Caterpillar D400
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar D400 is a 6x6 articulated dump truck built for off-highway hauling on loose or uneven terrain. The original D400 (1986, serial prefix 1MD) runs a mechanical, non-electronic Cat 3406B diesel rated at roughly 385 hp (287 kW) from about 14.6 liters (891 cu in) of displacement, with no ECM and no fault-code diagnostics. Operating weight on this early truck runs close to 28,000 kg (about 61,700 lb) empty with a rated payload near 36,000 kg (about 39.7 tons). Caterpillar carried the model designation forward through the D400D (prefixes 2JJ and 8TF), the D400E (prefix 2YR), and the D400E Series II (prefix 8PS), each riding on its own chassis and engine package rather than a running update of the original. Bodies were offered in standard dump configuration to suit quarry, mine, and heavy-construction haul cycles.
Each generation change moved the D400 further from its mechanical roots. The D400D carried an updated 3406B-based package, the D400E switched to an electronically governed 3406C with onboard diagnostics, and the Series II refined that electronic platform further while operating weight crept up from around 28,000 kg on the original truck toward the low 30,000 kg range on later, heavier examples. Because the original D400 was built in a short run before Caterpillar moved to the D-suffix and E-suffix trucks, surviving examples are scarce and parts support leans on shared 3406-family engine components and common articulated-truck driveline parts rather than model-specific stock. That scarcity, combined with the truck's simple mechanical fuel system, keeps it in demand among owners who want a haul truck without electronic engine controls to maintain.
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 D400 specifications
Engine
| Engine, base/D400D-generation (mid-1980s to mid-1990s) | Cat 3406, 6-cylinder diesel. Gross power 385 hp (287 kW). Displacement 14.6 L (891 cu in / 14,601 cu cm). Net power and emissions tier not published — this generation predates formal emissions-tier rating. |
| Engine, D400E-generation (including Series II, mid/late-1990s on) | Cat 3406-family diesel, 6-cylinder, higher output rating than the earlier generation. Gross power 405 hp (302 kW); net power near 399 hp (298 kW) is not independently confirmed — verify with your dealer for the exact rating. Displacement reported near 15.2 L (928.6 cu in), also unconfirmed — use with caution. Emissions tier not published. |
| Notes on naming | The bare model designation 'D400' is used by parts/spec aggregators as shorthand for this truck family. Every operating figure found under the plain 'D400' name matches the dedicated D400D data set exactly (same empty weight, payload, power, speed), so the base D400 and D400D are treated here as the same early generation. D400E and D400E Series II are later, heavier, higher-power generations of the same articulated truck line — do not blend their weight/dimension figures back into base D400/D400D. |
Weights
| Operating (empty) weight — D400 / D400D | 28,027 kg (61,789 lb) |
| Operating (empty) weight — D400E | 29,254 kg (64,495 lb) |
| Operating (empty) weight — D400E Series II | 31,643 kg (69,760 lb) |
| Gross (loaded) weight — D400 / D400D | 64,308 kg (141,775 lb) |
| Rated payload — D400 / D400D | 36,281 kg (79,986 lb) |
| Rated payload — D400E and D400E Series II | 36,300 kg (80,028 lb) |
| Ground pressure | Not published in available sources. |
Dimensions
| Overall length — D400 / D400D | 10.64-10.90 m (34.85-34.90 ft) |
| Overall length — D400E | 10.53-10.55 m (34.52-34.60 ft) |
| Overall length — D400E Series II | 10.65 m (34.95 ft) |
| Overall width — D400 / D400D and D400E | 3.30-3.32 m (10.83-10.90 ft) |
| Overall width — D400E Series II | 3.43 m (11.26 ft) |
| Overall height — D400 / D400D | 3.56-3.57 m (11.68-11.70 ft) |
| Overall height — D400E and D400E Series II | 3.58-3.60 m (11.75-11.80 ft) |
| Wheelbase — D400 / D400D | 6.05-6.07 m (19.85-19.90 ft). Not published for D400E/Series II in available sources. |
| Dump (bed) height — D400 / D400D | 6.73-6.74 m (22.09-22.10 ft) |
| Dump (bed) height — D400E | 6.58 m (21.59-21.60 ft) |
| Dump (bed) height — D400E Series II | 6.92 m (22.71 ft) |
| Dump angle — D400E and D400E Series II | 55 degrees. Not documented for the earlier D400/D400D generation. |
| Ground clearance | Not published in available sources. |
Performance
| Travel speed — D400 / D400D | 55.5 km/h (34.5 mph); varies by configuration/series, with figures up to 61 km/h reported for this generation. |
| Travel speed — D400E-generation | Around 56-59 km/h (35-37 mph); varies by configuration/series. |
