Caterpillarmotor grader
Caterpillar 120B
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar 120B is a medium-class, wheeled motor grader built around the Cat 3306 naturally aspirated diesel, an inline six-cylinder engine of about 10.5 L (638 cu in) displacement rated near 93 kW (125 hp). Standard operating weight runs about 12,000-12,030 kg (26,460-26,510 lb), varying with tires, counterweights, and attachments. Field evidence points to production spanning roughly the mid-1970s into 1990, identified by at least two known serial-number prefixes marking separate manufacturing runs. The 120B replaced the earlier Cat 120 (a direct-drive grader with manual stick-shift implement controls) and was itself succeeded by the Cat 120G. Configurations included standard grading trim plus front-mount ripper/scarifier attachments and optional blade extensions.
Across the Cat 120 to 120B transition, blade, circle, and steering control moved from mechanical stick-shift linkages toward full hydraulic control, a changeover Caterpillar phased in through the mid-1970s; control layout can vary by serial number within the 120B run itself. When Caterpillar replaced the 120B with the 120G, the engine changed again, this time down to the smaller-displacement four-cylinder Cat 3304, while operating weight increased. In today's used and parts market, the 120B matters mainly for its mechanical simplicity: no ECM, no electronic injection, and an engine platform shared with contemporary Cat dozers, loaders, and scrapers, which keeps rebuild components easier to source than the model's age would suggest. It remains a working grader in rural and export markets, where low-cost mechanical repair outweighs the appeal of modern electronics.
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 120B specifications
Engine
| Engine model | Cat 3306 diesel, inline 6-cylinder, water-cooled, naturally aspirated. Distinct from the D333A engine used in the earlier (1965-68) 120; the 3306 came in with the 120B in the mid-1970s. |
| Power (gross/net) | 125 hp (93 kW), rated in gear 5-6. Published figures list the same number for gross and net — no separate gross rating is broken out on available spec sheets. |
| Displacement | 10.5 L (638 cu in) |
| Cylinders | 6, inline |
| Emissions tier | Mechanically governed diesel, no ECM. Predates EPA/EU nonroad emissions-tier regulation, so no tier rating applies. |
Weights
| Operating weight | About 12,010-12,025 kg (26,460-26,511 lb). Figure varies slightly by source and configuration — treat as approximate. |
| Shipping weight | Not published on available spec sheets for this model. |
| Ground pressure | Not published on available spec sheets for this model. |
Dimensions
| Overall length (operating) | 7.92 m (26 ft 0 in) |
| Overall width | 2.36 m (7 ft 9 in) |
| Overall height | 3.12 m (10 ft 3 in) |
| Moldboard width | About 3.66 m (12 ft) on standard period listings. Individual used units from this era are also seen with a 4.27 m (14 ft) moldboard — confirm the blade fitted to a specific machine rather than assuming one figure. |
| Wheelbase / ground clearance | Not documented on available spec sheets for this model — verify with your dealer or the machine's data plate. |
Performance
| Travel speed | Not documented on available spec sheets for this model. The gear-5-6 power rating indicates a multi-range manual transmission (high/low split), but forward/reverse speed steps for the 120B specifically are not published — verify with your dealer or the machine's data plate. |
| Gradeability / drawbar pull | Not published on available spec sheets for this model. |
Service capacities (summary)
| Fuel tank | 60.2 L (15.9 gal) |
| Hydraulic system | Not published on available spec sheets for this model. |
| Engine oil | Not published on available spec sheets for this model. |
| Cooling system | Not published on available spec sheets for this model. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
120B fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (Cat 3306 naturally aspirated diesel, with filter) | 29.5 L (7.8 US gal) per grader-specific service data; the Cat 3306 family's published lube-oil-system range runs about 27-34 L (28.5-36 US qt) across applications, so treat this as approximate and confirm against the plate for your exact serial prefix | Caterpillar heavy-duty diesel engine oil, API CD performance or higher. Use SAE 10W below 0°C (32°F), SAE 30 in temperate conditions, SAE 40 in sustained heat above roughly 30°C (86°F), or an SAE 15W-40 multigrade where ambient temperature swings widely through the season. |
| Cooling system | Not documented for the 120B specifically in available sources - confirm against the OMM for your serial prefix (32C or 64U) or with your dealer before servicing | Caterpillar permanent-type ethylene-glycol antifreeze/coolant mixed to the OMM's climate chart. Check concentration with a refractometer and top off with the same mix ratio, not straight water. |
| Fuel tank | 60.2 L (15.9 US gal) | No. 2-D diesel fuel for normal service. Switch to No. 1-D diesel in cold weather to reduce fuel waxing and starting trouble. |
| Transmission (power-shift transaxle) | Not documented for the 120B specifically in available sources - confirm with your dealer or the OMM for your serial prefix | Caterpillar transmission/drivetrain oil per the OMM's viscosity-by-temperature chart, the era equivalent of today's Cat TDTO drivetrain oil. |
| Bevel gear and differential | Not documented for the 120B specifically in available sources - confirm with your dealer or the OMM | Caterpillar gear oil meeting an API GL-5-equivalent specification, viscosity selected per the OMM's temperature chart. |
| Final drive, each side (tandem housings) | Not documented for the 120B specifically in available sources - confirm with your dealer or the OMM; check and fill each side separately | Caterpillar gear oil meeting an API GL-5-equivalent specification, same grade as the bevel gear and differential fill. |
| Circle drive housing | Not documented for the 120B specifically in available sources - confirm with your dealer or the OMM | Caterpillar gear oil per the OMM's circle-drive specification, drawn from the same gear-oil family as the final drives and differential. |
| Hydraulic system and tank | Not documented for the 120B specifically in available sources - confirm with your dealer or the OMM for your serial prefix | Caterpillar hydraulic oil per the OMM's viscosity-by-temperature chart, the era equivalent of today's Cat TDTO/HYDO hydraulic fluids. |
| Grease (chassis, circle, blade-lift, and wheel-lean points) | Not applicable - service item, no reservoir capacity | Caterpillar multipurpose chassis grease, NLGI 2 for normal service; drop to NLGI 1 in sustained cold weather for easier gun feed. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 120B 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 120B beyond the schedule
Predictive Maintenance & Fluid Analysis
The 120B carries no electronic engine or transmission controls, so oil sampling is the primary early-warning tool. Pull samples from the 3306 engine sump, transmission/differential, and both tandem cases at each service interval and watch for iron and copper trends signaling final-drive or clutch-pack wear. Track coolant condition and corrosion-inhibitor level in the wet-sleeve cylinder block to head off liner pitting. Inspect circle teeth, drawbar ball, and wheel-lean cylinders visually every shift since worn linkage shows up as blade chatter before it shows up in an oil report.
