Low vacuum for brakes.



Royal Smart Person
Jan 2, 2006
I'd try a canister first if I couldn't get vacuum up with fine tuning. Much cheaper option and you can still add a pump to the can/booster system if you're not happy and then you should have vacuum for days.

As for the canister, once you close the throttle, vacuum will spike and suck the air out of the canister and booster and as long as the check valve on the canister doesn't fail, you'd have the vacuum you need trapped in the can and booster. Bigger vacuum volume.

BTW, you did check your booster's check valve to verify it's operating correctly? A leaky check valve can cause havoc.


Sep 18, 2009
Queens, NY
My cousin just went through this on his '69 Cuda. Radical 340 with no vacuum to speak of. He had a vacuum can and a vacuum pump and still had crappy brakes. I told him to get a new (expensive) booster but he balked at that and kept putzing around with band-aid fixes. I finally found him a deal he could afford and he got the new booster. Like magic the brakes worked like a new car. So do as suggested and try getting the vacuum up but also try a known good, or new booster.
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Jan 6, 2019
Upstate SC
What can you tell me about the engine? I first would want to know how radical or not this engine is before deciding on where the fix should be. At idle the car should at least have a softer pedal. That is the best vacuum the car will develop.
I am not sure exactly, it is a 350 40 over, flat top pistons and aluminum heads. Thanks


Master Mechanic
Jan 18, 2018
I am not sure exactly, it is a 350 40 over, flat top pistons and aluminum heads. Thanks
The reason I am asking is because it is common to blame weak brakes on the cam, but it may not be as radical as you think. I had a 357 in my 78 Malibu with power brakes with a 250/260 @.050 duration solid lifter cam with .533/.555 lift with 10.5:1 compression. I never had a problem stopping it.
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