Brake piston orientation

[robinfly]

While back, at my mechanic's recommendation, I had him "un-freeze" my front brake calipers. Since then, my pride-and-joy became a major embarrassment at every stop because front brake squeal. I have brought it back to him many times to no avail. Finally, last weekend, I pulled my right front pads off its caliper for a look-see.

I found one thing that I am not sure what to make of it. When I look at the outer piston, it has on its face a raised ring with a raised center. But 1/3 of the ring appeared to be lower than the rest of the ring. Is it the way that the pistons are suppose to be?

I then looked at both pads. They appeared to have a "C" and a center dot imprinted on their sides matching the face of their pistons. However, one has the opening of its "C" to the top while the other has the opening to the front.

That night, I found the article on Pelican Parts website on caliper rebuild: http://www.pelicanparts.com/techarti...er_rebuild.htm

The article says: "Orient the piston at a 20-degree angle from the top of the brake pad slot in the caliper. This angle is important to keep the brakes from squealing."

I don't have a copy of the factory manual. The orientation of the piston, is it referring to the opening of the "C"?

If yes, it appears my pistons are not oriented correctly. Do I need to rebuild both calipers to correct the squealing problem, or is there any other option?

Many thanks in advance.

[Rich Lambert]

The red circles on the white ring of the image are the edges of the piston's raised section. The depressed area of the piston is behind the angle template. Does that make sense?



You might be able to remove the calipers from the car, take out the circlip and rubber seal, and rotate the pistons. There may be some Porsche tool for this, but I used a towel as padding and adjusted the pistons with a pair of channel locks. If you do this, be very careful not to damage the piston.

[Neunelfer]

Rich is spot on there. The piston should be facing 20 degrees into the oncoming direction of the rotor. Funny thing is, most ATE kits don't include the piston positioners any more. The position of the piston is more likely to cause uneven or slanted pad wear. I've had people show me uneven pad wear and say it was because of S-Caliper flex... (whatever).



Squeaking can be cause by any number of things, the first being the pads. Organic pads can squeak (my bet) however, they stop the car the best. Semi-metallics won't squeak or stop.

Here's Porsche's squeak list:

Pads
Dirt and dust covers
20 degree piston alignment
Cross spring (dirty/binding)
Wheel bearing clearance
Disc and caliper mounting alignment
Lateral runout or thickness variation of the discs

My guess is, you'll go to all the trouble of repositioning your piston and be really pissed off at the very next stop light.