Brake booster vacuum

Trying to run down my vacuum issue. Car has been running with vacuum at 15-16. Couldn’t find a reason for the low vacuum. Disconnected the vacuum to the brake booster and my manifold vacuum reading jumped to about 20. Replaced the hose to the booster to eliminate that as the problem. Am I right to assume that manifold vacuum shouldn’t drop from 20 to 15 with a properly functioning brake booster? How much, if any, drop should the booster cause. I wasn’t expecting the brake booster to be the problem since my brakes perform pretty good.
Do I need a new brake booster or do I have any other options? (I haven’t seen any rebuild kits for a booster.)

Try replacing the connector to the booster. That is inexpensive, and if your brakes seem to be working fine it is worth a shot.


the brake booster should hold vacuum even when car is shut off. the one way valve on booster or rubber grommet might be at fault, but more than likely it is the booster itself. best way to test is with a vacuum pump to see if it holds vacuum. in most cases a previous leaking master cylinder allowed brake fluid inside the booster damaging it.

I wouldn’t mess around with brakes. They’re bad enough. Just replace the booster or find a brake shop that will rebuild yours.

After some further tests I agree that it is the booster itself. The current MC does not leak so I plan to just replace the booster. I’m just looking for something that works and is reliable. Anyone have a recommendation regarding midland vs. bendix? Brand? Most places have Cardone…anyone have issues with them?

Yea, I recently tried that with my brake bleeder pump, great way to watch a slow leak in the booster I have.

Cardone would be my last choice, I plan to get the MIdland from W.C.C.C., they say it has better performance than the Bendix.

Cardone are mix-n-match rebuilds from what I hear, may be odd ball specs.

Send it to Booster Dewey. End of problem!

I have a Midland currently, it looks like I would need a bracket to use a Bendix.

I would consider sending to Booster Dewey but I don’t want to have the car disabled while I wait.

Today at a show someone suggested that I replace the check valve as that is more likely the culprit than the booster. He says short of the master cylinder leaking into the booster he has rarely ever seen booster fail. Any comments?

Yes, check the valve and grommet for seal, but thats the easy part. Just suck on the booster end and make sure it seals. It’s like a $5 part, so I just put in a new one anyway. The old one leaked, but it was not the only place.

Lots of rubber seal in there to shrink, crack, and leak. Of course they fail or we would not have ‘Booster Dewey’.

Call WCCC. They may have a rebuilt in stock so your downtime wouldn’t be long. I think that they get theirs rebuilt from Booster Dewey anyway. You could also call Booster Dewey to see if he has any in stock and/or what the turn around time would be. In my research, I found references that said the Midland had more boost than the Bendix. I couldn’t determine if the comments about Bendix being more reliable were true or not. Sometimes the experiences get distorted and the conclusions aren’t correct. I got a Midland replacement since more boost is (I think) better.

Talked to Booster Dewey and he confirmed my suspicions of an early booster failure. I could probably have lived with it for a while longer but I didn’t want to live with low vacuum. So I’m using their exchange program and a rebuilt Midland booster is on the way. Thanks for all your help.

Booster Dewey: