Caterpillar 50
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar 50 covers two related track-type tractors built in Peoria, Illinois in the early 1930s: the gasoline Fifty (1931-1937) and the diesel-powered Diesel Fifty (1933-1936). The gas Fifty ran Caterpillar's 7500G four-cylinder, magneto-ignition spark engine rated at 52 drawbar horsepower at 850 rpm; the Diesel Fifty used the D7700 four-cylinder mechanical-injection diesel rated at 56 drawbar horsepower, started by a hand-cranked two-cylinder gasoline pony motor. Operating weight runs roughly 8,120-8,810 kg (17,900-19,425 lb) depending on engine and track gauge. Both versions were offered in narrow (60 in) or wide (74 in) track gauge and could carry cable-operated blades and implements from period attachment makers; there is no hydraulic system, powershift transmission, or electronic control on either version. The gas Fifty followed Caterpillar's Thirty and Sixty in the line-up; the Diesel Fifty was one of four diesel models Caterpillar launched in 1933 alongside the Diesel Thirty-Five, Diesel Seventy, and Diesel Seventy-Five, marking the company's early push into diesel crawler power. The Diesel Fifty was directly succeeded by the RD7 in 1935, which was renamed the D7 in 1938.
Change across the run was incremental rather than a hard model break. Early gas Fifty units carried the fuel tank ahead of the operator with the air cleaner under the hood; later production moved the tank behind the seat and the air cleaner forward behind the dash for better balance and easier service. Paint switched from factory grey to Caterpillar Highway Yellow in December 1931. The Diesel Fifty's pony-motor starting layout was the first version of the diesel-starting approach Caterpillar carried forward into the RD7 and D7. Both engines used individual crossflow cylinder heads with separate rocker covers, a design trait shared across the era's Cat line. Today the Fifty and Diesel Fifty are collector and parts machines rather than working iron; most survivors sit with vintage-equipment collectors, clubs, and museums, and parts supply runs entirely through reproduction and salvage channels since Caterpillar has not stocked components for this generation in decades. Its place as the direct forerunner of the RD7/D7 lineage is what keeps it relevant to collectors and parts buyers researching Caterpillar's gas-to-diesel transition.
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 50 specifications
Overview
| Machine | Caterpillar Fifty track-type tractor (vintage crawler tractor, sold simply as "50"/"Fifty"). A pre-war machine, not a modern D-series dozer — it predates modern spec-sheet documentation formats by decades. |
| Built | Peoria, Illinois, USA |
| Gasoline Fifty production | 1931-1937. Serial prefix 5A, running from unit 1 to approximately unit 1,808; roughly 1,700-1,800 units built (a gap in the serial sequence around unit 544-644 in 1933 accounts for the difference between serial-range span and actual unit count across sources). |
| Diesel Fifty production | 1933-1936. Serial prefix 1E, running from unit 1 to approximately unit 2,065 (also referenced with a 33E prefix in some listings), roughly 2,065 units built. Replaced in the lineup by the RD7, introduced 1935. |
| Configuration note | Offered as a gasoline-engine "Fifty" and a separate diesel-engine "Diesel Fifty" — these are distinct engine families sharing a broadly similar chassis/gauge layout, not a Std/XL/LGP spread like later D-series machines. Treat any spec below as varying by which engine/gauge variant is being referenced. |
Engine
| Gasoline Fifty — engine | Caterpillar 7500G, 4-cylinder spark-ignition (gasoline), overhead valve gear with individual cross-flow cylinder heads and separate rocker covers |
| Gasoline Fifty — bore x stroke | 140 x 165 mm (5.5 x 6.5 in) |
| Gasoline Fifty — rated output | 52 drawbar hp (38.8 kW) at 850 rpm per factory rating. Independent tractor-test data (source varies) lists a tested output around 64 drawbar hp / 72 belt hp — treat the higher figure as a bench/tested result rather than the catalog rating; varies by source. |
| Diesel Fifty — engine (primary) | Caterpillar D7700 diesel, 4-cylinder, liquid-cooled |
| Diesel Fifty — bore x stroke | 133 x 203 mm (5.25 x 8.00 in) |
| Diesel Fifty — displacement | 11.4 L (approx. 693 cu in) |
| Diesel Fifty — rated output | 56 drawbar hp at 700-850 rpm per factory/historical-club rating (rpm figure varies slightly by source). Tested output in other tractor-data listings runs around 64 drawbar hp / 72 belt hp, similar to the gasoline unit — treat as a bench test figure, not the catalog rating. |