| Forward/reverse gears — D400 / D400D | 4 forward gears (reverse count not published). |
| Forward/reverse gears — D400E-generation | 7 forward / 2 reverse gears reported for this generation, not independently confirmed — verify with your dealer. |
| Heaped dump capacity — D400 / D400D | 23.5-23.6 cu m (30.7-30.8 cu yd) |
| Struck dump capacity — D400 / D400D | 17.3-17.4 cu m (22.6-22.7 cu yd) |
| Gradeability | Not published in available sources. |
Service capacities (summary)
| Fuel tank — D400 / D400D | 450 L (118.9 US gal) |
| Fuel tank — D400E-generation | Not reliably documented for this generation — figures found conflict with the heavier D400E's expected range compared to the D400D baseline, so verify the exact capacity with your dealer. |
| Hydraulic system | Not documented in available sources for any generation with confidence; treat as verify-with-dealer. |
| Engine oil | Not documented in available sources for any generation with confidence; treat as verify-with-dealer. |
| Cooling system | Not documented in available sources for any generation with confidence; treat as verify-with-dealer. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
D400 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (3406B diesel, with filter) | 38 L (10 US gal) typical for the 3406-series engine fitted to this truck; standard-pan builds run closer to 34 L (9 US gal), extended/brakesaver pans closer to 42 L (11 US gal). Confirm against the pan option fitted to your serial number. | Cat DEO (Diesel Engine Oil). SAE 15W-40 covers general/moderate climates; step down to 10W-30 or a 0W-40/5W-40 synthetic-blend DEO for sustained cold-start conditions below 0°C (32°F), per Cat's climate-based viscosity guidance for the 3406 engine family. |
| Cooling system | Roughly 76 L (20 US gal) reported on the related D400E chassis. Not independently confirmed for the base D400 (1MD prefix) — treat as indicative only and verify the exact figure against the D400 OMM. | Cat DEAC (Diesel Engine Antifreeze/Coolant) or Cat ELC (Extended Life Coolant), pre-mixed to the correct freeze-protection ratio for the operating climate. |
| Fuel tank | 450 L (118.9 US gal) | No. 2-D diesel fuel meeting Cat's fuel specification. Switch to No. 1-D or a winter-blend diesel in cold climates to maintain cold-flow properties. |
| Powershift transmission compartment | Reported figures vary by configuration/series: roughly 38 L on the D400D-generation chassis versus roughly 72 L (19 US gal) cited for the related D400E. Treat as a range and confirm the exact figure against the OMM for your serial-number build. | Cat TDTO (Transmission/Drive Train Oil). Cold-climate builds may call for a lighter TDTO viscosity grade — check the OMM's temperature-selection chart. |
| Final drives (front and rear, each) | Not documented in available sources for this model. Capacity varies by axle configuration — confirm against the OMM or a dealer. | Cat TDTO, matching the transmission/drivetrain circuit fluid. |
| Hydraulic system (including tank) — hoist/steering circuit | Figures for the related D400E vary widely (roughly 69-235 L), so no single figure reliably carries over to the base D400. Treat any number as unconfirmed until checked against the OMM. | Cat TDTO commonly doubles as the hydraulic fluid on this generation of Cat articulated truck, since the hoist/steering circuit shares the drivetrain reservoir. Cat HYDO is the alternate spec where the OMM calls for a dedicated hydraulic oil. |
| Axles/differentials | Integrated into the front and rear final-drive housings on this chassis; no separate fill capacity documented in available sources. | Cat TDTO, same as the final-drive fluid. |
| Grease points (chassis pins, bushings, linkages) | Spec only — no fill capacity applies. | Cat multipurpose chassis grease, NLGI grade 2, lithium-complex or moly-fortified type depending on service severity. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar D400 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 D400 beyond the schedule
Predictive Maintenance & Fluid Analysis
The base D400 runs a mechanical 3406B with no ECM and no fault codes, so oil, coolant, and hydraulic sampling carry the diagnostic load a modern truck would get from telematics. Pull engine oil samples every 250 hours to track wear metals from the wet-sleeve liners and mechanical injection pump before they surface as smoke or a compression loss. Sample transmission and final drive oil on the same interval, and watch coolant for additive depletion since this generation predates extended-life coolant as standard fill.
