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Car Forum / Porsche / Porshe 944 / October 2006brake "pulsing" - probable cause?
my daughter's 944 has developed a brake "pulse" - you apply moderate brake force and the decelleration is decidedly non-uniform, like the brakes are grabbing and releasing - we just changed pads and rebuilt the calipers and the problem didn't get better - in fact it might have gotten worse. we did align the pistons to the proper 20 degree angle. I checked for any visible warpage on the rotors and could see none - they are true to within a thousandth. Any other suggestions?  Signaturebill to email me, to to my web page, www.wbnoble.com and find my email or unscramble the following by removing spaces and correcting the obvious spelling errors wil lia m_b_n obl e at msn daught com -- Posted via a free Usenet account from http://www.teranews.com How did you check the disc runout? With it on the vehicle? I had a Jetta GLI with a similar problem. I found that the hub was warped causing the brake disc to wobble creating a pulsating brake pedal. I let the engine spin the hub and used a file to true it. Worked much better afterwards. People are saying that the wheels must be properly torqued down when installed or it can create a warped disc. Now I have also seen bad wheels and tires causing problems too. ;-) Just a thought! later, dave (One out of many daves) http://vwdoc1.tripod.com/ > my daughter's 944 has developed a brake "pulse" - you apply moderate brake > force and the decelleration is decidedly non-uniform, like the brakes are [quoted text clipped - 3 lines] > visible warpage on the rotors and could see none - they are true to within > a thousandth. Any other suggestions? I checked the runout on the vehicle, turning the hub by hand - my only other theory is a post I saw on renlist about the retaining screws loosening causing problem - I'll try that next weekend - but I'm hoping someone else has a good idea - the brake pedal doensn't pulse (much), but the amount of decel varies significantly - this is what puzzles me > How did you check the disc runout? With it on the vehicle? > [quoted text clipped - 21 lines] >> checked for any visible warpage on the rotors and could see none - they >> are true to within a thousandth. Any other suggestions? SignaturePosted via a free Usenet account from http://www.teranews.com I had exactly the same problems - So get the rotors grinded down, and then you have to bed them in properly. Even if the rotors show they aren't out of round, if you dont properly bed them, sticky brake material transfers not uniformly to the rotors causing that to grab and loosen as you described. I also thought it was those recessed flat head screws holding the rotor to the hub - but you dont even need those screws. Look here at the bedding procedure: http://www.993faq.com/archives/cat_brakes.html I went through a brand new "oem" brake rotor that vibrated and it was just junk. Then I went to ZIMMERMAN, and properly bedded them and it seems to be ok for the last 9 months. So bed them rotors, and keep em hot! For years 20 years I drove a Porsche 944 and never heard of such a procedure - until now. Signaturejoliett -------- >I checked the runout on the vehicle, turning the hub by hand - my only >other theory is a post I saw on renlist about the retaining screws [quoted text clipped - 26 lines] >>> I checked for any visible warpage on the rotors and could see none - >>> they are true to within a thousandth. Any other suggestions? Does her 944 have ABS? I had a similar recent experience with my S2 that turned out to be ABS related. Simon > my daughter's 944 has developed a brake "pulse" - you apply moderate brake > force and the decelleration is decidedly non-uniform, like the brakes are [quoted text clipped - 3 lines] > visible warpage on the rotors and could see none - they are true to within > a thousandth. Any other suggestions? Also check your wheel bearings. Under loading, they might allow the hub to move laterally or wobble -- since the calipers are fixed and the rotor is mounted to the hub, any movement will move the caliper pistons in and out -- which will send brake fluid back to the master cylinder, which you'll feel through the pedal. > Does her 944 have ABS? > [quoted text clipped - 21 lines] > > -- > > Posted via a free Usenet account from http://www.teranews.com |
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