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This is the Caterpillar factory repair set for the 303C CR and 303.5C CR mini excavators, serial prefix DMY00001-Up, with the Mitsubishi S3Q2 and S3Q2-T engines. Cat published these as two-model family books, so one download covers both machines. The part you cannot get anywhere else is the printed wear checks: travel speed over 20 m timed by model and by track type, allowable travel drift of 1000 mm, swing of 90 degrees in 2.5 seconds or less, and cylinder drift limits of 2 mm on the boom and 5 mm on stick and bucket. Add pilot, main and swing relief tests, pump flow testing, engine overhaul, travel and swing motor work, undercarriage service, and the 303.5C CR electrical and hydraulic schematics.
What's Inside This Caterpillar 303C CR, 303.5C CR Repair Manual
| System | Pages | Key Topics |
|---|---|---|
| Air Inlet and Exhaust System | 2-11 | Turbocharger, Inlet and Exhaust Manifolds, Air Cleaner |
| Basic Engine | 12-323 | Mitsubishi S3Q2 and S3Q2-T Engines, Cylinder Head, Crankshaft, Pistons |
| Cooling System | 324-347 | Water Pump, Thermostat, Radiator |
| Electrical and Starting System | 348-1148 | Alternator, Starting System, Batteries, Product Link, EquipmentManager, Air Conditioning R134a |
| Engine Arrangement | 1149-1287 | Engine Mounting and Arrangement |
| Frame and Body | 1288-1356 | Frame, Body Panels |
| Fuel System | 1357-1421 | Injection Pump, Injectors, Fuel Filter |
| Hydraulic System | 1422-1965 | Pilot Relief Test and Adjust, Main Relief Test and Adjust, Swing Relief Test and Adjust, Main Pump Flow Test, Cylinder Drift Checks, Travel and Swing Performance Checks |
| Implements | 1966-2023 | Boom, Stick, Bucket, Blade Linkage |
| Lubrication System | 2024-2041 | Engine Oil Pump, Oil Filter |
| Machine Arrangement | 2042-2054 | Machine Arrangement and Layout |
| Operator Station | 2055-2449 | Cab, Controls, Seat |
| Power Train | 2450-2512 | Travel Motors, Swing Motor, Final Drives |
| Service Equipment and Supplies | 2513-2537 | Service Tooling and Supplies |
| Torque Specifications | 2538-2587 | Metric ISO Fasteners, English SAE Fasteners, Fittings, Plugs, Hose Clamps |
| Undercarriage | 2588-2656 | Rubber and Steel Tracks, Idlers, Rollers, Track Tension |
| Work Tools | 2657-2674 | Work Tool Hydraulics and Mounting |
| Schematic | 2675-2710 | 303.5C CR Electrical System Schematic, 303.5C CR Hydraulic System Schematic, Graphic Symbol Legends |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| 303.5C CR | ||
| Travel speed over 20 m, rubber tracks | 14.0 to 16.0 s high, 23.4 to 25.4 s low | |
| Travel speed over 20 m, steel tracks | 14.6 to 16.6 s high, 25.4 to 27.4 s low | |
| 303C CR | ||
| Travel speed over 20 m, rubber tracks | 15.9 to 18.5 s high, 24.5 to 28.0 s low | |
| Travel speed over 20 m, steel tracks | 16.1 to 18.7 s high, 25.8 to 29.1 s low | |
| Cylinder operating speed, boom | extension 2.8 +/- 0.4 s, retraction 3.1 +/- 0.4 s | |
| All Models | ||
| Travel drift over 20 m | 1000 mm (39.4 in) maximum | |
| Swing time, 90 degrees | 2.5 s or less; 2.8 s or less on a slope | |
| Swing overswing | 180 mm (7.1 in) or less | |
| Machine drift and swing drift on a slope | 0 mm | |
| Cylinder drift, boom | 2 mm (0.1 in) or less | |
| Cylinder drift, stick and bucket | 5 mm (0.2 in) or less | |
| Cylinder drift, blade and boom swing | 2 mm (0.1 in) or less | |
| Serial prefix | DMY00001-Up | |
| Engine fitted | Mitsubishi S3Q2 and S3Q2-T | |
Caterpillar 303C CR, 303.5C CR Common Problems This Manual Covers
Boom or bucket creeps down when parked
Run the cylinder drift check: measure rod movement over the set time and compare against the printed limits, 2 mm on the boom, 5 mm on stick and bucket. Beyond spec, the procedure separates worn cylinder seals from a leaking control valve section before you buy parts.
Manual Section: Testing and Adjusting - Cylinder Drift Check p. 1514Machine tracks crooked or feels slow on one side
Time each side over 20 m against the model-specific and track-specific spec, then check drift stays under 1000 mm. If one side lags, the book takes you into main pump flow testing, relief pressure checks and travel motor evaluation to find which is at fault.
Manual Section: Testing and Adjusting - Travel Speed and Travel Drift Tests p. 2450Swing is sluggish or overswings past the stop point
Measure the 90 degree swing time (2.5 s or less) and overswing (180 mm or less), then test swing relief valve pressure per the printed procedure. Out-of-spec readings point to the relief setting or a worn swing motor, and on a slope any drift at all means trouble.
Manual Section: Testing and Adjusting - Swing Relief Valve Pressure Test p. 1583Hard starting, especially cold
Work through the fuel system section: injection pump timing and delivery, injector testing, fuel filter service, and the glow circuit under the electrical and starting system. On these mechanical S3Q2 engines diagnosis is measurement against spec, not code reading, and the book gives every figure you need.
Manual Section: Fuel System - Injection Pump and Injectors p. 1357Frequently Asked Questions
The listing says 303.5C CR - is my 303C CR covered too?
Yes. Cat wrote these modules as family publications titled 303C CR and 303.5C CR (Testing and Adjusting, Systems Operation, Specifications, Disassembly and Assembly). Where the two machines differ, such as travel speed times, the book gives a separate figure for each model.
My boom sinks overnight. How much drift is actually acceptable?
The book gives hard numbers: boom cylinder drift is 2 mm (0.1 in) or less, stick and bucket 5 mm (0.2 in) or less, blade and boom swing 2 mm or less, all measured over a set time at the cylinder rod. If you are past those limits, the test procedure walks you toward cylinder seals or the control valve instead of guessing.
How fast should the machine cover 20 m, and does it depend on the tracks?
Yes, the spec splits by model and track type. A 303.5C CR on rubber tracks should do 20 m in 14.0 to 16.0 s at high speed (23.4 to 25.4 s low), on steel 14.6 to 16.6 s. A 303C CR on rubber is 15.9 to 18.5 s high speed, on steel 16.1 to 18.7 s. Travel drift over that 20 m run must stay under 1000 mm.
Does it cover the swing system? Mine feels slow and keeps going past the mark.
It does. Spec is 90 degrees in 2.5 seconds or less (2.8 s on a slope), overswing 180 mm (7.1 in) or less, and machine or swing drift on a slope must be exactly 0 mm. Testing and Adjusting includes the swing relief valve pressure test and swing motor checks to chase a machine that misses those numbers.
Is there full engine coverage, or just the excavator side?
Full coverage of the Mitsubishi S3Q2 and S3Q2-T: cylinder head, crankshaft, pistons, injection pump, injectors, fuel filter, water pump, thermostat, and the turbocharger and manifolds on the T engine. Alternator, starting system and batteries are in the electrical section, plus the 303.5C CR electrical and hydraulic schematics with symbol legends.
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