Riff

Patient is a '90 S2 with newish brake rotors, 4 days DE (2 days Mid-O and 2 days Putnam Park) plus the commute to and from the tracks. Anyway I have a bad pulse/shudder when the brakes are applied. This happened on the second half of the second day of the last DE @ Putnam. I have been told that it is pad deposition on the rotor (pads are MM Ultimates) since it is very difficult to warp the rotors at the speeds I am going (yes I am slow) and I was careful during the cooldown lap and did not use my brakes when parking after the sessions.

I had this same thing happen after the a previous DE @ Wakins Glen with these same pads, but old rotors. After driving the car for a bit, the pulsing went away.

Anyway, last night I took the front wheels off to inspect and could not see any definite signs of pad transfer/darker spots on the rotor. Upon trying to spin the rotor, it would spin easily up to a point, then drag, then spin freely again. Is this a definite sign that the rotors are warped rather than pad transfer?

I have read elsewhere that an aggressive pad (Hawk Blues) could be used to "scrub" the other material off and return the rotor to pulse free use? Anyone have success doing this?

TIA,
Riff

'90 S2 with brake pedal massage feature!

mitch236

I vote for pad transfer. I haven't seen a warped rotor yet. I know people who have spent time sanding their rotors with variable success.

BTW, the new track enthusiast usually has braking issues and it is almost always due to poor technique. Don't be insulted, it is almost universal. There are too many instructors that don't teach proper brake management.

Eric in Chicago

I would go with a set of Hawk Blues to scrub the rotors. I have a well worn set of fronts that I use for removing deposits (Pagids seem to give me the most deposit problems). If you are downtown Chicago any time soon, I would be happy to lend you the Blues to get rid of your build up. Shoot me a PM if you interested.
BTW, they are the MO30 calipers, not sure if you have the bigger calipers, if standard brakes, my pads will be too big.

Stuttgart

What pads were on the car previously? did the judder start when you installed new pads? All pads create a transfer layer, the thickness and consistency will vary with manufacturer and compound. I would suggest doing several heavy snubs in succesion from 40mph or so down to 5mph.

techno99

Axxis Ultimates are well known for pad deposits. I've had it happen numerous times on my M3. Try moving to a higher temp pad.

Riff

Eric-

Thanks for the offer it is much appreciated, but I have the non-MO30 calipers, so I am outta luck there.

Cheers,

jerome951

I've driven with Riff for years and it most certainly isn't braking technique. The Ultimates aren't a real hi-temp pad so you probably overheated them a little. I'm surprised the transfer layer doesn't scrape off when you're driving on the street.

Oddly, I used to use MM Deluxe pads to scrape off the transfer layer of the older PFC compounds.

techno99

After I got some nasty pad deposits with Ultimates at the track, I put on a set of Cobalt SpecVR race pads and drove around for a week. The shaking under braking got a little better (ie the SpecVR's did remove some of the deposits), but I finally gave up and put new rotors on.

Bull

Pagid Orange pads did the same to my rotors, and most of the other folks i run with that have 993s. I too found that Hawks would remove the deposits very quickly....and eventually switched to Hawk HT10s a couple of years ago. No deposit vibrations since the switch.

cstreit

A nice scuffer pad (scotch-brite or similar) on a hand drill run over the rotors will help remove the deposition. I was skimming rotors on a lathe like crazy a few years back thinking they were "warped" untill I got schooled.

Bull

This situation is a God-send for the rotor manufacturers. I have run into MANY people who I hear complaining about how bad the rotor manufacturers are. They go on to tell me how they are on their 3rd or 4th set of rotors due to constant warping!

RedlineMan

Hey;

I ran MMs for years, but can't vouch for this "Ultimate" version as they didn't exist then. I had no problems with the oldies, other than they disappeared quickly after a while.

90% of all shudder is transfer. You get another track pad (PFC-97, Hawk Black, etc), do a PROPER bed in, and you'll be fine. Like cstreit said, yer gettin schooled!

mikew968

You can also have the rotors turned but asked them to check the run-out first and only do a couple of thousandths. I did this and the rotors were fine. They told me the rotors had enough run-out to cause juddder. I have since used pfc-97's and pfc-01's and have not had the problem since. BTW the pads that seemed to be a problem were pagid blacks.


Mike

Riff

Guys-

Thanks for the input, I was hoping that it was pad transfer as these rotors are still new!

One other quick question about the dragging on the brake pads while spinning the rotor. The rotor drags during certain parts of the rotation, isn't this an indicator that the rotor is warped or is it the location of the "high" spots where there is pad transfer?

Cheers!

Bull

It is the location of the high spots. While pad transfer to the rotor happens (and is necessary) with all pads, the problem occurs when the deposits are not even and you develop high spots. If they are not dealt with, the material will become harden such that the rotor will wear more quickly and the high spots will become worse over time.