Caterpillaroff-highway trucktruck

Caterpillar 773

Maintenance schedule, common problems & OEM parts breakdown

The Caterpillar 773 is a rigid-frame, rear-dump off-highway haul truck in the roughly 80-ton gross class, built from the early-to-mid 1970s into the 1980s under the 63G serial prefix. This original 773 is powered by a mechanically governed Cat D346 turbocharged V8 diesel rated at approximately 447 kW (600 hp) gross, with no electronic engine management of any kind. Empty weight runs around 37,800 kg (83,300 lb) and gross loaded weight around 83,170 kg (183,300 lb), for a rated payload near 45 t (100,000 lb). Power reaches the wheels through a powershift transmission with a torque converter, with dry disc brakes at the front and Caterpillar's oil-cooled multiple-disc brakes at the rear. A single 680 L (180 US gal) fuel tank and 21.00-35 tires round out the base configuration; Cat's rock-truck line of this era was offered with standard dump-body variants (dual-slope, flat-floor, and quarry-duty bodies) to suit different material and haul-road conditions, though exact factory body options for this specific serial range are not fully documented and should be confirmed against the machine's own data plate.

Caterpillar replaced this generation with the 773B in 1987, moving to the 3412 engine, and carried the lettered line forward through the 773D, then the 773E and 773F (C27 power), and today's 773G, adding engine electronics, tighter emissions control, and higher payload ratings with each step. Decades later Caterpillar also reused the plain "773" nameplate on a new, C27-powered current-production truck rated near 825 hp gross; that machine is a separate, newer design that shares only the model number, not the engine, chassis, or driveline of this vintage truck. In the used and parts market, this original mechanical 773 holds value precisely because it predates electronics: no ECM, no wiring-harness diagnostics, and a driveline built around the D346 engine, torque-converter powershift, and oil-cooled disc brakes that a shop can service and rebuild with gauges and hand tools. Surviving units still work in quarries, landfills, and legacy mine and aggregate fleets, kept running on rebuilt engines, reconditioned transmissions, and refurbished disc packs rather than being retired for lack of parts support.

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 773 specifications

Engine

Engine model	Cat D346
Configuration	V8 diesel, turbocharged
Gross power	447 kW (600 hp)
Displacement	19.5 L (1,190 cu in)
Emissions tier	Predates emissions-tier regulation (pre-1996 mechanically governed diesel)

Weights

Empty (unladen) weight	37,800 kg (83,335 lb)
Loaded (gross) weight	83,170 kg (183,359 lb)
Rated payload	45,360 kg (100,000 lb)

Dimensions

Overall length	8.71 m (28 ft 7 in)
Overall width	3.80 m (12 ft 6 in); one spec source lists 4.06 m (13 ft 4 in) — varies by configuration/source
Overall height	4.20 m (13 ft 9 in); one spec source lists 4.29 m (14 ft 1 in) — varies by configuration/source
Wheelbase	3.96 m (13 ft)
Dump (body-raised) height	8.30 m (27 ft 3 in)
Dump ground clearance	3.45 m (11 ft 4 in)
Standard tire size	21.00-35, 32 PR

Performance

Maximum travel speed	67.6 km/h (42.1 mph)
Heaped body capacity	31.3 m3 (40.9 yd3)
Struck body capacity	23.4 m3 (30.6 yd3)
Gradeability / drawbar pull	Not documented for this configuration — verify with your dealer

Service capacities (summary)

Fuel tank	680 L (179.7 gal)
Engine oil	Not documented for this exact configuration — verify with your dealer
Hydraulic system	Not documented for this exact configuration — verify with your dealer
Cooling system	Not documented for this exact configuration — verify with your dealer

