How can I tell if my brake booster is bad?

[67chevy2wd]

On my 71 it feels like the manual brakes did in my 67. I really have to get after it sometimes to stop the truck. Someday I want to put 35's on it and I know I need to get the brakes sorted out first. Now that I think about it the wife helped me tow the 71 home the other night (distributor died) and I had both feet on the brake pedal pushing damn near as hard as I could and the wheels wouldn't lock up on a gravel road. Plus they (the brakes) didn't feel any different from when it is running.

[Piece of Work]

Start your truck and let it idle. Pull the vacuum line off the booster. If the idle drops, the booster is good, if it stays the same, the booster is bad. To check the vacuum, put your finger over the end of the hose, the idle will increase if you are drawing enough vacuum.

[68 TT]

Originally Posted by 67chevy2wd

On my 71 it feels like the manual brakes did in my 67. I really have to get after it sometimes to stop the truck. Someday I want to put 35's on it and I know I need to get the brakes sorted out first. Now that I think about it the wife helped me tow the 71 home the other night (distributor died) and I had both feet on the brake pedal pushing damn near as hard as I could and the wheels wouldn't lock up on a gravel road. Plus they (the brakes) didn't feel any different from when it is running.

How hard the brakes are to apply is a pretty good sign the booster isn't working or the vacuum supply to the booster is poor.

First check that the fitting to the brake booster is still in one piece. Some designs have a cap in the middle of the plastic fitting that can come out so you have complete vacuum loss. I have had it happen twice now on different vehicles. A 70 and a 72 Chevy so yours could have the same POS part on it.

Second check to make sure you have good vacuum to the booster. Pull the fitting out of the booster with the engine running and see if the supply line is pulling a vacuum. If it is pulling vacuum then hook it back up to the booster and let it run for minute or two and shut the engine off.

Pull the vacuum supply line off with the engine off now. If the booster doesn't pop from the vacuum loss when you pull the fitting out then the booster has a leak. They will hold vacuum for quite a while after being parked if they are good. Several days or longer.