Problem with brake hydraulics..
08-21-2005, 03:11 PM
#1
Burning Brakes
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Problem with brake hydraulics..
The brake pedal doesn't feel firm any more, i.e. it slowly sinks. Not to the floor, but doesn't pass the 15 second brake-hold test. Even after e.g. 30sec of pushing on the brake, it still doesn't feel firm, although much effort is needed to keep pushing deeper. And I can't make the pedal pumped firm with the engine off.
The brake booster is OK (the pedal goes down a bit upon starting the engine).
It started after a few track sessions yesterday, and I decided to quit. Luckily I had some fun before.
My first guess is that it leaks somewhere, but I couldn't see any wet areas (checked the caliprs and the master cylinder).
I also did a test, trying to pinpoint which caliper: I lift a wheel, a guy engages the brakes, and I try spinning the wheel with my hands. It felt holding strong on each wheel.
I don't think it's the water vapour bubbles from overheatuing the fluid (ATE super blue, replaced over a year ago; might be time to do it again anyways), because after it cools down, I would think the brakes should feel firm again.
What should I check?
Thanks
The brake booster is OK (the pedal goes down a bit upon starting the engine).
It started after a few track sessions yesterday, and I decided to quit. Luckily I had some fun before.
My first guess is that it leaks somewhere, but I couldn't see any wet areas (checked the caliprs and the master cylinder).
I also did a test, trying to pinpoint which caliper: I lift a wheel, a guy engages the brakes, and I try spinning the wheel with my hands. It felt holding strong on each wheel.
I don't think it's the water vapour bubbles from overheatuing the fluid (ATE super blue, replaced over a year ago; might be time to do it again anyways), because after it cools down, I would think the brakes should feel firm again.
What should I check?
Thanks
08-21-2005, 03:33 PM
#2
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Nope, once you boil the brakes, the fluid does not regain its original feel.
Flush the brakes with new fluid, and bleed the brakes before every track event.
You could also have a leak in the system, or a bad master cylinder.
gb
Flush the brakes with new fluid, and bleed the brakes before every track event.
You could also have a leak in the system, or a bad master cylinder.
gb
08-21-2005, 03:34 PM
#3
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Bleed the brakes. Pressure bleeder works best (Motive) for flushing and bleeding the system. On the NA, it's pretty easy (one bleed valve per caliper - I ramp the front of the car and could reach all four).
If you pump a liter of ATE Blue through there, it should firm right up. I used to have to bleed my 944 brakes after just about every other track day. Never showed more than a couple of bubbles, but the pedal feel was as you described.
The next thing to check after that is the 22-year-old rubber brake lines. If they're original, it is wise PM to replace them. They are at the end of their service life (not full failure, but swelling and degenerating overall).
If you pump a liter of ATE Blue through there, it should firm right up. I used to have to bleed my 944 brakes after just about every other track day. Never showed more than a couple of bubbles, but the pedal feel was as you described.
The next thing to check after that is the 22-year-old rubber brake lines. If they're original, it is wise PM to replace them. They are at the end of their service life (not full failure, but swelling and degenerating overall).
08-21-2005, 03:41 PM
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Burning Brakes
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Thanks guys, I'll get fresh brake fluid first.
Brake lines are "half-new": i.e. the front ones are new. I put SS braided lines up front, rated to be DOT legal. I'm not sure about the lagality issue, as I heard the braiding prevents from visual inspection for cracks. So how come mine are DOT legal?
Brake lines are "half-new": i.e. the front ones are new. I put SS braided lines up front, rated to be DOT legal. I'm not sure about the lagality issue, as I heard the braiding prevents from visual inspection for cracks. So how come mine are DOT legal?