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

773 fluids & capacities

System	Capacity	Recommended fluid
Engine crankcase (with oil filter)	Not documented for this exact serial range — verify with your dealer	Cat DEO-ULS (API CK-4, preferred) or Cat DEO (API CI-4/CI-4 PLUS). SAE 15W-40 for 14 to 122°F (-10 to 50°C) ambient; SAE 10W-30 for 0 to 104°F (-18 to 40°C); Cat DEO Cold Weather SAE 0W-40 down to -40°F (-40°C) start-up. This mechanically governed diesel has no exhaust aftertreatment, so no DEF or exhaust fluid is used.
Cooling system	Not documented for this exact serial range — verify with your dealer	Cat ELC (Extended Life Coolant), organic additive technology, glycol-based. Minimum 30% glycol required, 50% glycol recommended for full protection. Factory-fill extended-life coolant is rated to -35°C (-30°F).
Fuel tank	680 L (180 US gal)	Distillate diesel fuel meeting the Cat nonroad diesel fuel specification, minimum cetane 40. This engine has no exhaust aftertreatment device, so higher-sulfur fuel is tolerated where locally permitted.
Transmission / torque converter (common sump)	Not documented for this exact serial range — verify with your dealer	Cat TDTO SAE 10W is factory fill, usable -20 to 50°C (-4 to 122°F). SAE 30 suits warmer climates (0 to 50°C / 32 to 122°F). Torque converter and transmission share fluid and are serviced together.
Differentials and final drives (combined circuit)	Not documented for this exact serial range — verify with your dealer	Cat FDAO SAE 60 is factory fill, rated -10 to 50°C (14 to 122°F). Warm the oil per the machine warm-up procedure before operating below the minimum rated temperature.
Steering hydraulic system	Not documented for this exact serial range — verify with your dealer	Cat HYDO Advanced 10, SAE 10W, is factory fill, -20 to 40°C (-4 to 104°F). Cat HYDO Advanced 20 or 30 suit warmer climates.
Brake / hoist hydraulic system	Not documented for this exact serial range — verify with your dealer	Cat TDTO SAE 10W is factory fill, -20 to 50°C (-4 to 122°F). Minimum acceptable viscosity for an alternative commercial oil is 6.6 cSt at 100°C.
Grease (chassis lubrication points, spec only)	Not a fill-volume item; serviced on interval, not by capacity	Cat Extreme Application Grease, NLGI 1 or 2, for heavily loaded high-duty points such as the drive shaft slip spline, hoist cylinder bearing, front/rear axle A-frame bearing, steering cylinder ends, steering linkage, and tie rod pins. Cat Prime Application Grease NLGI 2 covers medium-duty points; Cat Utility Grease NLGI 2 covers low-duty points. Cat Ball Bearing Grease NLGI 2 is used on fan drive bearings.

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

Caterpillar 773 maintenance schedule

Service interval	Tasks
Every 10 h	Check engine oil level and top off with the specified diesel engine oil. Check engine coolant level and inspect the radiator core, hoses, and fan drive belts for cuts, cracks, or slipping. Drain water and sediment from the primary and secondary fuel filter/water-separator bowls. Check torque-converter/transmission oil level with the engine running at operating temperature. Inspect tires for cuts, uneven wear, and correct inflation, and check wheel rim nut torque. Grease steering cylinder pins, king pins, and body-hoist pivot points, and check the brake-cooling oil reservoir level.
Every 250 h	Change engine oil and replace the engine oil filter elements. Replace primary and secondary fuel filter elements. Check fan belt tension and inspect the turbocharger mounting and boost lines for leaks. Check final-drive (differential) housing oil level. Check the oil-cooled disc brake cooling circuit for leaks and correct oil level. Lubricate all remaining chassis grease fittings, including steering linkage and tailgate hinges.
Every 500 h	Change transmission/torque-converter oil and clean the transmission oil filter or screen. Change the hydraulic (steering and hoist) system oil filter element. Check differential and final-drive housings for oil condition and metal contamination. Inspect front and rear suspension cylinders for leaks and check oil/nitrogen charge. Check and adjust engine valve lash on the mechanically governed diesel. Inspect disc-brake wear indicators and check the brake-cooling oil for contamination.
Every 1,000 h	Change differential and final-drive gear oil. Change hydraulic tank oil and clean the hydraulic tank strainer. Inspect steering cylinders and linkage for wear and check king pin and wheel bearing condition. Check and adjust the fuel-injection pump timing and governor linkage. Pull an oil sample from the torque converter and transmission to check for internal wear. Inspect frame rails, hoist linkage, and body pivot pins for cracking or wear.
Every 2,000 h	Pull scheduled oil samples from the engine, transmission/torque converter, differential, hydraulic system, and brake-cooling circuit for lab analysis before changing fluids. Inspect the turbocharger for shaft play and check the exhaust manifold for cracks. Inspect brake-cooling oil coolers for internal leaks and replace discs found outside wear-indicator limits. Inspect engine mounts, radiator core, and fan hub bearing. Recheck and recalibrate the fuel-injection pump and governor settings. Inspect frame cross-members and hoist-cylinder trunnions for fatigue cracking.
Every 4,000 h	Evaluate the engine for a top-end or full inline overhaul based on oil-sample trends and compression/blow-by checks. Rebuild or exchange the torque converter and powershift transmission clutch packs. Rebuild differential and final-drive assemblies, replacing worn gears and bearings. Rebuild suspension and steering cylinders and replace all seals. Crack-check and recondition the frame and dump body before recoating.

Servicing the 773 beyond the schedule

Predictive Maintenance & Fluid Analysis

This D346-powered 773 has no ECM and no onboard fluid sensors, so condition monitoring means oil sampling and gauges, not telematics. Pull scheduled samples from the engine, torque-converter/transmission, differential, and brake-cooling oil circuits and track wear-metal trends over time rather than waiting for a failure. Watch coolant and oil-pressure gauges on every shift, and inspect the oil-cooled disc brakes' cooling-oil color and temperature gauge for early signs of disc glazing or a failing brake oil cooler before it strands the truck.

