airborne

here we go. with the car off i can pump the pedal and it will progressively stiffen. this is right according to the manual. i can hear air hissing and that is supposed to be vacuum i guess. so pedal is great with the car off.

with the car running there is some serious travel. when i press the brake i can hear a loud hissing coming from the pedal area. wtf? no leaks that i can find.

so far i've rebuilt the front calipers and bled the heck out of the system. any suggestions are appreciated.

mad_7tist

pump up the pedal till it is hard. then while still holding pressure start the car. what happens? check the booster vac line

airborne

it sinks which is right, but it sinks A LOT. vac line definitely on the list. could this be a symptom of a bad MC?

macdaddy

No - if the MC was bad, the pedal would sink with or without vacuum boost. If the vac line to the booster is OK, the booster itself may be bad.

airborne

I think we have a winner. The vacuum line on the intake side -from the UIM to the line running across to the booster. The manual says it should only flow one way, mine flows both ways with ease. It even has the arrow on it indicating which way air should flow. Just cut it open and there is nothing in it. Is there supposed to be a check valve or something? Where the heck could whatever was supposed to be in there go? Near both ends the inside was shiny but thats it. Anyone have experience with this???

Thanks for the advice macdaddy and mad_7tist

airborne

just found this thread:
https://www.rx7club.com/showthread.p...t=brake+vacuum

apparently my car (a 94) never had the recall. dang.

airborne

after talking to the dealer my car has had the recall so i checked the *other* line and it seems to have a working check valve. has anyone ever had a brake booster go bad on them? is this hissing noise accompanies by excessive pedal stroke a symptom?

Mahjik

iTrader: (1)

See if you can find or borrow a Power Bleeder. It will let you check to see if your MC (and braking system) is holding pressure.

airborne

i have the motive power bleeder and used it to bleed the brakes. it would lose pressure but i can't find a leak anywhere.

Mahjik

iTrader: (1)

If it won't hold pressure and there is no fluid leaking, then it's most likely a failed seal in the MC.

airborne

ray is sending me one today. $93 + $50 core. i forgot to ask, hope it comes with the bench bleeding kit...

Mahjik

iTrader: (1)

It will come with the tubes (as well as Mazda's cheapo brake fluid) to redirect the fluid back into the reservoir. Just use your hand to push the piston in for bench bleeding.

airborne

thanks mahjik, hopefully this'll do it.