X300 – Brakes

8 – Brakes ( )


The system has discs ( rotors ) on all wheels, with single piston calipers at the rear and single or double piston ( on some later models ) calipers at the front. The handbrake utilises a separate drum and shoes mounted inboard from the main braking system.

Power assistance is provided by engine vacuum an accumulator. The pedal should be capable of being pumped five to seven times after the engine is switched off before becoming hard, any shortfall suggesting a weakening accumulator or seals.

The ABS system uses speed sensors on each axle, coupled with electronically controlled valves in the main valve block to hold back braking pressure when a wheel begins to lock. The system is fail-safe, such that the valves will remain open and the system will act like a normal non-ABS system in the event of a system problem.

The speed sensors are also used by the Traction Control system.

Note that no pad wear indicators are fitted.


8.1 – Brake Pad Renewal ( )

Remove roadwheel. Check brake disc (rotor) for adequate thickness and absence of warp, and replace if necessary.

Unbolt the caliper guide pins using a 7mm allen key. The caliper can now be moved to one side and the pads pulled out. Avoid putting any strain on the caliper brake fluid pipe.

Put the caliper approximately back in position and undo the bleed nipple. Attach a piece of rubber pipe looped upward then leading to a jar on the ground, or use a brake bleeding kit. This will prevent air getting into the system. Releasing fluid when pushing the pistons back is significantly easier than pushing the fluid back up through the valve block and avoid risk of damaging or contaminating the sensitive ABS valves.

It is now necessary to push the piston back to be flush with the cylinder, so allowing sufficient space to install the new pads. To not exert force directly onto the piston, but use the old pad instead. Pulling the caliper toward you will push the piston back, as will levering between pad and disc with a stout piece of wood. Do not use metal which would damage the surface of the disc. Tighten the bleed screw and remove the old pad when the piston is pushed back.

Clean the caliper and coat the guide pins, piston head and areas of the caliper in contact with the pads with copper gresase. This will make removal next time that much easier!

Insert the new pads and rebolt the caliper in place.


8.2 – Brake Disc Renewal ( )

Undo the brake caliper, remove the pads, and suspend it out of the way without straining the fluid pipe.

Unbolt and remove the caliper mounting bracket.

Undo the disc retaining screw if fitted. The screw is only used in production to hold the disc in place whilst moving down the assembly line.

It should now be possible to remove the disc from the hub. In practice, it is often necessary to spray WD40 where the disc meets the hub, then use a hammer on the disc to initially release it. On rear discs, it may also be necessary to back off the handbrake adjustment.

Clean the hub and refit the new disc. Bolt the caliper bracket into position, fit the pads to the caliper and refit the caliper.


8.3 – Brake Bleeding and Fluid Replacement ( )

Bleeding can be done with a proprietary bleeding kit, or by the more traditional methods. Fluid replacement is achieved through an extended bleeding process, ensuring sufficient old fluid has been removed from the system to be replaced by new.

Bleeding should be done at each wheel, starting with the right rear, then left rear, right front and left front. Continually check and top up the level of fluid in the reservoir under the bonnet to ensure no air is introduced into the system. Free the bleed nipple, using a penetrating agent such as WD40 if necessary, before attaching bleed tubes etc.

If using the traditional two man method ( or one man, a piece of timber to jam between seat front and brake pedal and a lot of running around! ), attach some clear tubing to the bleed nipple and immerse the other end in a container of brake fluid.

Depress and hold the brake pedal down. Undo the bleed nipple just enough to allow fluid to flow. Any bubbles indicate air in the system and further bleeding is required. Gently retighten the bleed nipple as the fluid flow decreases, before all the pressure has gone, then release the brake pedal.

Repeat the above until all air bubbles have left the system or until the old fluid has been removed, whichever is the objective.


8.4 – Handbrake Adjustment ( )

The cable adjuster is located under the centre of the car, at the handbrake end of the cable.

Undo the locknut and turn the adjuster to remove slack from the cable so it is just taut. Retighten the locknut.

Unless the car has been driven with the handbrake applied, it is unusual for the handbrake shoes to wear and need adjustment or replacing. If the handbrake is inefficient, however, adjustment is possible,

The adjustment is done by a star shaped wheel on a threaded bolt which sits between the upper ends of the shoes. Turning the wheel pushes the shoes closer / further from the drum and so gives the necessary adjustment.

Jack the car up with the handbrake released, remove the wheel and spin the disc such that the access hole is in front of the adjustment wheel, at approximately the eleven o’clock position. Using a small bladed screwdriver, turning the adjuster so that the shoes are in contact with the drum, then back it off until the disc / drum assembly can spin without binding.

Adjusting one side can marginally affect the other, so best results can be obtained by doing both sides at one go, supporting the car on axle stands meanwhile.