924/944/968 Frequently Asked Questions

11.0 Brake Maintenance

The following articles will help guide you through basic maintenance of your car's brakes. A word of caution: making a mistake in servicing your brakes can create a great danger, to you, your passengers, and other people. Have someone show you these procedures, at least the first time you perform them. Most Porsche Club chapters sponsor tech sessions where you can learn first-hand how to safely service your car. Take advantage of them, then use the following notes as a reminder when you are ready to try it yourself.

11.1. Tools

The following tools are necessary:

You'll find the following useful:

11.2. Supplies

You'll also need some consumable items:

11.3. Picking Products

There are two consumables of interest: brake fluid and brake pads. What kinds should you use?

The original Porsche pads are a really great choice for most people. They work very well for street driving as well as for autocrossing. Porsche has generally become competitive in their brake pad pricing, and it is certainly worth checking with your local dealership before exploring the aftermarket.

If you are starting to get serious about driver's education events or club racing, you may want to look into pads made from composite materials, commonly referred to as "carbon pads" or "carbon/kevlar pads." While more expensive than conventional pads, composites are able to withstand the extreme temperatures generated during high performance driving. Unlike earlier materials, such as used by Ferodo in their DS-11 pads, composites work well hot and cold.

Same basic ideas for brake fluid. Castrol GT LMA is a fine fluid for most applications. It's cheap, it works, and its readily available. If you drive on the track and have problems with pedal fade, it may be due to boiling of your brake fluid. In that case, consider using a fluid with a higher dry boiling temperature, such as AP 550.

Do not use silicone brake (DOT 5) fluid in your car. Walk quickly away from anyone who suggests otherwise.

11.4. Safety

Repeat after me: I will always use good quality jack stands and wheel blocks before sticking myself under a car.

11.5. Changing Brake Pads

I'll describe the process for a single wheel.

  1. Block the wheels, jack the car, support it with jack stands, and remove the wheel. Use a "soft socket" if possible to avoid marring the lug nuts. Otherwise, use a 19 mm deep socket.
  2. Open the hood. Clean around the cap on the brake fluid reservoir. Remove the cap, then remove the basket. Pour the brake fluid from the basket into a catch bottle, being careful not to get any on painted surfaces. Clean the basket, wrap it and the cap in a paper towel, and set aside.
  3. The caliper on a 924S/944/944S is different in design to that on a 944 Turbo/944S2/968, as is the way pads are removed.

    3a. On a 944/944S, remove the spring lock or hairpin cotters on the retaining pins. Tap out the retaining pins with a hammer and punch, from the inside of the caliper. Once they're loose, or if you haven't a punch, grab their heads from the outside with linesman pliers, pull them out, and set them aside. Catch the flat spring and set it aside as well.

    3b. On a 944 Turbo/S2/968, compress the spring lock top-to-bottom at its center with linesman pliers, then pivot it out of the way.
  4. Remove the wear sensor carefully. Be sure not to lose the very small leaf spring which goes between the sensor and the pad body.
  5. Remove the pads. This generally requires a bid of creativity. Remove the inner bad first, grabbing one of its "ears" with pliers and wiggling while pulling. Then remove the outer pad. With the 944/944S floating caliper, this requires yanking the caliper assembly out, so that the caliper's tongue no longer locks the pad in via the slot in its backing plate.
  6. Clean the piston bearing surfaces. Pour rubbing alcohol on a towel and wipe the piston edge. Make sure the piston is correctly positioned, in rotation.
  7. Push back the piston(s) to make room for the new pads. While you do this, watch the reservoir to keep it from overflowing. Use the turkey baster to draw off excess fluid. Try to avoid scoring or damaging the piston edge when you push it into the caliper. Use the wooden handle of a paintbrush, for example, a large flat-blade screwdriver, or a special purpose tool.
  8. Clean debris out the caliper now that the pads are removed. Use a small steel "toothbrush," and pay particular attention to the top and bottom sides faces where any build-up of debris will interfere with installation of a new pad.
  9. Coat bearing surfaces of the new brake pads with a smear of anti-seize, particularly the top and bottom edges of the backing plate.. Insert the pads in the reverse order of which they were removed: first the outer, then the inner pad. The fit is tight, and you may find that you need to press back the piston(s) a bit more.
  10. Put the wear sensor back in the inner pad. Replace it with a new one if it has worn and turned on. The inner pads wear faster, which is why they get the sensor in single-sensor situations.
  11. Replace the hardware removed in step 3. If any parts are worn or damaged, a new hardware kit can be bought. On 944/944S', smear a coat of anti-seize on the retaining pins.
  12. Check the condition of the suspension, electrical, and hydraulic parts in the wheel well. Look for cracking or swelling of the brake lines. Check for any looseness in the suspension parts. Grab the tie rod and wiggle it.
  13. Put the wheel back on, torquing lightly each nut to centre the wheel. Then torque all five lug nuts to 96 ftlb. in a star pattern. Put the car back on the ground.
  14. When all wheels' pads have been replaced, top off the brake fluid reservoir to the "Max" mark, replace the basket and cap, and wipe up any spilled fluid.
  15. Very important: Start your motor with the parking brake applied. Pump the brake pedal several times, until it becomes firm. You have pushed the pistons back, and they need a pump or two to get them back to their operating point.

