Brake Pedal Fade
 

On very hot days I've had my brake pedal fade pretty bad a couple of times. I had it happen once at VIR last year where they kept us in the staging area for quite a while on a 95 plus degree day where the pedal just started going to the floor while I was sitting there, but once I got on track it went away immediately and was fine the rest of the day. The other times have been very hot days driving in traffic which is what happened Saturday (92 outside). Any other time I can nail the pedal and it never fades. Just days where it's absurdly hot and I guess not getting the airflow through the engine bay.

I flushed the system last week using DOT 3 fluid and bleed it twice so it's not the old fluid and there is no air in it. Still have the original rubber lines but they look good, no cracking or anything. Like I said, they work fine 97% of the time. Any ideas?

Have the brakes done it since you flushed them with new fluid? How often do you flush the fluid?

Yeah I flushed it last Wednesday and it happened Saturday so the same problem with both the old and new fluid and like I said, only when it's really hot outside.

Did some surfing and everything I find seems to point to if the pedal goes to the floor the MC is bad. I just found it odd it seemed heat related.

When the seals start to go in the MC you will find that light pressure on the pedal results in a slow drop in the pedal. But if you press really hard on the pedal it won't drop at all. The seals are going bad, and by pressing really hard you are "improving" the sealing. But when you press lightly, all the little imperfections in the seals allow the fluid to get by.

Good luck...



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You might want to consider building a heat shield for the master cylinder to shield it from radiant heat. That might just help.

Just an update. It didn't matter if I pressed hard or soft the pedal would slowly go to the floor on +90 degree days. I replaced the MC not long after I posted this thread and it fixed the problem.

change to DOT 4 it's a temperature issue. it has a higher boiling point

Geez people, the OP said it was the master cylinder that was bad.
That would've been my first suggestion since it didn't sound like the brakes were being that abused.
It takes a LOT of abuse to get the brakes to fade - the stock brakes are already pretty good for stock.
Even extemely hot ambient temps should not be enough to make them fade on you.
I've driven my FC in 105+ F Sacramento summers and 110+ F Vegas summers with no hiccups from the brakes.