Brake experts needed

Quick run down. 70 b body 4 wheel power drums. All new brake pads, wheel cylinders, and hardware. I had Ramman rebuild the booster and master cylinder. When driving the car it stops fine. (once in a while it hits harder on the brakes then you think it should with the given pedal pressure) But the main problem is after applying the brakes (say at a stop sign) When you let off it can take 3 seconds or longer for the pedal to come all the way back up and release the brakes fully. You can put your foot on the back side of the pedal and pull up. And it releases as soon as you do that. It stays down about 1 to 2 inches of pedal travel. Master cylinder sticking? Booster fubar? Thanks in advance.

How old are the hoses?

bad booster.

the catch when you are applying pressue and it suddenly brakes more is the internal check valve.
same for why it won't release.

you could do a little due dilligance and verify the pushrod adjustment is correct between the booster and master, but those symptoms are pretty clear.

I had same problem except front disc brakes grabbed and wouldn't release at all unless pet cock on caliper was loosened and fluid drained out. The fluid would not go back to the master cylinder because it was full of crud.
Make sure that the master cylinder is really clean and the shuttle valve is working smoothly.

As mentioned in previous post: replace the rubber hoses if old as they also act like one way valves if the inside linings are bad.

Sorry guys, forgot to say all new rubber hoses front and back also. I was afraid it was a booster issue. That one pesky nut took me forever to get to under the dash.

I don't think it is the booster, I think it has more to do with installation. Something is binding or too tight or missing or adjusted wrong. Got the primary and secondary shoes in the right places?

What did the Ramman say about it?

split the MC and booster & measure the rounded booster pushrod nub clearance to the bottom of the MC rear piston "thimble". want ~.020"

Yes, you have to have some free play between the pushrod and the master cylinder. Otherwise it just continues to build pressure and never releases correctly. Check that first before you do anything else. The pushrod should have an adjustment on the end.

Checked the pushrod looks good there. I did this test I got from the SSBC site.


This procedure will require the use of a hand operated vacuum pump with a vacuum gauge. If you do not own one it can often be rented or borrowed from most “big box” parts stores. (Note: 18”HG is the minimum engine vacuum at idle in gear to effectively operate a vacuum booster 1) Remove vacuum hose from check valve on booster. Place hose from vacuum pump onto check valve and draw booster to 20” of vacuum. 2) Let booster sit with vacuum applied for 5 minutes. If vacuum does not stay steady at 20” it is faulty and needs to be replaced. If vacuum does hold steady at 20” proceed to step 3. 3) With 20” of vacuum in booster depress brake pedal once and release it. The booster should transfer some but not the entire vacuum in reserve. Depending on how hard the pedal is depressed it is normal to see 5-10” of vacuum depleted from reserve. The most important thing is to ensure the booster does transfer vacuum but does NOT transfer the entire vacuum in its reserve. If vacuum remains at 20” OR goes to zero the booster is bad and will need to be replaced. If vacuum transfer is within the above parameter proceed to step 4. 4) Once again draw booster down to 20” of vacuum. Go inside car and depress brake pedal and hold down for 30 seconds. You should see the gauge drop slightly and then hold steady. Vacuum should stay steady as long as you are holding the pedal down. If vacuum drops while pedal is being held down the booster is faulty and will need to be replaced.




My booster held the 20"of vacuum. But when I pressed the pedal it lost 15" of vacuum. Taking it down to 5". And if I held the pedal it lost all vacuum. So if this is a relevant test. My booster looks to be bad.

Looks that way to me.

send it here, and send the bill later to Wayne... http://www.boosterdeweyexchange.com/

Loosen and lube the pivot bolts, especially the special bolt that connects to the pedal shaft.. leave it loose and try it.
then tighten after you confirm operation.

I'm going to give Booster Dewey a call today. And see what he thinks.

Good people.....

Received a call back from Booster Dewy already. Booster checks out bad. I guessed I learned my lesson with using the Ramman. But the good news is. It will work like it's suppose to soon.

Ramman doesn't have the greatest reputation. Seems he will sell but won't fix any mistakes.