Caterpillar 25
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar Twenty-Five is a pre-war, gasoline-powered track-type tractor built in Peoria, Illinois from 1931 to 1933, identified by its 3C serial prefix across roughly 638 units produced. It carries a 4-cylinder, 4.5 L (277 cu in) water-cooled gasoline engine rated near 1,100 rpm, producing in the neighborhood of 26-28 hp at the drawbar and 30-33 hp at the belt depending on source and tune, driving through a 3-speed sliding-gear transmission with cable-operated implement control and no hydraulics. Operating weight runs around 3,493 kg (7,700 lb) on available records. The Twenty-Five is a direct redesign of the earlier Caterpillar Twenty (PL), carrying forward much of its running gear, and was itself superseded within a couple of years by the higher-output Twenty-Eight. Caterpillar offered the Twenty-Five in two track gauges, a narrow 1,067 mm (42 in) and a wide 1,397 mm (55 in) configuration, with undercarriage components that do not interchange between the two.
Within its short run the Twenty-Five sat at a transition point in Caterpillar's early lineup, arriving as the company moved off the older Twenty (PL) chassis and just ahead of its broader shift toward later, more refined gas-engine designs. Because so few were built and no OEM parts supply chain has existed for this generation of Caterpillar tractor in decades, a surviving Twenty-Five today is valued mainly as a vintage collector and show machine rather than a working tool with a parts counter behind it. Owners and restorers lean on the parts overlap with the Twenty and Twenty-Eight for common wear items, track down era-correct fuel pumps, carburetors, and magnetos through private and salvage channels, and treat serial-prefix verification (3C) as the only reliable way to separate a genuine Twenty-Five from a re-tagged sibling model.
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 25 specifications
Identification
| Model | Caterpillar Twenty-Five (Model 25), gasoline crawler tractor |
| Production years | 1931-1933 |
| Built at | Peoria, Illinois, USA |
| Serial number prefix | 3C |
| Lineage | Direct successor to the Caterpillar Twenty PL, sharing most running gear. Renamed Twenty-Eight in 1933 as output rose further. Not related to later D-series or wheeled Cat models numbered 25. |
Engine
| Type | 4-cylinder, gasoline, water-cooled, overhead-valve |
| Displacement | 4.5 L (277 cu in) |
| Bore x stroke | 102 x 140 mm (4.00 x 5.50 in) |
| Rated speed | 1,100 rpm |
| Power (claimed) | Drawbar approx. 26 hp, belt approx. 30 hp |
| Power (tested) | Drawbar approx. 27.1 hp, belt approx. 33.0 hp. One source states 28 hp; treat exact rating as varying by test/tune. |
| Fuel | Gasoline (distillate-fuel option not confirmed for this model in available sources) |
| Emissions | Pre-regulation era; no emissions certification applicable |
Transmission and Drivetrain
| Transmission type | 3-speed sliding-gear, 3 forward / 1 reverse |
| Steering/drive | Crawler (track-type), clutch-brake steering typical of the era |
Weights
| Operating weight | Approx. 3,493 kg (7,700 lb); figure is approximate and not confirmed for this exact configuration. |
Dimensions and Undercarriage
| Track gauge options | Narrow gauge 1,067 mm (42 in) and wide gauge 1,397 mm (55 in) |
| Track/shoe length options | Sources reference 53 in, 56 in, and 74 in track assemblies; exact meaning (overall track length vs. shoe pitch) not clearly documented, verify against a period parts book |
| Overall length/width/height | Not documented in available sources |
| Ground clearance | Not documented in available sources |
Performance
| Travel speeds | Not documented per-gear in available sources; 3-speed transmission with typical low crawler speeds for the class (a few km/h in low gear up to roughly walking-to-jogging pace in top gear) |
| Drawbar pull | Not documented as a discrete rating; contemporary Nebraska-style tests report drawbar horsepower only (see Engine group), not peak pull force |
| Ground pressure | Not documented in available sources |
| Gradeability | Not documented in available sources |
Blades and Attachments
