MTR

My 964's brake setup for the track is 4-piston calipers with Pagid Yellow RS29 pads and OEM sized rotors. During my last track day I developed some vibration in the steering wheel while under braking, so I assumed my rotors were warping. I've read it's highly unlikely and most of the time vibrations are due to uneven material deposits, but I've tried to clean the rotor faces by rebedding with OEM pads and I'm still having issues.

So I'm looking for new rotors/discs all around. Anything with holes tends to develop cracks and need replacing sooner compared to other options. Slotted are nice but you can't turn/machine them, although some say that's not a good idea for a track setup due to removing material that can potentially hold and dissipate heat. Flat faced discs seem to hold up well, but other say without slots or holes that pad out-gassing can reduce braking efficiency. And finally there is the ongoing debate about the real world benefits of cryogenic treatment.

With all that said, does anyone running the OEM brakes for light to moderate track use have a brake rotor/disc that they prefer?

Thanks for the help.

Carrera51

Mike:
Get some steel wool and some brake cleaner and scrub the rotors by hand. For stick on some Hawk Blue pads and drive around on the street. Either of those methods will remove the Pagid transfer layer. Also check your wheel bearings. Afterwards, re bed your RS29s. To bed correctly, you really need to do it on the track.

As far as the rotors go, stock rotors are fine. I see plenty of 964s club racing on stock rotors using a variety of brands of racing brake pads and brakes function just fine. Just make sure you are running good fluid and have adequate cooling.

Kind regards,

MTR

Mark, interesting you mention wheel bearings. I'm not familiar but can bad bearings result in steering wheel vibrations under braking?

I just replaced one of my wheel bearings that was on it's way out but I didn't replace the others. So maybe the others are starting to go since I'm assuming all are the original hardware.

Also when you say stock rotors are fine do you mean Porsche OEM rotors, or are Sebro and Zimmerman rotors fine to use as well?

Goughary

This is long but well worth the read...

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

Carrera51

Mike:
Yes, any of the OE suppliers are fine. A loose wheel bearing will cause vibration under hard braking. They get subjected to a lot of heat.

MTR

Thanks for the help. I'll check the wheel bearings then pull the rotors to clean them before I replace them with something new.

Carrera51

Forgot to ask you, how much track time do you have on the current rotors? Also have you checked the thickness to make sure they are still in spec?

MTR

I'm not totally sure. The previous owner did some track days and I have a few days on them as well. The fronts look like new, rears not so much. I need to measure the rears to know for sure, but I think spec is 24mm new and 22mm minimum thickness? The rears are also starting to rust in the centers so I wouldn't mind replacing them for aesthetic purposes.

So do you have an opinion on blank, slotted, or drilled?

Carrera51

When my dad was driving his 964 in drivers ed events he always used standard OE rotors. I also have some track friends who club race 964s in G class and they use OE (not slotted or drilled) and they work fine.

apanossi

I went with Frozen Rotors. These are OEM rotors that have been through a cryogenics process. The data suggests that this process is good for longevity and reliability of the rotors. I'm not sure how much of that to believe. Also not sure if they would be any better for track purposes (I daily drive but do not track).

MTR

Pulled the rotors and the picture below is what I'm working with. The rears are at 23mm (24mm new, 22mm minimum) with no surface cracking, so they are OK to use. The fronts I think are the problem. The outside definitely shows more dark streaking (deposits?) compared to the inside of the rotor, which I'm assuming is due to the cooling ducts forcing air on the inside of the rotor only.



While cleaning I did notice that there is a spot on the rotor where you can see the pad imprint into the rotor. Must have accidentally held the brakes after a track session. I tried to smooth that out, but it's actually pitted some. Wonder if that's enough to cause the vibrations.



Everything is back together, but I still need to bleed the fluid then I can check and see if the rotor cleaning solved my vibration issue.

Bill Verburg

Do you know who makes the rotors you have
generally slotted work very well, I never used dimples but those appear to be in good shape.
just for comparison here are some well worn ones, you can see the cracks and heat stress


I have never had a deposition problem w/ 29s but that doesn't mean that isn't what happened, you can clean the rotors w/ scotchbrite or emory cloth and re bed, some like PFC pads

vibration can come from tire deposition, wheel bearings or bushing issues(w/ a 964 I'd pay particular attention to the front A-arm bushes)

MTR

I don't know the manufacturer of either set, but the rears do say made in Germany if that narrows down the suppliers. The dimpled fronts are in great shape with no signs of stress cracks. When I had the car on jack stands I did the tire shake to check the wheel bearings and everything felt tight. I also did a visual inspection once the rotors were off and no leaking grease, etc.

What's the best way to inspect the A-arm bushings? Look for cracks? The bushings are original and the car has 110k miles so it's probably time to upgrade. I will most likely do the Elephant Sport bushings when I decide to bite the bullet.

MTR

Quick follow-up. Brakes feel significantly better than before cleaning the rotor faces. I re-bedded my Pagid track pads and have no vibrations under heavy/threshold braking. Still a little shimmy in the wheel at slow speed but that might be the large chunks of rubber stuck to my track tires. Thanks for the advice Mark.