Corrective & Common Repairs
Mechanical injection pump wear and governor drift on the 3406B are the most common corrective jobs on this truck, along with turbocharger shaft wear and leaking wet-sleeve liner O-rings that show up as coolant in the oil. On the chassis, expect articulation hitch pin and bushing wear from constant frame oscillation, plus hydraulic steering cylinder seal replacement. Because the D400 predates onboard diagnostics, troubleshooting relies on mechanical checks, pressure gauges, and governor adjustment rather than a code reader.
Overhaul & Rebuild Points
The 3406B's wet-sleeve cylinder liners make a top-end or full in-frame overhaul more straightforward than a cast-in-block engine, with liners and pistons pulled as a matched set rather than bored in place. Plan the injection pump and turbocharger for rebuild alongside the liners at major overhaul. On the drivetrain, the torque converter and power-shift transmission are the other big-ticket rebuild items. Given the truck's short original production run, expect to cross-reference 3406-family industrial and marine parts when sourcing rebuild kits.
Seasonal & Environment Servicing
Cold starts on the mechanical 3406B benefit from an ether starting aid and a full coolant concentration check before winter, since there is no electronic cold-start strategy to compensate. In hot, dusty quarry or mine settings, shorten air filter service intervals and check the cooling system core for packed debris that cuts airflow. The articulation joint and steering cylinders pick up more grit in dry conditions, so tighten the grease interval on hitch pins when working abrasive ground.
D400 fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| Engine Oil Pressure lamp (red) | Engine oil pressure has dropped below the safe operating range, sensed by a mechanical pressure switch, not an ECM. | Low oil level, worn oil pump, plugged suction screen, or a faulty pressure sender/switch. | Stop the engine immediately, check oil level and the mechanical gauge, then inspect the sending unit before restarting. |
| Coolant Temperature lamp (red) | Engine coolant temperature has exceeded the normal operating range. | Low coolant level, blocked radiator core, slipping or broken fan belt, or thermostat failure. | Reduce load and let the engine idle to cool, check coolant level and radiator/fan belt condition before shutting down. |
| Transmission/Torque Converter Oil Temperature lamp | Power train oil temperature is above the safe limit. | Low transmission oil level, prolonged torque-converter stall (lugging on grade), or a plugged oil cooler. | Reduce throttle/load, let the converter cool at idle, and check oil level and cooler airflow. |
| Charging System (alternator) lamp | The charging circuit is not producing adequate voltage to the batteries. | Loose or broken alternator belt, failed alternator, or a wiring/ground fault in the charging circuit. | Check belt tension and battery voltage with the engine running, then inspect alternator output and wiring. |
| Hydraulic/Brake Oil Pressure lamp | Hydraulic or brake-accumulator pressure has fallen below the safe threshold. | Low hydraulic oil level, worn pump, or an external leak in the brake/hydraulic circuit. | Stop the machine safely, check hydraulic oil level and look for visible leaks before further operation. |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
D400 attachments & work tools
Dump body
Standard steel dump body sized for this truck's rated payload class (in the 34-40 t / 36000-40000 kg range depending on configuration). Body is bolted/pinned to the frame and tips via twin hoist cylinders; no bucket-style work tool is fitted on this haul truck.
