Rear brake pads caught on fire!

Stan.Shaw@Excell.Net;4814 wrote: Maybe I missed it, but are we certain it is the pads catching fire, as opposed to some foreign matter? CV boot grease, mice bedding, etc.

There is an adjustment on the brake pedal that can cause it to put pressure on the brake unintentionally. A 928 racer (not me) made an adjustment and after a few laps on the track the car would stall when the clutch was released. Apparently he did this in two separate track sessions, where he had to be towed back, the second time flat bedded as the wheels would not release. As I recall the pedal/master cylinder adjustment can be made so that the brakes do no release as they should, so the brakes are always on....

This is awesome information Stan that I will try and research.
Thanks, It would not surprise me that there is an adjustment like that on the Porsche.
I suspect that it would be a C-click notch adjustment on the back of the master but it could be on the peddle side.

I emailed the driver who knows, and will let you know what I hear back. Do you think this could be related to this issue?

Stan.Shaw@Excell.Net;4817 wrote: I emailed the driver who knows, and will let you know what I hear back. Do you think this could be related to this issue?

There are to many possabilities, but I don't think it would move on its own.

I have even seen where a mechanic squashed a brake line on a north Am. car by lifting it wrong on a hoist.

I have seen brake hoses that failed inside and would only flow one direction.

That valve I pointed to in the picture could stick intermitently.

Sometimes these things are hard to find if everything is working when you are testing it.

Sometimes it requires a long hour or two drive to get it to fail so that you can fix it.

We'll see what he finds.

Thanks for all the replies!

So I took the car to the shop and they were able to reproduce the problem on the rack.

After they ran the car on the rack for about 45 minutes, the rear brakes started to engage on their own. They pinpointed the problem to the master cylinder getting hot and expanding. This is why the problem always occurred after I've been driving on the highway for a while. The brakes were dragging on fast rotating wheels for long periods of time. It just so happened that I was lucky to be coming out of the highway in all those cases.

If anything, I think this might be a pretty unique and interesting case study. This is actually a pretty reputable shop and the guys working on my car have had 20+ years of experience. Both of them said they have never seen anything like this before.

-Julian

Bingo, this reminded me of an '87 that we had this issue with a few years ago. Totally forgot about that. His were actually locking up after 10 minutes or so of driving. They never had the chance to get that hot.

A small amount of corrosion in these things can cause a bunch of different issues.

masterchan;4820 wrote: Thanks for all the replies!

So I took the car to the shop and they were able to reproduce the problem on the rack.

After they ran the car on the rack for about 45 minutes, the rear brakes started to engage on their own. They pinpointed the problem to the master cylinder getting hot and expanding. This is why the problem always occurred after I've been driving on the highway for a while. The brakes were dragging on fast rotating wheels for long periods of time. It just so happened that I was lucky to be coming out of the highway in all those cases.

If anything, I think this might be a pretty unique and interesting case study. This is actually a pretty reputable shop and the guys working on my car have had 20+ years of experience. Both of them said they have never seen anything like this before.

-Julian

So Sean what is the answer to fix this problem??? I had never heard of this up till now...and certainly never heard of pads actually catching FIRE! OMG! That would suck...though not as bad as the engine fires when a fuel hose cracks all the way through...