Corrective & Common Repairs
Expect circle wear shoes, drawbar ball sockets, and moldboard cutting edges to be the highest-turnover wear items on a 120B in grading service. Steering and wheel-lean cylinder seals leak as packing hardens with age; reseal rather than replace the cylinder if the rod and barrel are still true. Tandem case output seals and final-drive plugs weep oil on high-hour units - check the ground under each tandem after every shift. King pins, tie-rod ends, and circle-drive slip-clutch linings loosen from age and vibration and need periodic torque checks.
Overhaul & Rebuild Points
Powertrain overhauls on the 120B center on the 3306 engine - injectors, liners, and bearings are common rebuild items, and parts stay available because the same engine served Cat dozers, loaders, and scrapers of the era. Tandem final drives and the circle-drive gearbox are the next wear points after high grading hours; rebuild rather than replace, since housings and gears usually outlast seals and bearings. Transmission clutch packs wear from years of directional shifting and are a common mid-life rebuild alongside hydraulic pump and cylinder reseal work.
Seasonal & Environmental Servicing
Cold starts are the main seasonal risk on a naturally aspirated 3306 with no glow-plug or ether-start electronics to lean on - fit a block heater, run correct winter-viscosity oil, and confirm coolant corrosion-inhibitor concentration before freezing weather. In hot, dusty grading conditions, shorten air-cleaner intervals and clean the radiator core more often; a clogged core overheats the 3306 faster than a newer turbocharged engine would. Wash mud from tandem cases and circle teeth after wet-season work so packed dirt doesn't hide wear and seal leaks.
120B common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 1P-2299 | Filter As-Fuel | Fuel system service | Check fitment → |
| 2Y-8670 | Filter As-Fuel | Fuel system service | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
120B fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| OIL pressure gauge + warning lamp (no numeric code) | Engine oil pressure below safe operating threshold; not a stored diagnostic code, just an analog gauge sweep into the red band with an accompanying panel lamp | Low oil level, worn oil pump, plugged suction screen, worn bearings, or a failed pressure sender/gauge line | Stop the engine immediately, check oil level and condition, inspect for leaks, verify sender and gauge before returning to service |
| TEMP gauge + warning lamp (no numeric code) | Engine coolant temperature above normal operating range; shown as a gauge needle in the red plus a lamp, not a fault code | Low coolant, plugged radiator core, slipping or damaged fan belt, faulty thermostat, or water pump failure | Idle down, check coolant level and belt condition once safe, inspect radiator and thermostat, do not remove a hot cap |
| ALT / charge warning lamp (no numeric code) | Charging system not producing current at the battery; an ammeter or simple lamp on the panel, not a diagnostic code | Broken or slipping alternator belt, failed alternator, bad voltage regulator, or a loose/corroded battery connection | Check belt tension and condition, check battery terminals, test alternator output and regulator with a multimeter |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
120B attachments & work tools
Moldboard / grading blade
Standard moldboard for this grader size class runs about 3.7 m (12 ft) wide with a bolt-on, replaceable cutting edge. A bolt-on extension can add roughly 0.6 m (24 in) of coverage on one side; exact width and edge profile vary by configuration/series.
Front-mounted dozer/angle blade
A straight or angled front blade pins to the front lift group ahead of the machine for dozing, stockpile work, and light snow clearing, with roughly 30 degrees of hydraulic left/right angle travel on graders in this class. It works independently of the main moldboard.
Scarifier
A front scarifier hooks to the front lift group for light-duty breakup of compacted material, asphalt skin, and rocky subgrade ahead of grading. A mid-mount/rear scarifier gives deeper, better-controlled cut depth and clearer operator visibility than the front-mount version.
Rear ripper
A hydraulically actuated rear ripper mounts on the swinging drawbar/A-frame at the back of the machine, normally fitted with a small number of straight shanks and replaceable teeth for breaking hard-packed ground or old pavement. It occupies the same rear-frame position as the mid-mount scarifier, so the two are generally alternates rather than run together.
Push block / counterweight
A push block bolts to the front nose plate and serves both as a counterbalance for a rear ripper and as a push point when the grader is used to shove other equipment. It is a common pairing with the rear ripper option on this size class.
Snow wing
An auxiliary side-mounted wing blade (mast-type or mastless) attaches to the frame to widen the cleared path or bench drifted snow, used with or without the main moldboard. Mastless wings can ramp to roughly 40 degrees of bench angle; wing choice depends on drift depth and application.
Mounting / coupler system
The main moldboard rides on the circle-drawbar-moldboard assembly as permanent equipment, not a swap tool, with cutting edges bolted directly to it. Front tools (blade, scarifier) pin to the front lift group (A-frame); rear tools (ripper, mid scarifier) pin to the rear drawbar/A-frame mount. This class has no universal quick-coupler shared across work tools.