Tailgate options
Full pivoting tailgate is the typical fit for retaining loose or fine material. A half (partial) tailgate is offered for free-flowing spoil that does not need full retention, reducing carry-back and speeding discharge. An open (no tailgate) body is used for sticky or oversize material that would otherwise hang up.
Body liners and wear packages
Impact and wear liners, sideboards, tail extensions, external reinforcement plates, and rock shedders are fitted to protect the body floor/sides, add heaped capacity, and cut spillage in abrasive or rocky duty. These are bolt-on wear items rather than quick-change tools.
Ejector body (generation note)
An ejector-body variant that discharges the load with a hydraulic ram and blade instead of tipping was introduced on the D400E update around 2001, aimed at low-clearance or fine-material (under roughly 150 mm) work. This is not documented as a factory option on the original bare D400 - treat ejector fitment as specific to D400E and later, verify before applying to an earlier serial range.
Tires
Radial tires in the 29.5R25 class are the documented fit for this truck size, matching the shared running gear used across the D330C/D350C/D400 size class of that era. Alternate tread patterns (rock, quarry, all-terrain) are offered within that same size for different ground conditions; exact size can vary by configuration.
Water tank / dust-suppression conversion
Third-party OEM integrators build water-tank bodies on this articulated-truck chassis for dust suppression and haul-road watering, replacing the dump body. Typical fitment includes front and rear spray bars or cannons, fill chute, ladders, tie-off points, and an optional foam-agent tank for fire-suppression duty; capacity varies by tank supplier and chassis.
Operator protection / guarding
Enclosed cab (ROPS/FOPS) is documented on this truck family for quarry and mining duty, with screens or mesh guarding added for overhead-hazard sites. Specific canopy or screen kits are not separately documented for the original bare D400 - confirm current cab/guarding fitment with the selling dealer for that exact serial range.
Mounting / coupler system
As a haul truck, work-tool bodies and tailgates mount via bolted or pinned subframe connections to the chassis, not through an excavator-style hydraulic quick-coupler. Any hydraulic function (tailgate power-open, ejector ram) is plumbed into the truck's existing dump-hoist hydraulic circuit rather than a separate tool circuit.
All D400 assemblies by section
Every catalogued assembly group for the Caterpillar D400. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Basic Engine
333-1672 Kit-Engine Parts
| 06***40 | Seal-O-Ring (Id=37.69mm) | 1 |
| 0T***00 | Plug (.5625" Diameter) | 1 |
| 10***47 | Cover-Flyweight | 1 |
321-1454 Kit-Hardware
| 00***01 | Ring-Retaining | 1 |
| 0S***94 | Bolt (1 In. Long 3/8 In. Dia.); Plate Assembly To Support Assembly | 8 |
| 0T***65 | Bolt--3/8" X 3 1/2"--Use As Required; Bolt 5t***56 Plate To Cover Gp 4n***72 | 8 |
Engine Arrangement
333-1671 Conversion Ar-Engine
| 03***79 | Seal-O-Ring (Id=10.82mm) | 1 |
| 0R***39 | Pin-Piston | 1 |
| 0R***81 | Rod As-Connecting | 1 |
Fuel System
124-5658 Control Gp-Fuel Ratio
| 10***93 | Washer | 1 |
| 11***58 | Washer; (12.7x6.65x0.79-mm Thk) | 1 |
| 12***57 | Spring-Fuel Ratio Control | 1 |
9y-4913 Fastener Gp-Fuel Inj Pump -Governor
| 1B***16 | Bolt; (1/4-20x5-In) | 2 |
| 4F***57 | Screw,Cap,Hexagon H Shock Mount To Bracket | 2 |
| 5P***37 | Washer 5t***54 Plate To 7t***28 Cable As | 2 |
7c-4797 Governor Gp
