored by the gauge cluster.Low oil level, worn oil pump, plugged suction screen or filter, or a failed pressure sender/wiring fault that keeps flashing even after a fresh oil and filter change.Stop the engine immediately, check oil level and look for external leaks, then verify the sender and its wiring before restarting.
Torque Converter / Transmission Oil Temperature warning lamp (high-temp alarm)Torque converter/transmission oil temperature has reached the machine's high-temperature alarm point, commonly cited around 125 C (257 F) on this machine.Sustained heavy pushing or repeated high-load cycles, low transmission/converter oil level, a clogged transmission oil cooler, or a slipping converter.Reduce load, shift to neutral and let the converter cool, check oil level and inspect the cooler for restriction, and confirm actual case temperature against the gauge if the alarm seems premature.
Transmission (Powertrain) Oil Filter Bypass indicator lampThe filter bypass valve has opened, so transmission/torque-converter oil is bypassing a restricted filter element.Filter element loaded with debris, cold oil viscosity at cold startup, or an incorrect filter.Replace the transmission filter and recheck after the oil warms up; if the light returns quickly after a fresh filter, inspect for internal contamination.
Charging System / Low Alternator Voltage warning lampSystem voltage has dropped below the threshold the monitor expects from a properly charging system.Worn or slipping alternator belt, failed alternator or regulator, or loose/corroded battery cable and ground connections.Check belt tension and condition, test alternator output at the battery, and inspect grounds and connections for corrosion.
Hydraulic Oil Temperature warning lampImplement hydraulic oil temperature has exceeded the machine's normal operating range.Low hydraulic fluid level, a plugged hydraulic oil cooler, or extended high-load ripping/blade work in hot ambient conditions.Idle to allow cooling, check fluid level, clean the cooler core of debris, and verify the temperature sender if the reading seems inconsistent.
Parking Brake Engaged indicator lampThe park brake switch shows the brake applied, normally lighting when the operator attempts to travel with the brake set.Standard safety interlock warning during normal operation; occasionally a stuck switch or wiring fault if it stays on with the brake released.Confirm the brake lever/switch position and release before traveling; if the lamp stays on with the brake released, check the switch and its wiring.
Monitor self-diagnostic flash code (technician-level, e.g. MID 030 sensor-circuit fault)The Caterpillar Monitoring System's own DIAGNOSTIC lamp can flash a two-digit module/component code identifying a shorted or open sensor circuit feeding the gauge cluster (coolant temp, oil pressure, or transmission/converter temp senders), separate from the analog gauge alarms themselves.Damaged sender, corroded connector, or chafed wiring on one of the monitored circuits rather than an actual out-of-range engine or transmission condition.Count the lamp flash sequence or connect a Cat diagnostic tool at the cab diagnostic connector to identify which sensor circuit is faulted, then inspect that sender and its wiring.

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

D8N attachments & work tools

Blades

Standard S (straight) blade measures about 3.96 m (13 ft) wide with roughly 8.7 m3 (11.4 yd3) capacity; an SU (semi-U) blade with shorter curvature and smaller side wings than a full U-blade is also documented for this class, trading some fine-grading control for more carrying capacity. Blade control is PAT (power-angle-tilt) hydraulic — raise/lower plus power angle and power tilt from the cab, no manual repinning. VPAT (variable-pitch-angle-tilt) is not offered on this size class; that option is reserved for Caterpillar's smaller D3-D6 dozers. A taller, higher-capacity waste/landfill blade (documented around 16.7 m3 / 21.8 yd3) was offered under the factory Waste Disposal Application package.

Rippers

Single-shank parallelogram ripper: one deep-penetrating tip for hard or rocky ground, with hydraulic lift and tilt cylinders fed from a rear auxiliary valve. Multi-shank ripper: a beam carrying several shank pockets for wider, shallower ripping in looser material, giving faster area coverage than the single-shank unit but less penetration depth per pass. A complete single-shank assembly (ripper structure, tyne with protector/tip, cylinders, hoses, mounting hardware, transmission guard) runs roughly 4.5 t (about 9,900 lb); the multi-shank assembly falls in a similar weight range.