Corrective & Common Repairs

Common failure points on this truck are the mechanical fuel-injection pump and governor linkage, turbocharger shaft seals, and the torque converter's stator and lockup hardware, all of which wear rather than fault-code out. Oil-cooled disc packs eventually glaze or the cooling oil breaks down, showing up as brake fade on long grades; disc replacement and cooler flushing address it. Steering and hoist cylinder seals, king pins, and tie-rod ends see heavy loading and need regular inspection under this truck's high axle weights.

Overhaul & Rebuild Points

At major overhaul intervals, the D346 V8 typically needs a top-end or full inline rebuild, liners, pistons, and injectors, once oil-sample trends or compression checks call for it. The powershift transmission and torque converter get clutch-pack and stator rebuilds, and final drives are stripped for gear and bearing wear given this truck's loaded axle weight. Frame rails, hoist-cylinder trunnions, and body pivot points should be crack-checked at overhaul; fatigue cracking is the main structural wear-out mode on trucks this size and age.

Seasonal & Environment Servicing

Cold-start reliability depends on the D346's mechanical injection: check the starting-aid system, block-heater use, battery condition, and fuel-filter water separators before winter, since cold, waxed fuel and slow cranking stress a mechanically governed engine hard. In hot, dusty quarry or mine settings, radiator core and turbocharger cooling packages need frequent cleaning, and the oil-cooled brakes need shorter cooling-oil change intervals under continuous grade-retarding duty. Wet or corrosive sites call for more frequent chassis greasing and inspection of the steering and hoist cylinder seals.

773 common service parts

Part number	Part	Notes
2N-2491	Oil Filter Assembly	Lubrication service	Check fitment →
7S-9896	Oil Filter Assembly	Lubrication service	Check fitment →
6H-6000	Film-Warning Left Side Of Filter Opening On Seat Frame	Scheduled service item	Check fitment →

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

773 attachments & work tools

Dump body types

Offered as Dual Slope (SAE 2:1, the original Cat standard body, low center of gravity, good load retention, available lined or unlined), Flat Floor (suited to metering material such as crusher feed), and Quarry body (one-piece floor intended to run the life of the truck without liners). Struck and heaped body volume for this configuration are covered in the specifications section; exact capacity varies by body type.

Body liner packages

Impact and wear liner kits are available for the dual-slope and flat-floor bodies to protect the steel structure from abrasive or sharp material. Unlined bodies are offered where light, well-fragmented or lower-density material (coal, overburden) does not need liner protection. Liner choice changes tare weight, so liner and body type are matched to hauled material density.

Tail extensions and sideboards

Wraparound tail extensions and sideboards raise heaped volume and help hold rated payload when hauling lighter, fluffier material. These bolt-on body components are matched to body type and material density rather than mounted through any tool coupler.

Impact protection and spillage control

Rock shedders, tumblebars, rockboxes, and external reinforcement plates are offered for this size class to shed oversize material off the cab canopy guard, reinforce the sidewall-to-floor junctions against impact loading, and cut spillage during loading and hauling.

Mine Specific Design (MSD) custom bodies

Beyond the standard catalog bodies, a custom-engineered body is available, sized and reinforced around a specific pit's material and loading tool, aimed at trimming tare weight while maximizing payload for that application.

Retarder and braking system

Braking uses dry disc brakes at the front and oil-cooled multiple-disc brakes at the rear, a design Caterpillar carried across multiple generations of this truck class; the rear discs run submerged in oil that also carries away brake heat. Retarding on grade comes from the torque converter and the transmission's braking range rather than an electronic retarder system on this mechanical-drive configuration. This rigid-frame haul truck has no work-tool coupler; the brake package is the closest factory 'option system' on the chassis.

Cold-weather / heated-body package

An exhaust-heated body option is offered for this truck class, routing engine exhaust to warm the body and stop sticky or freezing material from clinging to the floor and sides in cold climates. It pairs with cold-weather packages such as low-temperature-rated coolant and heated mirrors; exact heated-body plumbing (full-time muffler vs. exhaust diverter) can vary by build.

Bare-chassis and service/water-truck conversion

A bare-chassis version of this truck platform is offered for dealers and body-builders to fit water tanks, fuel-and-lube service bodies, or tow hitches for trailers, targeting dust suppression, road maintenance, fire protection, and field-service roles. This water-truck-ready configuration is documented on the later-lettered version of this chassis; confirm current-generation 773 availability with your dealer.

Tires

This configuration is documented with 21.00-35, 32 PR bias-ply tires as standard fitment. Later generations of this chassis moved to 24.00R35 radial tires; TKPH/TMPH-rated options exist across the class for higher-severity haul routes. Tire choice is matched to haul-road duty rather than being a work-tool style option.

All 773 assemblies by section

Every catalogued assembly group for the Caterpillar 773. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Attachments

7d4365 Air And Hydraulic Brake Control--Part 2--Type 3

7D***65