How to test a brake booster - Team Camaro Tech
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post #1 of 14 (permalink) Old Dec 31st, 06, 11:02 AM Thread Starter
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Jimmy
 
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How to test a brake booster

After replacing the MC and rear wheel cylinder on my 69 SS with Disk/drum setup. The pedal seems hard and the car will come to a stop but it is in no hurry and not correct at all. I'm trying to test the brake booster. I disconnected the vacum line from the manifold and applied a hand vacum pump and tried to see if the booster would hold vacum. I was not able to build up any vacum. Does that mean the booster is bad? Any more suggestions.

Jimmy
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post #2 of 14 (permalink) Old Dec 31st, 06, 12:09 PM
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Re: How to test a brake booster

Quote:
Originally Posted by redvetteharley View Post
After replacing the MC and rear wheel cylinder on my 69 SS with Disk/drum setup. The pedal seems hard and the car will come to a stop but it is in no hurry and not correct at all. I'm trying to test the brake booster. I disconnected the vacum line from the manifold and applied a hand vacum pump and tried to see if the booster would hold vacum. I was not able to build up any vacum. Does that mean the booster is bad? Any more suggestions.
With the engine off,pump the brake pedal 10 times to deplete any vaccum.Now hold the pedal down with your foot and start the engine.If the booster is assisting the pedal will drop further away from you.
Some other checks.Pull the check valve from the booster while running.Full manifold vacuum should be present.Also pull the check valve after shut off.The booster should have reserve vacuum and you will hear the audible hiss when you slowly roll the check valve out of the booster.Hope this gets you started.
George.
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post #3 of 14 (permalink) Old Dec 31st, 06, 12:33 PM Thread Starter
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Re: How to test a brake booster

I did a few more checks. After the engine is shut off I can pull the check valve out of the booster and ther is NO hiss of vacum. Some one said that if you depressed the pedal while the engine was running and shut the engine off, the pedal should stay where it is but when I do that the pedal comes back up some. Thanks for any suggestions

Jimmy
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post #4 of 14 (permalink) Old Dec 31st, 06, 01:45 PM
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Re: How to test a brake booster

The check valve is to prevent diaphram failure in case of a backfire. One should be able to pull some vacuum on the booster with a hand pump, and should take several strokes, small pump volume to large booster volume.

You might sub an A/C rough vacuum pump for the engine. Engine needs to create more than 13 in./Hg. for booster to work correctly. Any amount less between 0 to 13 in./Hg. is not enough.

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post #5 of 14 (permalink) Old Dec 31st, 06, 01:59 PM Thread Starter
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Re: How to test a brake booster

My point about the check valve was that there was no vacum in the booster as soon as I shut the car off. I pumped 50 strokes on a hand vacum pump and the needle never moved.

Jimmy
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post #6 of 14 (permalink) Old Dec 31st, 06, 02:16 PM
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Re: How to test a brake booster

Go back and reread my reply to your original post.As far as the check valve goes,it is a one way valve that retains vacuum after a stalling event.This allows you to stop the vehicle with assist without manifold vacuum present.After running the engine and then shutting down you should hear an audible hiss from the booster when the check valve is slowing removed.try it again.
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post #7 of 14 (permalink) Old Dec 31st, 06, 02:38 PM Thread Starter
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Re: How to test a brake booster

That is what I am saying. I tried it several times and I could not hear a hiss. but the check valve seems to be working fine

Jimmy
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post #8 of 14 (permalink) Old Dec 31st, 06, 04:24 PM
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Re: How to test a brake booster

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Originally Posted by redvetteharley View Post
That is what I am saying. I tried it several times and I could not hear a hiss. but the check valve seems to be working fine
You did not mention if the booster was operational before the M/C change.Sound like you have a vacuum leak in the booster or the pedal travel has changed allowing atmospheric pressure in on the pedal side.The internals of the booster has vac on both sides of the diaphragm.When applied the internal valve seperates the chamber into two sides with the 14.7 psi working against the negative pressure.This is assist.If you are sure the check valve is operational and the booster is centerd then it is time for a swap.
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post #9 of 14 (permalink) Old Jan 1st, 07, 06:09 AM Thread Starter
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Re: How to test a brake booster

Thanks very much for your help

Jimmy
1969 SS Camaro, 383 Stroker, Hooker Super Comps, Flowmaster Delta Flow mufflers,4-Speed, 3.42 Gears Posi , Coys' 17" Wheels.
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post #10 of 14 (permalink) Old Jan 3rd, 07, 01:58 PM Thread Starter
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Re: How to test a brake booster

UPDATE I think I have (With your help) solved my braking problem. After replacing the brake booster I have a much higher pedal and excellent brakes and with little effort to the pedal. Finally everything seems to be working fine. Now on to the nest project.

PS Would you turn in the old parts for core or keep them for some reason?

Jimmy
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post #11 of 14 (permalink) Old Jan 4th, 07, 04:28 AM
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Re: How to test a brake booster

If its date correct, there are booster rebuilders listed at www.hemmings.com Only if you're a date correct guy and have an original car, but I read your sig and its modified.

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post #12 of 14 (permalink) Old Jan 4th, 07, 07:55 AM Thread Starter
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Re: How to test a brake booster

Thanks I have no way of knowing if they are date correct and my car is not bone stock.

Jimmy
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post #13 of 14 (permalink) Old Jan 4th, 07, 09:09 AM
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Re: How to test a brake booster

Kindda reads like you might turn it in for a core.

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post #14 of 14 (permalink) Old May 1st, 13, 05:58 PM
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Re: How to test a brake booster

Old thread, Yes! Didn't want to start a new one. Along the same thing, should you hear a "vacuum leak" sound coming through the firewall? Definitely coming from the booster. Bad booster? Brakes are ok, not great. I was going to wait until I put the new rear end in with the new discs before I bled again.
Thanks.

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