polecat702

I'm wondering if deposits on the rotors would cause the pedal to pulsate, or are the rotors warped? Seems to me that the rotors a fairly stout, and it'd be very hard to warp a 928 rotor.

What does the forum think?

The Forgotten On

It is most likely your rotors warping. I had warped rotors on my 81 and had the same vibrating issue. It went away after I replaced them.

Chalkboss

Usually always warped rotors. I agree with you- they do seem pretty tough. Some imports really have a problem with this as their rotors are just crap, and people often over-torque the wheels.

Jim Devine

Unless someone used an air gun on the wheels, I think your problem is pad transfer related-
short article here: Article by Carrol Smith, long time Shelby race team mechanic

http://www.stoptech.com/technical-su...nd-other-myths

Second article by Raybestos-

http://www.hendonpub.com/resources/a...etails?id=1787

soontobered84

Warped.

dr bob

Easy enough to scuff the old deposits from the rotors with a disk sander or a handy flap wheel on the little disk grinder. Or do another few hard "break-in" style stops, end with a gentle brake application to stop and no hard clamp at the end.

Our cars have floating rotors, pretty much ruling out uneven wheel nut torque as a possible cause; by the time uneven bolt torque would distort a rotor (or hat...) it would, in my estimation, pull the threads out of the nut but only after the cone of the lugnut became one with the aluminum of the wheel. If you can remove the nuts without a holesaw, it wasn't enough torque to do damage under the best conditions.

----

My late Honda Pilot DD started to have pulsing-pedal issues early in life. I scuffed the rotors, and no more problem. Adjusted my stopping technique slightly, and it didn't come back. The Pilot weighs more, has slightly larger diameter rotors, larger tire diameter too, with less pad swept area. All say it has less stopping capacity than the 928. Rotors are a lot thinner with a lot less airflow redirection for brake cooling. One would surmise that it would have more problems with rotor warping than the 928.

mark kibort

its warped.... any hard braking tests would clean up a rotor, and sometimes, if your lug nuts are all the same torque, you can straighten the rotor out. .... ive done this before.

polecat702

I'll try the hard stop method first, then the disk sander. Should I go with an after market drilled disk rotor, or replace with OEM?

Thanks for all the feed back!

Mrmerlin

I think Roger has the Zimmerman rotors with the zinc coating,
they last a long time and wont corrode along the edges

bills928

Warped ..... Heat is the enemy.., especially if you use ceramic pads.....If you really want to see that it's warped, set up a dial indicator against the rotor and turn by hand, it should be very clear.

dr bob

Right on with the dial indicator. Follow up with multiple micrometer readings around the otor. Real warped rotors cause pulsing pedal from deviations in thickness a lot more than actual axial runout.

Bought a zet of "zinc plated" rotors recently for another (non-928) car. Warning on the box suggested that only soap and water should be used to remove fingerprints. No Brake Cleaner. So I used some brake cleaner to wash off the "zinc plating" on the friction surfaces. Turns out the "plating" is more like paint.

hacker-pschorr

I'm not saying they are warped or not, but one day at the track I thought the rotors in my 79 were warped (S4 brakes) but it ended up being deposits that cleared up during the next session.

I was running Pagid Orange pads.

Bilal928S4

If you get pulsation in the brake pedal and the steering wheel on application of the brake, the front rotors are the problem. If you are getting pulsation in the brake pedal only on application of the brake, then the rear rotors are the problem.

danglerb

Over torquing was a TSB on our Lincoln, new rotors and not letting clowns touch the wheels fixed it.

Given the heat and stress on brake rotors the amazing thing is that they don't warp all the time.

M. Requin

I would definitely check this out- had a case with new rotors and it mimicked a warped rotor exactly.