[j cAT]

Originally Posted by Ol'Jim

I put a vacuum gauge on the manifold port, and at idle, it only creates 3-5" of vac @ 1200 RPM. Increasing idle speed to 2,000 RPM produced about 8" of suction. If I bring the engine up to 3500 RPM, then quiclkly close the throttle, the vacuum spikes briefly to 10 inches. I then pulled the check valve out of the booster, and it did have stored vacuum in it. I unbolted the master cylinder, and moved it forward away from the booster, just to check the pedal action and resistance of the booster. Almost zero effort required to move the pedal to the floor. And the pushrod from the booster extends far enough out to ensure full travel of the M.C. pistons. So I am thinking the booster is fine, but it is simply not getting enough engine vacuum, because of the long-duration cam. Wondering if I should switch over to a manual-brake (non-power) master cylinder? Although I would still think that the 10-11" of vacuum produced during deceleration should be enough to provide some power braking effect from the booster?

you need 15 inches of vacuum .. you have a big leak somewhere ..