Hydraulic kit / arrangement notes
A front lift group and a rear ripper are not base equipment on this class of grader; fitting either calls for an auxiliary hydraulic valve section, hoses, and a mounting kit tied into the machine's hydraulic system. Once installed, control is normally by a dedicated lever or roller switch separate from the main blade/circle controls.
Guarding / factory configuration notes
Rock or debris guarding (belly pans, screens) for quarry- or forestry-duty work is a common dealer-fitted option across graders in this size class rather than one catalogued item. Confirm the exact guarding package for a given 120B serial range with a dealer.
All 120B assemblies by section
Every catalogued assembly group for the Caterpillar 120B. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Air Inlet And Exhaust System
7s6748 Air Cleaner Gp
| 7S***48 | Air Cleaner Group | 1 |
7s6748 Air Cleaner Group
| 7S***48 | Air Cleaner Group | 1 |
4n9586 Fastener Gp-Exhaust Manifold
| 4N***86 | Fastener Group-Exhaust Manifold; Exhaust Manifold Fastener Group | 1 |
2p6838 Air Lines Group
| 2P***38 | Lines Group-Air; Air Lines Group | 1 |
2p6572 Exhaust Manifold Group
| 2P***72 | Manifold Group-Exhaust; Exhaust Manifold Group | 1 |
1p1241 Muffler Group
| 1P***41 | Muffler Group | 1 |
2p7351 Exhaust Pipe Group
| 2P***51 | Pipe Group-Exhaust; Exhaust Pipe Group | 1 |
Basic Engine
1n4406 Camshaft Gp
| 1N***06 | Camshaft Group-Single; Camshaft Group--Single | 1 |
2y5174 Cylinder Block Cover Group
| 2Y***74 | Cover Group-Cylinder Block | 1 |
2p6530 Cover Gp-Cylinder Head
| 2P***30 | Cover Group-Cylinder Head; Cylinder Head Cover Group | 1 |
2y5248 Front Housing Cover Group
| 2Y***48 | Cover Group-Front Housing; Front Housing Cover Group | 1 |
2p6516 Cover Gp-Valve Mechanism
| 2P***16 | Cover Group-Valve Mechanism; Valve Mechanism Cover Group | 1 |
Crankshaft Bearing Replacements
| 8N***25 | Bearing (1.25mm Undersize) | 7 |
| 8N***26 | Bearing (0.51mm Undersize) | 7 |
| 8N***27 | Bearing (0.76mm Undersize) | 7 |
2y5206 Crankshaft Gp
| 2Y***06 | Crankshaft Group; Crankshaft Group | 1 |
7n6550 Cylinder Block As
| 7N***50 | Cylinder Block As | 1 |
2y5235 Cylinder Block As
| 2Y***35 | Cylinder Block As | 1 |
2y9363 Cylinder Block Gp
| 2Y***63 | Cylinder Block Group | 1 |
8n3021 Cylinder Block Gp
| 8N***21 | Cylinder Block Group; Cylinder Block Group | 1 |
1n3576 Cylinder Block Gp
| 1N***76 | Cylinder Block Group | 1 |
2y9518 Cylinder Head Gp
| 2Y***18 | Cylinder Head Group | 1 |
2p6476 Cylinder Head Gp*R
| 2P***76 | Cylinder Head Group; Cylinder Head Group | 1 |
8n1187 Cylinder Head Gp
| 8N***87 | Cylinder Head Group | 1 |
2p7838 Damper Group
| 2P***38 | Damper Group; Damper Group | 1 |
2p7831 Fan Drive Group
| 2P***31 | Drive Group-Fan; Fan Drive Group | 1 |
2y9484 Engine Ar-Part 1 Of 2
| 1N***06 | Camshaft Group-Single; Camshaft Group--Single | 1 |
| 1P***44 | Breather Group | 1 |
| 2P***29 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
2y9484 Engine Ar-Part 2 Of 2
| 2P***26 | Valve-Mechanism Group; Valve Mechanism Group | 1 |
| 2P***37 | Pump Group-Oil; Engine Oil Pump Group | 1 |
| 2P***72 | Manifold Group-Exhaust; Exhaust Manifold Group | 1 |
7n9536 Fastener Gp-Cylinder Head
| 7N***36 | Fastener Group-Cylinder Head; Cylindetr Head Fastener Group | 1 |
2p6546 Fastener Gp-Cylinder Head
| 2P***46 | Fastener Group-Cylinder Head; Cylinder Head Fastener Group | 1 |
5y0376 Fastener Gp-Cylinder Head
| 5Y***76 | Fastener Group-Cylinder Head | 1 |
2y5717 Front Housing Fastener Group
