Best way to test Brake Booster? - JeepForum.com
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post #1 of 22 Old 07-20-2005, 12:22 PM Thread Starter
longlimb
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Best way to test Brake Booster?

I think my brake booster is shot. When I press on the brake pedal and then start the engine, it doesn't go down any. The pedal is pretty far to the floor, if that gives anyone an idea as to whats wrong. I tried pumping the brake pedal and then turning the key, but nothing again.

Is there a way to test the vacuum line? can I just pull it off the booster and feel for air? I'm just learning how the vacuum system works so please excuse my ignorience.

Thanks all.


'79 CJ7 304 V8 T150, Dana 20, D30, AMC20 Rusty Beast! Stock except for the rust...
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post #2 of 22 Old 07-21-2005, 06:35 AM
dawgates
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Do you have a vaccum tester/gauge? Disconnect the booster from the intake/carb and hook up a tester/gauge. pump up the tester and see if the vacuum gauge stays up. If these a leak you see the gauge drop. I would replace the line as cheap insurance.

Another way if you don't have a gauge if to start you're Jeep with your foot on the brake pedal. Feel if the pedal try's to push your foot up. That won't tell you if you have a leak, but it will tell you if the booster is working or not.

If the M/C and booster has never been replace, remember it's at least 25 years old and the rubber inside does go bad after awhile. Maybe instead of testing this and that, you should just replace the whole set-up. Save a bunch of your time and money.

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post #3 of 22 Old 07-21-2005, 07:29 AM Thread Starter
longlimb
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I was thinking the same thing. How much are the vaccum testers anyway? I can get a used wrangler booster for $65, but will have to mod. it to fit.

'79 CJ7 304 V8 T150, Dana 20, D30, AMC20 Rusty Beast! Stock except for the rust...
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post #4 of 22 Old 07-21-2005, 07:48 AM
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The vaccum for a power booster usually comes directly of the intake manifold, you can of course check the line to be sure that it has not collapsed internally. At the end that connects to the booster there is a one way check valve, that sometimes fails. you should be able to blow air into it from the flat side(the side inside the booster), but not from the side that connects to the vaccum line.
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post #5 of 22 Old 07-21-2005, 11:12 PM
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Quote:
When I press on the brake pedal and then start the engine, it doesn't go down any.
Bad booster and if its going to the floor possibly more is bad.
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post #6 of 22 Old 07-22-2005, 05:28 PM
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A bad booster will make the pedal harder to push not easier. I'd be looking at the master.
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post #7 of 22 Old 07-23-2005, 01:43 PM
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Quote:
Originally Posted by pyro9862
A bad booster will make the pedal harder to push not easier. I'd be looking at the master.
You're right, what the hell would I know.
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post #8 of 22 Old 07-25-2005, 07:34 AM Thread Starter
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Id does seem hard, but I have nothing to reference. I bought the jeep this way and it's the 1st CJ I've owned with power brakes.

'79 CJ7 304 V8 T150, Dana 20, D30, AMC20 Rusty Beast! Stock except for the rust...
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post #9 of 22 Old 07-25-2005, 08:01 AM
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Throwing parts right and left at somthing trying to fix it gets expensive unless you have money and you just want to be safe and replace all the 25 year old parts.

To test the booster you need a vacuum pump like this. You can the cheap plastic version with no case at autozone for about $25, I think craftsman has one to or do what I did and find a used one on eBay for the same price with a case and loads of hoses and adapters. If you go the used route just make sure the seals are good and it holds vacuum. I don't find myself using this very often so if you can borrow one for a few days you're better off saving the money. On the plus side it does double as a vacuum gauge.

Anyway as has already been said put that on the line to your booster and pump it up. The vacuum should stay constant. If it doesn't remove the line completly from the booster plug one end and put the pump on the other and pump it. If you loose vacuum the line is bad if you don't you're loosing vacuum from the booster.
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post #10 of 22 Old 07-25-2005, 12:04 PM
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You guys are making this too hard.

1. Start the car let it run 30 seconds turn it off. Wait 30 seconds.

Remove the check valve (the plastic piece the hose connects to in the booster). Did vacuum release? Yes, go to 2. No bad booster.

2. Start the car let it run 30 seconds turn it off. Step on the brake pedal and hold it.

A good booster will stay down, a bad booster will either immediately come back up or come back up after a few seconds.
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post #11 of 22 Old 07-25-2005, 12:06 PM Thread Starter
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Thanks pyro- I'm definitely don't want to be replacing parts just for the fun of it. I'll see if I can find someone with a vacuum pump.

'79 CJ7 304 V8 T150, Dana 20, D30, AMC20 Rusty Beast! Stock except for the rust...
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post #12 of 22 Old 07-25-2005, 12:08 PM
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Quote:
Originally Posted by alindbloom
Thanks pyro- I'm definitely don't want to be replacing parts just for the fun of it. I'll see if I can find someone with a vacuum pump.
Don't do it! Just call me when you're by the Jeep I'll walk you through it.

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post #13 of 22 Old 07-25-2005, 12:14 PM Thread Starter
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Hey vancopbs-

I'll give your idea a try. No money is always better. But if the boosters bad on your step 3, wouldn't the lack of vacuum keep the pedal down? Or am I thinking of it backwards? I'm thinking of it backwards, the vacuum would pull the brake pedal down for assistance. duh.

'79 CJ7 304 V8 T150, Dana 20, D30, AMC20 Rusty Beast! Stock except for the rust...
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post #14 of 22 Old 07-26-2005, 11:16 AM
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Quote:
Originally Posted by Vancopbs

2. Start the car let it run 30 seconds turn it off. Step on the brake pedal and hold it.

A good booster will stay down, a bad booster will either immediately come back up or come back up after a few seconds.
How long do you hold the pedal down in step 2? Do you mean that the pedal will stay down if the booster is good?
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post #15 of 22 Old 07-26-2005, 11:18 AM
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About 10 seconds. If the booster is good you'll apply the brake and hold it. It'll stay down if it's good. If it comes back that means it's loosing vacuum. Just hold down normally.

Van
Vanco Power Brake Supply
9738 Atlantic Ave
South Gate, Ca 90280
800-256-6295
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