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Another booster question
I had my booster rebuilt by A-1 Cardone a couple years ago, but my pedal has always felt pretty stiff. Now granted I have had 2 engines with bigger cams, and my vacuum has been under 15 hg. Will this NOT operate the booster at all? I tried the test the other night of keeping my foot on the brake pedal when I started it, and the pedal did not move at all. None of this is to say my brakes are bad, they aren't. They are just very stiff. I'm just trying to figure out if my booster is working at all? Any info or insight would be appreciated!! Thanks!!
For the booster test to work you need to pump the brakes pedal a few times, with engine off, to make sure all of the vacuum is out of the booster before starting the engine with your foot on the pedal.

Did you replace the check valve when you replaced the booster?

Did you adjust the push rod gap?

Connect a vacuum pump and gauge to it to see if it holds vacuum.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
Run the car few minutes, then shut off. Pull the vacuum line off booster and listen for the swoosh of air. If you don't hear anything, booster isn't holding vacuum. Do same test again but let motor sit for an hour after running, then pull line off booster, should still hear a swoosh of air. Booster should hold a vacuum for a while. If not could be booster or check valve.


1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]

At 15 it should run well. Have you ever changed the master cylinder? Maybe the bore is too big.

Sent from my SAMSUNG-SM-G930A using Tapatalk

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
If you have a brake bleeding vacuum pump they usually come with adapters so you can check the brake booster. Should hold a vacuum and not leak. The master cylinder should have a 15/16" dia. piston for PDB and 1" for no power.

When a man is in the woods and talks and no women are there is he still wrong??
Another thought, the brake pedal rod cannot be pressing on the control valve in the booster, it also have to have clearance. For instance, if the rubber bumper is too big and doesn't allow the brake pedal to fully release it will cause problems.

You can look at post #8 in this thread to see how the booster and parts fit together.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
They did install a new check valve when rebuilt. And I actually paid a garage to adjust the push rod because I didn't know how. I did replace the MC, but just with a parts house replacement, I did not check that the bore was a certain size. I do have a mighty mite vacuum pump and I believe I have the adapter. I will try the few tests you guys descibed and will get back to you. Thank You Gents!! Always so much knowledge on this site!!
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