20Bforme

i got the brakes bled finally! had a friend come out and give me a hand. i was initially having trouble bleeding the front, but now that i had some help... it went smoothly. the leak that i thought i had in the driver side caliper turn out to be that the bleeder screw... things were going great. fired her up on the first crank... smoked a bit, but thats fine. went to test the brakes on a little drive up the road and thats where we noticed a problem.

the brake pedal wont hold pressure. when the car is off, you can build pressure by pumping the pedal... but when the car is running the pedal pressure is minimal and goes to the floor. we checked for leaks in the system... found none... and the reservoir was still topped off. after brainstorming we came to the hypothesis that the brake booster is shot. does this sound like a typical symptom when one fails?

20Bforme

https://www.rx7club.com/showthread.p...+power+booster

hmmm... ill have to check this out.

EvilWankel

iTrader: (2)

I think if your brake booster was shot it would be very stiff, the opposite of hitting the floor with no pressure. Did you recently chenge the pads? When I did that once it took a while before the pistons in the calipers rested right where they needed to, causing a very soft pedal for a while.

20Bforme

everything on the brake system is new except the hardlines. when the pedal is pushed the pads stop the wheel from spinning, so the brakes are working. theyre just extremely mushy.

EvilWankel

iTrader: (2)

That's what mine would do as well, almost hit the floor for decent stopping. When you push you car around and hit the brake without it being on, you notice how stiff it feels? That's without brake booster.

I'd say drive it (slowly) around your neighborhood for a while. Should build pressure back up. Or you have air in your brake lines.

DaMaCCa

iTrader: (1)

You changed the rear calipers too? I ran into this same problem when I swapped all of my calipers out, ended up having a lot of air trapped in the rear calipers. Turns out I continued to bleed from the lower screw. Maybe retry bleeding the rears first with the bottom bleeder than up to the top bleeder screw. Hope that helps.

20Bforme

yes... the rears are also new. i did bleed from the top screw per the fsm. im gonna try and limp the car home... after midnight once traffic is at its lowest. once its home... ill try what you said.

edit: should i re-bleed the entire system while im at it?

clokker

iTrader: (2)

You have nothing to lose by rebleeding the system- who knows, you may get lucky.

If you don't, inspect the brake booster vacuum line, specifically the function of the internal one-way check valve.

Failing joy there, the only thing left is the booster itself.

Black Knight RX7 FC3S

iTrader: (7)

if you are 100% positive you bleed the system, then the only real explanation is the Brake master cylinder. A bad brake booster will give you no assistance in pedal pushing, meaning the pedal will be VERY tight, just like when the car is off, and the car will have a very bad idle and shut off or so.
A internal leak in the master cylinder will not hold the pressure and leak it back into the resovior, hence the pedal dropping when pushed with the car on.
But you can always try and rebleed everything all over. Going with the closest to the master cylinder and going out.

If the master cylinder is new or rebuilt, they can go bad. I had a friend who bought a new master cylinder for his Integra, bench bleed it and everything, went to put it on and still had mushy pedals. Went to change the master cylinder for another and it worked.

But the best thing you can do now is to bleed everything to make sure, also you said that everything in the brake system is new? Did you bench bleed the master cylinder?

20Bforme

yes, everything is new. maybe i didnt bench bleed the correct way? i bench bled the master after installing it to the car. would bench bleeding really make that much of a difference though? is it REALLY that important? just curious. also... you said to rebleed starting from the closest caliper? not the furtherest according to the FSM? i guess if the master did go bad on me (even though it is new), i can always just rebuild this one instead buying another new one.

Black Knight RX7 FC3S

iTrader: (7)

If you didnt bench bleed it properly air bubbles will stay trap in the master cylinder no matter how many times you bleed it with it on the car.
if the fsm says the furthest, then bleed the furthest, I always forget to start from where hahaha

Also, when you bench bleed it, put it in a vice or in something to hold it down. usually when they give you the fitments and tubes for bench bleeding, if they didnt then you are going to have to make ur own fittings. Just be sure to keep the hose submerge in the brake fluid resovoir when pumping the rod.

20Bforme

almost missed your edit...

whats the difference in bench bleeding the master if its attached to the car or in a vice done by hand?

misterstyx69

iTrader: (142)

You still have air in the Brakes.
If I am doing brakes I Start by Opening up the Rear bleeders.I let the Fluid run out on the ground(use something to Catch this Stuff!).Once I see Fluid,I tighten the bleeders.Then I get a buddy to Pump(say six times).I open the Passenger rear bleeder while the brake pedal is being held(it will go to the floor when opened).Then Buddy holds the brake pedal.Tighten the Bleeder..do the Rear passenger 3 Times..then TOP up fluid.
Do the Rear Driver's Side..same thing..PUMP Six..hold..open bleeder..HOLD pedal down.Tighten.Rebleed..
then the Front Passenger..Same thing..
then the front Driver's ..same thing
IF the brakes Do not Feel Better after this,Then Something is Wrong.
Just remember For Each caliper being bled,you have to TOP UP the Fluid.If you let the Master go below the Reservoir Level then you have to Prime the master and then start all over again.

20Bforme

out of curiosity... would not having the front brakes bled for 6 months and the rears bled have any substantial effect on this?

i ran out of time last year (cold/snow) while troubleshooting the front brake problem i was having.

68Sniper

iTrader: (1)

I have replaced 2 master's and the guy (auto parts store) told me that their was a seal at the very end of the cylinder and if you push the pedal to hard it pushes the rod to the end of the cylinder thus pushing the seal off and it will not hold pressure after this occures. I have no idea if this is true. BTW i am still having trouble with my brakes