| 2Y***17 | Fastener Group-Front Housing; Front Housing Fastener Group | 1 |
5s3451 Flywheel Group
| 5S***51 | Flywheel Group; Flywheel Group | 1 |
2y5707 Front Timing Gear Group
| 2Y***07 | Gear Group-Front; Gear Gp-Front Timing | 1 |
2p6129 Flywheel Housing Group
| 2P***29 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
2y8429 Housing Gp-Front
| 2Y***29 | Housing Group-Front | 1 |
2y5250 Housing Gp-Front-Timing Gear
| 2Y***50 | Housing Group-Front; Front Housing Group | 1 |
6n8326 Lifting Eye Gp-Engine
| 6N***26 | Lifting Group; Lifting Eye Gp-Engine | 1 |
2y7719 Lifting Eye Gp-Engine
| 2Y***19 | Lifting Group-Engine; Lifting Eye Gp-Engine | 1 |
2s6981 Parts Gp-Miscellaneous
| 0S***09 | Bolt (3/4") Filler Tube Assembly To Transfer Drive Case | 1 |
| 1A***37 | Bolt Clutch Assembly To Bracket (Fan Support) | 4 |
| 1D***17 | Nut-Plate And Angle Assembly To Hydraulic And Fuel Tanks; Nut Plate And Angle Assembly To Hydraulic And Fuel Tanks | 1 |
4n4028 Rod & Piston Gp-6 Required
| 4N***28 | Piston & Rod Group; Connecting Rod And Piston Group | 1 |
2y2943 Pulley Group
| 2Y***43 | Pulley Group; Pulley Group | 1 |
6n0220 Crankshaft Seal Group
| 6N***20 | Seal Group-Crankshaft | 1 |
2p7751 Support Gp-Engine
| 2P***51 | Support Group-Engine; Engine Support Group | 1 |
7n9589 Trunnion Gp
| 7N***89 | Trunnion Group-Engine | 1 |
2p6526 Valve Mechanism Gp
| 2P***26 | Valve-Mechanism Group; Valve Mechanism Group | 1 |
Blade Controls, Hydraulic/Steering System
1g1305 Control Gp-Power-Side View-Part 2 Of 2
| 1G***05 | Control Group-Power | 1 |
1g1305 Control Gp-Power-Front View-Part 1 Of 3
| 1G***05 | Control Group-Power | 1 |
1g1305 Control Gp-Power-Front View-Part 1 Of 2
| 1G***05 | Control Group-Power | 1 |
1g1305 Control Gp-Power-Side View-Part 2 Of 3
| 1G***05 | Control Group-Power | 1 |
1g1305 Control Gp-Power-Side View-Part 3 Of 3
| 1G***05 | Control Group-Power | 1 |
6g4415 Cylinder Gp-Blade Side Shift
| 6G***15 | Cylinder Group | 1 |
2y8488 Cylinder Gp-Blade Side Shift
| 2Y***88 | Cylinder Group | 1 |
4j4115 Steering Cylinder Group
| 4J***15 | Cylinder Group-Steer | 1 |
2y4314 Power Control Drive Shaft Group
| 2Y***14 | Drive Shaft Group-Power Control | 1 |
2d2150 Filter Gp
| 2D***50 | Filter Group | 1 |
2y2160 Hydrostatic Gp-Steering-Part 2 Of 2
| 2Y***60 | Hydrostatic Group-Steering | 1 |
2y2160 Hydrostatic Gp-Steering-Part 1 Of 2
| 2Y***60 | Hydrostatic Group-Steering | 1 |
2y7205 Joint As-Universal
| 2Y***05 | Joint As | 1 |
2y7207 Joint As-Universal
| 2Y***07 | Joint As | 1 |
2y5396 Joint As
| 2Y***96 | Joint As | 1 |
2y5394 Joint As
| 2Y***94 | Joint As | 1 |
2d7836 Lift Gp-Blade-Part 2 Of 2
| 2D***36 | Lift Group-Blade | 1 |
2d7836 Lift Gp-Blade-Part 1 Of 2
| 2D***36 | Lift Group-Blade | 1 |
3g9801 Metering Pump Group
| 3G***01 | Pump Group-Metering | 1 |
2y3734 Pump Gp-Vane
| 2Y***34 | Pump Group-Vane | 1 |
4b8580 Shaft Gp-Control
| 4B***80 | Shaft Group-Control; Control Shaft Group | 1 |
2d4125 Shaft Gp-Leaning Wheel Control
| 2D***25 | Shaft Group-Leaning Wheel Control | 1 |
1g0642 Steering Gear Tank Group
| 1G***42 | Steering Gear Tank Group | 1 |
1g0643 Tank And Pump Group
| 1G***43 | Tank And Pump Group | 1 |
2y2250 Valve & Lines Gp
| 2Y***50 | Valve & Lines Group | 1 |
2y1947 Valve As
2y3697 Valve Gp
| 2Y***97 | Valve Group | 1 |
2y2175 Valve Gp-Relief
| 2Y***75 | Valve Group-Relief | 1 |
Brakes
4b8759 Brake As-Cylinder
| 4B***59 | Brake As-Cylinder | 1 |
1g2298 Brake As-L.H.
| 1G***98 | Brake As-Lh | 1 |
1g2299 Brake As-R.H.
