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This is the Cat SIS service bundle for the 311 and 312 excavators, serial prefix 6GK, with the 3064 and 3066 engines. It is not one authored book - Cat stitched the individual service publications together, so you get systems operation, testing and adjusting, and disassembly/assembly side by side. The heart of it is the hydraulic testing material: main and line relief settings, swing crossover, power shift pressure, pump flow and calibration - the numbers that tell you whether a tired machine needs a pump or just a screwdriver on a relief valve. Engine, fuel, cooling, electrical schematics for the 311/312, undercarriage, travel and swing drives, cab and linkage service are all in here. This is a gauges and stopwatch machine, and the book is written that way.
What's Inside This Caterpillar 312 Repair Manual
| System | Pages | Key Topics |
|---|---|---|
| Air Inlet and Exhaust System | 2-52 | Turbocharger, Exhaust and Air Intake Service |
| Basic Engine | 53-390 | Cylinder Head, Block, Pistons, Crankshaft and Engine Service |
| Cooling System | 391-474 | Radiator, Water Pump, Thermostat and Cooling Service |
| Electrical and Starting System | 475-1648 | Starting and Charging, System Schematics and Testing, Plus Cat's Bundled Add-On Publications (EquipmentManager, Product Link, R134a Air Conditioning) |
| Engine Arrangement | 1649-1691 | Engine Arrangement Systems Operation and General Information, Testing and Adjusting, Troubleshooting, Engine Speed Check, And Engine-To-Main-Hydraulic-Pump Separation |
| Frame and Body | 1692-1708 | Frame, Covers and Body Panels |
| Fuel System | 1709-1979 | Injection Pump, Injectors and Fuel System Service |
| Hydraulic System | 1980-2808 | Systems Operation, Testing and Adjusting (Main and Line Relief Valve Settings, Swing Crossover, Power Shift Pressure, Pump Flow and Calibration), Pumps, Valves and Cylinders |
| Implements | 2809-2881 | Boom, Stick and Bucket Linkage Service |
| Lubrication System | 2882-2949 | Oil Pump, Filters and Lubrication Service |
| Machine Arrangement | 2950-2962 | Machine Arrangement Systems Operation, Service Intervals, Testing and Adjusting, And Heating and Air Conditioning Service References |
| Operator Station | 2963-3529 | Cab, Seat, Controls and Monitor |
| Power Train | 3530-3592 | Travel Motors, Final Drives and Swing Drive |
| Service Equipment and Supplies | 3593-3647 | Dealer Service Tools and Shop Supplies |
| Undercarriage | 3648-3702 | Track, Rollers, Idlers and Recoil Spring Service |
| Work Tools | 3703-3711 | Work-Tool Mounting and Coupler Service |
| Torque Specifications | 3712-3760 | Cat's Generic Torque Charts (Metric ISO, English SAE, Fittings, Plugs, Hose Clamps) |
| Schematic | 3761-3849 | Named Schematic Sheets - the 311 and 312 Excavators Electrical System (2003) - Plus the Fluid Power and Electrical Graphic Symbol Legends |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| 312 | ||
| Main relief valve pressure (standard setting) | 27500 +/- 490 kPa (4000 +/- 72 psi) | p. 2214 |
| Main relief valve pressure (high-pressure / travel) | 34300 +/- 490 kPa (5000 +/- 72 psi) | p. 2328 |
| Swing crossover relief valve pressure | 23000 +/- 980 kPa (3350 +/- 140 psi) | p. 2215 |
| Line relief valve pressure (boom / bucket) | 26000 +/- 1470 kPa (3750 +/- 215 psi) | p. 2216 |
| Line relief valve pressure (higher circuit) | 31400 +/- 1470 kPa (4550 +/- 215 psi) | p. 2217 |
| Line relief valve pressure (highest circuit) | 36300 +/- 1470 kPa (5250 +/- 215 psi) | p. 2218 |
| Power shift pressure (test constant) | 1780 +/- 50 kPa (260 +/- 7 psi) | p. 2229 |
| 311 and 312 | ||
| Proportional reducing valve | 0.16 to 0.63 A, pressure range 0 to 3150 kPa (0 to 455 psi) | p. 2171 |
| Engine speed by dial setting | 700 rpm (low idle, dial 1) up through 1100 / 1210 / 1320 / 1430 / 1540 / 1650 / 1760 rpm | p. 2176 |
Caterpillar 312 Common Problems This Manual Covers
Machine feels weak, slow cycle times, will not dig like it used to
Before condemning the pump, put a gauge on it. The Hydraulic System testing and adjusting section walks you through checking main relief pressure against 27500 +/- 490 kPa standard and 34300 +/- 490 kPa in high pressure mode, then pump flow and calibration.