| Diesel Fifty — secondary engine option (unconfirmed) | A larger 13.6-13.9 L (831-851 cu in) 4-cylinder diesel, bore/stroke 146 x 203 mm (5.75 x 8.00 in), rated around 1,000 rpm, appears in some generic secondary listings for this model but is not documented in the historical-club record for the Diesel Fifty. Verify against a specific serial number before relying on it. |
| Emissions | Not applicable — predates all emissions regulation; no Tier/Stage certification exists for this engine family. |
| Starting/ignition | Gasoline Fifty used manual/hand-crank style starting with a generator charging system typical of the early-1930s Caterpillar range; diesel units of this era commonly used a gasoline pony-motor or hand-crank starting aid. Not fully documented for this specific model — verify against the service manual for the exact serial range. |
Weights
| Gasoline Fifty — operating weight | Approx. 8,120-8,275 kg (17,900-18,245 lb), depending on source |
| Diesel Fifty — operating weight | Approx. 8,810 kg (19,425 lb) |
| Note | No separate Std/XL/LGP weight spread is documented for this model; weight differences across sources reflect narrow-gauge vs wide-gauge configuration and equipped attachments (blade, etc.), not a formal factory configuration line. |
Dimensions
| Track gauge options (both gasoline and diesel Fifty) | Narrow gauge: 1,524 mm (60 in) between track centers. Wide gauge: 1,880 mm (74 in) between track centers. |
| Standard track shoe width | 406 mm (16 in) on narrow-gauge units; 508 mm (20 in) on wide-gauge units. Other shoe widths and grouser styles were factory-optional. |
| Track shoe width — gasoline Fifty specific note | 381 mm (15 in) track width is cited on one general tractor-data listing for the gasoline Fifty; this conflicts with the 16 in/20 in narrow/wide figures documented for the model family elsewhere, so treat the exact standard shoe width as varying by source/serial range. |
| Overall length/width/height, wheelbase, ground clearance | Not documented in available literature for either the gasoline or diesel Fifty. No public source lists complete transport dimensions for this model — consult an original Caterpillar operator's or parts manual for the specific serial range. |
Performance
| Transmission — gasoline Fifty | Sliding-gear transmission, 4 speeds forward and 1 reverse |
| Transmission — diesel Fifty | Gear transmission; some listings show 5 forward/reverse speeds, differing from the gasoline unit's 4F/1R layout. Exact gear count and ratios vary by source — not fully reconciled across available references. |
| Travel speeds per gear | Not documented in available literature for this model. No source lists individual forward/reverse gear speeds in km/h or mph — consult the original operator's manual for exact figures. |
| Drawbar pull | Not published as a distinct rated figure in available literature (drawbar horsepower is documented — see Engine group — but peak drawbar pull in kN/lbf is not listed for this model in any source found). |
| Gradeability, ground pressure | Not documented for this model in available literature. Period Caterpillar crawler tractors of this class did not publish gradeability or ground-pressure figures in the same catalog format used for later D-series machines. Verify with a dealer or original factory literature if exact figures are required. |
| Steering/brakes | Steering by clutch/rod-and-lever type typical of the era (documented as "rod" steering in period data); detailed brake specifications not documented in available sources. |
Blades
| Factory blade program | No Caterpillar-branded S/SU/A/VPAT blade line existed for this model — that blade nomenclature belongs to later D-series machines. When fitted as a dozer, Fifty/Diesel Fifty tractors of this era typically carried third-party bulldozer blades (commonly LeTourneau), cable-operated via an overhead winch and blade rope rather than hydraulics. |
| Blade capacities | Not published for this model — third-party blade attachments of the period did not carry a standardized Caterpillar capacity spec. No capacity figures found in available literature. |
Service capacities
| Fuel tank | Not documented in available literature for this model. |
| Engine (crankcase) oil | Not documented in available literature for this model. |
| Cooling system | Not documented in available literature for this model. |
| Hydraulic system | Not applicable in the modern sense — the era's dozer/winch controls (where fitted) were cable-operated, not hydraulic. |
| Note | Service capacities for this vintage model are not carried in current parts/spec aggregators. Confirm against an original Caterpillar operator's or service manual for the exact serial range before use. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
