RX7_GTR

Maybe some brake gurus can help me here..

Here is the problem, I have a 87 TurboII with ABS, one day the brake pedal all of a sudden goes to the floor. I first checked for leaks and did not find any, just happened out of nowhere. The brakes were pretty good before then.

Here is what I have done so far:
-I have replaced the brake lines to SS lines
-Bled the system...same thing.
-Replaced the Master Cylinder ..bench bled the MC prior to install.
-Re-bled the brakes, abs unit...Same problem.

I know the brakes are bled correctly because I did it with my friend who happens to be a competent mechanic I do get some pedal now but goes aways when I'm driving. The funny thing is that when I'm pumping the brakes to bled them out, they feel great...really solid. But once i start driving the pedal goes away.

We are thinking that its the brake booster or ABS unit itself? Any inputs?

Thnx

Rxmfn7

iTrader: (4)

Have you looked over your entire brake system to ensure there are no leaks anywhere? Cracked rubber tubes, even a split metal line, leaking ABS unit?? Are you losing any fluid at all? If the brake booster went bad you should still have a pedal, it just will not supply enough pressure to stop you at all.

Turbonut

iTrader: (1)

I assume when you bled the brakes, you did so with the engine not running, which naturally is no problem, but creates a great deal of resistance in pedal. Start engine and apply pressure to pedal and hold. See if pedal drops. If ABS goes bad, it will not inhibit your stopping, or cause the pedal to drop. We all know the reason the pedal is dropping...No resistance. Master cyl, which could be bad(was it new or used?), or leak in system. Also, don't know how much of the system you had apart, but there are 2 bleeders on rear calipers. This shouldn't have made a difference if you didn't have the rear calipers apart.

Gene

iTrader: (1)

Actually... the ABS box could be the culprit. When it goes bad, it often starts leaking like a bitch. Check all around it for brake fluid, the ABS box on these cars is terrible. I went thru two of them before I had the whole thing removed.

Turbonut

iTrader: (1)

Sorry, should have explained. Naturally it could leak.....I meant if the ABS itself was caput, from an electronics standpoint, the brakes would still function properly.

RX7_GTR

I think it might be my ABS unit...I have a new Master Cylinder, Brake Lines, and have checked all the hard metal lines and fittings. Everything looks OK...so I suspect that its the ABS..If it is the ABS, how do I re-route the lines to bypass it?

Thnx.

Castrol86GXL

brakes are my fav parts of all cars i dunno why but i love stopping power. i know im an idiot but anyways check out the brake booster.

Castrol86GXL

oh yeah and if the abs had a leak (to check) start the car fill the brake fluid and if you see a leak (you got a leak) anyways check the cables the the brake pedal itself if you havent, but it sounds like something inside the brake booster went bad.

jg1bad10th

I had this same problem last summer.I first thought the mc was the problem so I replaced it and still to the floor.The problem was the proportioning valve.check this I have one that's in good shape if you need one.just p.m. me.

Jaared

my brake petal goes to the floor.. but the car has been sitting for almost 3 years... it held its fluid! when the weather gets better ill try bleeding the system and i hope it will be fixed...

jaared

RX7_GTR

hmm....never thought of the porportioning valve. How does this go bad, I thought it was just there to balance brake bias from the fronts and rears in a ABS equipped car. I am not too sure how it works...please enlighten me

Thnx

jg1bad10th

I don't fully understand what it does I take it that it's a very simple setup.My problem started when the back brakes locked up on me a couple of times the year before.I had it checked at the mazda dealer that I worked at and they found nothing.didn't have the problem again for another year then the brakes started fading.quick.within 2 days no brakes.I just replaced the mc thinking that was the problem.Not.the dealer wanted 135.00 parts my cost to replace it.I had a friend bring me one for 45.00 and replaced it myself.no problems since.try this I don't really know if there is a way to test it.I'm shore there is but if this sounds like what your can done It's a cheep fix.sounds like you've coverd everything else.