Another brake booster question
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Another brake booster question
Last year I had to replace my brake booster on my '85. I had read so much on here about the metal housing version being superior to the plastic one so I bought metal. Most of the time I have great brakes but every once in a while, usually right after startup I will step on the pedal to stop and it is almost like there is no vacuum to assist the pedal. I know I have plenty of vacuum before I even pull out of the garage because I installed a reservoir with a gauge on it so I could monitor vacuum. The engine holds about 12-14 inches of vacuum and it stays for a while after I shut off the engine. After the brakes fail the one time everything is fine when I use them again. This is such an unusually intermittent problem it is hard to tell just what the problem may be. I did not have this until I swapped boosters, (my plastic one had cracked) I'm just about convinced the metal booster is the problem but can't really tell. I'm hoping someone else may have had the same issue so they may shed some light on this. I am not going to buy another booster unless I can find a problem with the one I have.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
I'm going to assume that your reservoir is "before" the booster check valve and I don't know of an easy way to do it differently but you've added the reservoir so thought I might mention. Is that a correct assumption?
If it's as I assumed maybe just do a new check valve and grommet. Grommet only? I'd doubt.
I've no idea what these after-market folks are using for check valves but as inexpensive as they are I'd be "buying and trying"!!
You mentioned "intermittent" so .....................
If it's as I assumed maybe just do a new check valve and grommet. Grommet only? I'd doubt.
I've no idea what these after-market folks are using for check valves but as inexpensive as they are I'd be "buying and trying"!!
You mentioned "intermittent" so .....................
Last edited by WVZR-1; Jan 7, 2017 at 09:55 AM.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I do believe I found it, vacuum had nothing to do with it. The pushrod in the booster was too short by almost half an inch! I can't explain that one other than I made one hell of a mistake, or, the adjustment lock nut was not very snug so maybe it let the pushrod turn a fraction of a turn each time I pressed the pedal down. I have not driven it yet but the pedal feels great. Thanks for the responses guys. If I still have a problem I will post it.
Last edited by Midnight 85; Jan 7, 2017 at 08:04 PM.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
I do believe I found it, vacuum had nothing to do with it. The pushrod in the booster was too short by almost half an inch! I can't explain that one other than I made one hell of a mistake, or, the adjustment lock nut was not very snug so maybe it let the pushrod turn a fraction of a turn each time I pressed the pedal down. I have not driven it yet but the pedal feels great. Thanks for the responses guys. If I still have a problem I will post it.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I know, and I agree with you. I will just have to keep my fingers crossed until I can get it out. Our roads here are white with salt so it is staying in the garage.
Pro
Joined: Sep 2012
Posts: 610
Likes: 12
From: Seattle Wa
Mine just started doing the same thing. Let us know if you get it fixed. I figured it was the booster too, as it is intermittent like yours. My car sat in a heated garage for a couple years before I got it, so I had to replace a lot of rubber, just figured the booster had deteriated too. Maybe you got a bad booster, or a bad master cylinder? If the master leaks into the booster at all, even a little bit, it will destroy the new booster. Ask me how I know! Lol. h
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Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Mine just started doing the same thing. Let us know if you get it fixed. I figured it was the booster too, as it is intermittent like yours. My car sat in a heated garage for a couple years before I got it, so I had to replace a lot of rubber, just figured the booster had deteriated too. Maybe you got a bad booster, or a bad master cylinder? If the master leaks into the booster at all, even a little bit, it will destroy the new booster. Ask me how I know! Lol. h
Instructor
Joined: Sep 2013
Posts: 198
Likes: 2
I do believe I found it, vacuum had nothing to do with it. The pushrod in the booster was too short by almost half an inch! I can't explain that one other than I made one hell of a mistake, or, the adjustment lock nut was not very snug so maybe it let the pushrod turn a fraction of a turn each time I pressed the pedal down. I have not driven it yet but the pedal feels great. Thanks for the responses guys. If I still have a problem I will post it.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I put a long prybar between the brake pedal and the seat so I could get to the adjustable end of the rod. I then put a small dab of chassis grease in the cup on the master that the rod sits in. I adjusted the rod out a little and put the master back in place just holding it against the firewall. After several small moves I just barely saw grease on the tip of the rod. I then cleaned off the grease and placed a chalk mark on the rod snd fitted the master again. When I took it off I could judt see a speck of chalk on the tip so I locked the adjusters down, put another small dab of grease on the rod and put the master back on. It's just a trial and error thing until you get it where you want it.
Add: I'm sure everybody understood the fact that I removed the prybar so the rod was in the retracted position after each adjustment. Obviously, if you forget to do this you'll never get it right.
Add: I'm sure everybody understood the fact that I removed the prybar so the rod was in the retracted position after each adjustment. Obviously, if you forget to do this you'll never get it right.
Last edited by Midnight 85; Jan 8, 2017 at 09:35 AM.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
If you're reading this thread, you have probably seen "Red89"'s similar problem, but I'll post my answer anyway, just to be sure. After you get the pushrod between the booster and the m/c adjusted close to it's correct length, check your adjustment with this procedure:
https://www.corvetteforum.com/forums...ment-help.html
If you use any grease inside your m/c, be sure to get ALL of that grease removed! That will create havoc in your m/c! There should be NO petroleum products used in your hydraulic system!
https://www.corvetteforum.com/forums...ment-help.html
If you use any grease inside your m/c, be sure to get ALL of that grease removed! That will create havoc in your m/c! There should be NO petroleum products used in your hydraulic system!