no[little] power brakes assist

-
22dog22

22dog22

Well-Known Member
Joined
Oct 10, 2010
Messages
401
Reaction score
87
Location
northampton ,pa
have power brakes on my car, have fresh not fully broken in 318 with a comp cam, and high dome pistons, have just checked the engine vacuum with the engine warmed up at idle the best I get is 15 for vacuum, when I increase the engine rpms the vacuum does increase to about 18-20 for vacuum, my questions is will the vacuum amount increase as the engine breaks in ? if not I may need to look into a vacuum pump kit so I have good power brake assist. or maybe would a vacuum resiovor help ?
 
The amount of vacuum will basically not change as the engine breaks in. It's dependent on the camshaft.

The rule of thumb is you'd want about 18" of vacuum for power brakes to work correctly. You may be able to get by with having a vacuum canister if it seems to work well after you've cruised for a while.

Otherwise, I suggest just swapping to a manual setup with 15/16 master cylinder assuming you have the basic large bolt disk/10" rear drum setup.
 
15 inches is PLENTY enough vacuum to operate power brakes. Inspect the vacuum line and check valve. Start the engine and let it idle a minute or so. Then grab the check valve and unplug it from the brake booster. If you hear air rushing into the booster, the booster, check valve and hose are all good. If not, then it is not getting vacuum somehow. At that point, inspect the vacuum line closely for cracks, remove the check valve and verify that you can pull air through it from where the hose plugs in. If you cannot, it's bad. If you can and you've not found a crack in the hose then the booster is at fault.
 
thanks for the information, when I spoke to the company I bought the front power disc. brake kit from told me I need a min. of 16 hg, 18 would be best. I will check out what you say , also I will install a fitting into the intake manifold to draw vacuum direct I now have a 't' in the line at base of carb,so I can hook up the power brake booster and my pvc valve
 
You must log in or register to reply here.
-

Back
Top