testing power brake booster - JeepForum.com
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post #1 of 5 Old 08-01-2021, 07:10 AM Thread Starter
fibersport
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testing power brake booster

My '84 has manual brakes. The previous owner gave me a well used power brake booster and master cylinder that he never put on. I plan on replacing (or rebuilding) the master cylinder however I have no idea of the condition of the booster. Is there an easy way to test it off the vehicle to make sure it's good? I would rather not install it only to find out it's shot.


1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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post #2 of 5 Old 08-01-2021, 03:21 PM
devildog80
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Waiting for response on this too, as I just got a 1980 OEM booster from a friend, and it was working just a few months back when he replaced it with a new one on his rig. Also, aside from the outside metal, is there a way to possibly treat the inside bladder with something that would "refresh" it? And can these be bench rebuilt, rather than replace the whole thing?
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post #3 of 5 Old 08-01-2021, 03:56 PM
Mongo228
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This can be done off-vehicle, or still mounted.

You'll need the check valve for the booster if you don't have one, and the proper vacuum line.

Connect the tube to a vacuum source (vacuum pump of one flavor or another), or a vacuum port on a vehicle. The booster can be installed or not. Apply vacuum, roughly 20 inches Hg or 10 PSI (1 psi ~~ 2" Hg). Disconnect the booster from the vacuum source.

If you're able to easily "pump" the plunger a couple of times by hand, the booster is working and holding vacuum. After that, it gets HARD to depress the plunger by hand.

There's supposed to be a "bench test" to see if the diaphragm is good just by depressing the plunger, plugging the vacuum port with a finger, and listening for a hiss. No hiss means good diaphragm. My fingers, though, don't plug the port.

Shoulda thought of this when I dropped off the booster or when I was cleaning it up. I claim brain-fog from fatigue. That's my story and I'm sticking to it!

Dave
Mesa, AZ

"Grinders and Paint Make You The Welder You Ain't!" -- from a t-shirt

Last edited by Mongo228; 08-01-2021 at 03:58 PM. Reason: Edited for clarity.
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post #4 of 5 Old 08-01-2021, 06:01 PM
devildog80
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Will bench check it just to be sure it is good working order, after being ripped out of Klooge's grasp, and some day to give Gramps brakes new life. Could not ask for a better organ donor.....thanks Dave
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post #5 of 5 Old 08-01-2021, 07:43 PM Thread Starter
fibersport
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Thanks Mongo, will try it later this week.
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1984 CJ7 Renegade
4.2 with 4 speed
researching other details!
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