This is the factory repair manual for the Caterpillar 311 and 312 hydraulic excavators built from 1995 to 2003, both machines in one bundle. It covers the 3064 engine from cylinder head to crankshaft, the fuel injection pump and governor, and the full hydraulic system - main pump, control valves, swing and travel motors, relief valves and the accumulator. You get the actual test numbers: 34300 kPa (5000 psi) main relief on travel, 3450 kPa (500 psi) pilot pressure, cycle times for boom, stick, bucket, swing and travel on both models. Electrical coverage includes the alternator, starter, monitor system, sensors and harness continuity testing, plus complete hydraulic and electrical schematics for the 311 and 312. Undercarriage, implements and torque specifications round it out.
What's Inside This Caterpillar 311, 312 Repair Manual
| System | Pages | Key Topics |
|---|---|---|
| Air Inlet & Exhaust | 1-10 | Air Heater, Air Cleaner, Muffler, Turbocharger |
| Basic Engine | 11-46 | Cylinder Head, Pistons, Crankshaft, Camshaft, Valve Mechanism |
| Cooling System | 47-70 | Water Pump, Radiator, Oil Cooler, Thermostat |
| Electrical & Starting System | 71-840 | Alternator, Starter, Batteries, Monitor System, Sensors, Wiring Harness Testing, System Schematic |
| Engine Arrangement | 841-853 | Engine Mounting, Engine Supports |
| Frame & Body | 854-869 | Main Frame, Guards, Covers |
| Fuel System | 870-1042 | Injection Pump, Injectors, Fuel Transfer Pump, Governor |
| Hydraulic System | 1043-1639 | Main Pump, Pilot Pump, Main Control Valves, Swing Motor & Drive, Travel Motor & Final Drive, Relief Valves, Accumulator, Cycle Times, Pressure Testing & Adjusting |
| Implements | 1640-1711 | Boom, Stick, Bucket, Cylinders, Linkage |
| Lubrication System | 1712-1720 | Engine Oil Pump, Oil Filter, Oil Cooler |
| Machine Arrangement | 1721-1732 | Overall Layout, Component Location |
| Operator Station | 1733-2272 | Cab, Controls, Seat, HVAC, Monitor Panel |
| Power Train | 2273-2334 | Travel Motor, Final Drive, Swing Drive & Bearing |
| Schematics | 2335-2417 | 311 & 312 Hydraulic System Schematics, 311 & 312 Electrical System Schematics, Pilot & Attachment Circuits |
| Service Equipment & Supplies | 2418-2466 | Special Tools, Shop Supplies |
| Torque Specifications | 2467-2514 | Fitting Torques, Track Adjuster Torques |
| Undercarriage | 2515-2572 | Track Chain, Track Adjuster, Rollers, Idler, Sprocket |
| Work Tools | 2573-2580 | Bucket, Attachments |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| 312 | ||
| Hydraulic pump flow (main pump, no load) | 120 liter/min (32 U.S.gpm) | p. 1043 |
| Engine speed (high idle) | 1980 ± 80 rpm | p. 1341 |
| Oil temperature | 55 ± 5°C (131 ± 9°F) | p. 1341 |
| Boom raise cycle time | 3.2 ± 0.5 seconds | p. 1341 |
| Boom lower cycle time | 2.6 ± 0.5 seconds | p. 1341 |
| Stick out cycle time | 2.5 ± 0.5 seconds | p. 1341 |
| Stick in cycle time | 3.9 ± 0.5 seconds | p. 1341 |
| Bucket close cycle time | 3.7 ± 0.5 seconds | p. 1341 |
| Bucket open cycle time | 2.1 ± 0.5 seconds | p. 1341 |
| Swing cycle time | 4.4 or less seconds | p. 1341 |
| Travel cycle time at high speed | 14.0 or less seconds | p. 1341 |
| Travel cycle time at low speed | 20.5 or less seconds | p. 1341 |
| 311 | ||
| Hydraulic pump flow (main pump, no load) | 108 liter/min (29 U.S.gpm) | p. 1043 |
| Line relief valve pressure setting (bucket cylinder head end) | 26 000 kPa (3750 psi) | p. 1043 |
| Engine speed (high idle) | 1880 ± 80 rpm | p. 1341 |
| Oil temperature | 55 ± 5°C (131 ± 9°F) | p. 1341 |
| Boom raise cycle time | 2.9 ± 0.5 seconds | p. 1341 |
| Boom lower cycle time | 2.4 ± 0.5 seconds | p. 1341 |
| Stick out cycle time | 2.0 ± 0.5 seconds | p. 1341 |
| Stick in cycle time | 3.5 ± 0.5 seconds | p. 1341 |
| Bucket close cycle time | 4.1 ± 0.5 seconds | p. 1341 |
| Bucket open cycle time | 2.4 ± 0.5 seconds | p. 1341 |
| Swing cycle time | 4.2 or less seconds | p. 1341 |
| Travel cycle time at high speed | 14.1 or less seconds | p. 1341 |
| Travel cycle time at low speed | 20.3 or less seconds | p. 1341 |
| 311 & 312 | ||
| Hydraulic pump flow (pilot pump, full rpm) | 15 liter/min (4.0 U.S. gpm) | p. 1043 |
| Pilot system pressure (relief setting) | 3450 kPa (500 psi) | p. 1043 |
| cylinder circuits | ||
| Line relief valve pressure setting (general) | 31 400 kPa (4550 psi) | p. 1043 |
| main hydraulic system | ||
| Main relief valve pressure setting (travel operation) | 34 300 kPa (5000 psi) | p. 1043 |
| Main relief valve pressure setting (implement/swing operation) | 27 500 kPa (4000 psi) | p. 1043 |
| Swing Motor | ||
| Maximum case drain oil (new swing motor) | 15 liter/min (4.0 U.S. gpm) | p. 1043 |
| Maximum case drain oil (rebuilt swing motor) | 17 liter/min (4.5 U.S. gpm) | p. 1043 |
| Swing relief pressure setting | 23000 ± 980 kPa (3350 ± 140 psi) | p. 1043 |
| Travel Motor | ||
| Maximum case drain oil (new travel motor) | 20 liter/min (5.3 U.S. gpm) | p. 1043 |
| Maximum case drain oil (rebuilt travel motor) | 23 liter/min (6.1 U.S. gpm) | p. 1043 |
