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Vacuum servo unit - testing, removal and refitting
Braking system / Vacuum servo unit - testing, removal and refitting

1 To test the operation of the servo unit, depress the footbrake four or five times to dissipate the vacuum, then start the engine while keeping the footbrake depressed. As the engine starts, there should be a noticeable УgiveФ in the brake pedal as vacuum builds up. Allow the engine to run for at least two minutes, and then switch it off. If the brake pedal is now depressed again, it should be possible to hear a hiss from the servo when the pedal is depressed. After four or five applications, no further hissing should be heard, and the pedal should feel harder.

2 Before assuming that a problem exists in the servo unit itself, inspect the non-return valve as described in the next Section.

3 Refer to Section 11 and remove the master cylinder.

4 Disconnect the vacuum hose adaptor at the servo unit by pulling it free from the rubber grommet. If it is reluctant to move, prise it free, using a screwdriver with its blade inserted under the flange.

5 Unscrew the four nuts securing the servo unit to the mounting brackets on the bulkhead in the engine compartment.

6 On right-hand drive models, withdraw the servo unit so that its studs are just clear of the brackets. Have an assistant hold the brake pedal depressed, then extract the spring clip and remove the clevis pin securing the servo unit pushrod to the pedal cross-link arm.

7 On left-hand drive models, unscrew the nut securing the pedal trunnion to the servo unit pushrod inside the passenger compartment.

The nut is located near the top of the pedal, and is accessible through an access hole. For improved access, remove the lower facia panel first.

8 Withdraw the servo unit from the bulkhead, and remove it from the engine compartment.

On left-hand drive models, take care not to damage the bulkhead rubber grommet as the pushrod passes through it.

9 Note that the servo unit cannot be dismantled for repair or overhaul and, if faulty, must be renewed.

10 Refitting is a reversal of the removal procedure. Refer to Section 11 for details of refitting the master cylinder.

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