Gearbox and axle parts are matched to a specific unit. Here is which transmissions and axles are fitted to JCB 3CX and 4CX backhoe loaders and how to tell them apart. The data comes from the JCB service manual for 3C, 3CX and 4CX backhoe loaders (machines with serial numbers 960001–989999, 1327000–1349999 and 1616000–1625999).
Gearboxes
Synchro Shuttle SS700
4 forward and 4 reverse gears. Gears are selected with a mechanical lever, direction with a column switch. The parking brake is a disc on the rear axle flange.
SS700 Type 2
The same design; it differs in having no layshaft access cover.
Powershift PS764
4 forward and 4 reverse, power shifting with a single column switch. A block of 7 solenoid valves on the gearbox; a wet parking brake inside the transmission.
Powershift PS766
6 forward and 4 reverse, electronic ShiftMaster control only, a block of 8 valves.
All these gearboxes work with a 310 mm torque converter, for example 04/600784. The gearbox number is stamped on its plate; when ordering gears, also check the number stamped on the gear itself and the number of teeth.
Axles
- Front SD55 — four-wheel-drive machines with front-wheel steer.
- Front SD80 — all-wheel-steer machines.
- Front non-driven axle — two-wheel-drive machines.
- Rear PD70 — front-wheel-steer machines.
- Rear SD80 — all-wheel-steer machines.
Every driven axle has a 5.4:1 planetary reduction in the hubs. The rear axles have wet brakes: 5 friction and 6 counter plates per half shaft.
Why the axle ratio matters
Axles were built with different crown wheel and pinion sets, giving overall ratios from 13.7:1 to 19.2:1 (for example 15.78:1 with a 38/13 set or 18.16:1 with a 37/11 set). A replacement axle must have the same ratio as the one removed, and the front and rear axles must match each other and the gearbox. Take the data from the axle plate and, for the crown wheel and pinion, the number and tooth count stamped on the gear.
What is replaced most often
- axle pinion seals — they can be replaced without removing the axle;
- friction and counter plates of the rear axle brakes;
- Powershift solenoid valves — if a coil fails, the whole valve cartridge is replaced;
- transmission oil pressure and temperature sensors (not repairable);
- SS700 synchromesh;
- propshaft universal joints and straps — the straps are always renewed when removed.
Water in the gearbox oil is dangerous: as little as 0.1 % water starts the clutch linings separating. Common causes are a damaged or wrong dipstick and working in deep water.
Parts are in the Transmission and Undercarriage sections.
Help with choosing
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335/Y6895
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