PontiacBonnevilleClub.com

93 SSEi - 82K miles.

Had problems off and on with the brakes - particularly after the car sits in storage for a season.

Changed the master cylinder (rebuilt from Advance) a few months ago.
Bench bled the MC. Bled the brakes & adjusted the rears.

A month or so later, mushy brakes. Bled again - noticed some air bubbles.
Bled again - 3 or 4 times.
Finally got a good, hard pedal feel.

A month later, mushy pedal, off and on. After a pump or two, it is good and hard.
Next time to stop, mushy pedal - pump once or twice, good and hard again.

Wonder if the master cylinder is failing...

edit: Air should never get into the lines, but for that amount of pedal mush (1-2 pumps) and entire line to one of the brakes would have to be air. If air isn't significant in the lines, the pedal would just feel softer. /edit

Sounds like the auto adjusters in the rear aren't working correctly. The nut with the spikey thing on the adjuster likes to rust and stick. If you can't easily turn it by hand, it won't work when assembled. If that's the case, get some good heavy disc brake wheel bearing grease, its really thick and dark grey.



Get a new auto-adjuster kit, or just cleanup the one you have.

Stuff the threads of the adjuster with the grease, so the nut doesn't stick to the rod. Also stuff the sleeve for the rod with grease. Wipe any excess off. The auto adjusters should work for a long time then.

The pedal mush continued - so I inspected the rear hardware again. No problems there.

I decided to make my own power bleeder. Got a spare cap and tapped it to fit my air fitting. Talked to a brake shop and they said they use 20 psi. It sort of worked, but I need to make a strap to hold the cap down against the gasket. It was never intended to hold back pressure. So it made more of a mess (fluid mist blasting our from under the cap). Gave up on that and went the old fashioned two-person way.

The rears belched a fair amount of air. No air on the fronts. Pedal good and firm now.

The air must have been there all along, but I don't know why it was fine for a month or so after the previous bleed.

Maybe there was air in the ABS module and it cycled, passing the air into the lines?

J Wikoff wrote:Maybe there was air in the ABS module and it cycled, passing the air into the lines?

I wondered about that - but the ABS light has been on for several months, so I assume it has been non-functional. I suppose air could still be trapped in there.