brake pulsation problem

Hi all. 20K miles on this '99 996 cab I purchased new. Bad brake pulsation started ~ 10K miles and has gotten dangerously bad now. I need to know the CAUSE of this problem and its SOLUTION, please. Car never raced and never driven or braked hard. Only thing I suspect is rotors always had rust on them the morning after an evening wash. Even after rust is scraped off by pads, pulsation is bad. Dealer says cause is not the rust after washing, but rust from leaving car outside at night and/or not driven for weeks/months. Also says rotors probably warped and not covered under warranty. Any help greatly appreciated.

Are the brakes really pulsing like anti-lock is kicking in or... are you really feeling warped rotors? Loren (99 996)

I also get some ABS action under hard braking. So mabye this is what you are feeling but better safe then sorry.

[quote]Originally posted by Loren..99..996: <strong>Are the brakes really pulsing like anti-lock is kicking in or... are you really feeling warped rotors? Loren (99 996)</strong><hr></blockquote>

Thanks for reply. However, not ABS. I have experienced the ABS, and this is definitely not it. Pulsation happens at all speeds and under light braking and heavy braking. Do you get rust on your rotors?

PHIL. my car is indoor garaged so i dont seem to have these problems and also i use it for daily commute. good luck

Thanks, Bloke. Do you dry your rotors after washing the car? If not, are the rotors pitted with rust the next morning?

I find it hard to believe that leaving a Porsche sitting outside at night is going to warp the rotors besides surface oxidation (rust) and warping are not the same thing. Obviously something is wrong and I think it merits the dealer investigating a little further. Are the pads seated correctly in the calipers? Are the rotors grooved? I am not a brake person but this is more than just surface oxidation. Just my .02 Jim

Sure sounds like warping to me. You don't get warping from washing your car unless your brakes are red hot (like from a track event) and you hit them with water. I haven't heard of any instances where Porsche brakes have warped (at least in the 90's) but it may be possible. I would have a reputable garage check the rotor runout -- warpage is usually pretty easy to spot. Loren (99 996)

Ok, How often and how long does your car sit for? If your car sits for a long period of time, your tires will become out of round or square. If that happens, you will feel pulsating while you drive and a heavy pulsation when you apply the brakes. Now if the previous owner let this vehicle sit for long periods of time, allowing the tires to be squared, the pulsation may have damaged the the front end of the car. The front end cannot take the beating of pulsating or shimmying wheels. The warping of the rotors is a problem too. If the previous owner drove excessively with warped rotors, he may have damaged the front end, so much that, even with the rotors replaced you will still feel pulsating b/c of the pounding that warped rotors give to a front end. It happened on my old Tahoe. Heavy breaking caused the rotors to warp. The warped rotors inturn caused shimmying and damaged the steering box, so much that even with new rotors, my front end still bounced around. Chevy has been notorious for this, Cadillac's are especially bad for this. I am sure the Porsche front end is better, but regardless, no front end was designed with warped rotors in mind. Washing the vehicle and finding rust on the rotors is nothing new or out of the ordinary. Just make sure you drive the vehicle after a wash to remove rust.

When I did track school instructors informed us not to use the handbrake after tracking when at the pit because that would warp the rotors. Did you buy this new or did you do any tracking whatsoever and used the handbrake? Regards. Mike

Ignore my post- read your original post. Regards. Mike

Thanks all for taking time to reply. Roschpe: I am the original owner. The car usually sits for 2-3 weeks. However, it has sat for 3 months twice. It does not pulse while accelerating or coasting, but only while braking. j2nh: Interesting note re: grooving. The car is in storage now, so I can't check until this weekend, but I don't remember seeing any grooves.

Remember reading an interesting post about radial tires developing flat spots (squaring) during storage and the bottom line was that they do not due to the radial design. I think that your dealer needs to look at runnout on the rotors and inspect everything from bearings to calipers to pads. What you are experiencing is not normal to storing your car for 3 months. At 20,000 miles this car should be driving like it is brand new. Lots of Porsche owners store there cars in the winter and do not experience this (stored my 993 for 5 winters no problems) Talk to your dealer and if he won't investigate find another dealer. Regards Jim

Phil, if the wheels were removed and not torqued down properly (to specs)over time this will eventually warp the rotors as well.

I have an 01 AWD RX300 that acts as you describe if I'm in the wet especially. Mechanic explained to me that the "automatic brake force distribution" system will sometimes "hunt" causing the same affect as ABS at the brake pedal but much lighter.

I think LastV8 may have hit on it. If the wheels were removed for a pad inspection etc. and then replaced and retorqued with to much force this could have warped the rotors (the infamous "revenge of the impact"). Mentioned in this months Popular Mechanics. Let us know what you find out. Jim

Tires will absolutely flat spot if left sitting for long periods. Driving at a speed of 100mph for a short time seems to correct this. I work at the Porsche dealer. I suggest you complain a bit more about the brakes. Its good to be nice, but sometimes its the squeaky wheel that gets the oil. Good Luck!

On the wheel torquing issue, some recommend torquing the lugs in stages. Example, 50n/m, 90n/m, 130n/m. Just a thought.