2002M3Drew

Hi guys,

I noticed during track days that my brakes become spongy. I actually have to pump them a couple of times between runs to get better pressure. The strange thing is that the pedal feel returns to normal (pretty stiff) by the next day. My calipers have been rebuilt, and the fluid is racing type, and is fresh and bled. Is this a master cylinder issue?

ked

could be, but could also be your brake lines - have you replaced / upgraded them recently?

Steve Weiner-Rennsport Systems

Hi Drew:

Do your brakes feel OK before the event? Nice hard and high pedal?

If thats not the case, I'd suspect the MC.

If not, this sounds like a heat problem and you might need one or all of the following:

1) Brake cooling kit

2) Castrol SFR fluid (nothing better)

3) Big brake upgrade of some kind. I have many choices,...

autobonrun

I rebuilt my calipers, changed the fluid, lines, and pads. The brakes felt spongy when I tried them. One of the guys on Pelican noticed I said I slid the pads in easily. I thought they would just make up the space the first time I pressed them. He suggested I press the pistons in just enough for the pads to barely slip in. I removed the pads and followed his suggestion. The difference was immediately noticeale. No sponginess and the brakes feel better and stronger than they ever have and they don't drag at all. Nothing like a SC when it's running like it was designed.

2002M3Drew

I am running the ATE Super Blue (i know, it stains!), and I have the AJUSA coolers o the fronts. The funny thing is that the pedal is firm and normal feeling before I get on the track, but after the first session and all throughout the day, it is spongy. Then, after a day or so of being back in the garage not being driven, it is back to normal again. Strange, huh? I don't lose enough pressure for it to have become dangerous (yet), as during my sessions, I'm not noticing the problem. But right before I get on the track to start a new session, that is where I notice it most.

2002M3Drew

Hi,

Yes, they were replaced last season with new rubber ones (OEM).

DGaunt

When I was learning, my pedal became spongy on the track, but once i got faster, I used them much less and have never had a problem since.

Sean F

You're probably boiling your brake fluid. Some good responses to my identical question here:

http://forums.pelicanparts.com/showt...hreadid=294081

Brian_77_3.6

I had this same thing happen to me for about a year and then I started to use (loose) brake fluid as well. It was the Master cylinder leaking into the power booster. Not enough to notice at first but once the fluid started to disapeer I had the system disasembled and the missing fluid was found.

Steve Weiner-Rennsport Systems

Hi Drew:

From the sounds of things, I think you are getting close to the thermal limits of your current brake system; rotors-calipers-pads-fluid.

The first thing I'd suggest is installing Castrol SRF fluid and see if that helps. Its not cheap but thats really the right stuff for the "Mission".

Can I assume that you have a brake cooling kit on there???

What pads do you use?

2002M3Drew

Hi Steve,

Yes, I've got the brake cooler kit (the AJ USA one with the aluminum air ducts). I'm running the ATE Blue stuff, and BHP pads. The BHP pads are wearing thin after my last track day, and need to be replaced (I realize that this contributes to the problem of heat.) I have a brand new set of Pagid Yellow RS-19s that I'm going to try, though. Perhaps for the next track day, I'll swap to the Yellows, and replace the fluid with Castrol SRF. Doesn't the Motul 600 stuff have similar boiling properties to the SRF at a much lower cost?

Chris M.

Sean I read the Pelican thread but you never came back and said how you solved this problem.

Sean F

I've never solved it

I have tried many, many things since that thread, but the fundamental conclusion that I have come to is that the stock brake system on the SC is not up for the task of serious racing/track work. That is my personal experience. I know there are others who don't have a problem and there are others that have a problem worse than mine. In fact, the driver who set all the PCA club racing track records on the East coast this last year in an SC would get so much heat in his brakes that he would melt the calipers to the point where the bores would go out of round. He replaced (not rebuilt) calipers after almost every event.

I have tried just about everything. I have experimented with a brake cooling kit, Motul 600, Castrol SRF, frozen slotted rotors, non-frozen slotted rotors, drilled rotors, stock rotors, PFC 97's, Pagid, master cylinder, etc., etc. Nothing has solved the problem and in some cases it got worse. I went through a stage recently where I was cracking rotors after one day. Right now I am running a brake cooling kit, SRF, Pagid yellow in front and black in the rear and frozen non-drilled, non-slotted rotors with better results but not optimal results.

I have resigned myself to boiling the fluid and changing it after every event. Again, I know of guys running identically prepared G cars who have no problem at all and change their fluid once or twice a season. But, I've been through/replaced every component in the system with no luck.

MUSSBERGER

Have you considered an upgrade to 930 brakes?

Sean F

can't do it without moving to F...I'm staying in G for now