50 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (w/ filter) | Not documented in accessible sources. The Caterpillar Fifty (gasoline, 1931-1937) and Diesel Fifty (1933-1936) predate the modern Cat fluid-recommendations literature; period lubrication charts are not published online. Diesel Fifty engine is a 4-cylinder, 11.4 L unit (146 mm x 203 mm bore/stroke), rated around 700 rpm. | Not documented in accessible sources. Period Caterpillar practice called for a straight mineral engine oil graded by ambient temperature (no branded synthetic or API-rated products existed for this era); exact grade/brand designation not available online - verify against the original Fifty/Diesel Fifty Operation and Maintenance Instructions or Parts Book. |
| Cooling system | Not documented in accessible sources. | Not documented. Water-cooled, thermostat-equipped radiator system; no antifreeze/coolant brand spec located for this model. |
| Fuel tank | Not documented in accessible sources. Two configurations exist: gasoline Fifty and Diesel Fifty; neither tank size is published in the sources checked. | Gasoline Fifty: leaded gasoline of the period. Diesel Fifty: diesel fuel. No further spec (cetane, sulfur, etc.) documented. |
| Transmission (powershift) | Not applicable to this generation - the Fifty/Diesel Fifty use a mechanical 4-speed selective gear transmission, not a powershift unit. Capacity not documented. | Not documented. No powershift clutch oil spec applies; a straight gear-case oil would have been used per period practice, exact grade not found. |
| Steering / bevel gear compartment | Not documented in accessible sources. Steering is by mechanical clutch-and-brake (rod-actuated), not a separate powershift-style steering clutch as on later D-series machines. | Not documented. |
| Final drives (each) | Not documented in accessible sources. | Not documented. |
| Hydraulic system / tank | Not confirmed for this model generation. Cable-operated blade/implement control was standard on machines of this era; a factory hydraulic blade control was offered as a period attachment on some Caterpillar crawlers, but no hydraulic tank capacity for the Fifty specifically is documented in the sources checked. | Not documented. |
| Pivot shaft | Not documented in accessible sources. | Not documented. |
| Grease specification (chassis/track) | Not documented (no interval/point count located). | Not documented. Period Caterpillar practice used a general-purpose chassis grease; no branded spec (e.g. modern Cat grease designations) applies to a machine of this age. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 50 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
Servicing the 50 beyond the schedule
Predictive Maintenance & Fluid Analysis
There is no lab fluid-sampling program for a Fifty; "predictive" here means reading the machine by eye and ear at every service point. Check engine oil color and grit at each interval. On the Diesel Fifty, watch injector spray pattern and injection-pump timing marks for drift, since that is the earliest sign of wear in the D7700. On the gas Fifty, watch magneto point gap and listen for detonation, since ignition drift shows up before real damage does. Track sag and roller play are the best early gauge of undercarriage condition.
Corrective & Common Repairs
Most call-backs on a Fifty trace to the steering clutches and brake bands, which need relining or adjustment as track tension work compounds their wear. On the Diesel Fifty, injection-pump calibration drift and pony-motor clutch slippage are the top diesel-specific fixes. On the gas Fifty, magneto timing and carburetor float or needle wear cause hard starting and rough idle. Final drive gear and bearing wear is the other recurring repair, usually showing up as track slack that further tightening can no longer take up.
Overhaul & Rebuild Points
A full rebuild centers on the crossflow cylinder head - valve seats, guides, and port wear - plus main and rod bearings. On the Diesel Fifty, the D7700 injection pump and nozzles need bench calibration, not field adjustment. Undercarriage overhaul means turning or replacing track pins and bushings, relining steering clutches and brake bands, and rebuilding final drives once backlash exceeds tolerance. Since this machine carries no powershift transmission or hydraulics, every overhaul point stays mechanical: gears, clutches, bands, and cable-operated linkage only.
Seasonal & Environment Servicing
Cold starts hit the Diesel Fifty hardest: the pony motor needs fresh points, plugs, and fuel before any cold-weather startup, and the cooling system needs seasonal draining or antifreeze protection since period cooling systems carry no long-life coolant. The gas Fifty's magneto and carburetor need a seasonal check for moisture and corrosion after storage. Both versions need the crossflow head and exposed cable linkage cleared of dust and mud each season, since caked debris accelerates track pin and bushing wear faster than hours alone.
