Master cylinder push rod problem

[gtwiggy]

So I’ve been reading these forums for a long time while building my 69 Camaro, but now I find myself needing a little help from those with more experience than myself. So I’ve got a small brake problem that I can’t seem to figure out. Here is the basis of the issue. I have installed a complete Baer brake package (front and rear discs with PBR style calipers) that came with a master cylinder from Baer to use for this application. Other than the fact that the reservoirs are reversed (front bowl feeds back brakes etc.) it seems fairly typical and has a deep push rod hole.
When I mounted everything up, I found that I had to push on the master to be able to get the nuts on. This lead to the master being preloaded and I couldn’t bleed the brakes. The main cause at the time wasthe push rod between the booster and the pedal was too long. I tried to shorten the rod by turning the clevis but wound up with the rod shoved in the back of the pedal and still too much preload. I wound up cutting an inch off the threaded rod put it all back together and can now adjust the pedal so there is no booster preload, and the pedal arm is just short of the bump stop. Yes the pushrod is in the lower hole which I read is a common mistake. So here isthe current dilemma. Everything I have read says that there should be a 1/4 to 1/2 inch of pedal "freeplay”. I’m not sure what this eludes to exactly but I believe it’s the amount of space that the pedal can travel before the booster side pushrod bottoms in the master cylinder bore and begins to compress the master plunger.
I have measured the depth of the master bore and it appears to be approx. 1.75 inches I also measured the length of the booster pin as it protrudes from the face of the relaxed booster and it is at approx. 1.61 inches. So if everything is bolted up and there is no more pedal preload that gives me about 1/10 of an inch of "freeplay”. Is that enough? Is there something that can be done about it? And if so what?
The pushrod is nonadjustable and the shorter rod all but disappears into the booster and would never work to compress the plunger. Help please if you have experience in this issue.
Gary














































So this is the project


496 Big block booster mounted to firewall after having the pedal pushrod cut to eliminate preload on booster

















Pedal now sits just short of bumpstop





























pushrod height with pedal at rest approx. 1.61















Master cylinder bore hole depth approx. 1.75


Brakes look good just cant get them to work yet.

[JD'sTT55]

Gary, it sounds like to me you got the mounting issues solved and just need to bleed the brakes. How you described the booster and master cylinder rod clearances should be ok. So to begin with did you bench bleed the master cylinder? If so are you able to get fluid out to all the calipers now?

[gtwiggy]

I did bench bleed originally but once I "pushed" the master onto the booster, the preload prevented any fluid from flowing. Or so I was told by Baer brakes. Since I have it the pedal rod I have not bolted the master back up. Iw as waiting for insight on the small amount of push rod Clearence before I bolt it all together and bleed again. So many things I read said that you can adjust freeplay but with this booster I don't see how short of switching pistons or by grinding some off of the long piston or by spacing master with washers. If you think that .10 is enough, I'll hook it up tonite try to bleed it and get back with you. Thanks for the input.
Gary