Dead space!!

[newschool72]

I need a little help from the brake gurus on my brake system. I have front and rear brakes from ABS on my 72 Camaro. 13" with 4 piston calipers on all four corners, 1 1/8" bore dual master with vacuum power.
My problem is about 1 1/2-2" of dead pedal before the brakes start doing their thing. It was much worse before I drilled a new hole in my brake pedal shaft in a lower position to give the booster rod a straighter push into the master, but it still has more than it should, in my opinion. I have bleed the whole system several times, but it makes no difference.
Anyone have this problem in the past? Everything is new with less than 130 miles. Could it be a bad booster? Or......... Thanks in advance for the advise.

[dontlifttoshift]

Sounds like to much free play between the booster and master cylinder.

[newschool72]

Interesting theory . How would I check that? The booster/master came as a complete unit from ABS and I never separated them. I just double checked for tightness and called it good.

[dontlifttoshift]

We have a tool, I can't find a a picture of it at the moment. We got it from MasterPowerBrakes. You are looking for .020" to .025" clearance. between the piston in the master and the pushrod or pin that comes out of the booster.

[newschool72]

How would you go about adjusting clearance. If that is my problem, I would assume too much clearance?

[Racerxtx]

You say you didn't separate the master from the booster.
It may have the wrong push rod in there, or it's missing completely.

[newschool72]

It could be that, I guess. I did have to extend the rod that connects the booster to the brake pedal because the pedal would be just about right on the floor if I hooked it up to the booster at the length it came from ABS.

[newschool72]

Anyone else with some ideas? I want to fix this problem once and for all. Im almost at the point of buying a new booster/master set-up. The more I think about it ,the more I think ABS sent me the wrong unit. It has been a battle with that company from the start with this brake setup.

[dontlifttoshift]

So that wasn't the problem?

[newschool72]

I havent checked it. To be honest, I dont know how to check the clearance. Are you talking about the freeplay in the pushrod?

[dontlifttoshift]

Here is a quick writeup of how to use the tool. CPP part number CP2003.


http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#pushrod

70875

Here is a generic, less precise way to do it. If you use this method and make progress then you are on the right track. http://www.doityourself.com/stry/how-to-perform-a-brake-booster-push-rod-adjustment


Diagnosing problems in any system must be methodical or you will waste time and money chasing your tail.

Let us know what you find.

[newschool72]

Thanks Donny. I will separate the master and booster and lengthen the rod, then check for a difference. First up, I will have my son help me do the fluid test in the master. At one time ,going back and forth with ABS the tech had me check the fluid rush thing and it moved fluid but Im not sure how far my son pushed the pedal during the test. I will have to come up with a way to regulate that variable . Thanks again.

[newschool72]

There shouldnt be any reason for fluid to come out of the system by separating the master from the booster, right? I just want to make sure before I do it because I dont want brake fluid eating the paint off my frame. I should be able to manipulate the master by gently bending the brake lines to get to the rod.

[dontlifttoshift]

No fluid will come out when separating the master from the booster.

[exwestracer]

While you have it apart, check that the booster output rod moves immediately when you press on the brake pedal. No reason I can think of that it shouldn't, but that will at least eliminate lag through the booster and pedal as a possibility.

[newschool72]

Will do. Thanks for the input. If I can shake this Superbowl hangover, I might work on it this evening.

[newschool72]

Donny, it seems to have worked. I separated the booster/master and found the adjustment bolt at the end of the rod was somewhat loose and had a sideways taper. I straightened the taper out and lengthened the rod by 3/16ths, to take a big swing at it, and the brakes feel very good now. Unfortunatly the 72 is really low on fuel and I have a sick 6yr old with the flu, so I just drove around the yard and hit the brakes 10-12 times. I will drive some distance at some point next week to make sure I didnt go too far with the adjustment.
Thanks again for the assist! David