50 attachments & work tools
Blades (types S/SU/A, VPAT availability, widths/capacities)
The Fifty (gasoline, 1931-1937) and Diesel Fifty (1933-1936) predate Caterpillar's own S/SU/A blade-type nomenclature and VPAT hydraulic angling system by decades; those designations only came in with the post-war D-series line. Dozing on a Fifty was done with a bolt-on blade from an outside implement house - LaPlant-Choate's cable-operated bulldozer blade line (documented on a Fifty-class machine as an RB-50 unit) was the common fitment, raised and lowered by cable off the tractor rather than by a factory hydraulic circuit. No standard factory blade width or capacity is documented; it was set by the implement builder and the job, not by a Caterpillar option sheet.
Rippers (multi-shank vs single-shank, weights)
No factory single- or multi-shank ripper frame is documented for this model; Caterpillar's own hydraulic ripper attachments did not appear until the 1950s, well after Fifty/Diesel Fifty production ended. Where deep-tillage or scarifying work was done on a Fifty-class tractor in period, it would have used a pull-type single-shank "rooter" or ripper-plow on its own wheeled frame, drawn and pivoted by cable off the tractor's cable control unit - equipment supplied by outside builders such as LeTourneau or LaPlant-Choate rather than Caterpillar itself. No weights are documented for this class of pull ripper.
Winches (class fit, towing winch options)
Cable-operated attachments (blade lift, pull-ripper control) on a Fifty were run off a rear cable control unit or PTO-driven cable winch, with Caterpillar sourcing this style of gear from outside winch builders such as Hyster and Allied from the late 1920s onward; Caterpillar's own factory Cable Control Unit line did not launch until 1945, after both Fifty variants were out of production. A dedicated straight towing winch (independent of implement control) is not documented as a factory option for this model; drawbar towing was the standard method.
Drawbars/counterweights
A rear drawbar was standard equipment, consistent with contemporary Cat literature calling out the swinging drawbar as the main towing point on tractors of this class; documented PTO options include a 540-rpm belt pulley, a direct-drive tapered-spline shaft, and a standard 10-spline shaft. No factory counterweight or ballast package is documented for either Fifty variant; added front ballast for blade work, where used, was an implement-builder or field fix rather than a cataloged Caterpillar line item.
Cab/ROPS guarding (forestry/waste configs)
No ROPS or FOPS structure exists for the Fifty or Diesel Fifty; those crush-protection standards postdate this model by decades. Both variants shipped with an open operator's station, and period practice across this generation of Cat crawlers offered a simple sunshade canopy (with the fuel tank moved to the side) as an alternative to the plain "tail seat" layout used for low-clearance orchard work (fuel tank down the tractor's centerline, no canopy) - the closest thing to a specialized guarding option, though it is not confirmed as a catalog item specific to the Fifty by name. No forestry- or waste-handling guarding package is documented for this model.
Hydraulic arrangement notes (front/rear tools)
Both the gasoline Fifty and the D7700-diesel-powered Diesel Fifty are mechanical, gear-drive machines (four-speed transmission) with no factory hydraulic implement circuit front or rear. Blade lift and pull-ripper control, where fitted, worked through cable-and-sheave rigging run off a PTO- or engine-driven cable control unit supplied by the attachment builder, not through any Caterpillar-installed hydraulic pump or valve bank; true hydraulic blade/ripper control only entered the Cat track-type tractor line long after this model's production run.
All 50 assemblies by section
Every catalogued assembly group for the Caterpillar 50. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Hydraulic Control Arrangements
1j5549 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
2j1558 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***99 | Steering Clutch And Brake Booster Lines Group | 1 |
2j5617 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Ripper Kickout Group | 1 |
| 2J***17 | Hydraulic Control | 1 |
1j5550 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
1j5555 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
2j2819 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***99 | Steering Clutch And Brake Booster Lines Group | 1 |
