You may need more vacuum here

Question:

I have a 427 Ford engine in a 1948 Ford pickup truck. The engine has been built up some with an 11:1 compression and a solid lifter cam with a .574-inch lift. I have installed a vacuum pump and have run lines in various configurations to the C6 transmission, the 8” booster brake unit, and the engine.

But I can’t seem to hit on the best possible results. I have installed not one but two vacuum canisters that connect to each other to add some storage to the system. Each change has different results. Sometimes I have a harder brake pedal but the engine idles correctly upon coming to a stop while another method results in a better brake pedal but the engine wants to stall when coming to what I would call a normal stop. However, if I needed to stop fast, the engine would quit. Also, I have run the correct vacuum hose. The tranny line is 1/4” while the brake line is 3/8” and the engine line is 5/16.”

Is there a proper way to run vacuum? I have 20-inches of vacuum coming from the pump that runs directly to the booster with a line tapped into that to the vacuum tanks where I then ran lines to the tranny and engine. Do you have any suggestions that might help me out?

Answer:

As a preliminary question you should determine whether or not your engine makes sufficient manifold vacuum to support the power brake booster and transmission modulator.

The engine’s compression ratio, cam type, and even cam lift don’t mean much as far as vacuum is concerned. Just how much vacuum is “normal” for your engine depends on various other factors, including intake manifold design, intake and exhaust valve duration and overlap, valve size, etc.

If your engine is functioning normally, which is to say there are no vacuum leaks or other malfunctions that are causing it to make less vacuum than it is capable of, and there’s still not enough vacuum to support brake booster and transmission modulator function, then you have several options.

You can convert to manual brakes, eliminating the need to deliver vacuum to the booster. You can change the camshaft, cylinder heads, and/or intake manifold to enable the engine to produce more vacuum.

If you don’t want to make changes to the engine, you can add a supplemental electric vacuum pump to your truck. There are aftermarket electric vacuum pumps or you can buy a used or new OEM unit.

Various GM vehicles, including the 1982-85 Buick Skylark-X, 1982-84 Oldsmobile Omega-X, 1984-86 Chevrolet Celebrity-A, 1982-85 Citation-X, 198284 Pontiac Phoenix-X, 1985-86 Pontiac 6000, and 1982 Cadillac Cimarron, Olds Firenza-J, Caprice-B, Cavalier-J, J2000, and Skyhawk-J, were factory equipped with supplemental electric vacuum pump systems. There are still plenty of salvage yard units out there and the pump assembly is normally located on the driver side fender well.

You may also be able to buy a new one (GM part #22034995). Master Power Brakes (mpbrakes.com) sells a complete kit with an automatic switch to turn the pump on when vacuum is needed and check valves to prevent vacuum from “flowing” in the wrong direction. The kit retails for about $345.