Tuscany964

What is "off gassing"? And what should you look for in the case of pad transfer on the disk?

Indycam

Off gassing is when you heat up an object and fumes / smoke comes out .

Pad transfer is suppose to happen , it should be even all the way around the disc , sometimes that does not happen , it will happen on some parts of the disc and not on others . Where the build up is the disc is thicker and the pads drag more , where the build up is not the disc is thinner and the pads don't grip as well .

Tuscany964

Thanks for the explanation

boxsey911

Looks like even the video camera on the rear shelf picked up the shudder in the braking zones!

http://www.youtube.com/watch?v=HPa5W4XhU5Q

Steve Weiner-Rennsport Systems

Those look overheated to me; note the chunks of material missing from the edges.

JMHO, but I wouldn't be using RS-15's,.......

Those are a VERY high CoF pad; well above RS-14 Blacks and those have likely put too much heat into the rotors, especially with the street pads in back,.... What you had was a poorly balanced brake setup.

A MUCH better choice would have been RS-29 Yellow's at all four corners or perhaps RS-14 Black's in the rear calipers for better brake bias for track use.

Indycam

That's what I would have said
if I had a clue .

boxsey911

Enough to have warped the front rotors or do you think the juddering when hot is being caused by deposits of the RS15s that needs to be cleaned off? While it is easy for me to put on new rotors and fit some matching pads all round, it wouldn't answer the question as to whether the rotors have been ruined.

Indycam

Warped discs stay warped , they don't unwarp .
Warped discs will feel warped all the time .

What do your discs look like ?
Can you post a photo ?

boxsey911

The discs don't feel warped now that they're not operating at track temperatures. The front discs have a dark blue tinge which is more prominent in the middle. Rear discs look in good shape, no discoloration or scoring. I'll get photos at the weekend.

The current pad combo (Pagid RS15 front and road pagid rear) is still in. Again, I'll pull them at the weekend and get photos. I could then put equivalent road pads in the front, drive it hard to try and clean them up and then try your gas and brake technique to see if the judder comes back.

I've got new front discs arriving tomorrow but putting them straight on will just put a gap in this story. It would be nice to see, for me and for others, whether the judder is reversible. If not, I'll just accept that the front discs are now warped junk.

Steve Weiner-Rennsport Systems

Steve,

Just for your edification, check your rotor axial runout (before replacement) with a dial indicator so you KNOW whether they are warped or not.

I would need to see a picture of the rotors to tell you whether your vibration was due to uneven pad deposition or not.

No matter what you do, I'd strongly recommend reviewing your pad setup to help prevent a recurrance.

boxsey911

Hey Steve, yes I've fully taken that on board about changing the pad combo. I'll be keeping the same compounds front and rear. I'd had no problems with judder when using RS15 all round. Trying a pagid road pad on the rear looks to have been the problem here. As you say, one was too harsh and one too soft. Something less harsh on the front like RS4-2 would have been OK.

I'll run the road pads all round for the next day (which is the last day of the season) and then invest the required $750 in a set of RS29s for next season.

Nader Fotouhi

Can stock pads be used for cleaning the rotor? I would like to swap out the current pads (Pagids sports) on my wife's car and let her drive it for a couple of weeks on the street before her next track weekend.

I am giving up on same pads for street and track. Although she is still in the instructed group, I plan to put on track pads (Pagid blacks that I also use on the my race car) for track only and swap to street pads for driving on the street.

BTW, Boxy911 pads look glazed to me which as mentioned is due to heat. In addition to proper balance of pads, more cooling would help.

joey bagadonuts

As suggested, a set of Hawk Blues will give you the answer. They're also a capable trackday compound, so there's no problem running them all day (provided you're not late-braking-into-the-ABS into every corner ).

sundog

There is another problem that may be the culprit here. I have experienced the exact same problems, and while part of the problem was pad deposition, the shudder has not completely gone away.

Upon checking it appears as if the front bushings on the suspension arm are shot, not surprising with 180K miles. So I'm going to get a new set, from one of the guys on here, and see if that cures the rest of the problem.

boxsey911

AFAIK Hawk pads are not available in the UK so I don't think getting a set of those to see if they can clean up the rotors is going to be an option. The pads that we can easily get for the 964 over here are Textar, the Pagid range and the EBC range. With a set of rotors costing about $200 and a set of performance pads being about the same, the cost benefit of buying pads to clean up rotors seems quite marginal.

The glazed/fried pads above were achieved even without getting into the ABS. I don't get into the ABS in the dry and think my threshold braking is pretty good. So I don't think it was braking technique. HOWEVER, the pads pictured above were taken out after a friend drove the car quite a lot on a previous trackday (the first day that the judder started to appear). He's a better/faster driver than me and uses left foot braking on some corners.

Poweflex wishbone bushes were fitted to the car 18 months ago when I had the KWV3 suspension put on.