1j5551 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
2j2818 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***99 | Steering Clutch And Brake Booster Lines Group | 1 |
1j5552 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
2j5618 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Ripper Kickout Group | 1 |
| 2J***18 | Hydraulic Control | 1 |
1j5553 Hydraulic Control Arrangement--For Use With No. 9 Ripper
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
1j5554 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
2j2820 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***99 | Steering Clutch And Brake Booster Lines Group | 1 |
1j5556 Hydraulic Control Arrangement--For Use With No. 9 Ripper And Blade Tilt
| 1J***25 | Tank And Valve Group | 1 |
| 1J***76 | Pump Assembly | 1 |
| 1J***77 | Pump Lines Group | 1 |
No. 50 Hydraulic Control
2j1557 Adapter Group
| 2J***57 | Adapter Group | 1 |
1j5587 Adapter Group
| 1J***87 | Adapter Group | 1 |
1j5503 Control Linkage Group--No. 2 Valve
| 1J***03 | Control Linkage Group | 1 |
2j5964 Control Linkage Group--No. 2 Valve--Type 2
| 2J***64 | Control Linkage Group; Control And Linkage Group | 1 |
2j5964 Control Linkage Group--No. 2 Valve--Type 1
| 2J***64 | Control Linkage Group; Control And Linkage Group | 1 |
1j8122 Control Valve Group
| 1J***22 | Control Valve Group | 1 |
1j5426 Control Valve Group
| 1J***26 | Control Valve Group | 1 |
3h8504 Coupling Assembly
| 3H***04 | Coupling Assembly | 1 |
1j5544 Floor Plate Group--Type 2
| 1J***44 | Floor Plate Group | 1 |
1j5545 Floor Plate Group--Type 1
| 1J***45 | Floor Plate Group | 1 |
1j5545 Floor Plate Group--Type 2
| 1J***45 | Floor Plate Group | 1 |
2j5832 Floor Plate Group
| 2J***32 | Floor Plate Group | 1 |
1j5544 Floor Plate Group--Type 1
| 1J***44 | Floor Plate Group | 1 |
2j5960 Hydraulic Pump Assembly--Type 2
| 2J***60 | Hydraulic Pump Assembly | 1 |
2j5960 Hydraulic Pump Assembly--Type 1
| 2J***60 | Hydraulic Pump Assembly | 1 |
2j1551 Mounting Group--No. 1 Valve--Type 1
| 2J***51 | Mounting Group | 1 |
2j1551 Mounting Group--No. 1 Valve--Type 3
| 2J***51 | Mounting Group | 1 |
2j5962 Mounting Group--No. 1 Valve--Type 1
| 2J***62 | Mounting Group | 1 |
1j5504 Mounting Group--No. 1 Valve
| 1J***04 | Mounting Group | 1 |
2j5962 Mounting Group--No. 1 Valve--Type 2
| 2J***62 | Mounting Group | 1 |
2j5962 Mounting Group--No. 1 Valve--As Viewed From Rear R.H. Side Of Machine--Part 1 Of 2--Type 3
| 2J***62 | Mounting Group | 1 |
2j5962 Mounting Group--No. 1 Valve--As Viewed From Rear R.H. Side Of Machine--Part 2 Of 2--Type 3
| 2J***62 | Mounting Group | 1 |
2j1551 Mounting Group--No. 1 Valve--Type 2
| 2J***51 | Mounting Group | 1 |
6h3862 Oil Filter Group
| 6H***62 | Oil Filter Group | 1 |
1j5476 Pump Assembly--Type 1
| 1J***76 | Pump Assembly | 1 |
1j5476 Pump Assembly--Type 2
| 1J***76 | Pump Assembly | 1 |
2j5961 Pump Lines Group--Type 2
| 2J***61 | Pump Lines Group | 1 |
2j795 Pump Lines Group--Type 2
| 2J***95 | Pump Lines Group | 1 |
1j5477 Pump Lines Group
| 1J***77 | Pump Lines Group | 1 |
2j795 Pump Lines Group--Type 1
| 2J***95 | Pump Lines Group | 1 |
2j5961 Pump Lines Group--Type 1
| 2J***61 | Pump Lines Group | 1 |
2j5961 Pump Lines Group--Type 3
| 2J***61 | Pump Lines Group | 1 |
6h8267 Relief Valve Assembly
| 6H***67 | Relief Valve Assembly | 1 |
1j7876 Ripper Kickout Group
| 1J***76 | Ripper Kickout Group | 1 |
2j5965 Ripper Lines Group
| 2J***65 | Ripper Lines Group | 1 |
1j5502 Ripper Lines Group--Type 1
| 1J***02 | Ripper Lines Group | 1 |
1j5502 Ripper Lines Group--Type 2
| 1J***02 | Ripper Lines Group | 1 |
1j5499 Steering Clutch And Brake Booster Lines Group
| 1J***99 | Steering Clutch And Brake Booster Lines Group | 1 |
1j5425 Tank And Valve Group--Side View--Part 2 Of 2
| 1J***25 | Tank And Valve Group | 1 |
1j5425 Tank And Valve Group--Rear View--Part 1 Of 2
| 1J***25 | Tank And Valve Group | 1 |
2j3276 Tank Assembly
| 2J***76 | Tank Assembly | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 2
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 1
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 1
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 4
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 2
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 5
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 6
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 5
| 1J***56 | Tilt Dozer Lines Group | 1 |
2j5966 Tilt Dozer Lines Group
| 2J***66 | Tilt Dozer Lines Group | 1 |