Manual Section: Hydraulic System p. 2214Swing is soft, spongy, or the house drifts when you stop
The swing crossover relief valves are the usual suspect. The Hydraulic System section gives the test hookup and the 23000 +/- 980 kPa (3350 psi) setting, plus the adjustment procedure, so you can confirm the reliefs before pulling the swing motor for nothing.
Manual Section: Hydraulic System p. 2215Boom or bucket circuit down on power, or a cylinder that will not hold
Check the line reliefs against spec: 26000 +/- 1470 kPa on boom and bucket, 31400 and 36300 kPa on the higher circuits. The Hydraulic System testing procedures show where to tee in the gauge and how to bring each valve back to setting.
Manual Section: Hydraulic SystemPump response feels off after a repair, machine bogs or stalls under load
The pump control needs setting up, not guessing. The Hydraulic System section covers power shift pressure at the 1780 +/- 50 kPa (260 psi) test constant and the proportional reducing valve at 0.16 to 0.63 A over 0 to 3150 kPa, with the full calibration procedure.
Manual Section: Hydraulic SystemFrequently Asked Questions
Does this manual cover my 312, or is it a 311 book?
Both. Cat published this as a shared 311/312 bundle, and the schematic section is literally titled for the 311 and 312 electrical system. The engines covered are the 3064 and 3066, and the 312 serial prefix is 6GK. Procedures that differ between the two models are called out in the text. p. 3772
How do I reset error codes on a Cat 312?
On this machine there is no code table to reset. The 6GK-era 312 is diagnosed the old way: a pressure gauge on the test port, a tachometer and a stopwatch. If the monitor is showing a warning, the manual sends you to the actual sender or circuit through the Electrical And Starting System testing procedures and the schematics for both the 311 and 312, not through a code list. Anyone selling you a fault code chart for this serial range is selling you paper. p. 475
Are the torque specs for the main hydraulic pump in here?
The Torque Specifications section is Cat's generic chart set - metric ISO and English SAE fasteners, fittings, plugs and hose clamps - not a machine torque table. Torques specific to a given assembly, pump included, live inside that component's own disassembly and assembly text in the Hydraulic System section, where they belong so you see them at the step you need them. p. 2214
What should my relief valve pressures be on a healthy 312?
Main relief is 27500 +/- 490 kPa (4000 psi) standard and 34300 +/- 490 kPa (5000 psi) in high pressure travel mode. Swing crossover reliefs set at 23000 +/- 980 kPa (3350 psi). Line reliefs run from 26000 +/- 1470 kPa (3750 psi) on boom and bucket up through 31400 and 36300 kPa on the higher circuits. These numbers, and the test procedures to check them, are what separate a worn machine from a healthy one. p. 3712
What engine rpm should the 312 run at?
There is no single answer - engine speed is set by the dial in the cab, ten positions from 700 rpm at low idle (dial 1) stepping up through 1100, 1210, 1320, 1430, 1540, 1650 and 1760 rpm. The testing section gives the rpm for each dial position, so you can verify the governor is delivering what the dial promises before you blame the pump for a slow machine. p. 2176
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