Winches

The documented winch fit for this dozer class is a rear-mounted, two-speed towing/logging winch, originally a Hyster unit and later continued under Allied, driven off the tractor's power take-off rather than an auxiliary hydraulic circuit. It mounts in the same rear position used for a ripper or drawbar and was typically paired with a crawler-mounted logging arch for skidding logs to a landing. No Caterpillar-branded factory winch is documented for this model — winches were fitted as a specialist aftermarket/OEM attachment.

Drawbars/Counterweights

The rear of the tractor accepts either a rigid drawbar or a combined counterweight/hitch casting, mounted in the same position used for a ripper or winch. When a ripper or rear winch is fitted, a rear counterweight option rebalances the machine and properly loads the rear frame. The rear striker bar is counterweight-ready, so extra rear ballast can be added if the rear attachment calls for it.

Cab/ROPS Guarding (forestry/waste)

Base machine ships with a ROPS-protected operator station. For logging/forestry duty, dealer-fit guarding packages add screens over the glass, front and side window guards, light guards, and brush/limb protection around the blade area. For waste/landfill duty, the factory Waste Disposal Application (WDA) configuration bundled extra sealing, cab guarding, and cab air-handling equipment together with the taller, higher-capacity waste blade to cope with debris and contamination.

Hydraulic Arrangement (front/rear tools)

Front: PAT blades (S and SU) run off the tractor's implement hydraulic pump through lift plus angle/tilt cylinders, giving full hydraulic control with no manual repinning. Rear: a ripper draws off a separate rear-mounted auxiliary hydraulic valve circuit dedicated to its own lift and tilt cylinders. A rear winch, where fitted, is mechanically PTO-driven rather than hydraulically powered, so it does not share or compete with the ripper's hydraulic circuit.

All D8N assemblies by section

Every catalogued assembly group for the Caterpillar D8N. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Basic Engine
304-6674 Kit-Hardware
03***19Bolt; --To Bearing Ret. At Lower Front Shaft Bore11
0L***70Bolt (2-1/4") Filler Tube Assembly To Transfer Drive Case1
0S***71Screw,Cap,Hexagon; Tube Assembly To Turbocharger And Elbow Mounting3
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308-2942 Kit-Hardware
0S***94Bolt (1 In. Long 3/8 In. Dia.); Plate Assembly To Support Assembly2
0T***65Bolt--3/8" X 3 1/2"--Use As Required; Bolt 5t***56 Plate To Cover Gp 4n***728
11***87Seal-O-Ring (23.16 mm Id)1
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Engine Arrangement
304-6670 Conversion Ar-Engine
03***79Seal-O-Ring (Id=10.82mm)1
0R***80Rod As-Connecting1
0R***72Crankshaft As1
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304-6671 Conversion Ar-Engine
03***79Seal-O-Ring (Id=10.82mm)1
0R***80Rod As-Connecting1
0R***47Cylinder Pack Group6
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Fuel System
124-5658 Control Gp-Fuel Ratio
10***93Washer1
11***58Washer; (12.7x6.65x0.79-mm Thk)1
12***57Spring-Fuel Ratio Control1
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9y-4913 Fastener Gp-Fuel Inj Pump -Governor
1B***16Bolt; (1/4-20x5-In)2
4F***57Screw,Cap,Hexagon H Shock Mount To Bracket2
5P***37Washer 5t***54 Plate To 7t***28 Cable As2
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7c-4797 Governor Gp
03***16Bolt-Self Locking; (1/4unc X 3/4)3
0S***47Bolt; (1/4-20x0.75-In)(Drilled Head)2
0S***88Bolt,Machine; Hose Assembly Mounting,Hose Assembly To Transmission,And To Torque Converter1
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108-6633 Pump Gp-Fuel Injection
10***02Bonnet-Valve1
10***04Plunger & Barrel As1
10***33Pump Group-Fuel Injection1
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104-4409 Pump Gp-Fuel Injection
0S***15Bolt 19 mm (.75 In.) Long Return Air Console To Enclosed Rops14
10***09Pump Group-Fuel Injection1
10***52Camshaft-Fuel Pump1
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2w-8628 Torque Control Gp
1P***52Insulator,Bushing Governor1
2P***85Spacer (.635 mm Thk); (0.635-mm Thk)1
2W***34Bar-Load Stop; (4.0mm Thk)1
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Service Equipment And Supplies
304-6667 Kit-Engine Parts
03***46Elbow, 90 Deg Adj., 1/4in. J.I.C. X 7/16in.-14 Str. Thd.1
06***40Seal-O-Ring (Id=37.69mm)1
10***48Ring-Guide1
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304-6666 Kit-Engine Parts
03***46Elbow, 90 Deg Adj., 1/4in. J.I.C. X 7/16in.-14 Str. Thd.1
06***40Seal-O-Ring (Id=37.69mm)1
10***48Ring-Guide1
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309-3790 Kit-Engine Parts
03***46Elbow, 90 Deg Adj., 1/4in. J.I.C. X 7/16in.-14 Str. Thd.1
06***40Seal-O-Ring (Id=37.69mm)1
10***48Ring-Guide1
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D8N serial number reference

