Marc 2000

Hi there !

Almost 2 years ago I bought a ´90 Trans AM 5.0 TPI with not working brakes.
Since then I replaced / overhauled everything:Calipers, Hoses, Master Cylinder and so on. Problem is it still wont stop. The pedal goes halfway down and it takes a lot of force, as if the booster is not working. When I rev it up it the pedal gives a bit more. But in idle it gets hard again.

The vaccum hose is replaced, check valve seems to work. The pressure resides even 24hours after the engine has been shut down. I.e. the membrane should be ok ? I heard there is another valve letting atmospheric pressure inside the booster, could this be bad ?


I already tried a booster from a V6, Code AK. (Mine is FL, where is the difference ?) Unfortunately I received this one with a loose part inside so I had to open it up. Then it wouldnt hold the underpressure so I guess I ruined this one.... Also I put in the V6 Prop Valve which had a different thread size for the rear input. Does this matter ? Both have rear drums.


Any help is highly appreciated !

Regards from Germany :-)

Wishmaster's87IROC

iTrader: (4)

hmmm....i was just about to post a thread about mine booster...wanting to know if its bad.

I have replaced everything over the years too even braided lines...xcept for the booster.

I just dont have any stopping power...pedal feels hard like it should feel but if i have to make a panic stop im hittin the car or person or whatever it is i cant make the car lock the brakes and skid if my life depends on it.

no pedal fade at all.....actually pedal feels normal......but its like i have no clamping power on the rotors.......brakes bleed fine. I even went as far as to ad a vacccum canister for the brakes and i have a gauge on it and its pulling 25psi on the canister

I took it to have it checked out and thy told me it was the booster but i would reather find out from here.


so im keeping an eye out on this thread.

Wishmaster's87IROC

iTrader: (4)

come on all you brake guys....whats the deal?

norcalz28

iTrader: (13)

Similar issue with mine, except I replaced everything, including the booster. I Went with Ed Millers 12" C4 kit upfront, kept the PBR rears, added earls lines, new master, new booster, bled the system thoroughly, TWICE, including bench bleeding the master initially. The car stops, but I still don't think well enough. Pedal is hard and requires intense work to make the car stop. I have a bit of a cam, so I added a vacuum reservoir which might have a helped a touch, but not the improvement I was hoping for. I remember my iroc never stopping particularly well, but that was 5 years ago and now that I want to get it back on the road, I really trying to get this figured out.

Will

Wishmaster's87IROC

iTrader: (4)

yeah i know what you mean......surely back in the day when the cars were new...GM did not send them out on the road with such difficulty in stopping.....thier would have been lawsuits everywhere.

RBob

iTrader: (1)

Have the 12" C4 fronts but with drum rears. Car stops very well. Original booster, M/C, and combo valve are in place. Also have the Earl's lines front & rear.

The calipers came with nearly new PBR FF rated pads. So used them along with new rotors. Once the rotors were broken in (heat cycled) and the pads then bedded in, the car stops.

It may be that the pads you have are not that good. Or they are not yet bedded in. It is also possible that they glazed over before being bedded.

I've been partial to CarQuest semi-metallic pads. The mid-grade ones, which I believe are Raybestos. These too are rated FF.

The other part of this is the rear brakes. I know that the previous Delco rears have issues. Even a recall kit for them.

But in reading here, it seems that the PBR's also have issues. Just not enough braking from them. So the car will be down about 30% of it''s braking capacity. Some gut the proportional valve out of the combo valve to get better rear brakes.

RBob.

Marc 2000

Does anyone know the difference between a "FL" and a "AK" booster ?
If I remember right the piston springs are different.....