| Factory blade options | Not documented in available sources; dozer blades for machines of this era were typically aftermarket/third-party attachments rather than a factory-cataloged S/SU/A/VPAT lineup |
Service Capacities
| Fuel tank | Not documented in available sources |
| Engine oil | Not documented in available sources |
| Cooling system | Water-cooled (radiator capacity not documented in available sources) |
| Final drive/track roller lubrication | Not documented in available sources |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
25 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (4-cyl. gasoline engine) | Not documented in accessible sources for this model. | Not documented in accessible sources. The Twenty-Five ran a straight gasoline-fired engine; period Caterpillar literature of this era generally called for a straight-grade SAE engine oil (commonly SAE 30, with lighter grades in cold weather) rather than a branded multi-service oil line — Cat DEO-family branding postdates this machine by decades. Verify against an original Twenty-Five operator's or servicemen's reference book if one can be sourced. |
| Cooling system | Not documented in accessible sources for this model. | Not documented in accessible sources. Period practice for gasoline crawler tractors of this generation was plain water with anti-freeze added for cold climates; no ethylene-glycol long-life coolant existed yet for this era. |
| Fuel tank | Not documented in accessible sources for this model. | Gasoline (the Twenty-Five used a 4-cylinder gasoline engine, not diesel). |
| Transmission (main gear transmission) | Not documented in accessible sources for this model. | Not documented in accessible sources. Note: the Twenty-Five predates Caterpillar's powershift transmissions entirely — it used a 3-speed sliding-gear (selective gear) transmission. Era-typical practice across the gasoline crawler line was a straight SAE 30 gear/transmission oil, but this is not confirmed against a Twenty-Five-specific source. |
| Bevel gear / steering clutch compartment | Not documented in accessible sources for this model. | Not documented in accessible sources. If the OMM splits this compartment out separately (as on sibling gasoline models of the period), era practice used the same straight SAE gear oil as the transmission, but this has not been confirmed specifically for the Twenty-Five. |
| Final drives (each side) | Not documented in accessible sources for this model. | Not documented in accessible sources. |
| Hydraulic system / tank | Not applicable / not documented. | The Twenty-Five is a pre-hydraulic-implement-era crawler (1931-1933); blade and implement control on machines of this generation was cable-operated, not hydraulic. No hydraulic tank fill is expected in its lubrication chart. |
| Track frame pivot shaft | Not documented in accessible sources for this model. | Not documented in accessible sources. Equalizer/pivot-shaft points on crawlers of this era were typically grease-lubricated via zerk fittings rather than an oil-fill compartment. |
| Grease points (track rollers, idlers, clutch linkage, etc.) | Not documented — chassis grease points are service-interval items, not fill-capacity items. | Not documented in accessible sources for this specific model. Era-typical Caterpillar practice called for a general-purpose chassis grease (period literature referenced specs such as 'Superior All-Purpose Lubricant' / general chassis grease equivalents) applied via grease gun at zerk fittings; no synthetic multi-purpose grease lines existed yet in this machine's era. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 25 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 100 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
Servicing the 25 beyond the schedule
Predictive Maintenance & Fluid Analysis
With no factory lubrication chart to follow, daily oil level and appearance checks are the best read on engine health available: dark, gritty, or fuel-diluted oil on a gasoline engine like the Twenty-Five's usually points to worn rings or a leaking carburetor float before a gauge ever moves. Watch coolant color and level for early signs of a leaking head gasket or cracked block. Listen for magneto ignition miss or steering clutch chatter at idle; both surface as sound and feel long before outright failure.