The D8N serial/PIN plate is riveted to the frame on the right side near the rear of the machine, with the number also stamped into the frame itself as a backup. The plate shows the Product Identification Number: the first three characters are the letter/number prefix that identifies the model's build series and configuration (e.g. 9TC, 1XJ, 5TJ), and the digits following it are the sequential unit number within that series.

PrefixIdentifies
9TCD8N track-type tractor, suspended (bogie) undercarriage
1XJD8N track-type tractor, non-suspended (rigid) undercarriage
5TJD8N track-type tractor, suspended (bogie) undercarriage
7TKD8N track-type tractor, suspended (bogie) undercarriage
8WCD8N track-type tractor (configuration not documented)

Frequently asked questions

What engine does the Caterpillar D8N use?

A Cat 3406 turbocharged, aftercooled inline-six diesel. Early production tractors used the mechanical 3406/3406B; later-production D8N units moved to the electronically-assisted 3406C. Gross output is about 228 kW (306 hp) and net output about 213 kW (285 hp) at 2100 rpm, depending on the exact engine variant and rating source.

What is the operating weight of a Caterpillar D8N?

Bare shipping weight runs about 26,400 kg (58,300 lb). Loaded operating weight with a standard S-blade lands near 37,500 kg (82,600 lb), while a dozer-plus-ripper configuration runs closer to 36,000 kg (79,400 lb). The exact figure varies by blade type, ripper, track shoe width, and other attachments.

What replaced the Caterpillar D8N?

The D8R replaced the D8N starting in 1996, keeping the differential-steer transmission the D8N introduced while stepping up engine output. The D8R was later replaced by the D8R Series II, and eventually by the D8T.

