loss of brakes!!!!!

[05barbee]

1993 subaru legacy awd sedan. heard thump/pop from under the hood and then had complete loss of braking. pumping brakes helped a little but could not build up pressure. master cylinder is full and can find no loss of fluid. hear hissing like there's air in the lines and this is what it acts like, but the brakes were working fine right before this happened (at highway speed). also, this same car had an intermittent braking problem about a week ago. same thing happened, but only for a minute then brakes worked fine. thought it was a momentary glitch. no brake lights or any other warning lights on. possible master cylinder maybe? did all legacys have abs in 93? i work on older (classic muscle cars and trucks) vehicles so i'm not real good on newer systems. any help would be greatly appreciated by this newbie.

[gijonas]

Because of the hissing noise you point out I would definately say that the vacuum line from the manifold to the brake booster came off or broke.This would cause extremely hard braking and a hissing noise,also would effect engine performance.

[Kecksauce]

I agree with Jonas. There is also the remote possibility that the power booster failed, but that would be a worst case scenario and not as likely.


Definitely give the vacuum lines a good looking over.

[roundeye]

if the pedal goes to the floor, and no fluid's leaking out, you either blew the master cylinder, or a valve in the abs. When does it hiss? Where is it coming from? if it's inside the booster, with the engine running, the diaphragm is leaking. was the pop noise while you were braking? if so, i'd lean towards the master cylinder, especially since it's happened intermittantly before. not too tough to pull the master and test it.

[05barbee]

the hiss is when you push down on the brakes. they go all the way to the floor and if i pump them about 3 or 4 times, i get about a third of the pedal, but it feels like it is very slowly losing pressure. i wasn't driving it when it happened (it's my sons car) so i'm not exactly sure what the sequence was as far as the pop and trying to brake. he was pretty frazzled being as he was driving down the highway in traffic and all. i'll get to checking all the lines coming off the booster and where they go. i'll keep checking back to see if anyone has any more ideas. once again, thanks for all the help. you guys are lifesavers.

[05barbee]

keeps getting weirder. went out to pull it in the garage, no brakes. eased it in the garage, popped the hood and with it running i removed the master cylinder lid. pumped the brakes to see if the level changed, and suddenly i had brakes. the fluid level did go down about a half inch so i refilled it. put the cap on, still had brakes. i took it for a drive around the block and the brakes work fine. it does sound like my son picked up a rock in the right rear and it's rubbing when you put the brakes on so i'll pull that apart and remove it. my question is, could that have caused a momentary overpressure and brake failure? i don't see how, but i'm not used to working on abs systems.

[gijonas]

I would just bleed out all the fluid and change with new.Its a good easy thing to do anyways.Has there been any brake work done on it any time in the recent past.

[05barbee]

nothing recent was done. going to check all of them and probably bleed the system while i'm at it.