KLR

I have a heavy vibration under braking from 15mph or greater that causes both the steering wheel and the car to shake. This started towards the end of day 1 at a DE on the pocono full course saturday with a pretty new set of rotors. I've never had trouble warping a set before at DEs or otherwise, so I was a bit surprised. The car is a stock '87 951 (non-m030) with stock calipers. A couple of quick questions:

1. If the steering wheel shakes more noticeably than the car shaking, is it definitely the fronts?

2. One of the tension springs in my right rear parking snapped on Sunday after a run, causing the parking brake to disassemble itself inside the rotor hat. I pulled the rotor and removed the debris with no problem, but am now wondering whether the parking brake could have been dragging slightly all weekend and caused the rear rotor to warp. Is this possible?

3. How do I prevent this from happening again? I have already removed the backing plates on the front brakes. Do I need to look into a ducting kit? If so, is it possible to install one without removing the fog/driving lights? I really want to keep the car looking stock. I believe that I have the 968 control arms with the mounting tabs -- is adding the 968 ducting worthwhile? Where does one get the parts -- I don't see any of the mail order houses advertising it.

RedlineMan

Man...

There are MANY MANY MANY ways this can happen. You are probably correct in assuming it is the front. If the wheel is shaking bad, it usually is the front. I'm going to guess that it is brake pad related, and further that you may have pad transfer from not doing a good enough cool down.

If you do not cool the car properly when you come in, the pads will literally fuse to the rotors and some of the material will tear off and be deposited there. This will shake your teeth out, the worst vibration you will ever experience. Far worse than "warped" rotors.

Have a look at the rotor face for signs of pad material.

shiners780

Is there a way to remove this pad transfer material? I've heard you can use garnet paper to "sand" it off. Does this work?

I have a similar situation on 10 day old rotors. They don't appear to have any material on them, but I find it difficult to believe that I have warped them. I have recently added cooling ducts, but the damage had already been done. Zimmerman slotted rotors with Porterfield R4 pads and Ate fluid.

docwyte

I'd take some sand paper and sand both the pads and the rotors, then go out and rebed the pads. Let them temper overnight and see what you have...

shiners780

I knew I read it somewhere, so I did a quick search through my files and found this from www.stoptech.com:

"If only a small amount of material has been transferred i.e. if the vibration is just starting, vigorous scrubbing with garnet paper may remove the deposit. As many deposits are not visible, scrub the entire friction surfaces thoroughly. Do not use regular sand paper or emery cloth as the aluminum oxide abrasive material will permeate the cast iron surface and make the condition worse."

I have never tried the garnet paper trick, but will purchase some this week and give it a try.

KLR

This describes my situation to a tee. The car still stops great, but the vibration is certainly a lot more pronounced than the foot or hand massage you normally associate with warped discs.

I'll try the the garnet paper trick as well. I'm not too hopeful, but I guess I might luck out. The cool down lap at Pocono full is indeed way too short (only half a lap) and I was parked on a slope in the paddock, and therefore was tapping the brakes when I came to a stop before shutting the car off. Live and learn.

I think I will call sunset and look into getting the 968 cooling ducts since I already have the mounting tabs. Can't hurt -- I'm due for 2 days at Summit Point in late July, which is really tough on brakes.

jeeper31

I think this may be my problem too. Where do you get Garnet paper?

shiners780

Sherwin Williams paint stores sell it around here. FWIW, it didn't help my situation. I truly believe the rotors had been warped. No problems with the new rotors and brake cooling ducts though.

JEC_31

FWIW, that Stoptech site has some awesome writeups on the how-to and the importance of proper bed-in to avoid warping new rotors.

jeeper31

Toward the end of my second day at my 3rd DE (at Lime Rock) my brakes started to grind. When I tood off the pads it appeared as though the were disentegrating. The face of the pad seemed pitted and chunks were coming off the end. I was using PBR Ultimate pads. I jsut picked up a set of KFP Magnums and amd going to install them. I turned the rotors by hand and they didn't look warped so I am assuming it is the problem stated above. Any other ideas?

arbeitm

Dan I found this on that Stoptech Website...maybe that why they got eaten up....

On front engine platforms, the Ultimate is excellent for aggressive street and autocross use in the front calipers. It also works very well in the rear for applications ranging from aggressive street to moderate track use. Ultimate is NOT recommended for use on road courses in front calipers. Doing so can cause pad deposition on rotors as well as the resulting vibration. Street only. OK for club level track use in rear calipers.

jeeper31

Is this something that can be cleaned up with the garnet paper of should I just get new rotors? Time is of the essence with a GTG this weekend and a DE in two weeks.

Techno Duck

The garnet paper is worth a shot, just take the wheels off and and hit both sides of the disc. Garnet paper is essentially sand paper used for wood, available at any Home Depot really.

Your going to have to rebed the pads in essentially afterwards. Meaning take care you dont roll through that first stop sign like i seem to do every single time i change the pads.

jeeper31

Does garnet paper come in different grits? should I rebed the old pads or or put on the new ones? Just wondering of the garnet paper does not do the tricdk will it ruin the new pads before I can replace the rotors?

shiners780

Garnet paper does come in different grits, I used 220. FWIW, I couldn't find it anywhere and tried 6-7 different places (I looked in H. Depot, Lowes, NAPA, A. Zone, etc.). I just happened to come across it at Sherwin Williams while I was in there.

I would scrub the rotors down with the garnet paper, install the new pads (not the Ultimates), and bed them in properly using that specific pad's recommendations.

Keep your Ultimates for street use if you want to. In case they're glazed, file or sand the surface off (or use a smooth area of concrete to rub them against -- seen it done at the track,) and bed them in after your track event before using on the street.

If you do a lot of track events, having an extra set of brake rotors with you is not a bad idea. You will need them eventually anyway, and they could save you from having to pack up early and go home.