What D8N owners discuss

What's the real story on the D8N's engine across its production run, and what wear issues show up at high hours?
The D8N ran the Cat 3406 inline-six diesel for its entire production life. Early machines from the 1987 introduction used the mechanically-governed 3406B; later production shifted to the electronically-assisted 3406C, which is the rating most commonly quoted (285 net hp / 213 kW). Owners report engines still running well past 15,000-18,000 hours, with an in-frame overhaul typically done somewhere in that 17,000-18,000 hour window rather than on a fixed schedule. Rising oil consumption at high hours (reports of roughly a gallon burned per 8-10 hour shift near 17,000+ hours) usually traces to worn piston rings, worn bearings, or valve stem seals rather than one single failure. Turbo shaft wear/play and clogged injectors are the most commonly cited causes of power loss and smoke short of a full rebuild. Before committing to an in-frame rebuild, check cylinder counterbore wear — if it's past the cuttable limit in-frame, the block has to come out regardless.
What differential-steer transmission quirks does the D8N have, and what does 'won't move' usually mean?
The D8N was the first Cat track-type tractor to get differential steer as standard equipment, replacing the older steering-clutch arrangement. Owners report the transmission running hot and feeling weak under load, sometimes paired with sludge or a coolant sheen around the dipstick — that combination points to the oil cooler letting coolant and transmission oil cross-contaminate, not a clutch fault by itself. When a D8N won't move in either direction but the driveshaft still turns when you try to stall the converter, the usual diagnosis is the bull gear or clutch packs inside the transmission/differential-steer unit, not a simple pressure or linkage problem; a commonly cited cause is a prior operator shock-loading the unit by shifting hard between forward and reverse. A delayed engagement when shifting into forward is often the directional clutch filling before the speed clutch picks up, which can worsen as seals and friction material wear. Because this unit also carries the steering function, have your dealer verify any transmission or differential-steer diagnosis before returning the machine to work.
How does the D8N's undercarriage differ across serial ranges, and what wear pattern should I expect?
Cat built the D8N with two different track roller frame layouts tied to serial-number breaks: a suspended (bogie) frame on most of the production run, and a non-suspended (rigid) frame on a mid-production batch. Rigid-frame machines transmit more shock into the frame and undercarriage on rough ground; bogie-suspended machines ride softer but carry more wearing pivot points. Across either layout, sand and abrasive soil wear rails, bushings, and sprockets faster, while rock work stresses idlers, rollers, and the frame itself — wear pattern reflects the machine's job history as much as its age. Track sag on this size of Cat dozer platform should sit around 105-125 mm (4.1-4.9 in), measured without carrier rollers; sag outside that range or repeated de-tracking points to a worn track adjuster or recoil spring rather than just needing tension topped up. A rolled or wobbly roller, unusual grinding noise, or a flat-spotted roller tread are the field signs of a failing bearing or seal.
What electrical or gauge problems come up most on the D8N?
This generation's instrumentation is largely analog/sender-based rather than a full electronic monitor, so most reported issues trace to corrosion, loose grounds, or a weak battery/charging circuit rather than a control module. If every gauge on the cluster misbehaves at once, check the main fuse box, wiring harness connections, ground points, and battery/alternator output before suspecting the cluster itself. If only one gauge reads wrong, the sending unit feeding that specific gauge — not the wiring — is the more likely culprit; a resistance or voltage check at the sender against a known-good reading usually confirms it. Corroded connectors at senders and bulkhead pass-throughs are the most common physical find on machines that have sat outdoors for years.
Are there cold-starting quirks specific to the D8N?
The factory ether-injection start aid on this era of machine works well when maintained. Owners flag two habits that keep it reliable: keep a full ether can loaded (an empty can does nothing), and check that the line from the can to the intake manifold isn't pinched, cracked, or leaking at the solenoid. Technique matters too — short bursts during cranking, roughly a second on and a couple seconds off, are easier on the starter and batteries than holding the trigger down. An engine that won't turn over at all after sitting, versus one that just cranks slowly, is a different problem: check oil and coolant level first, then suspect hydraulic lock or a stuck internal component (pulling injectors is a common first step before disconnecting pumps) rather than forcing the starter repeatedly. Have your dealer verify before continued cranking on an engine that won't turn over — forcing it risks a bent rod or cracked block.
What should I check before buying a used D8N?
Start with paperwork: ask for full service history and hours on major components, not just the hour meter, since undercarriage and powertrain condition often diverge from engine hours. Get it running through a full work cycle — a healthy engine idles steady, holds temperature, and responds to throttle without excess smoke; heavier smoke under load points to injector or turbo wear. Cycle the transmission through every gear and direction; hesitation, harsh engagement, or heat buildup under load are the same red flags owners report as early failure signs. Walk the undercarriage for uneven side-to-side wear, flat-spotted rollers, sprocket tooth wear, and track sag outside roughly 105-125 mm (4.1-4.9 in); also note whether the machine has the suspended or rigid track frame, since that affects ride and wear pattern. Inspect the frame and blade push arms for cracks or repair welds, and check hydraulic lines and cylinders for leaks or scoring. A machine worked in rock or ripping duty shows more frame and final-drive stress than one that only graded soil — match the wear you see to the history you're told, and have your dealer verify anything that looks inconsistent before you commit.

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

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