Front brake caliper - removal, overhaul and refitting

Braking system / Front brake caliper - removal, overhaul and refitting

Note: Before starting work, refer to the warning at the beginning of Section 2 concerning the dangers of hydraulic fluid, and to the warning at the beginning of Section 4 concerning the dangers of asbestos dust.

Removal
1 Apply the handbrake, then jack up the front of the vehicle and support it on axle stands see “Jacking and vehicle support”). Remove the appropriate roadwheel.

2 Minimise fluid loss by first removing the master cylinder reservoir cap, and then tightening it down onto a piece of polythene, to obtain an airtight seal. Alternatively, use a brake hose clamp, a G-clamp or a similar tool to clamp the flexible hose.

3 Clean the area around the union, then loosen the brake hose union nut.

4 Follow the procedure described in Section 4 for the removal of the brake pads, however leave the pads in the carrier bracket.

5 Unscrew the caliper from the end of the brake hose and remove it from the vehicle.

Overhaul
With the caliper on the bench, wipe away all traces of dust and dirt, but avoid inhaling the dust, as it is injurious to health.

7 Withdraw the partially ejected piston from the caliper body, and remove the dust seal.

8 Using a small screwdriver, extract the piston hydraulic seal, taking great care not to damage the caliper bore (see illustration).

8.8 Extracting the piston seal - take care not to scratch the surface of the bore

9 Thoroughly clean all components, using only methylated spirit, isopropyl alcohol or clean hydraulic fluid as a cleaning medium. Never use mineral-based solvents such as petrol or paraffin, as they will attack the hydraulic system’s rubber components. Dry the components immediately, using compressed air or a clean, lint-free cloth. Use compressed air to blow clear the fluid passages.

10 Withdraw the spacers/sleeves from the caliper body bushes.

11 Check all components, and renew any that are worn or damaged. Check particularly the cylinder bore and piston; these should be renewed (note that this means the renewal of the complete body assembly) if they are scratched, worn or corroded in any way.

12 Similarly check the condition of the spacer sleeves and their bushes/bores; both spacer sleeves should be undamaged and (when cleaned) a reasonably tight sliding fit in their bores. If there is any doubt about the condition of any component, renew it.

13 If the assembly is fit for further use, obtain the appropriate repair kit.

14 Renew all rubber seals, dust covers and caps disturbed on dismantling as a matter of course.

15 On reassembly, ensure that all components are spotlessly clean.

16 Dip the piston and the new piston (fluid) seal in clean hydraulic fluid. Smear clean fluid on the cylinder bore surface.

17 Fit the new piston (fluid) seal, using only your fingers (no tools) to manipulate it into the cylinder bore groove. Fit the new dust seal to the piston, and refit the piston to the cylinder bore using a twisting motion; ensure that the piston enters squarely into the bore. Press the piston fully into the bore, then press the dust seal into the caliper body.

18 Apply the grease supplied in the repair kit, or a good quality high-temperature brake grease or anti-seize compound, to the spacer sleeves and insert them into their bushes.

Refitting
19 Screw the caliper fully onto the flexible hose union.

20 Check that the brake pads are correctly located in the carrier bracket, then refit the caliper with reference to Section 4.

21 Securely tighten the brake hose union nut.

22 Remove the brake hose clamp or polythene, as applicable, and bleed the hydraulic system as described in Section 2.

Note that, providing the precautions described were taken to minimise brake fluid loss, it should only be necessary to bleed the relevant front brake.

23 Refit the roadwheel, then lower the vehicle to the ground and tighten the roadwheel bolts to the specified torque.