Brake Booster working TOO much
 

Hey guys,

Finishing up a '71 Super Cheyenne and threw on a brake booster.

Unlike all the other threads I've found about this, I'm having the opposite problem. The brakes seem to get at full force with a minimum of effort, and the travel of the pedal is only about an inch to get that full force.

The wheels don't lock up, but it's concerning that they're so touchy and quick to grab that much.

Any thoughts? Thanks in advance.

Re: Brake Booster working TOO much
 

Did you adjust the booster so the rod that goes into the master is set right. Almost sounds like you have the rod length too long and it's already partially applying the brakes.

Re: Brake Booster working TOO much
 

X2
Exactly what I was thinking.

Re: Brake Booster working TOO much
 

X2 on Bigrig.
You need the power brake rod.
If I remember right, the manual is longer.
I did the same thing when I did the upgrade.
The first time I pressed the brake, I almost ate the steering wheel. :lol:
Just change out the rod and you're golden. :metal:

Re: Brake Booster working TOO much
 

Or adjust the rod ( Shorter ) if it's adjustable, mine was.

Re: Brake Booster working TOO much
 

Does this mean the pedal should be partially depressed when attached? The rod isn't long enough to attach when the pedal is up.

Re: Brake Booster working TOO much
 

Appreciate the heck out of the help, thanks.

I know it's always more fun when pics are involved...here are 2 before and 2 after...the patina on the hood was so gorgeous we fixed her up and did our best to re-paint the wear on the truck...a case of beer and 6 hours later we got her looking like this from rattle cans...took a mix of 3 colors, but got the match pretty darn close!

Re: Brake Booster working TOO much
 

Something doesn't sound right. There should be a pedal return spring that should pull the pedal back all the way against the rubber bumper under the steering column. The rod we are talking about you have to remove the master cylinder to access. It's between the master cylinder & the brake booster !

Re: Brake Booster working TOO much
 

So there's one adjuster under the dash and another between the master cylinder and the brake booster if I'm understanding correctly?

I'm trying to translate here between the guy doing the work and here...thanks again for the input!

Re: Brake Booster working TOO much
 

Yes, there are two places to possibly adjust .

If you had manual brakes and added a booster, and used the manual brake rod
( The one between the master cylinder & the booster ) the rod is most likely to long, and if it's adjustably it would need to be shortened, if it's not adjustable you may need to replace it with one from a power brake set-up.

Re: Brake Booster working TOO much
 

Here's a picture of the booster push rod I'm talking about. If it's to long your brakes could be dragging without even touching the pedal, or engage the brakes when you hardly even touch the pedal.

Re: Brake Booster working TOO much
 

It's the latter, engaging when you barely touch it.

Will get to it when I'm done with the day job and able to head over to the garage where we're working on it.

Again..lots of thanks.

I'm sure I'll be back with a few other questions down the road; next up is a C-20 we picked up, another '71 with 48k original miles...in great shape, or should I say shapes...it's largely disassembled.

I'll check back in if that's the issue, greatly appreciate y'all's time and effort to help out.

Re: Brake Booster working TOO much
 

Did you use a master cylinder meant for power brakes?

IIRC, power brakes also have a different attachment point on the brake pedal

Re: Brake Booster working TOO much
 

Wow....what a weekend.

So what happened...the booster was a used one we got with a mess of parts we accumulated from a build-gone-bad that the guy was just dumping everything he had for $1200...got a lot of good stuff, but the power steering pump had a hole in it and the brake booster...

the master cylinder was bad, and we did end up throwing the old manual one back on..mistake #1. Changed that out and it still wasn't working right, so step #2 was noticing the rod from the brake pedal was way off...removed that, redrilled the hole and installed again, only to realize that while it was working MUCH better, the pedal wasn't returning back up after letting off. After some hair pulling and head scratching we came to the realization that the spring in the booster wasn't acting right, so pulled another booster from the corner pile-o-parts and put that one in instead...it's a little slow on the spring-back, but the brakes aren't lagging/staying on, so i think we're in pretty good shape (whew).

Thanks for the input/advice/thoughts/help...very much appreciated!!

Re: Brake Booster working TOO much
 

Yup, if you just tap the booster and it hits hard, and doesn't fully return its internal valving problems.

Glad you found the issue!

Re: Brake Booster working TOO much
 

Ok I have heard you can grind down the pushrod that comes out the BB into the MC to be able to make it work better....does anyone know about how much grinding is needed? thanks

Re: Brake Booster working TOO much
 

With most things brake related grinding up to a 1/4" is good....

Re: Brake Booster working TOO much
 

Just a note:
The brake pedal doesn't go all the way back to the rubber bumper and rest. There should be some gap but can't remember what it is. :chevy:

Re: Brake Booster working TOO much
 

You used the manual master. So it probably had the RPV for a drum setup and was holding pressure on the disc. Were the brakes still touchy after changing the master to a disc drum? I used a drum drum master for quite a while, just removed the Valve on the disc side of the master. I recently changed to disc disc master though.

Re: Brake Booster working TOO much
 

Glad you got it sorted out. One more thing that might be worth mentioning - I believe there are two separate clevis pin locations on the brake pedal lever itself (i.e. the bar connected to your actual brake pedal). I believe the UPPER one is for manual (provides more mechanical leverage to a manual system) and the lower for power (less mechanical leverage needed or desired when a booster is used).

Re: Brake Booster working TOO much
 

I do not see another clevis pin location other than the original...If i try to drill another one lower im afraid my brake lights are going to stay on bcus the pedal will be moved down closer to the floor...can the brake light switch be adjusted if I do move it down?? Glad to see you are local Jocko...lol

Re: Brake Booster working TOO much
 

The switch can be adjusted by rotating the two nuts that clamp it in the metal opening. However, if you don't have another hole in the brake pedal rod to stick the clevis in, then I'm not sure I'd drill one. I should go look under my 72's dash - now that I think about it, this 2nd hole may have been a 60-66 thing... (the holes were about an inch apart on the pedal rod) Anyway, to answer your question - the switch is easily adjusted.

EDIT: pic of a brake light switch below (in a different bracket, but you get the idea) - not 2 nuts in this case, just a threaded shaft and one jam nut. Anyway - I went and checked both 72s in the barn, only a single hole. Sorry, I was thinking there were two, but that may have been my 66. I would not drill another one if there weren't two originally - should work without making a non-factory mod.

Re: Brake Booster working TOO much
 

Not sure but on some vehicles the diameter of the master cylinder piston is a different diameter on a disc brake set up vs. a drum set up.

made that mistake before, 15/16th dia. vs. 1 inch dia. makes a BIG difference and you feel it right away with a power booster

disc brakes usually have the larger diameter piston because disc brake calipers require a larger VOLUME of fluid to opperate

Re: Brake Booster working TOO much
 

Thanks for all the great info guys... I forgot to mention my 71 was originally a manual disc brake setup and I added a booster.... Im leaning more on replacing the pushrod inside the booster with the original one that was attached to the brake pedal bcus Im still using the original MC....