GregBBRD

That's a good idea/test, Mark. Will tell how much "friction" there is within the caliper.

Nicole

Brake perforance was good, but not smooth. After driving for about half an hour, you could not slow down gradually without the car "jerking" to a stop. At high speed that would translate into vibration of the whole car. Replacing all discs and pads prior had not made any difference. I have not been able to verify that this is gone now.

Then a bleeder nipple broke, and since I wanted to refinish the brakes anyway, I bought a pair of used front calipers, replaced the seals with Zeckenhausen seals, refinished the outside, and put them on with new flex lines. That's when the trouble started.

GregBBRD

You replaced both the inner 0-ring and outer dust seal? What did you use to assemble?

mark kibort

jerking performance is strange. sounds like you might have had a contaminated rotor surface or a warped rotor. You said all of this happened after changing the pads and rotors as well? some times the monkeys at the shop will use the impact driver to tighten the lugs. (some at 150ft-lbs and others at 70ftlbs) this could warp your rotors and give you some major braking feel issues. i had this happen, and never let a shop touch my lugs again, without me being there to double check. I warped the heck out of the rotors and gave huge braking vibration . I was able to retorque, go back out and cook the brakes again and it went back to smooth again. Ive never had a problem like that since. what kind of pads and rotors are you using?

mk

Nicole

That's one thing I don't know, because this was done by a friend. I can try to find out, but it has been some time since the actual rebuild of the calipers.

Do you think a wrong lubricant could have made them soften or swell?

Bill Ball and I replaced the brake discs with Zimmerman discs. No change in the "jerky" brake feel.

mark kibort

Its just a strange thing for the brakes to do, especially since I would imagine the caliper falure mode to be either, leaking, dragging or no brakes. I wonder how the caliper could cause the braking to be pulsating (jerky). Does it feel like a warped rotor? the other think ive heard, is if the rotor isnt clean, (it has a coating of junk on it to protect it before installation), it can contaminate the pads. This can cause some strange things to happen in the braking feel department. also, there could be spots on the rotor that have a film of this stuff built up during bedding.
Bill is too good in the prep department to have let hat happen, but you never know. maybe the pads were a different type that deposited a film in a spot on the rotor? very puzzling

mk

Nicole

The only thing I could imagine was that as calipers warm-up, they do something weird, or the old brake lines had some swelling. I really did not know. But when the bleeder nipple broke, and the fronts needed refinishing anyway, I decided to overhaul the system and thought that would rule out all these potential causes.

Now I find that I have made things worse, to the point where the car cannot be driven safely until the source of this problem has been found and fixed.

Bill and Christoph have helped so much in this, that I feel bad bugging them any more.

Nicholbry

Thanks Greg and Mark, I will check this stuff out and report back once I have them tore down. At this point, I was asking some preliminary questions in preparation for the job and haven't gotten to the point of tear down yet.

I appreciate the input and will certainly work with the pistons independently to see if there is need for replacement or if there is an issue with the pads, rotors, etc. using your method/suggestion.

KenRudd

Nicole,

Did you ever get to the root of this issue?

-Ken

Vilhuer

Has anyone tried Zeckhousen kits on late type calipers and can confirm mm they quote is same mm size Porsche uses? I'd need to rebuild several calipers and at least some pistons are usable. Geting Porsche sets for them all gets very expensive.

http://store.zeckhausen.com/catalog/...h=82_1169_1172

Hilton

The other place I spotted in the US is Paragon..

http://www.paragon-products.com/Brem...-kits-late.htm

I ended up buying my seals from a local Brembo carrier, except for the hardline that joins the caliper halves on the front calipers, which I got from Porsche.

Vilhuer

If PP-... kits include piston then prices are little better. Some years ago they were $50-60/piston from Porsche. In any casefixing these brakes is way too expensive compared to what big black calipers cost.

Van

Another source for parts is Stop Tech - I recently rebuilt my calipers with seals from them. Made a video, too:

http://www.youtube.com/watch?v=HCLqUREvKm8