Overheated brakes and bleeding
06-19-2001, 12:05 PM
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Overheated brakes and bleeding
1979 911 SC w/stock brakes:
The PCA club here sets up their auto-x course so you can run continuous laps in the morning to learn the course. After my second session of hard driving, my brake pedal got VERY soft and the brake warning light on the dash came on. I assumed that the brake fluid had boiled. After pulling off the track and driving around slowly for a few minutes and letting the car sit for an hour or so, there was no change.
The next day, I flushed and bled the brakes using a vaccum type bleeder at all four corners.
*background: the master cylinder was replaced when I bought the car about 3k miles ago, brake fluid type unknown.
Now for the questions:
1. The pedal still feels a little soft, is there any other place in the system that might still have a bubble that can be bled in some other place? Is this type of bleeding inefficient?
2. The Brake warning light is still on. Does this need to be "reset", or is there something still going on in the master cylinder?
3. Was I even correct in assuming that the fluid boiled?
Other comments on this subjuct are welcome.
Thanks, hep
The PCA club here sets up their auto-x course so you can run continuous laps in the morning to learn the course. After my second session of hard driving, my brake pedal got VERY soft and the brake warning light on the dash came on. I assumed that the brake fluid had boiled. After pulling off the track and driving around slowly for a few minutes and letting the car sit for an hour or so, there was no change.
The next day, I flushed and bled the brakes using a vaccum type bleeder at all four corners.
*background: the master cylinder was replaced when I bought the car about 3k miles ago, brake fluid type unknown.
Now for the questions:
1. The pedal still feels a little soft, is there any other place in the system that might still have a bubble that can be bled in some other place? Is this type of bleeding inefficient?
2. The Brake warning light is still on. Does this need to be "reset", or is there something still going on in the master cylinder?
3. Was I even correct in assuming that the fluid boiled?
Other comments on this subjuct are welcome.
Thanks, hep
06-20-2001, 12:08 AM
#2
Technical Specialist
Rennlist
Lifetime Member
Rennlist
Lifetime Member
hep,
You can turn off the brake warning light by disconnecting your battery. If it comes back on, then one of the two brake switches has probably gone bad. They are mounted on the master cylinder. When the master cylinder was replaced, they may not have replaced the switches, just transferring the old ones to the new master cylinder. If you do need to replace one, replace both, and source the parts through VW, as they are a VW part, and cheaper that way.
I've heard mixed things about vacuum bleeding. I prefer pressure bleeding where you hook something up to your master cylinder to provide air pressure. Take a look at the article on brake bleeding on the TECH forum at tech.rennlist.com, as it might give you some ideas. Also, you might tap each caliper as you are bleeding it to ensure no air bubbles hide and stay behind.
You can turn off the brake warning light by disconnecting your battery. If it comes back on, then one of the two brake switches has probably gone bad. They are mounted on the master cylinder. When the master cylinder was replaced, they may not have replaced the switches, just transferring the old ones to the new master cylinder. If you do need to replace one, replace both, and source the parts through VW, as they are a VW part, and cheaper that way.
I've heard mixed things about vacuum bleeding. I prefer pressure bleeding where you hook something up to your master cylinder to provide air pressure. Take a look at the article on brake bleeding on the TECH forum at tech.rennlist.com, as it might give you some ideas. Also, you might tap each caliper as you are bleeding it to ensure no air bubbles hide and stay behind.
