stock brakes, w/ ABS, new (Autozone reman) 929 MC, car has been sitting for 4 years. ABS pump was emptied out (simple pouring) and reinstalled.

So I bench bled the master and have been bleeding the car several times the past couple of weeks. I've done vacuum pump bleeding and buddy brake bleeding. I would say overall I've done about 50-60 bleeds per wheel so far. I've tried bleeding with the car [ABS] turned on. I've pumped the brakes a couple times with the engine running to see if the booster helped. I've tapped all calipers, the ABS pump, and the master with a mallet to try to free up any sticky bubbles.

-No more air has been coming out for a while, not even tiny bubbles, yet the brakes still feel spongy.
-The pedal goes to the floor on the first 1-2 pumps, then starts tightening up on the 3rd and feels very firm after that.
-The back brakes bleed normally, but the front brakes don't seem to have as much pressure buildup. When I open the bleed screw, my buddy tells me the pedal doesn't go all the way to the floor, and I notice not as much fluid comes out of the bleeder (although what does come out comes quickly). This must be due to the back brakes tightening up on the rotor before the pedal gets to the ground. Not sure how to fix this, though.

Thanks in advance. This is the last thing to get my car on the road and it's had me stopped (rather, hasn't) for months now.

 

First off, do you have big brakes? That's the only reason for the 929 master cylinder. If not, get a stock MC and do that.

It's quite possible the problem lies with the master cylinder. Especially how it has to be pumped up.

Another possibility is the pads on the front brakes. Can they move freely? Can the pistons move freely? If the pads get knocked back from the rotor or bound up you can have a few pumps to build pressure.

I don't think it's a problem with air in the system, I think it's a master cylinder or caliper issue.

Dale

 

Stock brakes, which have worked fine with the 929 MC countless other times, so I don't see how that would be a prevailing issue. I took it apart and reassembled it, also, so I could see that the seals were in good shape and nothing looked busted or rusted.

It's worth mentioning that this one replaced another 929 MC that was surely bad, and while trying to bleed with it, the fronts bled fine and the rears pushed almost no fluid whatsoever, and I couldn't get a solid pedal no matter how many pumps. Just seems to be a different problem associated with a bad MC, not to rule your suggestion out completely, though.

The calipers are grabbing the brakes, I can see, hear and feel movement at all four, and they stop the rotors, but only after those first couple of pumps. Not sure how else to test them. I would think if it were a caliper issue, it would be isolated to one caliper, but the rears and the fronts behave identically to one another.

 

Ran into a similiar problem with my 929 MC with the pressure between front and rear chambers in the MC, opened it up and it was rusted and blatently shot. Got a new MC and bled the lines out works flawlessly now.

The only reason for a sponge brake I can think of is air in the system or a leak. You mentioned your have ABS, maybe there's air still stuck in there. That or there's air still in the MC even after bench bleeding it.

 

Air somewhere in there is all I can think of, but where could it possibly be that insane amounts of bleeding do nothing?

Regarding the MC, I'm under the impression that a symptom of a bad MC is a pedal that slowly loses pressure as you're stepping on it. My pedal is squishy for two pumps, then consistently firm.

 

I think it is the MC also. I would bench bleed again. Hurry up and finish your car so we can go play at Sebring.

 

Been dying to. The car has been ready to roll for months, just can't stop.

 

Have always wondered about this... air bubbles high in any system (like in the ABS unit) can just sit there as brake pedal is pushed; the fluid can just flow around the bubbles without moving them.

http://www.rangerovers.net/MAINTENANCE/brakebleed4.html

http://forums.bimmerforums.com/forum....php?t=1787641

(I realize the links don't go to RX-7 info, but tried to research ABS unit problems and these were the best I could find.)

 

I had a similar problem with my 929 master cylinder after the car was sitting for years. It turned out to be bypassing internally. Check if there are bubbles present in the reservior when depressing the brake pedal

 

i have also spongy pedal after filling the whole system again. ( was complety empty )
i have a bbk from atomic rex , 929 mc and steel brake lines.
have done bench bleeding several times also on every brake caliper.can't get it good.

 

pressure bleed system from the top down. find a shop with a power pressure bleeder. if it is air in the system this will be your best bet. also look up the bleed procedure for your car. for a lot of cars these days the traditional rr-lr-rf-lf bleed sequence isn't adequate.

i would also suggest clamping off the lines with line locks and checking the pedal. you can get a set at you local napa dealer for cheap - just ask for "hose pinchers." don't use vice-grips on the lines, they can actually crack the hose internally and cause bigger problems.

Ray

 

ok will try that. thanks

 

either of the two guys in this thread figure this out?

similar problem here

 

same. the car could be on or off, but the first press is very squishy with abnormal travel, every press afterward has about 1/2 the travel and feels normal. This happens every time I slowed the car down driving around the block.

I will say that when I bled the brakes I didn't do anything special with the abs, but I suspect it may be the MC. There was a ton of gunk in there, maybe something got jostled after the brakes have been bled for the first time in god knows when and messed up the seals. Any ideas?