| 1G***99 | Brake As-Rh | 1 |
3d9200 Brake Gp-Hydraulic Rear Wheel
| 3D***00 | Brake Group-Hydraulic | 1 |
4d4170 Control Gp-Clutch & Brake-Front View
| 4D***70 | Control Group-Brake & Clutch | 1 |
4d4170 Control Gp-Clutch & Brake-Side View
| 4D***70 | Control Group-Brake & Clutch | 1 |
2y4902 Control Gp-Hydraulic Brake
| 2Y***02 | Control Group-Hydraulic Brake | 1 |
3d2219 Cylinder As
| 3D***19 | Cylinder As | 1 |
5t7161 Cylinder Gp-Wheel
| 5T***61 | Cylinder Group-Wheel | 1 |
2y1040 Tandem Drive Housing Group
| 2Y***40 | Housing Group-Tandum Drive | 1 |
2y5565 Lever As-Brake
| 2Y***65 | Lever As-Brake | 1 |
Cab, Gauges And Accessories
2y2000 Cab Door Gp
| 2Y***00 | Cab Door Group | 1 |
2y1270 Cab Gp
| 2Y***70 | Cab Group | 1 |
2y2020 Cab Gp
| 0T***42 | Bolt | 5 |
| 2D***34 | Glass (Untinted) | 1 |
| 2P***52 | Spring | 1 |
2y1982 Door Gp-Lh
| 2Y***82 | Door Group-Lh | 1 |
2y1981 Door Gp-Rh
| 2Y***81 | Door Group-Rh | 1 |
8d8175 Gauge Gp
| 8D***75 | Gauge Group | 1 |
2y7633 Gauge Gp
| 2Y***33 | Gauge Group | 1 |
2y6835 Gauge Gp
| 2Y***35 | Gauge Group | 1 |
8f9866 Grease Gun Gp
| 8F***66 | Grease Gun As | 1 |
2y7212 Hardware Gp-Cab
| 0T***24 | Bolt 9.525 mm(.375 In.) Dia. N. C. | 4 |
| 1B***03 | Nut Exhaust Pipe To Starting Engine Cylinder Block | 8 |
| 1D***17 | Nut-Plate And Angle Assembly To Hydraulic And Fuel Tanks; Nut Plate And Angle Assembly To Hydraulic And Fuel Tanks | 18 |
1g1553 Platform Gp-Seat Frame & Fuel Tank
| 1G***53 | Platform Group | 1 |
2y5468 Seat Belt Group
| 2Y***68 | Seat Belt Group | 1 |
2y2232 Seat Frame Assembly
| 2Y***32 | Seat Frame As | 1 |
6g2090 Seat Group
| 6G***90 | Seat Group | 1 |
2y2576 Tool Gp
| 2Y***76 | Tool Group-Hand | 1 |
2y1995 Windshield Gp
| 2Y***95 | Windshield Group | 1 |
Chassis
2d4140 Axle Gp-Front-Part 1 Of 3
| 2D***40 | Axle Group-Front | 1 |
2d4140 Axle Gp-Front-Part 3 Of 3
| 2D***40 | Axle Group-Front | 1 |
2d4140 Axle Gp-Front-Part 2 Of 3
| 2D***40 | Axle Group-Front | 1 |
3d2329 Hub Cap Assembly
| 3D***29 | Cap Group-Hub | 1 |
2d6400 Centershift Gp
| 2D***00 | Centershift Group; Centershift Group | 1 |
2d7900 Circle Gp-Part 2 Of 2
| 2D***00 | Circle Group | 1 |
2y1760 Circle Gp-Part 1 Of 2
| 2Y***60 | Circle Group | 1 |
2d7900 Circle Gp-Part 1 Of 2
| 2D***00 | Circle Group | 1 |
2d7900 Circle Gp
| 2D***00 | Circle Group | 1 |
2y1760 Circle Gp-Part 2 Of 2
| 2Y***60 | Circle Group | 1 |
Circle Reversing Mechanism
2y2280 Frame Gp
| 2Y***80 | Frame Group | 1 |
2y2875 Hood & Dash Gp
| 2Y***75 | Hood & Dash Group | 1 |
6d4430 Radiator Support Group
| 6D***30 | Support Group-Radiator | 1 |
1g1655 Front Wheels And Tires Group
| 1G***55 | Wheel & Tire Group-Front | 1 |
Cooling System
8n4457 Base Gp-Oil Filter
| 8N***57 | Base Group-Oil Filter; Base Group-Engine Oil Filter | 1 |
8n4457 Base Gp-Engine Oil Filter
| 8N***57 | Base Group-Oil Filter; Base Group-Engine Oil Filter | 1 |
2p6215 Cooler Gp-Engine Oil
| 2P***15 | Cooler Group-Engine Oil; Oil Cooler Group Engine | 1 |
2y8054 Cooler Gp-Filter & Engine Oil
| 2Y***54 | Cooler Group-Filter & Engine Oil | 1 |
2w6954 Cooler Gp-Filter Base & Engine Oil
| 2W***54 | Cooler Group-Filter Base & Eng Oil | 1 |
2y8053 Cooler Gp-Filter Base & Engine Oil
| 2Y***53 | Cooler Group-Filter Base & Eng Oil; Cooler Gp-Filter Base & Engine Oil | 1 |
2w6953 Cooler Gp-Filter Base & Engine Oil
| 2W***53 | Cooler Group-Filter Base & Eng Oil | 1 |
7s3739 Fan & Guard Gp-Blower
| 7S***39 | Fan Group-Blower | 1 |
2p8172 Housing & Regulator Gp
| 2P***72 | Housing & Regulator Group; Regulator And Housing Group | 1 |
7n7211 Lines Gp-Water
| 7N***11 | Lines Group-Water; Water Lines Group | 1 |
8n4112 Lines Gp-Water
| 8N***12 | Lines Group-Water; -Bypass Relief | 1 |
2p7740 Lines Gp-Water
| 2P***40 | Lines Group-Water; Water Lines Group--Elbow | 1 |
2y8079 Lines Gp-Water
| 2Y***79 | Lines Group-Water; Water Lines Group | 1 |
7n5909 Water Pump Group
| 7N***09 | Pump Group-Water; Water Pump Group | 1 |
2w8001 Pump Gp-Water*R
| 2W***01 | Pump Group-Water | 1 |
7n5909 Pump Gp-Water
| 7N***09 | Pump Group-Water; Water Pump Group | 1 |
2p8195 Radiator Gp-Side View-Part 1 Of 2
| 2P***95 | Radiator Group | 1 |
2p8195 Radiator Gp-Rear View-Part 2 Of 2
| 2P***95 | Radiator Group | 1 |
Engine Arrangement
2y5175 Engine Ar-Part 1 Of 2
| 1N***06 | Camshaft Group-Single; Camshaft Group--Single | 1 |
| 2P***29 | Housing Group-Flywheel; Flywheel Housing Group | 1 |
