Brake Fade - Help

[bluecb7]

My problem is stated in the title. It only happens durring constint braking, like at long red lights or stop and go traffic. Other than those times they are fine. But when it does happen, the pedal will go down like normal and make pressure like normal. But after a few seconds it will loose pressure and need to be pressed down further or I start to move forward. If I let off the pedal and then reapply it, it will be fine few a little bit, but then the same thing. Any ideas? I have some SS lines for the front, still waiting on the back. If that fixes it I will be sure to post, but if it doesn't any other ideas? Thanks in advanced.

[quickangel93]

master cylinder

[benji]

Yeah, that definitely sounds like the master cylinder. There is a way to check it, it involves turning the car off, pumping the pedal a couple times, and then holding the pedal down. If the pedal sinks, then you have bad lines, bad caliper, or bad master cylinder (most likely the MC).

After you put on the SS lines, you bled the system thoroughly, right?

Another thing you could check is the white plastic check valve, which is in the vacuum line between the IM and the brake booster. At idle, you should have vacuum on the break booster side of that valve.

But I would vote for your MC, I had to replace mine the end of last summer. What happened with mine is that the brakes would still work, but I had no resistance in the pedal, it would just sink when I stepped on it. What happens to them is the rubber seals wear out over time and begin to let brake fluid around them, which is what causes the pedal to go down.

You aren't loosing any fluid, are you? That would mean that you had a leak, of course, and then you would just have to look at all the lines.

[bluecb7]

I haven't put the SS lines on yet. And thanks for the tip on how to check if its the MC, never heard that before. And for the tip on the booster.

[johnl]

You aren't loosing any fluid, are you? That would mean that you had a leak, of course, and then you would just have to look at all the lines.

If you have no external signs of leakage the the seal in one of the pistons is leaking (the MC is effectivelty two 'cylnders' with effectively two pistons housed in the same 'tube', one 'cylinder' for each diagonally opposite pair of wheels), so fluid is leaking past the pressure seal on one of the pistons then leaking back into the reseviour, but not out of the rear seal, so no sign of leakage.

The problem is potentially dangerous, and may occur at higher speeds not just when trying to hold the car still on the brakes. In this case you'll lose pressure in one of the diagonally split braking circuits and braking performance may be unexpectedly and suddenly seriously impaired, most likely in an emergency...

Replace the MC asap.

[92bently]

what he said, defiantely a master cylinder problem if there is no leakage,my car did the same thing replaced the master and it was good...if u havent done it yet, when u replace the master cylinder i would rec a full brake fluid flush to get new juices flowing

[benji]

what he said, defiantely a master cylinder problem if there is no leakage,my car did the same thing replaced the master and it was good...if u havent done it yet, when u replace the master cylinder i would rec a full brake fluid flush to get new juices flowing

Yeah, when I did mine I pretty much had to do flush, because bleeding out all 4 wheels made me go through it all just to make sure I got all the air... If there's anything to be anal about bleeding, its the brakes.