1j5501 Tilt Dozer Lines Group
| 1J***01 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 6 Part Of Hydraulic Control Arrangements Listed On Pages 8, 9 And 10
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 1 Of 2--Type 3
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 4
| 1J***56 | Tilt Dozer Lines Group | 1 |
1j7456 Tilt Dozer Lines Group--Part 2 Of 2--Type 3
| 1J***56 | Tilt Dozer Lines Group | 1 |
50 serial number reference
On the Caterpillar Fifty and Diesel Fifty there is no modern 17-character PIN plate; these predate that standard. The serial number is a letter-number prefix (5A for the gasoline Fifty, 1E for the Diesel Fifty) immediately followed by a sequential unit number with no dash, e.g. 5A123 or 1E45. No plant or year code is embedded in the string, so the prefix alone identifies the engine family and the trailing digits place the unit within the production run. For general Caterpillar machinery of this era the number rides on a small riveted tag (roughly 1.5 in by 2.5 in, aluminum, plated steel, or brass) most often found on the engine block near the head gasket line, on the bevel gear case above the drawbar, or on the transmission case near the bell housing; if the tag is missing, the number may still be stamped into the casting between the rivet holes. Exact tag placement for the Fifty specifically is not documented in the factory literature reviewed - confirm the reading against the engine block or transmission casing on the actual unit, or check with an antique-Caterpillar owners' club, before ordering parts.
| Prefix | Identifies | Notes |
|---|---|---|
| 5A | Caterpillar Fifty (gasoline) | Serial prefix 5A, running from unit 1 to approximately unit 1,808 (exact day-level start/end dates are not documented and are omitted). Spark-ignition 4-cylinder gas engine rated 52 drawbar hp at 850 rpm. Offered in 60 in and 74 in track gauge versions under the same 5A prefix - gauge is a build option, not a separate serial series. Early units (roughly unit 1 to unit 757) carried the fuel tank ahead of the operator with the air cleaner under the hood; later production moved the fuel tank behind the seat and the air cleaner in front of the driver behind the dash. A production gap exists around unit 544-644 with no documented cause. Painted grey at first, switching to Caterpillar Highway Yellow on 7 December 1931. |
| 1E | Caterpillar Diesel Fifty | Serial prefix 1E, running from unit 1 to approximately unit 2,065, built 1933-1936, replaced by the RD7 introduced in 1935. 4-cylinder diesel engine rated 56 drawbar hp. Offered in 60 in and 74 in track gauge versions under the same 1E prefix - gauge is a build option, not a separate serial series. Low production volume, tapering to only a few units in the final year, makes this prefix uncommon in the field. The gasoline Fifty (5A) and Diesel Fifty (1E) are separate engine families on a shared chassis lineage, not variants of a single powertrain. |
Frequently asked questions
What engine does the Caterpillar 50 have?
It depends on version. The gasoline Fifty (1931-1937) runs Caterpillar's 7500G four-cylinder, magneto-ignition gasoline engine rated at 52 drawbar horsepower at 850 rpm. The Diesel Fifty (1933-1936) runs the D7700 four-cylinder mechanical-injection diesel rated at 56 drawbar horsepower, started by a hand-cranked two-cylinder gasoline pony motor.
What is the operating weight of the Caterpillar 50?
Operating weight runs roughly 8,120-8,810 kg (17,900-19,425 lb), varying by whether it is the gas Fifty or Diesel Fifty and by track gauge (60 in narrow or 74 in wide).
What replaced the Caterpillar 50?
The Diesel Fifty was directly succeeded by the RD7 in 1935, which ran a larger D8800 four-cylinder diesel. Caterpillar dropped the "R" prefix in 1938 and the model became the D7, which stayed in production into the 1940s.
What 50 owners discuss
What's the steering system like on a Cat Fifty, and what do owners watch for?
What undercarriage wear should I expect on a Fifty, and how do collectors check it?
The magneto on my gas Fifty makes it hard to start - what's the usual cause?
How do you start the Diesel Fifty's engine, and why do people describe it as finicky?
Is this engine finicky about oil and cooling compared to a modern machine?
How many speeds does the Fifty have, and what do owners say about shifting it?
What should I inspect before buying a used Cat Fifty, gas or diesel?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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