Help - pedal to floor - only sometimes

[RedTRex]

87 325i resurrecting

ABS light on - right away - so Computer or relay.

Pedal was on floor. Pressure bleed all. Eng off - pedal firm - no sink.

When running 1/2 the time pedal firm, 1/2 the time goes to floor (only rears barely working), a double pump firms it right up.

I think bad MC.........

[KenC]

I think bad MC.........

most likely culprit

[BigD]

most likely culprit

Agreed, busted a seal.

Did you bleed your brakes recently? I've had this happen when I bled the brakes on a beater I just bought. It was explained to me that the pedal pump method makes the piston explore areas of the stroke that are normally never used and are quite grungy - ripping up the seal.

[RedTRex]

Agreed, busted a seal.

Did you bleed your brakes recently? I've had this happen when I bled the brakes on a beater I just bought. It was explained to me that the pedal pump method makes the piston explore areas of the stroke that are normally never used and are quite grungy - ripping up the seal.

Yes - this was a busted timing belt car I acquired. Pedal was pretty much on the floor already, I just got it running again yesterday - noted bad pedal - so yes I bleed (pressure bleed + pump pedal) .... and like I said pedal felt great engine off, but once I got it back on the ground and drove, I was having the intermittent pedal......

[jlevie]

On the assumption that you've carefully examined the brake lines and calipers for leaks, the master cylinder becomes the prime suspect. I'll bet that if you really lean on the pedal with the engine off you'll feel the pedal sink.

[BigD]

Yeah, without boost there's just not enough pressure for you to feel the busted seal. My beater teg felt the same way. It was a bit springy with the engine off but it gave the impression of being fine, because half of the circuit was still resisting normally. Time for an MC swap.

[RedTRex]

Okay, sounds like MC bad, thanks for the help everyone!

[twothrees]

Before you put in the new mc, don't forget to bench bleed it. I had the same issue a couple of months ago and a new mc did the trick.

[Z3Jonathan]

Probably bad seals. I would just replace the M/C with a new one... they're a little pricey, but to me it's not worth buying used brake parts.

FWIW, I prefer to just use a pressure bleeder. It's a little easier on the seals inside your M/C. Although, the trade-off is that it can put a little more stress on the grommets between the reservoir and the M/C. So, it's a good practice to line your engine bay area with some garbage bags in case the grommets decide to let loose.