Corrective & Common Repairs
The most common corrective job on a Twenty-Five is freeing steering clutches rust-bonded from storage; soak a mildly stuck pack with penetrating fluid first, but a genuinely seized pack means pulling the final drives to split, clean, and inspect each disc. Surging or runaway idle almost always traces to a carburetor or governor linkage reassembled with the throttle plate or knob-pull arm reversed rather than a worn part. Fuel pumps are the hardest component to source, so inspect and rebuild the original rather than assuming a replacement is readily available.
Overhaul & Rebuild Points
A full mechanical overhaul centers on decarbonizing the combustion chambers and resetting valve clearance, standard work on any period gasoline engine after extended service. Steering clutch discs, final-drive gearing, and track-frame pivot bushings are the wear points that decide whether a rebuild is worth the labor, so inspect all three before committing. Rebuild the magneto and breaker assembly on the original unit rather than assuming a swap-in replacement exists. Confirm the 42 in or 55 in track gauge before ordering any undercarriage component, since parts do not cross between them.
Seasonal & Environment Servicing
Outdoor storage is the single biggest threat to a Twenty-Five: moisture works into the final-drive housings and bonds steering clutch plates together even on a machine that ran fine when parked, so confirm clutch-pack freedom before putting a long-stored machine back to work. Drain or condition fuel before layup, since old gasoline gums the carburetor and fuel pump. In cold-weather service, expect a gasoline, magneto-ignition engine of this era to need a slower warm-up and more deliberate choke and governor handling than a modern diesel before it will pull a full load.
25 attachments & work tools
Machine identification
The Caterpillar 25 ("Twenty-Five") is a pre-war crawler tractor built roughly 1931-1933 (some registries extend production into the late 1930s), powered by a 4-cylinder gasoline engine of about 4.5L displacing roughly 30 hp at the belt. It replaced the Twenty and was itself succeeded by the Twenty-Eight. It predates hydraulics entirely and is a cable-control (mechanical) era machine, not a modern D-series dozer, so blade-type letter codes (S/SU/A) and VPAT do not apply to it.
Blades
No factory hydraulic blade line exists for this model; blade work was done with cable-operated dozer blades fitted by independent implement builders of the era (LeTourneau and similar cable-control makers) rather than a Caterpillar-branded blade family. Width and capacity figures for a Twenty-Five-specific blade are not documented in surviving specification sheets; treat any blade fitment as a period aftermarket conversion, not a catalog option.
Rippers
Rooter/scarifier attachments of this era were single-shank, drawbar-towed or cable-lifted implements rather than the multi-shank rear-mounted rippers used on later diesel dozers. No documentation ties a specific multi-shank ripper or shank weight to the Twenty-Five; single-shank rooters pulled behind the drawbar are the only period-correct option referenced for this tractor class.
Winches
Where cable-controlled work tools were fitted, the "winch" is really a rear-mounted power control unit (PCU) that spools cable through an overhead frame or boom to the front-mounted blade or towed scraper, not a dedicated towing winch as understood on modern machines. LeTourneau was the dominant PCU builder for Caterpillar tractors of this size class through the 1930s and 1940s; Caterpillar did not begin building its own in-house cable controls until the mid-1940s, after this model's production run.
Drawbars/counterweights
As primarily an agricultural/orchard crawler, the Twenty-Five used a conventional rear drawbar for towed implements such as plows, discs, scrapers, and wagons. No factory counterweight package is documented for this model; any added mass for blade or winch balance would have been part of the aftermarket cable-control installation rather than a Caterpillar option.
Cab/ROPS guarding
The Twenty-Five was built with an open operator's station; no cab and no ROPS structure existed for this era, as rollover protection standards postdate this tractor by several decades. No forestry or waste-handling guard packages are documented for this model; such guarding did not exist as a factory or aftermarket category until much later dozer generations.
Hydraulic arrangement
The Twenty-Five has no hydraulic system for work tools. All blade, rooter, or scraper actuation on machines of this era relied on mechanical cable control (rope and sheave/PCU) rather than front or rear hydraulic circuits; hydraulic implement control did not become standard on Caterpillar track-type tractors until later, hydraulically-controlled tractor generations.