| 2P***99 | Fastener Group-Oil Pan; Oil Pan Fastener Group | 1 |
2y5175 Engine Ar-Part 2 Of 2
| 1P***44 | Breather Group | 1 |
| 2P***15 | Cooler Group-Engine Oil; Oil Cooler Group Engine | 1 |
| 2P***75 | Filter Group-Engine Oil; Oil Filter Group (10z1 ~ 10z7023) | 1 |
Fuel System And Governor
2y5993 Control Gp-Governor
| 2Y***93 | Control Group-Governor | 1 |
2y9252 Cover As
| 2Y***52 | Cover As | 1 |
2y6115 Cover Gp-Governor
| 2Y***15 | Cover Group-Governor | 1 |
2y8982 Cover Gp-Governor & Detent
| 2Y***82 | Cover Group-Governor & Detent | 1 |
1p2299 Filter As-Fuel
| 1P***99 | Filter As-Fuel; (Advanced Efficiency)(Secondary) | 1 |
2y8670 Filter As
| 2Y***70 | Filter As-Fuel | 1 |
2y5711 Filter Gp-Fuel
| 2Y***11 | Filter Group-Fuel; Fuel Filter Group | 1 |
2y6518 Flyweight Gp
| 2Y***18 | Flyweight Group | 1 |
2y8980 Flyweight Gp
| 2Y***80 | Flyweight Group | 1 |
2y6160 Governor Gp- Part 2 Of 2
| 2Y***60 | Governor Group | 1 |
2y8993 Governor Gp-Part 2 Of 2
| 2Y***93 | Governor Group | 1 |
2y8993 Governor Gp-Part 1 Of 2
| 2Y***93 | Governor Group | 1 |
2y6160 Governor Gp-Part 1 Of 2
| 2Y***60 | Governor Group | 1 |
5y1157 Governor Gp-Part 2 Of 2
| 5Y***57 | Governor Group | 1 |
2y6160 Governor Gp-Part 2 Of 2
| 2Y***60 | Governor Group | 1 |
5y1157 Governor Gp-Part 1 Of 2
| 5Y***57 | Governor Group | 1 |
2y6105 Governor Gp
| 2Y***05 | Governor Group | 1 |
2y5709 Fuel Injection Lines Group
| 2Y***09 | Lines Group | 1 |
2y5907 Lines Gp-Fuel
| 2Y***07 | Lines Group-Fuel | 1 |
2y5708 Fuel Injection Lines & Mounting Gp
| 2Y***08 | Lines Group-Fuel Injection; Fuel Injection Lines & Mounting Gp | 1 |
2y5708 Lines Gp-Fuel Injection
| 2Y***08 | Lines Group-Fuel Injection; Fuel Injection Lines & Mounting Gp | 1 |
2y5712 Lines Gp-Injection Pump Lube Oil
| 2Y***12 | Lines Group-Lube Oil; Injection Pump Lubrication Oil Lines Grp | 1 |
2y5800 Governor & Fuel Injection Pump Gp-Part 2 Of 2
| 2Y***00 | Pump Group-Fuel Injection | 1 |
2y5800 Pump Gp-Fuel Injection-Part 2 Of 2
| 2Y***00 | Pump Group-Fuel Injection | 1 |
2y5800 Governor & Fuel Injection Pump Gp-Part 1 Of 2
| 2Y***00 | Pump Group-Fuel Injection | 1 |
2y5800 Pump Gp-Fuel Injection-Part 1 Of 2
| 2Y***00 | Pump Group-Fuel Injection | 1 |
2y5787 Pump Gp-Fuel Transfer
| 2Y***87 | Pump Group-Fuel Transfer | 1 |
2y5716 Governor And Fuel Injection Pump Gp
| 2Y***16 | Pump Group-Gov & Fuel Inj; Governor And Fuel Injection Pump Group | 1 |
2y8994 Governor & Fuel Injection Pump Gp
| 2Y***94 | Pump Group-Gov & Fuel Inj; Governor & Fuel Injection Pump Gp | 1 |
5y1156 Governor,Fuel Injection & Fuel Transer Pump Gp
| 5Y***56 | Pump Group-Gov, Fuel Inj & Tfr; Governor & Fuel Injection Pump Gp | 1 |
2y6133 Rack Gpoup
| 2Y***33 | Rack Setting Group | 1 |
2y9250 Setting Gp
| 2Y***50 | Setting Group | 1 |
2y6158 Shim Group-Calibration Set
| 2Y***83 | Shim--10 mm (0.40 In. Thick) | 6 |
| 2Y***84 | Shim--11 mm (0.45 In. Thick) | 6 |
| 2Y***85 | Shim--13 mm (0.50 In. Thick) | 6 |
Implements
2y2260 Blade Ar-Power-Type 2
| 2Y***60 | Circle Group | 1 |
| 2Y***50 | Valve & Lines Group | 1 |
| 2Y***60 | Blade Ar-Power | 1 |
2y2260 Blade Ar-Power-Type 1
| 2Y***56 | Boss Group | 1 |
| 2Y***60 | Circle Group | 1 |
| 2Y***50 | Valve & Lines Group | 1 |
1g2227 Blade Gp-Type 2
| 1G***27 | Blade Group | 1 |
1g2227 Blade Gp-Type 1
| 1G***27 | Blade Group | 1 |
5d4790 Blade Gp
| 5D***90 | Blade Group; Blade Group | 1 |
1g2227 Blade Gp
| 1G***27 | Blade Group | 1 |
6d3300 Scarifier Gp-Part 3 Of 3
| 6D***00 | Scarifier Group | 1 |
6d3300 Scarifier Gp-Part 1 Of 3
| 6D***00 | Scarifier Group | 1 |
6d3300 Scarifier Gp-Part 2 Of 3
| 6D***00 | Scarifier Group | 1 |
4d8510 Support Gp-Blade Bracket
| 4D***10 | Support Group-Blade Bracket | 1 |
Lubrication System
1p4244 Breather Group
| 1P***44 | Breather Group | 1 |
2p6199 Fastener Gp-Oil Pan
| 2P***99 | Fastener Group-Oil Pan; Oil Pan Fastener Group | 1 |
2p6855 Filler Gp-Engine Oil
| 2P***55 | Filler Group-Oil | 1 |
2p6475 Filter Gp-Oil
| 2P***75 | Filter Group-Engine Oil; Oil Filter Group (10z1 ~ 10z7023) | 1 |
2y6278 Fumes Disposal Group
| 2Y***78 | Fumes Disposal Group; Fumes Disposal Group | 1 |
2y8416 Gauge Gp-Oil Level (Dipstick)
| 2Y***16 | Gauge Group-Oil Level (Dipstick) | 1 |
2p6493 Gauge Gp-Oil Level (Dipstick)
| 2P***93 | Gauge Group-Oil Level (Dipstick); -Engine | 1 |
2p6861 Lines Gp-Engine Oil
| 2P***61 | Lines Group-Engine Oil; Engine Oil Lines Group | 1 |
2y5231 Oil Pan Group
