Brake booster issue.

[darndart]

I have a 72 Duster with OE 73 Disc brakes and 11” drums in the rear. When I bought the car, it was manual brakes. I recently added a 73^ original power booster. As soon as I hook up vacuum to the booster, the brakes apply themselves. Is there something wrong with the booster? Is there some type of adjustment that would stop this?

 

[Dana67Dart]

Either the booster is defective OR the brake pedal linkage is not correct and is depressing the booster as if you had your foot on the brake pedal.

When you apply pressure does the pedal also go down?

Does the booster lockup the brakes?

Go to mymopar.com and get your cars factory service manual might have to get the year before or or Plymouth vs Dodge.

Also Google "Chrysler master tech video power brakes" and see what they have to say

 

[Professor Fate]

I can't tell in your picture, but did you also install the master cylinder spacer/booster filter assembly?

If you did not, the master cylinder will be partially applied when bolted to the booster.

 

[darndart]

Either the booster is defective OR the brake pedal linkage is not correct and is depressing the booster as if you had your foot on the brake pedal.

When you apply pressure does the pedal also go down?

Does the booster lockup the brakes?

Go to mymopar.com and get your cars factory service manual might have to get the year before or or Plymouth vs Dodge.

Also Google "Chrysler master tech video power brakes" and see what they have to say

Yes, the booster locks up the brakes without touching the panel when the vacuum line is installed.

 

[darndart]

I can't tell in your picture, but did you also install the master cylinder spacer/booster filter assembly?
View attachment 1716433413
If you did not, the master cylinder will be partially applied when bolted to the booster.

I will check for that, but I’m pretty sure it’s there. I will remove the master cylinder and take a picture.

 

[Dana67Dart]

Yes, the booster locks up the brakes without touching the panel when the vacuum line is installed

Disconnect the brake pedal linkage and see if it still doescit

 

[darndart]

UPDATE: I adjusted the rod and replaced the vacuum valve, and it still does the same thing, as soon as you start the engine, the brakes apply themselves. So I pulled the brake booster off of my 72 demon and installed it on the duster and now it doesn’t do it anymore. But I believe the diaphragm may be leaking in the demon booster, because when I touch the brake pedal the RPMs go up about 300 to 400, which would normally indicate a vacuum leak.

 

[RustyRatRod]

Sounds like the return spring in the other booster is broken. When that happens, it will suck the diaphragm and apply the brakes.