OK, here's one for the brake guru's:

When I'm stopped, I have a firm brake, but as I sit, waiting to go, the brake pedal slowly drops, and drops, and drops towards the floor. If I release and put them back on, the pedal is firm again, then slowly drops again.

Any ideas on what I should check?

 

Check for fluid leaks. Especially around the brake booster where the master cylinder mounts. If it is wet, replace master cylinder.

 

PonchTA, Does your T/A have any type of high performance cam? Mine did the same thing after I installed a CompCams 270Magnum.
Low manifold vaccuum,etc..

------------------
82Z 305 w/comp 270 magnum cam,Edelbrock Performer RPM,Holly 1850-4,serpentine belt drive.TH700R4 w/B&M holeshot 2000 converter,& megashifter.1LE front brakes, 9bolt 3.27 w/1LE rear brakes.Aluminum driveshaft,boxed rear susp.poly everything,IROC swaybar+wonderbar. 70mph@2200rpm ASE Master Tech plus L2
also recently obtained a
'69 chevelle SS396 w/Turbo 400,3.31 posi,11.0 to 1, headers,etc. Latest project car,'86 IROC stock 305TPI hit on left side,but not too bad

 

No leaks, at the wheels, or at the MC/booster. The lines are in OK shape (I'll be changing those later $$$)

No performance cam that I know of, a previous owner may have put one in, but knowing them, I really doubt it! (these are the guys who wouldn't even get a flat _repaired_, they just put a couple of cans of fix-a-flat in the damn tire! <stupid!>

It probably won't really matter as I hope to do an upgrade to rear discs anyway!!

 

Replace the brake shoes,wheel cyls,And clean the drums with brake kleen. That should do it.

 

This is common with a bad master cylinder.

Sometimes they won't leak , they just bypass inside. Remove the mounting bolts on the master and look behind it, sometimes the fluid will go into the booster and not show leakage from the outside.

------------------
ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...

R.I.P. #3
"He can see air"

 

Yep...internal seal leak.

 

Thanks guys! I plan to replace the rear with a disc system anyway, so I'll live with it for now and replace the M/C when I do the change-over.

Thanks for the diagnoses!

 

You have a leak. Check the rear wheel cylinders by pulling the brake drum.

 

Do not replace the master cylinder with anything exept the original J50 type. Also retain the propotioning valve.