| 2Y***31 | Pan Group-Oil | 1 |
2p7830 Gear Pump Group
| 2P***30 | Pump Group-Gear | 1 |
2p6537 Pump Gp-Oil
| 2P***37 | Pump Group-Oil; Engine Oil Pump Group | 1 |
Power Train-Power Transmission Unit
7d7630 Rear Axle Group
| 7D***30 | Axle Group-Rear | 1 |
4d2150 Transmission Brake Group
| 4D***50 | Brake Group-Transmission | 1 |
5d3400 Transmission Case And Covers Group-Side View
| 5D***00 | Case & Covers Group-Tmsn | 1 |
5d3400 Transmission Case And Covers Group-End View
| 5D***00 | Case & Covers Group-Tmsn | 1 |
6d1590 Clutch Gp-Flywheel
| 6D***90 | Clutch Group-Flywheel | 1 |
7d5460 Filter Gp-Oil
| 7D***60 | Filter Group-Oil | 1 |
7d9550 Transmission Lubrication System Group
| 7D***50 | Lubrication Group-Transmission | 1 |
4d2790 Shift Gp-Gear
| 4D***90 | Shift Group-Gear | 1 |
4d3300 Transmission Gp-Part 4 Of 4
| 4D***00 | Transmission Group | 1 |
4d3300 Transmission Gp-Part 3 Of 4
| 4D***00 | Transmission Group | 1 |
4d3300 Transmission Gp-Part 1 Of 4
| 4D***00 | Transmission Group | 1 |
4d3300 Transmission Gp-Part 2 Of 4
| 4D***00 | Transmission Group | 1 |
1g1660 Wheel & Tire Gp-Rear
| 1G***60 | Wheel & Tire Group-Rear | 1 |
Service Equipment And Supplies
Gasket Kits
| 5P***68 | Kit-Gasket; (Single Cylinder Liner)(Single Cylinder Liner) | 0 |
| 5P***98 | Valve Grinding; - Serial No. 3n55880 To 3n79762 Inclusive | 0 |
| 5P***02 | 8n***60, 8n***61, 8n***15, 8n***16; 1w***78, 1w***79, 1w***86, 1w***87 | 0 |
Name Plates And Transfers
| 1G***08 | Plate-Instruction-On Instrument Panel | 1 |
| 1G***47 | Plate-Gearshift-Under Instrument Panel | 1 |
| 1G***83 | Cap-Grease | 74 |
Starting And Electrical System
2y4212 Alternator Gp
| 2Y***12 | Alternator Group-Charging | 1 |
2y2935 Alternator Gp
| 2Y***35 | Alternator Group-Charging | 1 |
2y8945 Alternator Gp
| 2Y***45 | Alternator Group-Charging | 1 |
2y8310 Alternator Gp
| 2Y***10 | Alternator Group-Charging | 1 |
2y1955 Battery & Wiring Gp-Part 3 Of 5
| 2Y***55 | Battery & Wiring Group | 1 |
2y1955 Battery & Wiring Gp-Part 4 Of 5
| 2Y***55 | Battery & Wiring Group | 1 |
2y1955 Battery & Wiring Gp-Part 5 Of 5
| 2Y***55 | Battery & Wiring Group | 1 |
2y1955 Battery & Wiring Gp-Part 2 Of 5
| 2Y***55 | Battery & Wiring Group | 1 |
2y1955 Battery & Wiring Gp-Part 1 Of 5
| 2Y***55 | Battery & Wiring Group | 1 |
5s8501 Glow Plug Group
| 5S***01 | Glow Plug Group; Glow Plug And Wiring Group | 1 |
2y2074 Harness Assembly
| 2Y***74 | Harness As | 1 |
7m7147 Lamp As-Stop & Tail
| 7M***47 | Lamp As-Stop & Tail | 1 |
1m3387 Dash Lamp Assembly-24 Volt
| 1M***87 | Lamp Group | 1 |
1m6052 Head Lamp Assembly-24 Volt
| 1M***52 | Lamp Group | 1 |
2y1780 Lamp Gp-Head
| 2Y***80 | Lamp Group-Head | 1 |
2y2930 Regulator As
| 2Y***30 | Regulator As; (Separate Illustration) | 1 |
2y1920 Starting Motor Gp-Electric
| 2Y***20 | Starting Motor Group-Electric | 1 |
2y1921 Starting Motor Gp-Electric
| 2Y***21 | Starting Motor Group-Electric | 1 |
7n0718 Switch As-Disconnect
| 7N***18 | Switch As-Disconnect; -Battery-Ground Level | 1 |
2y8441 Switch As-Disconnect
| 2Y***41 | Switch As-Disconnect | 1 |
7n4160 Switch Gp
| 7N***60 | Switch Group | 1 |
120B serial number reference
On a 120B the serial (PIN) plate sits on the main frame rather than in a cab-mounted location used on later graders, commonly near the front chassis or engine compartment area; if the plate is missing or unreadable, the number is also stamped directly into the frame. Read the first three characters as the prefix, which identifies the serial-number block the unit was built in (and the matching parts/service manual to use); the digits that follow are the sequential unit number within that block. This model predates Cat's 17-character PIN format, so the plate shows only the prefix-plus-digits serial number.
| Prefix | Identifies | Notes |
|---|---|---|
| 32C | 120B motor grader | Covers the serial block from 32C00001 up (parts documentation references 32C00100-UP as a build point within this block). Fitted with the Cat 3306 engine. Full parts and service manuals exist for this prefix as a standalone serial-number break. |
| 64U | 120B motor grader | Covers the serial block from 64U02061 up. Fitted with the Cat 3306 engine, confirmed for the blade control and steering system parts listing. Full parts and service manuals exist for this prefix as a standalone serial-number break. |
Frequently asked questions
What engine does the Caterpillar 120B motor grader use?
