1978 Pontiac Bonneville needs more brake vacuum?

Asked by Jun 05, 2014 at 08:24 PM about the 1978 Pontiac Bonneville

Question type: Maintenance & Repair

Okay. So I'm fixing up this 78
Bonneville and the thing is, it's been
sitting because of a problem no one
wanted to fix about 10 years back.
My uncle switched engines and
dropped a 400 hp 6.6 L engine in it.
The problem is...the brake booster
doesnt have enough vacuum in it to
stop the car...it has about 6 lbs and I
need somewhere above 11 lbs...how
can i increase vacuum? Thanks!

4 Answers


An engine that size should have excellent vacuum, enough to run your booster, test the vacuum inches at the manifold supply port then compare it to the vacuum at the supply hose at the booster, the readings should be the same, if not, there is a problem with the supply line, if it is the same, but drops when you hook it up to the manifold vacuum then there is a leak in the booster. HTH

Best Answer Mark helpful

Unless the engine is supercharged then it won't work that way at all. You will have to install an auxiliary vacuum pump on the engine to provide enough stable supply for your brakes.

You know alot about this can you get in touch with me?


I guess I could, give me your number or e-mail and I'll try to get back to you in the afternoon pacific time, got a lot going on Friday..

Your Answer


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