well i got a new master cylinder for my '89 GTU hoping it would solve my soft brake pedal and poor braking performance. put it in there, bled the crap out of the system, and still had the same braking power. i took a look at the front right caliper, and the top pin was froze to the caliper, not allowing it to float back and forth. so i cleaned that all up, put new pads in all around, and the brakes work a lot better. now i can lock up the potenzas on pavement the pedal is still kinda squishy, but the brakes work awesome. do you think the squishy feeling is from the 4 old rubber lines? is the brake pedal in these cars ever rock hard?
thanks for your time and help

 

did you bench bleed the master cylinder before installation? If not, that's crucial to getting a nice solid pedal.

Have you flushed all the old fluid out? At any time while bleeding did you let the master cylinder run out? If so, bench bleed it again.

Those rubber lines are pretty old (assuming stock) so replacement isn't a bad idea, but I'd focus more on making sure the lines and MC are fully bled..

PaulC

 

I have the same problem. The master that was on my car when I bought it was 'soft'. So I had arebuilt one put on. Same feeling. Then I had the shop put a brand new unit on. Still the same.
I have a suspicion it may be 'booster' related (there is an adjustment between the booster and the master) or, possibly, a difference in masters for single piston and four piston calipers. Nothing conclusive, yet.

 

Did you guys see if the vacuum line that goes to the intake manifold was connected good? I too had the same problem and this went on for about 2 months the damn vaccum line was loose...the only reason i found out was that the line became so loose that it was causing an idle problem so i poped the hood and heard this major hissing looked and saw it was that waala fixed brakes and idle problem....

 

No large leaks, but an idle that drops with your foot on the brake is an indicator. Not proof, just an indication of a hose leak or booster diaphragm leak.

 

Yeah, but a booster problem would be a much harder pedal, the booster is there to make pedal effort easier..

PaulC

 

This might or might not work.
I have the same problem with my master cylinder and it turned out to be defective. But I also found out that alot of times when you change the MC on the RX-7 you have to power bleed it. As in take it to your local brake shop and ask them to do it unless you have the right equipment and know how. Now don't confuse this tybe of brake bleeding as the regular pedal and bleed screw. this method pressurizes the brake lines. You should have a nice stiff pedal after this, given that you don't have any leaks or the like.

 

Not always. I have a car (non RX7) that had a booster problem that resulted in a sinking pedal. Something internal was sticking and letting it 'assist' a little. Lower pedal, too. It had different symptoms than this. I would start the car and the brakes would start dragging. Eventually, they would lock up. I found this out after changing the calipers and put a booster on from a parts car (old booster had a BIG diaphragm leak. Step on the brake and the car immediately stopped running). Whatever was sticking wouldn't let the pedal return alll the way and prevented decent bleeding of the brakes. Soft low pedal that drove me nuts. The hazards of doing multiple repairs on the same system. You don't always know where to look. And the first piece of advice anyone gives is - bleed 'em!

 

I couldn't get a feel to mine that I really liked... even with new calipers, MC, and new lines.

I vacuum bled the system, which made a bit of a difference, then hooked up a pressure bleeding system running on 10 psi of compressed air. BIG difference in feel.

 

i bench bled the MC really well, and bled the brakes completely. i made sure that new clean brake fluid was coming out of each bleeder with no bubbles.
i'll have to check on that vaccum line though. my idle does drop a little when i hit the brakes. i thought it was just because the brake lights were coming on and putting a load on the alternator. when at a stop, the brake pedal will slowly go to the floor. this shouldn't happen with a brand new MC should it? assuming no leaks

thanks for the replies

 

You could disconnect the stoplight switch and press the brake to see what happens.

 

well, i did some experimenting at lunch. i'm pretty sure there isn't a vacuum leak, when the idle does drop with the brake on, i'm pretty sure it is because the brake lights come on. the idle will do the same thing when i turn on the headlights or blower fan on full blast. so it isn't much of a drop in idle, just enough to notice.
i might try bleeding it some more tonight