| 03***16 | Bolt-Self Locking; (1/4unc X 3/4) | 3 |
| 0S***47 | Bolt; (1/4-20x0.75-In)(Drilled Head) | 2 |
| 0S***88 | Bolt,Machine; Hose Assembly Mounting,Hose Assembly To Transmission,And To Torque Converter | 1 |
111-9363 Pump Gp-Fuel Injection
| 0S***15 | Bolt 19 mm (.75 In.) Long Return Air Console To Enclosed Rops | 14 |
| 10***33 | Pump Group-Fuel Injection | 6 |
| 10***06 | Seal-O-Ring (10.52mm Id) | 1 |
108-6633 Pump Gp-Fuel Injection
| 10***02 | Bonnet-Valve | 1 |
| 10***04 | Plunger & Barrel As | 1 |
| 10***33 | Pump Group-Fuel Injection | 1 |
126-6710 Torque Control Gp
| 12***91 | Spring-Torque; (0.254-mm Thk) | 1 |
| 12***10 | Torque Control Group | 1 |
| 1P***52 | Insulator,Bushing Governor | 1 |
D400 serial number reference
The PIN plate on this articulated truck is riveted to the front frame, right-hand side, near the cab access step / articulation joint area; on some units it is repeated on the instrument panel. The first 3 characters are the letter/number prefix tied to the specific model and production run; the remaining 5-6 digits are the sequential unit number within that run.
| Prefix | Identifies | Notes |
|---|---|---|
| 1MD | D400 articulated truck, base/early series (pre-D400D) | Range 1MD00001 through roughly 1MD00246. Fitted with the mechanical 3406B inline-six. Predates the D400D update; a short, low-volume run rather than the long-lived D400D/D400E/D400E II lineage. Pull fluid and torque data from documentation keyed to this prefix specifically, not from D400D or D400E manuals. |
Frequently asked questions
What engine does the Caterpillar D400 use?
The original D400 runs a mechanical Caterpillar 3406B diesel rated at roughly 385 hp (287 kW) from about 14.6 liters (891 cu in) of displacement. It has no ECM and produces no electronic fault codes. Later D400D, D400E, and D400E Series II trucks moved to updated and eventually electronically governed 3406-family engines, so electronic diagnostics don't apply to the original D400.
What is the operating weight of the Caterpillar D400?
The original D400 runs close to 28,000 kg (about 61,700 lb) empty with a rated payload near 36,000 kg (about 39.7 tons), putting loaded weight in the low 60-ton range. Later D400E-generation trucks grew heavier, with empty weights reported from about 29,000 kg up to roughly 31,600 kg depending on configuration, so weight varies by series.
What replaced the Caterpillar D400?
Caterpillar followed the original D400 with the D400D, then the D400E, then the D400E Series II. Each is a distinct chassis and engine generation carrying the same model number rather than a direct running change, so parts and service data don't cross freely between them.
What D400 owners discuss
The base D400 runs a mechanical 3406B. What do owners say about oil consumption and blowby at high hours?
I keep seeing complaints about D400 ECM faults, data-link errors, and a gear shifter that loses calibration overnight. Does that apply to a mechanical D400?
What do operators report about the transmission, torque converter, and retarder behavior?
What wears out first at the articulation/oscillation joint, and how much does it cost to fix?
What tire and rim wear patterns are typical for a loaded articulated hauler like this?
What should I check when looking at a used D400, regardless of which generation it is?
Are there recurring complaints about the dump box or hoist hydraulics not responding?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Need a specific D400 part?
Search live OEM part data, check fitment, and cross-reference alternatives with Heavy Parts AI.