Porsche 928 S4 Service

John Pirtle, March 3, 2001
http://members.rennlist.com/pirtle

Brakes

The brake system consists of several wear items: pads (two per wheel), rotors (one per wheel), and fluid. Additionally the rear contains the parking brake shoes (two per wheel) which will last a long time if properly adjusted.

Most of the brake system hydraulics will also last a long time with fluid changes every 1-2 years. Many enthusiasts recommend ATE Super Blue fluid, as well as Speed Bleeders which contain a check valve and replace the stock bleeder screw. Note that the S4 brakes have a separate bleeder screw for each side of the caliper (a total of eight per car).

Pad replacement

Front pads wear much quicker than the rears and all should be checked at every opportunity. Do not wait for the pad wear sensor indicator!

1. Lift car and remove wheel.
2. Check brake fluid reservoir. If the fluid is high or near the fill indicator open the top and siphon off some fluid, or place rags around the reservoir.
3. Carefully remove the brake pad wear sensor from the center of the inside pad.
4. Using a wrench, pinch the pad retainer to release it from the upper clip and swing it away.
5. Before removing the pad attempt to press it against the caliper to push the piston back into the caliper. This will push fluid back into the reservoir so check for spilling. Other methods of pushing the pistons back into the caliper include using a brake piston compressor tool, a piece of wood and a C-clamp, a screwdriver or other tool as a lever, etc. Be sure to protect the caliper, the rotor, and the pads (if you intend to reuse them).
6. With the piston sufficiently compressed, the pads should lift straight out.
7. Fitted into the pistons may be some pad dampeners. These are used to stop brake squeal. Often they can be reused. Often they are not even there any more.
8. Position the new pads in the caliper.
9. Close the pad retainer.
10. Position the pad wear sensor.
11. Close the fluid reservoir.
12. Start the car and pump the brakes to bring the pedal back to firm.

Rotor and parking brake shoe replacement

Rotors will warp over time especially under stressful heated conditions. Heat buildup can be exacerbated by not replacing the pads before they are thin. New rotors are smooth all the way to the edge, while worn rotors will have a lip at the edge.

Warped rotors create a vibration while braking. In the front this can be felt through the steering wheel. In the rear there will be a rumbling vibration. Typically the rotor can be machined, or turned, to remove the warping so long as the rotor thickness remains within spec - 30.6mm front/22.6mm rear. Other specifications are in the Tech Specs booklet.

Rotors that have hair-line cracks cannot be machined and must be replaced.

To remove the rotor:
1. Squeeze the pads to move the piston back into the caliper.
2. Remove the two caliper mounting bolts. The rear calipers use two standard 19mm bolt. The front calipers are held on with two 10mm hex socket bolts (accessable from the top - do not confused these with the inner ones which should not be loosened!).
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
3. Lift the caliper assembly from the rotor and secure it aside without stressing the lines or connections. String may be used to tie the caliper to the spring.
4. Remove the two Phillips head screws. Often they cannot be removed without an impact driver.
   
   
   
   
5. To assist pulling the rotor from the hub, use two M8-1.25 bolts (uses a 13mm socket). Two bolt holes are already in the rotor for the purpose of pressing the rotor off.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   Parking brake shoes:
6. My parking brake shoes looked as though someone had done a fair amount of stunt-driving!!!
7. Remove the two vertical springs and the star adjuster.
8. Each brake shoe is held to the hub with a spring mounted horizontally in the center of the shoe. Press in to unlock it (which is visible on the inside of the hub) and remove the shoe.
9. When installing the new shoes I found it easier to install the upper, and with the forward vertical spring in place install the lower shoe.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
10. Check that all the springs are properly seated over the lip on the inside of the shoe or the wheel hub.
11. With new shoes I left the adjuster screwed all the way in and adjusted the tension from the parking brake handle. The spring on the adjuster also acts to keep the adjuster from turning.
    
    Installing the rotor:
12. Install the rotor and tighten it to the hub with the two Phillips head screws.
13. Check that wheel turns freely without tension from the parking brake.
14. Pull the parking brake handle and check that rotors cannot turn.
15. Compress the pistons sufficiently in the caliper and mount on the rotor.
16. Mount wheel.
17. Check parking brake operation. If necessary remove the two parking brake handle covers and adjust the tension cable nut.

928 S4 Page

John Pirtle
March 7, 2001