1974 c10 New Reman Brake Booster/Master Low Pedal (Not Spongy)

[Cadillac Kid]

Hello everyone.


I hate having to do things twice,but I'm afraid thats what I'm going to have to do. When I got my 74' it had been sitting for 10 years. The brake booster/master were completely shot. My truck has factory HD Brakes (JB5) Dual diaphram booster. I replaced the booster/master with a Orilleys reman unit. I've used them in the past with no issues. I bench bled the master, bled the entire system about 4 different times, all brake parts and hoses are brand new with no leaks in the system. Here is where it gets complicated to explain, so please bear with me. The pedal feel is good, but it is too low to the floor. In other words, the hydraulic side of the brakes feel fine, it honestly feels like the booster is giving to much assist causing the low pedal. When you push the brakes it stops the truck sufficiently, but the pedal goes almost all the way to the floor. I have had a hand full of old cars and I know what spongy brakes feel like, this is not it.

Other symptoms are when the engine is idling and you push the brakes, the rpm increases. I am not sure if this is normal. I have never had a car that did this. The 2nd thing is that, in a normal car when you shut off the engine and push the brakes down a few times the pedal eventually gets hard, correct? Well in the truck when you pump the brakes after shutting the engine off, the brake pedal never hardens up and has the same consistency with each pump. And there is a hissing noise from the booster when doing this. Any ideas?

I've been told that my culprit could be the length of the pushrod between the booster and the master. But arent the pushrods on these GM booster non adjustable? I removed it when I purchased the unit to look at it, when I put it back in it sat at the same depth, no problems. Something is just not right.
The unit I bought has a limited lifetime warranty and I'm tempted to just rip it all out again and return it.

Completely unrelated, we had a small fire at my house yesterday, nobody hurt, all water damage, house is uninhabitable but I'll have to go back because I know the receipt for the booster is in there somewhere.
Problems like this are so hard to diagnose over the internet.
If you actually read this far I applaud you, and thank you!
Ah, life..

-Gavin

[nonstop]

Wow! Sorry about the fire, glad everyone is okay!

As for your question - two things come to mind - adjustment of the booster pushrod and/or pedal pushrod, or master cylinder bore. Too small of a bore will cause a lot of travel. Your symptoms sound similar to too small of a master cylinder bore. Oreilley and Autozone are generally fine for parts, but I like to go in there with the part numbers of what I want. That way I know what I am getting and have researched it first.

[Dead Parrot]

My replacement booster from Autozone was adjustable. Don't know about the OE booster.

Yes, a normal booster will hold enough vacuum for a few pedal pushes, then you have to push much harder to get the brakes to work. It should hiss somewhere in the process until the vacuum is gone.

Idle increasing when pressing brakes is odd IMO. Mine doesn't do it.

Sounds like yours isn't holding a vacuum or isn't getting a vacuum to begin with.

Good luck on recovering your stuff from the house.

[Cadillac Kid]

Thanks for the quick responses guys!

Originally Posted by nonstop

As for your question - two things come to mind - adjustment of the booster pushrod and/or pedal pushrod, or master cylinder bore. Too small of a bore will cause a lot of travel. Your symptoms sound similar to too small of a master cylinder bore. Oreilley and Autozone are generally fine for parts, but I like to go in there with the part numbers of what I want. That way I know what I am getting and have researched it first.

I am the same way. I always look at their website and write down part numbers before I go in and buy parts. I bought the booster/master together as one item. It was only about $10 more to buy it with the master, so you wouldn't think that the master cyclnder bore would be the wrong depth/size, but who knows these days? I think the brake pedal pushrod is not a problem because as it sits right now, the brake pedal sits much higher than the gas pedal. And the adjustment rod is turned all the way in. Its actually so high that it bothers me, but I can worry about that later because I dont think it contributing to the problem.

For what its worth, I've only driven the truck around the block a few times. It's still unregistered, and has a leaky radiator. But on the road and even in the driveway, you can tell the brakes aren't right. I'm kinda reluctant to get the same unit again. If I'm going to do all of this work again, I dont want to be doing it a third time.

Thanks

-Gavin