Have searched around without finding this particular problem. I have a 79 GS. The master cylinder was leaking into the booster so I replaced the booster and the master cylinder. I bench bled the master cylinder and then the lines. The brakes feel... I will say, acceptable... until you start the engine. The pedal travels nearly to the floor with VERY little resistance and then the brakes grab. I tried rebleeding the lines more but it didn't help at all. Any suggestions would be great.

 

did you check the vac hoses from the booster to the intake manifold? they tend to get old and crack.

:AA:

 

in what order are you bleeding the lines? i bleed mine RR, RF, LF, due to the drum brake models not having a bleeder on the RR brake. you need to ensure that the pedal is firm and that no air bubbles are present before you stop. no foaming, no air, no contaminated fluid coming out of the bleeder screws.

 

eddie - as Mr. Bill said "ah feel yor pain"
Did exactly the same thing on my 80SA (rebuilt, bench-bled Master, replacement USED vac booster), PLUS Dave's above bleed order with the SAME result. Even my mechanic could not improve with a "professional" bleed

Vac Assist is definitely working, because when we get to the last 1/3rd of travel, it just about puts you threw the windshield!! Been driving mine like this for 2 yrs now! ugh!

I have a spare Br. master I might swap in in case the rebuild I used was somehow bad (no leaks!) - but I am missing something here. Glad to hear I'm not the only one - BUT: sorry to hear your having this ag!

So. Anyone???

Stu Aull
80GS
Alaska

 

I messed with a problem like yours in my car forever. Exact same symptoms. I bled it a million times. Even with a little vacuum brake hand pump. It turned out I still that I had a little air in my lines nonetheless.

What I ended up doing was bleeding the brakes with 2 people (even though I had a one man setup like you). I had the brake pumping person pump the brake pedal super hard during the pushing-the-pedal-in-stroke. I think the bubble were able to stick around until I did this. Because it has worked perfectly since, and that was seriously the 6th or 7th time I bled the brakes. But it fixed the prob for good.

I hope this helps. Good luck!

 

I did bleed them RR RF LF. 3 times now. I am going to see if adjusting the rod for the brake pedal helps. If not, bleed them again. I had better pedal when I bled the system with the old master cylinder and boost. But there was a slow leak from the master into the boost so I lost pressure overnight. Never had this much problem with brakes on any vehicle.

 

yeah, its a pita.

:AA:

 

yeah, these drum brake systems are a pain in the a** to bleed. I got new wheel cylinders and they were bled as good as they could be in apinch, and I have a mushy pedal. Gonna have to get some help and bleed this sucker right.

 

It could also be your brake proportioning valve being stuck or with air in it.
You really need 2 people to bleed this good. I had this issue twice now and
both times its when the MC is removed. The first time was to replace the MC.
The second time was more recently when I had to replace the booster.

So the symptoms are you start bleeding in the rear and it appears to bleed
but the volume of fluid that comes out is small or slow to come out. Then you
move to the fronts and it bleeds fine. If your in a hurry you may not notice it
at first. Then you get in and the brakes are still mush and if you drive it and it
takes a lot of travel and effort to stop the vehicle. The first time this happened
I was like, WTF. It took me a few tries to figure it out.

The solution is to get in the seat and stomp really hard a few times on the
brake pedal until it will all of a sudden feel like something changed. Hard
to describe. Anyway, this will recenter the proportioning valve and you can
then bleed the rears correctly.

 

For those of you with drum brakes. keep in mind that sometimes the rear brakes need to be adjusted manually. As the shoes wear , they don't always take up the slack. If pedal travel seems excessive yet the brakes work fine, then it's time to adjust the star wheels.

 

in addition to adjusting the rear brakes (its crucial!) there is also a couple of pages in the FSM about adjusting the push rod to the booster, and the master/booster clearance too.

also if the front wheel bearings are loose, it can push the front brake pistons all the way in, and when you hit the brakes the first push of the pedal will be low, with the second being normal.

 

No star wheel on an SA, I wish it was that easy.

Those damn adjusters on the SA drums suck because they get all frozen up
over the ages and are impossible to deal with. I replaced mine last year and made
sure they had coat of brake grease on em.

 

This is good stuff guys - will use all this to try to re-do mine this Spring Resurrection!
THANK YOU.

Stu Aull
80GS
Alaska

 

Good luck to you! I'm going to tackle the bleeding this weekend on my car. I hope I can get all the air out.

 

I have found that sometimes you need to pump the pedal very fast (through the full stroke) to get some of the hidden bubbles out of the system. I always do this:

one end of a clear hose that fits snugly over bleeder over the bleeder, the other end in a quart of brake fluid.

Fill MC

open bleeder

pump very fast through almost a whole MC of fluid

fill MC

close bleeder

rinse and repeat until firm pedal is found.

order: rear axle (drums) or Passenger Rear, drivers rear (disc), passenger front, driver front.

the small changes in direction in lines can cause air bubbles to get trapped. The fast pumping can help force air bubbles past these choke points.

 

Whitey - confused ...
I thought the idea of pumping was:
-open the bleeder on the push-stroke, close bleeder, release pedal,
-push-stroke-again as bleeder re-opened....
-repeat...
Presume your idea is to leave the bleeder open the whole time (which would be great because the above is soooo tedious....!)

How does the rapid stroke allow the air to work its way thru the brake line and out...
??
Thanks
Stu Aull
80GS
Alaska