Brake power booster
Thread Starter
Pro
Joined: Jun 2000
Posts: 732
Likes: 0
From: Goshen NY
Brake power booster
I purchased a new master cylinder and calipers for my ’80 vette. Long story short…It seems some years ago bubba replaced the power booster and MC with a late model GM booster. The booster has an adjustable push rod which actuated the master cylinder. The old MC had a counter bore so that the push rod penetrated into the MC about 1.5”. The new MC does not have this counter bore and the push rod needs to sits flush. I shortened the push rod by the difference between the old and new MC. Now when I bleed the brakes the rear bleed okay, the fronts do not bleed. I am thinking the MC piston is not coming back far enough. How can I determine the correct length of the push rod?
Or should I stop screwing with it and buy the correct power booster? I am trying to avoid this because getting to the bolts does not seem like fun.
Or should I stop screwing with it and buy the correct power booster? I am trying to avoid this because getting to the bolts does not seem like fun.
Melting Slicks
Joined: Aug 2001
Posts: 3,050
Likes: 124
From: Wichita KS
Remove the driver's seat to give you more room to work. Get a socket with a built in universal joint to access the fasteners (only one is really any problem).
Burning Brakes
Joined: Oct 2006
Posts: 1,006
Likes: 28
From: Lutz Florida
I purchased a new master cylinder and calipers for my ’80 vette. Long story short…It seems some years ago bubba replaced the power booster and MC with a late model GM booster. The booster has an adjustable push rod which actuated the master cylinder. The old MC had a counter bore so that the push rod penetrated into the MC about 1.5”. The new MC does not have this counter bore and the push rod needs to sits flush. I shortened the push rod by the difference between the old and new MC. Now when I bleed the brakes the rear bleed okay, the fronts do not bleed. I am thinking the MC piston is not coming back far enough. How can I determine the correct length of the push rod?
Or should I stop screwing with it and buy the correct power booster? I am trying to avoid this because getting to the bolts does not seem like fun.
Or should I stop screwing with it and buy the correct power booster? I am trying to avoid this because getting to the bolts does not seem like fun.
Possibly either (A) Bubba replaced the master cylinder/booster unit with an earlier design (like mine) or (B) you got the wrong replacement master cylinder. The bore diameters are different, I believe, between a MC for power brakes and one for manual brakes, and one has a deeper inset for the rod than the other.
Hopefully somone else will chime in with more info to help you.
Burning Brakes
Joined: Oct 2006
Posts: 1,006
Likes: 28
From: Lutz Florida
I found something that may help. Go to http://mbmbrakeboosters.com and download and look at the "technical guide". It is for their products but there is a lot of useful general info that may help.
Good luck.
Good luck.
