Engine Vacuum and Power Brakes

[Alabama65stang]

I just finished degreeing my cam, new rings and finally getting everything tuned. The car runs better than it ever has...except for the power brakes now. I don't know if it is a problem with the power brake unit or lack of engine vacuum. At idle the vacuum guage is about 12-15. I don't know what it was before I did the work. What kind of vacuum is normal and what is the minimum needed to make power brakes work right?

The PB unit is off a 78 Fairmont. Ignition timing is at 13 degrees BTDC and idle speed about 700 rpm.

Thanks for your input.

 

[rbohm]

8) you dont have enough vacuum to operate the power brake system properly. you can solve this by adding an electric vacuum pump from a mid 80's olds diesel or from a cadillac.

 

[LaGrasta]

yeah, you really want at least 18. Cams will lower your vacuume; thus making it difficult for items such as boosters. the external vacuume suggested by rbohm will solve this for you.
Your only other alternative is to sacrifice your cam power and retune the car. One thing to check first though, tap into the closest area near the carb base/intake manifold. You might get lucky and pick up a few pounds there.

 

[addo]

A vacuum reservoir used to be the standard way for achieving the result needed. Surely that's possible?

 

[Alabama65stang]

Advanced the timing a little and got a little more vacuum. Brakes work fine slowing from cruising speed, pedal is really hard when idling though. Any suggestions on what kind of vehicle to look for a vacuum reservoir on??

 

[addo]

Over here, they seemed to come in the barges and "GT" versions of Ford stuff. The check valve is transferred to the reservoir, with a direct hose to the booster.

 

[wallaka]

If nothing else, switch to a "hard pedal" like I have and get a workout while you drive! Also, I've seen hydroboost setups used where vacuum and space are limited. Power steering pump to booster from Chebby Astro van booster/MC. Probably overkill for your situation, though.