I have been working on Liz's 68 trying to run down some brake (among many other) problems.

Background:
The car had manual brakes when she bought it about 8 years ago. They did not work well so she had someone put power brakes (vacuum booster, and correct master cylinder) on it. She was satisfied with it for years, but the first time I drove the car I could tell the brakes were severely lacking in stopping power.

I replaced all the calipers, master cylinder, and hoses only to find that the brakes were worse than before.
Then I checked the vacuum to the booster and found that it was only getting about 8-9 inches of vacuum. Apparently the booster needs at least 16 inches in order to work properly. I'm sure the vacuum issue is due to the big cam she has in it, not due to leaks.

I ordered and installed a electric vacuum pump, and had the rotors turned. Big improvement, but the brakes still didn't work or feel as good as they do on my 73. I decided I should crawl under the dash(es) of both cars and compare the setups to see if there were any differences.
I soon found the problem(s). The booster on her car is mounted incorrectly. The push rod clevis for power brakes is supposed to connect to the bottom hole in the brake pedal with power brakes, but on her car it was connected to the top hole. Whoever put the booster on her car didn't bother to read the direction on how to mount the thing properly, and drilled four new holes in the firewall (and pedal assembly) so he could mount it higher than intended.

The other problem I found today while taking everything apart again was that the push rod between the booster and MC is the short style, and the MC has the deep hole that requires the longer rod.

I have removed the booster so I can glass up the holes in the firewall and re-mount it in the correct position, and I have pulled the pedal assembly out to rebuild it (the pin to connect the clutch push rod to the pedal was broken too). I have found all the parts I need so far except the booster-MC push rod.

Does anyone know where I can buy the longer push rod?
Failing that, does anyone know the proper length of the long push rod so I can just make one?

Thanks

 

If I remember right its 3.750

 

One for the short master is 4.67" so the long one has to be around 1-1/2" longer. I can measure one tomorrow.

 

Your right,that doesn't sound correct,hold off Kevin one of us will get you the correct length. I have an old mast/booster combo in the shed,I'll pop it apart and measure if Noonie doesn't beat me to to it.

edit - snows coming down, its cold and I can't get the door open on the shed so I searched for previous posts.
Here is one of mine from awhile ago,now I'm confused.
OK 2nd edit- I made my way through the snow ( little whine ! ) and dug out what I believe to be an original 73 mast/booster combo and the "adjustable" pushrod measured 6 1/4".
Kevin, the original type boosters use a different style of pushrod than the aftermarket boosters. To further complicate things the aftermarket is matching up some odd masters cylinders to the boosters.I ordered one in last year and it was shipped with brass adapters for the lines because the fitting sizes were reversed.
You might have to figure out the correct length for your combination.
I posted some pics in another thread of the 2 different style boosters,I'll see if I can find them.
Here is a pic of the master they sent me with adapters and a shallow hole piston.

 

I seem to recall that the original rod in my 73 was an adjustable one, and I thought it was ~6" long.
It appears that the combination I am looking at now needs one about 3.875". I didn't realize there was that much variance in these things.
I think I am just going to have to make one to be sure I have the correct length.

Thanks for the help guys.

 

I measured the oem long adjusted properly and it is 6.154" long.
The short rod at 4.67" works with the short master on the same booster.
Full stroke of the oem pb master piston assembly is only 1.17"

You might have a non corvette booster, because a oem short rod with a oem deep master would result in no piston movement at all.
The booster to firewall mounts are the same on many boosters.

 

I am pretty sure I have a cheap Chinese knock off booster since the firewall mounting studs are all metric threads, and the case is stamped steel instead of cast.

 

lets see some other views of this photo / the cover i can tell you in NOT correct, does it have bleeders ?

 

Sorry I don't have any more pics of this piece. The only reason I took a pic was to point out the 2 line holes are reversed , the vendor put in the brass adapters so it would work Not sure what it came off of but it sure didn't go on anything I was working on,it went back for a refund.