The 120B uses the Cat 3306, a naturally aspirated diesel inline six-cylinder of about 10.5 L (638 cu in) displacement, rated near 93 kW (125 hp). This replaced the smaller D333-family engine used in the earlier Cat 120 and was itself replaced by the four-cylinder Cat 3304 in the following 120G.
What is the operating weight of the Caterpillar 120B?
Standard operating weight is about 12,000-12,030 kg (26,460-26,510 lb), depending on tire size, counterweighting, and attachments such as a front ripper or scarifier. Treat any single published figure as a base-configuration number and verify it against the specific machine's equipment list.
What replaced the Caterpillar 120B motor grader?
Caterpillar replaced the 120B with the 120G, which kept the same general size class but switched to a smaller-displacement four-cylinder Cat 3304 engine and ran a higher operating weight. The 120G line later gave way to the 120H, 120K, and 120M generations.
What 120B owners discuss
What engine does the 120B actually run, and what's its reputation?
The 120B uses the Caterpillar 3306 inline six-cylinder diesel, naturally aspirated in this grader application, rated around 93 kW (125 hp) gross. It replaced the older D333 six used in the earlier 120-series grader before the B suffix. On high-hour, aged units, the recurring pattern failures are cracked cylinder heads, dropped valves, and worn liners - normal end-of-life wear on this engine family, not a defect tied to one production run. Leaking injectors or a tired injection pump letting fuel wash into the crankcase oil is another common finding, along with front main seal and water pump seepage. Don't confuse this with the higher-output turbocharged/aftercooled 3306 ratings used in trucks and generator sets - the grader version here is the lower-output naturally aspirated build.
How does the hydraulic system behave compared to newer Cat graders?
This grader runs a fixed-displacement gear-type hydraulic pump feeding an open-center valve bank, not the load-sensing circuits Cat introduced later on H- and K-series graders. Blade and circle response speed tracks engine rpm directly, so sluggish lift and circle rotation at low idle or in cold weather is normal for this design, not a sign of a failing pump. Response should even out once the engine is at working rpm and the oil has warmed. If the machine still feels slow at operating rpm with warm oil, that points to a real pump, relief valve, or cylinder seal problem worth chasing.
What wears out first in the drivetrain and undercarriage?
Tandem drive chains running in an oil bath are the classic wear item on this grader family - they stretch with age and use, and mechanics judge them by elongation and slack rather than a fixed hours interval. Oil level and condition in the tandem cases matters as much as the chain itself; running them low accelerates stretch. On the circle end, a slip clutch in the circle drive protects the drawbar, circle, and moldboard from shock loads when the blade hits something solid. Repeated slipping under normal grading load means the clutch needs adjustment, not that it's failing. Circle segments and moldboard wear strips are consumables - check for backlash and even wear at each service interval.
What electrical problems actually show up on a grader this old?
This is a pre-electronic machine: a conventional alternator-and-regulator charging system with basic gauges or warning lights, not the ECM-controlled transmission and sensor network Cat added later on H- and K-series graders. There's no shift-solenoid or transmission-control-module fault code to chase here. What actually turns up on a 120B this age is corroded or loose ground connections, weak or failing alternator output, and brittle or cracked wiring insulation after decades of heat and vibration. An intermittent gauge or charging complaint on this machine usually starts and ends with cleaning grounds and checking alternator output.
Why does the steering feel loose or noisy at full lock?
With the engine running, turn the wheel fully to each lock and listen. A loud bang or groan there commonly points to the steering cushion (relief) valve. If the front and rear frame halves don't line up straight when centered, suspect a bent or loose articulation hitch rather than tire wear pulling it. A failing cushion valve or worn articulation hitch can lead to a steering failure mid-job, so have your dealer or a qualified hydraulic tech verify and pressure-test the steering circuit before the machine goes back into regular service.
The front wheels feel like they have some play - is that normal?
Some play is normal, but it has to stay within spec. With the front end raised, both wheels should spin freely by hand; a wheel that drags or feels rough points to a worn bearing. Push down on one raised front wheel to check the axle pivot - it should move freely without bouncing or clunking. Excess play in the axle pivot or wheel bearings shows up directly as a wavy finish grade, so it's worth chasing even before it affects steering feel.
What should I check before buying a used Cat 120B?
Walk the whole machine looking for oil weeping at the circle drive, cylinder rod seals, and tandem cases first - leaks there are the cheapest tell on a machine this age. Check the circle and moldboard for backlash and uneven wear, and check the blade linkage for play or loose/missing bolts. Cycle the blade and circle at operating rpm to confirm hydraulic response isn't sluggish once the oil is warm. Check the articulation hitch for alignment and looseness, and turn the wheel lock-to-lock listening for cushion-valve noise. Check power shift transmission oil condition and level, and look for fuel-diluted or milky engine oil, which points to injector or head problems on the 3306. Confirm tire condition and front wheel bearing/axle pivot play. Given the machine's age, have your dealer or an independent heavy-equipment mechanic run a full pre-purchase inspection, including the steering and brake systems, before putting it to work.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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