Spongy, Why? - Third Generation F-Body Message Boards

noroxus · 08-09-2009, 06:07 PM

My brakes died while in the highway last week. They got spongier and spongier until they were able to drop to the floor without stopping the car.

Sounded like the master cylinder seal going, but since this event I've replaced the master cylinder, all lines, and all hoses (I've wanted to this for a while now) and it's still spongy (it stops a little better than it did when it stopped working).

So really my question is, would the proportioning valve or the caliper do something like this? they are the only things i haven't changed.

Chevy8588 · 08-09-2009, 07:49 PM

are you losing fluid?

noroxus · 08-09-2009, 10:12 PM

no not losing fluid.

Chevy8588 · 08-09-2009, 10:35 PM

completely flush the system, run allfour lines till you get clean fluid

noroxus · 08-09-2009, 10:43 PM

that was done during the install. my question is would the proportioning valve or the caliper do something like this?

Chevy8588 · 08-09-2009, 10:50 PM

take a look at your prop valve and see if the little rod has popped out the front or rear, our font and rear systems are independant and if there ispressure loss in either th front or rear, the prop valve will shut off pressure to that system, if there is a little rod sticking out of the front or rear of the prop (remove the little black caps) check for a leak in the system. my old 88 did it when my reat libe broke

UNCLE TOM · 08-09-2009, 10:53 PM

pretty much a no brainer , spongy = air still in the system . bleed and bleed well , start at rt. rear , lt. rear , rt. frnt. , & lt. front . bleed each wheel untill ALL air bubbles are gone . bleed with a tube & container with brake fluid . good luck .

skirkland1980 · 08-09-2009, 11:00 PM

it doesn't sound like the prop valve. i would check the rear brakes. drums right? make sure they're adjusted and not work out. those cylinders could be leaking slightly also.

Chevy8588 · 08-09-2009, 11:24 PM

yea that's a possibility too , i say either air or poorly adjusted rear brakes, if you've bled it thoroughly

noroxus · 08-09-2009, 11:51 PM

I have bled the lines and bench bled the master cylinder. oem rear disc brakes. i have driven with no rear brakes and it felt much better than this. entire system was checked for leaks before and after all parts were replaced.

noroxus · 08-09-2009, 11:58 PM

should i check my overseer cylinder?

Chevy8588 · 08-10-2009, 12:04 AM

your what?

skirkland1980 · 08-10-2009, 12:30 AM

only other way i can think of to diagnose is to rig up a pressure gauge and see where the pressure is going?

noroxus · 08-10-2009, 01:39 AM

Chevy8588, does this look like the rod you were talking about, and if so, does it look like it is out more than it should be? By the way, the crinkled paint is from the previous owner, apparently he didn't know how to fill the brake/clutch reservoirs, NOT a current leak or anything.

Chevy8588 · 08-10-2009, 02:28 AM

no, see tat thing on the very front of the prop valve? it will look like a big bleeder, there is one on the back too, have someone push the brake pedal and check to see if a little rod pushes out the front or rear, also judging by that picture you took, you have had ALOT of brake fluid spilled or leaked out there, you paint is peeling right off (brake fluid eats paint)

noroxus · 08-10-2009, 02:32 AM

that is a picture of the back of the proportioning valve (the front brake side). if it pops out the back, would that mean it shut down the front or rear brakes? never really had to deal with proportioning valves. thank you for your help.

Chevy8588 · 08-10-2009, 02:35 AM

out the black shurts of pressure to the rear brakes, out the front shuts of pressure to the front, also judging by that picture you took, you have had ALOT of brake fluid spilled or leaked out there, you paint is peeling right off (brake fluid eats paint)

noroxus · 08-10-2009, 02:58 AM

Quote:

Originally Posted by Chevy8588

also judging by that picture you took, you have had ALOT of brake fluid spilled or leaked out there, you paint is peeling right off (brake fluid eats paint)

like i said,

"By the way, the crinkled paint is from the previous owner, apparently he didn't know how to fill the brake/clutch reservoirs, NOT a current leak or anything."

I'll check it in a few minutes to see if it moves, thank you so much.

Chevy8588 · 08-10-2009, 03:07 AM

no problem, sorry missed the previous owner thing, but that will rust like hell if its not taken care of man

RevItUpZ28 · 08-10-2009, 06:45 AM

I'm kind of going through the same thing. I replaced all the front brakes (calipers/rotors/hard lines/flex lines/master cylinder) and also replaced the rear drum cylinders, back when I upgraded to LS1 front brakes, and my brakes haven't worked right since. The master cylinder was purchased from autozone, so not sure if I trust that part or not. Anyway, I bench bled the master before putting it in, and have bled the brakes again and again. The pedal will get firm and when I start the car, it sinks back down and gets spongy. I keep telling myself its just air in the system and needs to be bled again, but now I'm leaning more towards vacum leak? Someone also mentioned to me that it could be the brake booster on its way out. Its beginning to get frustrating so I've decided to do the LS1 brake booster/master cylinder swap to try and solve the issue.

noroxus · 08-10-2009, 07:19 AM

brake booster would cause the opposite to happen, they would be firm all the time.

transam85dudeman · 11-16-2009, 01:25 PM

Quote:

Originally Posted by noroxus

brake booster would cause the opposite to happen, they would be firm all the time.

did you ever get the system firm?

noroxus · 11-18-2009, 02:22 PM

I did actually, it turns out it was a very small hole in the line under the engine, and all the fluid that would leak out, already did. i guess i was stopping (or not stopping) on air pressure alone until the pressure leaked from the hole.

in any case, having everything in the braking system brand new is good assurance for a good while.