All 25 assemblies by section
Every catalogued assembly group for the Caterpillar 25. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
No. 25 Cable Control
5f9336 Adapter Group--Type 2
| 5F***36 | Adapter Group | 1 |
7f7995 Adapter Group
| 7F***95 | Adapter Group | 1 |
6f6055 Adapter Group
| 6F***55 | Adapter Group | 1 |
3h6344 Adapter Group
| 3H***44 | Adapter Group | 1 |
5f6550 Adapter Group--Type 1
| 5F***50 | Adapter Group | 1 |
4f5372 Adapter Group
| 4F***72 | Adapter Group | 1 |
6f520 Adapter Group--Type 3
| 6F***20 | Adapter Group | 1 |
5f7413 Adapter Group--Type 2
| 5F***13 | Adapter Group | 1 |
5f6550 Adapter Group--Type 2
| 5F***50 | Adapter Group | 1 |
5f7413 Adapter Group--Type 1
| 5F***13 | Adapter Group | 1 |
4f5406 Adapter Group--Type 2
| 4F***06 | Adapter Group | 1 |
5f8233 Adapter Group--Type 1
| 5F***33 | Adapter Group | 1 |
1j663 Adapter Group--Type 1
| 1J***63 | Adapter Group | 1 |
6f520 Adapter Group--Type 2
| 6F***20 | Adapter Group | 1 |
5f8233 Adapter Group--Type 2
| 5F***33 | Adapter Group | 1 |
1j663 Adapter Group--Type 2
| 1J***63 | Adapter Group | 1 |
4f3416 Adapter Group
| 4F***16 | Adapter Group | 1 |
4f3417 Adapter Group
| 4F***17 | Adapter Group | 1 |
5f9336 Adapter Group--Type 1
| 5F***36 | Adapter Group | 1 |
4f5406 Adapter Group--Type 1
| 4F***06 | Adapter Group | 1 |
7f2124 Adapter Group
| 7F***24 | Adapter Group | 1 |
5f9336 Adapter Group--Type 3
| 5F***36 | Adapter Group | 1 |
4f3415 Adapter Group
| 4F***15 | Adapter Group | 1 |
6f520 Adapter Group--Type 1
| 6F***20 | Adapter Group | 1 |
2j3567 Adjustment Group
| 2J***67 | Adjustment Group | 1 |
6j2532 Brake Band Assembly--2 Assemblies Required
| 6J***32 | Brake Band Assembly | 1 |
8f4189 Brake Band Assembly--2 Assemblies Required
| 8F***89 | Brake Band Assembly | 1 |
1j6311 Brake Band Assembly--2 Assemblies Required
| 1J***11 | Brake Band Assembly | 1 |
7f8006 Cable Control Case Replacement Group--Type 2
| 7F***06 | Cable Control Case Replacement Group | 1 |
7f8006 Cable Control Case Replacement Group--Type 1
| 7F***06 | Cable Control Case Replacement Group | 1 |
Clutch, Brake And Drum
Clutch, Brake And Drum--2 Groups Required
Clutch, Brake And Drum--2 Required
Controls And Case (7f5993 N/S)--Side View --Part 1 Of 2
| 7F***93 | Controls And Case | 1 |
Controls And Case--Rear View Part-- 2 Of 2
Controls And Case--Side View-- Part 1 Of 2
Controls And Case--Side View --Part 1 Of 2
Controls And Case--Rear View --Part 2 Of 2
Controls And Case--Rear View-- Part 2 Of 2
Controls And Case (7f5993 N/S)--Rear View--Part 2 Of 2
| 7F***93 | Controls And Case | 1 |
Controls And Case--Side View--Part 1 Of 2
Controls And Case (7f5993 N/S)--Side View--Part 1 Of 2
| 7F***93 | Controls And Case | 1 |
Controls And Case--Rear View--Part 2 Of 2
8b7403 Cable Cutter
| 8B***03 | Cutter Group-Cable | 1 |
Sheaves--Side View --Part 1 Of 2
Sheaves--Rear View-- Part 2 Of 2
Sheaves (7f5994 N/S)--Rear View --Part 2 Of 2
| 7F***94 | Sheaves | 1 |
Sheaves (7f5994 N/S)--Rear View-- Part 2 Of 2
| 7F***94 | Sheaves | 1 |
Sheaves--Side View--Part 1 Of 2
Sheaves (7f5994 N/S)--Side View --Part 1 Of 2
| 7F***94 | Sheaves | 1 |
Sheaves (7f5994 N/S)--Side View-- Part 1 Of 2
| 7F***94 | Sheaves | 1 |
Sheaves--Rear View --Part 2 Of 2
Sheaves--Side View-- Part 1 Of 2
