New booster, now sticky brakes

[Trimpe.bob@gmail.com]

I installed a new brake booster and now I have LOTS of brakes! Anything more than minimal pressure and the brakes are on hard.

i was careful to measure the lengths of the brake rods and the master cylinder rod, so the new booster is set up exactly the same. They don’t seem to be hanging up; none of the wheels show excessive heat after a short drive. The brakes worked ok before the booster swap; the old booster just had an air leak. 

any suggestions?

Edited February 10, 2021 by Trimpe.bob@gmail.com

[Zed Head]

Must be nobody looking because this is - first! - a classic sign of a missing reaction disc.  A rubber disc between the rod and the booster surface that sometimes falls out and ends up in the bottom of the booster.

Search "reaction disc" and you'll find a bunch.

[Terrapin Z]

I agree with Zed Head, Reaction disc. Happens a lot and had to tell if you are not looking out for it. 

Most gue them back on to the push rod piece. The manual says to use grease, but I didn't think that would hold as well. 

 

Edited February 10, 2021 by Terrapin Z
Double pic's

[Trimpe.bob@gmail.com]

So this disc is inside the booster?  Is that item 18 in the drawing? 

[Terrapin Z]

Yes #18 it sits in the pocket normally but when pulled out even just enough it can fall off and ends up in the bottom of the booster. 

Hard to get out with the booster still mounted in the car. Usually have to pull the booster and shake it around until you can grab the little sucker. 

[Trimpe.bob@gmail.com]

I’m trying to remember, but I seem to recall that when I pulled the rod out of the booster, it was just that - a rod. I didn’t see a steel cup, never mind a rubber disc. Am I missing more than a reaction disc?

[Terrapin Z]

In the 240Z booster there would be a lock washer type plate as seen in the pic here, down in the plunger hole. (not shown in book diagram) 

Then the three pieces in my first picture above a disc with the rubber seal (#1), the plunger itself (#2) and the reaction disc (#18)

I found all this out a while ago when I bought a rebuilt booster from MSA. I don't know when the disc was lost, but it was not where it was supposed to be. 

I had brake problems as you describe. With the reaction disc out of place you would had to have readjusted the plunger rod to get any brakes as you would be missing a quarter inch of set up. 

 

[Diseazd]

Amazing what that little rubber disc does. I am very surprised that no one makes a replacement disc so you wouldn’t have to pull the booster, but I’ve never seen one offered. I super glued mine on to keep it from falling off on installation.

[Trimpe.bob@gmail.com]

I pulled the booster out. Mine doesn't look like the factory pic. I don't see a plunger with a rubber disc on the end. The rod is attached to a large disc and it is captured by the spring, won't pull out.

I don't see or hear anything rattling around. 

 

[Terrapin Z]

That does look strange, Where did you get the Booster? 

Was there a lock washer and seal disc in there? It looks like scrape marks where the lock washer was pulled out. 

It almost looks like the spring is in backwards. If you look at my third picture above the spring gets larger toward the back.

Yours looks to me like it gets smaller in the back thus blocking the plunger.

The rod should be attached to the plunger piece and the reaction disc is on the back side of that. They usually come right out with no interference from the spring.

Did you send your old booster in for a core? If not maybe compare the two.

[Trimpe.bob@gmail.com]

The booster is from Autozone. I sorely regret turning in the core. The was a lock washer and seal in the unit. I took them out.

 

since I have it out, and it came with a warranty, I may see about getting a replacement, just because. 

Edited February 11, 2021 by Trimpe.bob@gmail.com

[Terrapin Z]

2 minutes ago, Trimpe.bob@gmail.com said:

The booster is from Autozone. I sorely regret turning in the core. The was a lock washer and seal in the unit. I took them out.

If you bought it recently maybe they still have it in with their cores, They usually don't get picked up until they have a good amount to make the load haul worthwhile. It would be worth a shot to ask.

If it is gone I would at least try and get it swapped out for another one. Explain the issue with the brakes and content you think it was rebuilt incorrectly. 

If the spring is on backwards it will not push against the diaphragm correctly and will not function as intended. Auto Zone  should get you another one. Those stores often get bad rebuilds with core product (reman's)