CJ 7 Brakes - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-30-2004, 11:29 AM Thread Starter
 
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CJ 7 Brakes

Well, the pulled out of the junk yard CJ is still running like a top...BUT this morning, the brakes started acting up...

When I first got it, the power brake booster was bad, so I changed it..that's all that's been done since I pulled it out...

OK, driving down the road, come to a stop, brakes work fine...after you first stop, the brake petal becomes hard as a rock and doesn't hold very strong. Drive a little more, brakes are fine the FIRST time you touch them....vacuum leak???
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post #2 of (permalink) Old 08-30-2004, 01:12 PM
 
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Re: CJ 7 Brakes

Yeah, you're in the right area. Gotta be something to do with that booster. Either the internals of the booster are malfunctioning, or there is a check valve on the fitting going in that is possibly faulty.

The way a booster works, is that there is a diaphragm with vacuum applied to both sides. When you hit the brakes, the source of vacuum to the pedal side is closed off and air is leaked in. The air that leaks in, pushed the diagraphm towards the master cylinder and provides boost.

Hows the motor running at idle? Is there decent vacuum to run this whole process?
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post #3 of (permalink) Old 08-30-2004, 01:54 PM Thread Starter
 
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Re: CJ 7 Brakes

It's running OK...I surely wouldn't rule out any vacuum leaks...
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post #4 of (permalink) Old 08-30-2004, 02:03 PM
 
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Re: CJ 7 Brakes

If there is a leak in the intake system and lines, it would make it idle rough. Try pinching off the line to the booster and other lines one at a time. If that changes the idle speed there is a leak in line or booster. If pressing on the brake pedal changes the idle speed, there is a leak in the booster and it needs to be replaced.

A good booster should hold vacuum, such that you can shut off the engine, and depress the brake pedal once, and still feel assist. After pressing it a few times, all the vacuum bleeds off and it has no more boost. The pedal should now be stiff. While holding pressure on the pedal, start the engine, as soon as it starts idling, you should feel it pull in the boost. If it fails the above, or the problem is intermittant, then I suspect it is the booster and it needs replacing.
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