The following information is presented as a best practice guide and should assist in avoiding some of the most common pitfalls when carrying out this task. This information is relevant each time these parts need replacing, in addition to this the Vehicle Manufacturers instructions for the particular vehicle must be followed.
Ensure all the right tools are at hand. In the course of this task access is gained to areas that are normally unseen, this opportunity should be used to inspect inner walls of tyres, wheels, suspension components, steering and drive components, doing this can help to avoid a further problem. Care should be taken not to contaminate the new Brake Pads with any oil grease or brake fluid.
Brake Discs and Brake Pads should always be replaced in pairs (Axle sets) to ensure efficient and balanced braking.
1. With the hand brake applied, chock the wheels as an additional safety precaution.
2. Loosen wheel bolts/nuts on the relevant wheels.
3. Raise the bonnet and loosen the Brake master cylinder reservoir cap.
4. Raise the vehicle using an appropriate Jack and for safety purposes provide additional support with axle stands or similar.
5. Remove the relevant road wheels.
6. When replacing Brake Discs and Pads the new ones will obviously need more space than the old ones did within the Caliper so now is the time to push the pistons back into the Caliper bodies. This is done by prising the gap between the old Brake pad and Discs with a wide scraper or screwdriver, if only replacing the pads care should be taken not to damage the brake disc face. During this operation the bake fluid is pushed back into the system consequently a regular check should be taken on the level within the master cylinder reservoir to prevent it from overflowing. From this point on, measures should be taken to prevent anyone from sitting in the driver’s seat and depressing the brake pedal.
7. Remove the Pad retaining clips and pins.
8. Remove the Brake Caliper and independently support it’s weight with a cable tie or wire i.e. do not let it hang by the Brake hose causing unnecessary strain or damage.
9. To remove the disc, undo the disc securing screws and remove the disc from the hub mounting flange.
10. Remove all traces of rust, dirt or burrs from the face of the mounting flange. This part of the operation is very important pay particular attention and leave as clean bright metal with no burrs.
11. Clean the anti corrosion protection oil off the new Brake Disc using methalayted spirit or another suitable solvent. Inspect and clean inside of the brake disc, again pay particular attention to the face that sits on the mounting flange, it should have no raised points or burrs.
12. Assemble the brake disc onto the Hub Flange. Between the inner Brake Disc and the hub flange do not apply lubricant eg. Copper based lubricant. Tighten brake disc locking screws to manufacturers recommended torque. Brake Discs are made from a cast iron alloy which is a particularly hard material, ideal for the purpose of conducting heat away and giving a long life of friction against the brake pads, on the downside however this makes them also quite brittle, consequently overtightening can cause distortion and cracks!
13. On problem vehicles it is necesary to check the ‘run out’ of the Brake Disc before assembly this is done by rotating the Brake Disc against a Dial gauge or a fixed point with feeler gauges this should not exceed 0.15mm or 0.006in, take this reading about 10mm in from the outer edge of the disc. If you record a higher reading than 0.15mm disassemble and repeat items 10, 11 and 12 when you refit the brake disc, rotate it through 180 degrees from the first position.
14. Reassemble the brake Caliper and at this point check and that the sliding mechanism is clear, fit the new Brake Pads and depress the brake pedal several times to bring the pads into contact with the Brake Disc. Top up the brake fluid in the master cylinder reservoir.
15. Fit wheel and tighten to manufacturer’s recommended tightening torque in the correct sequence usually crosswise but in practice often in two stages clockwise.
16. During the first 200miles (320Km) gently use the brakes as they are ‘bedding in’ try and avoid severe braking or high speeds during this period.