Jake951

Recently I was noticing the brake pedal had a slightly soft feeling. I bled the brakes and they became firm as they should be. But within a couple days it was going soft again, so I bled the brakes a second time. Same thing. It was firm for a day or two but then went soft. It's not grossly bad but there is an extra 1/2" or so of travel before the brakes start to bite. I'm assuming I have air leaking in from somewhere. Any suggestions on diagnostics I could perform to track down where the problem is??

Sam Lin

When you bleed, are you getting air every time?

Sam

RKD in OKC

You got to bleed both nipples on the each caliper.

Jake951

1. Yes, I bled both nipples on each caliper.
2. The first time I bled the brakes, I drew a significant amount of air out of two calipers, which I thought accounted for the original problem. The second time I bled them, there was much less air, only some very tiny bubbles, but this was only after a couple days from the first bleed.

If it makes any difference I used a Power Bleeder and did the brakes in this order (following what was on Clark's Garage): RR, LR, RF, LF.

Alpine951

Do you have to do the clutch slave as well at the same time?

Matt H

You have a bad Master Cylinder, check it for leaks around the seal areas.
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Jake951

I did just the brakes, although Clark's Garage says to do both. Don't know if that makes a difference, but my clutch has been fine.

Trucho-951

I bleed my brakes with the power bleeder (love that tool), but not the clutch, and never had any problems. If your rotors are warped and out of round, they could be causing exessive movement of caliper pistons and possibly entrapping air... just a thought. Also I would recommend removing the brake pads and visually inspecting for any signs of brake fluid seepage around any of the piston seals.

MPD47

I had the same issue last summer when doing my brake job. New master cylinder, no problems. Yours is most likely shot.

Van

A bad wheel bearing will also give the same symptom... If the rotor doesn't spin prefectly true (because a wheel bearing is loose), it will push the pads and pistons back into the caliper. Then when you go to step on the brake, first the pads have to move back to the rotor (making the pedal feel soft.)

When you get this "soft" condition, do the brakes feel firm if you double pump it? If it does, I'd suspect wheel bearings (and most likely it'll be a rear).

Good luck!

Matt H

The rotor would have to be SEVERLY warped to have this be the problem. In general, you would also feel the worst pulsation on earth (for that matter if they were that warped the car would be hard to drive and you would feel it all the time).

Simple answer for a simple problem, the MC is no good. It is likely leaking around the seals to the reservoir or even more likely leaking internally.
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Van

No, the rotor doesn't have to be warped for a wheel bearing to be bad. Wheel bearings just wear out, and when they develop play, the cornering forces cause the rotor to move sideways -- this is why we grab the wheel and shake it to check wheel bearings. (Of course, cornering a 3000 lb car at .75 Gs puts a little more force on the wheel than you or I can by shaking it on a jack.) Anyhow, this movement of the entire wheel, hub, and rotor push the pistons back into the caliper.

When you step on the brakes, you're usually going straight-ish, so there's no side deflection on the wheel. The pads come back in contact with the rotor, they squeeze nicely, and, with a second pump of the brake pedal, the brakes feel nice.

If this is the case, IF the pedal is firm on the 2nd pump, then the MC is probably good.

I've had good personal experience with rear wheel bearings failing, and they are hard to diagnose early on. However, this is a good test (once front wheel bearings get loose, it's easy to feel in the steering...)

Jake951

Yes, the brakes do firm up when I double-pump the pedal. I would never think of the bearings as being a source of the problem but I'll check them next. No harm in doing that and it's easy enough to check.