IceWater

I'm having a problem with air getting in the brakes of my 93 coupe (non M030). The pedal is spongy at the top, but then firms up as it is depressed. It won't keep traveling if I keep weight on it like it should if it were a bad master cylinder. If I pump it, it firms up a little. After bleeding the system, it takes hardly any time to get spongy again.

I thought the threads on my speed bleeders might be letting air in when bleeding, but I tried some teflon tape and the problem still persists.

Are there any usual suspects for letting air in?

Thanks,
Tom

Dave951M

I had a similar problem. The culprits were- bad master cylinder, bad resevoir seals, leaking proportioning valve. (Obviously a problem child) The rubber seals between my mc and the resevoirs were cracked and allowed air in intermittently. The mc was sucking minute amounts of air in from the pedal side. The prop valve was toast internally. Working together, it was an interesting troubleshooting problem. Hope this helps.

IceWater

Thanks Dave.

Can the seals between the MC and reservoir be purchased separately? If so, from where?

Haven't done much work on this brake system yet...where is the proportioning valve?

Thanks again,
Tom