Brake servo 334/D9781 JCB, aftermarket

For the JCB machines: brake servo 334/D9781, an aftermarket part.

When looking for a servo fault, check the vacuum source first: with the engine running, take off the vacuum hose and feel the suction at its end or measure it with a gauge. If the vacuum is good, the problem is in the servo itself. A simple test is to stop the engine, press the pedal several times to use up the vacuum, then hold the pedal down and start the engine; on a sound servo the pedal drops slightly. The servo may also be replaced as a unit with the master cylinder, and then the push rod length setting is especially important. The seal or O-ring between the servo and the master cylinder is renewed as well, since fluid leaking there can damage the servo diaphragm. After the servo is changed, pedal height and free play are checked against the maker's values.

Specifications

Compatibility

According to the product card, 334/D9781 is a brake servo. Fit is confirmed by the part number. The catalogue also has the OEM version of this part. Other parts are in Vacuum pumps and brake boosters.

Fitting

Before removing the servo, stop the engine and press the pedal several times to release the vacuum. If the master cylinder can be separated from the servo without disconnecting the lines, leave them in place. After fitting, check the push rod setting, bleed the system if necessary and test the brakes at low speed.