Front caliper piston assembly - removal, overhaul and refitting
Warning: Brake hydraulic fluid may be under considerable pressure in a pipeline, take care not to allow hydraulic fluid to spray into the face or eyes when loosening a connection.
Warning: Never refit old seals when reassembling brake system components.
Removal
1 Proceed as described in paragraphs 2 to 8 in the previous Section.
2 Disconnect the brake flexible hose from the caliper. This can be carried out in one of two ways. Either disconnect the flexible hose from the rigid hydraulic pipeline at the support bracket by unscrewing the union, or, once the caliper is detached, hold the end fitting of the hose in an open-ended spanner and unscrew the caliper from the hose. Do not allow the hose to distort an excessive amount.
Overhaul
3 Brush away all external dirt and pull off the piston dust-excluding cover.
Caliper and piston components
A Piston cover
B Seal
C Piston
D Housing
4 Apply air pressure to the fluid inlet hole and eject the piston. Only low air pressure is needed for this, such as is produced by a foot-operated tyre pump.
Caliper piston removal method with compressed air. Note wooden block fitted
to avoid damaging the piston
5 Using a suitable hooked instrument, pick out the piston seal from the groove in the cylinder bore. Do not scratch the surface of the bore.
6 Examine the surfaces of the piston and the cylinder bore. If they are scored or show evidence of metal-to-metal rubbing, then a new piston housing will be required. Where the components are in good condition, discard the seal and obtain a repair kit.
7 Wash the internal components in clean brake hydraulic fluid or methylated spirit only, nothing else.
8 Using the fingers, manipulate the new seal into its groove in the cylinder bore.
9 Dip the piston in clean hydraulic fluid and insert it squarely into its bore.
10 Connect the rubber dust excluder between the piston and the piston housing and then depress the piston fully.
Refitting
11 Refit the caliper by reversing the removal operations.
12 When reconnecting the brake hose check that it is fitted and secured so that it is not distorted and will not interfere with any adjacent steering or suspension components.
13 Bleed the hydraulic circuit, then refit the roadwheel (s) and lower the vehicle.
14 If new pads have been fitted, heavy braking should be avoided where possible for the first hundred miles or so to allow them to bed in and reach full efficiency.