The new pads you have are "green." During the first couple of hundred miles, they will provide slightly less braking force than broken-in pads. Drive accordingly!

If you put on new pads before going onto the track, expect an even more noticeable loss of braking - "green fade." What is happening is that chemicals used in formulating the pad compound boil out of the pad. They form a microscopic liquid or gas film on the pad surface, drastically reducing the coefficient of friction.

11.6. Bleeding and changing brake fluid

Brake fluid should be changed once a year. And you should bleed your brakes before each trip to the track.

"Changing" or "flushing" the fluid means a complete flush of the system. "Bleeding" removes less fluid, concentrating instead on ridding the system of broken-down fluid and air bubbles in the calipers.

Bleed one wheel's caliper at a time, doing them in order of decreasing brake line length. This means:

  1. rear right,
  2. rear left,
  3. front right,
  4. front left.

You don't have to remove the wheels or jack the car to bleed its brakes. You may, however, find it easier to do the fronts if it's jacked.

Bleeding fluid is a two-person job.

  1. Open the hood. Clean around the cap on the brake fluid reservoir. Remove the cap, then remove the basket. Pour the brake fluid from the basket into the catch bottle, being careful not to get any on painted surfaces. Clean the basket, wrap it and the cap in a paper towel, and set aside.
  2. Go to the first wheel caliper you plan to bleed. Take tools, paper towels, and the work light.
  3. Remove the dust boot from its bleed valve. On a 944 Turbo, 944S2, and 968, each caliper has two valves, and you have to bleed through each valve separately.
  4. Place the correct wrench over the valve. Push the vinyl hose over the valve, capturing the wrench. Put the other end of the hose into your catch bottle.
  5. Get your accomplice (#2) into the driver's seat, with his/her foot on the brake. #2's job is going to be pumping the pedal, to force fresh fluid from the reservoir to the caliper.
  6. Have your friend apply pressure to the pedal. You (#1) crack the valve on the caliper, open its, and let fluid drain into the catch bottle. When #2's foot has pushed the pedal to the floor, s/he signal's #1, who then closes the valve lightly.
  7. #2 should not release the brake pedal until #1 has closed the valve. Otherwise, the rising pedal will suck air back into the caliper.
  8. The two of you now need to establish a coordinated rhythm. Something like:
     
    #1 (in driver's seat) #2 (at caliper)
    applies pedal pressure,  
    says: "Pressure!"  
      opens valve,
      says: "Open!"
    pushes pedal to floor,  
    then says: "Floor!"  
      closes valve,
      then says "Closed!"
    releases pedal,  
    says: "Releasing...Up!"  

    You need to repeat this cycle a number of times. If you're just bleeding, anywhere from four to ten pumps may be necessary to remove dirty-looking fluid and air bubbles. Look through the vinyl hose, watching the quality of the fluid coming out the valve.

  9. If you're changing the fluid, the number of pumps needed depends on the line length. Look for fresh, clean fluid coming down the hose.
  10. In all cases, watch your fluid level in the reservoir. Do not let it fall more than half-way down! If the reservoir runs dry, you will suck air into the lines and have to start all over. Watching the reservoir and keeping it filled is a good job for a third person.
  11. When you're done with a valve, close it snuggly, remove the hose and wrench, and replace the dust boot. Wipe up any fluid which has dripped.
  12. And when you're done all 'round, check the pedal feel. If you have any doubt about the work you've done, don't drive the car. Get help!
  13. Top off the brake fluid reservoir to the "Max" mark, replace the basket and cap, and wipe up any spilled fluid.

Brake fluid is toxic. Dispose of it using your town's hazardous waste program.

11.7. Brake Pad Wear

Uneven wear of your car's brake pads can have a very noticeable effect on performance and feel, particularly when autocrossing or at the race track. See the accompanying article for an explanation of how uneven wear occurs, what happens, and how to minimize or eliminate the problem.

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