| Main relief pressure | 34300 ± 490 kPa (5000 ± 72 psi) | p. 1043 |
| Accumulator | ||
| Nitrogen gas pressure | 1770 ± 100 kPa (255 ± 14 psi) | p. 1043 |
| Torque for cap (1) | 2.9 ± 0.2 N·m (2 ± 1 lb ft) | |
| Radiator & Oil Cooler | ||
| Weight of the radiator & oil cooler | 68 kg (150 lb) | |
| Oil Cooler | ||
| Weight of the oil cooler | 36 kg (80 lb) | |
| Counterweight | ||
| Weight of the counterweight | 1453 kg (3200 lb) | |
Caterpillar 311, 312 Common Problems This Manual Covers
Machine loses travel power on one side or will not track straight
Measure travel motor case drain flow against the limits in the Hydraulic System section - over 20 liter/min on a new motor means internal bypass. Then verify main relief holds 34300 kPa during travel and run the travel cycle time test, 14 seconds or less at high speed.
Manual Section: Hydraulic System - Travel Motor & Final Drive / Pressure Testing & AdjustingHydraulics slow and weak, worse as the oil warms up
Run the cycle time checks in Pressure Testing & Adjusting with oil at 55 ± 5°C and compare against the per-model tables. Slow times with correct relief pressures point to pump wear or internal leakage; the section walks through isolating pump, control valve and cylinder drift one at a time.
Manual Section: Hydraulic System - Pressure Testing & Adjusting / Cycle TimesRandom stalling, hard starting, or dead monitor panel
Follow the wiring harness testing procedure in the Electrical & Starting System section and trace the circuit on the full system schematic. Check alternator output, battery condition and every ground strap - voltage drop from corroded connections is the usual culprit on machines this age.
Manual Section: Electrical & Starting System - Wiring Harness Testing / System SchematicHydraulic oil running hot, sometimes tripping the temperature warning
Start with the oil cooler removal and cleaning procedure in the Cooling System section - the cooler core packs with debris on these machines. If the cooler is clean, check for a relief valve set low or stuck partially open using the pressure test procedures, since constant relief flow is the other common heat source.
Manual Section: Cooling System - Oil Cooler / RadiatorFrequently Asked Questions
My 311 shuts down randomly while working. Does this manual help me find the cause?
Yes, and on these machines it is almost always electrical, not electronic. The Electrical & Starting System section walks you through testing the alternator output, battery condition, and harness continuity, and the full electrical schematic lets you chase voltage drops through corroded terminals and ground straps. These are mechanical injection engines, so once the engine has clean fuel and stable voltage it runs. Start with the charging circuit and grounds before touching anything else.
How do I know if my main pump is worn or if it is a relief valve problem?
The Pressure Testing & Adjusting section gives you the procedure and the numbers: main relief at 34300 ± 490 kPa (5000 ± 72 psi), implement/swing relief at 27500 kPa (4000 psi), pilot at 3450 kPa (500 psi). Then you run the cycle time checks at 55°C oil temperature - boom raise should be 2.9 seconds on a 311 and 3.2 on a 312. If pressures set correctly but cycle times are slow, you are looking at pump wear or internal leakage, and the case drain flow limits in the manual tell you which motor or pump is bypassing.
Can I pull error codes from a CAT 311 or 312 like on newer machines?
No, and any listing that promises a code reader procedure for these serial ranges is selling you the wrong era. These machines have a basic monitor panel with warning indicators, not a CAN bus with stored fault codes. Diagnosis is done the old way: pressure gauge on the test ports, cycle time stopwatch checks, and multimeter continuity tests on the harness. This manual documents exactly those procedures, plus what each monitor panel indicator actually means.
Does one manual really cover both the 311 and the 312?
Yes. The two machines share most of their architecture, and where they differ the manual gives separate values - main pump flow is 108 liter/min on the 311 versus 120 liter/min on the 312, high idle is 1880 rpm versus 1980 rpm, and each model gets its own cycle time table and its own hydraulic and electrical schematics. You will not be guessing which spec applies to your machine.
Does it cover the swing and travel drives, or just the engine and pump?
Full coverage. The Power Train and Hydraulic System sections take the swing motor, swing drive and bearing, travel motors and final drives through disassembly and assembly, and give you the wear limits that matter: maximum case drain of 15 liter/min on a new swing motor, 20 liter/min on a new travel motor, and the swing relief setting of 23000 ± 980 kPa (3350 ± 140 psi). Undercarriage is in there too - track chain, adjuster, rollers, idler and sprocket, with adjuster torques in the Torque Specifications section.
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