Sheaves--Rear View--Part 2 Of 2
25 serial number reference
On the Twenty-Five, the serial number was stamped into a metal tag (historically a brass plate, roughly a hand's width square, mounted on the tail of the fender), with the same number also die-stamped into the steel underneath the tag as a backup; many surviving tractors have lost the tag but retain the underlying stamped number. Read the 2-character prefix (3C) first to confirm model/series, then the digits that follow as the production sequence number within that run.
| Prefix | Identifies | Notes |
|---|---|---|
| 3C | Twenty-Five (Model 25) track-type tractor, all gauge configurations | Covers the full Twenty-Five production run, serial 3C1 through 3C638, built 1931-1933. The Twenty-Five was a re-engined, redesigned version of the preceding Twenty PL (which itself carried L1 then PL1 serial prefixes through 1931), and most chassis parts interchange between the two lines; very low-range 3C serials close to the start of the run are the likeliest to show holdover Twenty PL-sourced parts, so treat those as needing a dealer or club cross-check. Offered in standard (42 in / 1.07 m) and wide (55 in / 1.4 m) track gauge, both built under the same 3C prefix; gauge is not distinguished by the prefix itself. Gasoline engine, rated around 28 hp drawbar (roughly 30 hp belt), operating weight near 3490 kg (7700 lb). Built at the Peoria, Illinois plant. Superseded in 1933 by the Twenty-Eight, which carries its own distinct serial prefix and ran through 1935, so 3C serials do not extend past that changeover. |
Frequently asked questions
What engine does the Caterpillar 25 (Twenty-Five) use?
A 4-cylinder, water-cooled gasoline engine displacing 4.5 L (277 cu in), bore and stroke 102 x 140 mm (4.00 x 5.50 in), rated around 1,100 rpm. Reported output runs roughly 26-28 hp at the drawbar and 30-33 hp at the belt depending on the source and how the individual engine was tuned. Ignition is magneto-based, with no electronic engine controls of any kind.
What is the operating weight of the Caterpillar 25?
Operating weight is approximately 3,493 kg (7,700 lb). Treat this as an approximate figure rather than a confirmed factory rating.
What replaced the Caterpillar 25 (Twenty-Five)?
Caterpillar replaced the Twenty-Five with the Twenty-Eight within a couple of years, a higher-output evolution of essentially the same 1930s cable-control chassis and gasoline-engine design rather than a modern D-series machine. The Twenty-Five itself had been a redesign of the earlier Twenty (PL), so all three share a common running-gear lineage.
What 25 owners discuss
What's known about parts availability for a Caterpillar Twenty-Five today?
Why do steering clutches often seize on a Twenty-Five that has sat outdoors for years?
What engine and ignition quirks come up around the Twenty-Five's gasoline engine?
What track and undercarriage wear should be expected on a surviving Twenty-Five?
Is a Caterpillar 25 the same machine as a Caterpillar Twenty or Twenty-Eight?
What should someone check before buying or committing to restore a Twenty-Five?
How much restoration effort does a rough Twenty-Five typically take?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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