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post #1 of (permalink) Old 06-14-2004, 01:38 PM Thread Starter
 
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CJ7 Brake Problem

I'm having some problems with the brakes on my CJ7. It is a 78 CJ7 304/TH400/Qtrac with the stock power braking system and 11" rear drums.

The problem is after driving the jeep for a short while (<2 miles) both the front calipers will not release. The entire brake system is new except for the master cylinder, vacuum booster, and proportioning valve.

After the fist incident I suspected the calipers had locked up because I could not move the piston back into its bore. The calipers, rotors, and pads were replaced under warrenty. This fixed the problem while I took it for a test drive but when I drove it again yesterday the problem came back.

When installing the calipers it seemed to me like there is just too much distance the piston much travel before it even reaches the pad, about 1.5". Is this normal for this setup?

Also, anyone have any other ideas as to what could be causing the problem? I've run out of ideas.
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post #2 of (permalink) Old 06-14-2004, 08:35 PM
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Re: CJ7 Brake Problem

Something radically wrong there. With new pads it's usually hard to get the caliper on the rotor, tight fit. Piston should barely move. Note the 78 and 79 used different components as I recall, maybe they got the wrong parts? Might get the brakes tight as you describe, then loosen the bleeder screw on each caliper and see if they are holding pressure, could be a restriction in the lines, usually a hose going bad near the wheel.
post #3 of (permalink) Old 06-14-2004, 09:11 PM
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Re: CJ7 Brake Problem

It could be the wrong calipers. Sounds like the sold you the calipers for the 6 hole bracket instead of the 2 hole bracket. The 6 hole bracket uses 1 1/8" thick rotors vs. 7/8" rotors for the 2 hole brackets. That wouldn't explain away all the 1 1/2", but it would explain some of it
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post #4 of (permalink) Old 06-14-2004, 10:21 PM
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Re: CJ7 Brake Problem

4WD lists two different calipers for '78 so it appears that there was a mid-year change. Check to see how many bolts hold your caliper bracket on, 2 or 6. If it's 6, it should use the same caliper as the '77. If it's 2, it should use the same caliper as '79 to '81.

If you're getting 1 1/2" piston travel before the pads contact the disk, I'd say you've got the wrong calipers. If there is too much travel, there is not enough piston left in the bore to keep it from cocking and it won't return.
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post #5 of (permalink) Old 06-14-2004, 10:26 PM
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Re: CJ7 Brake Problem

If you haven't replaced the rubber lines yet, they may be swelled shut. When you press the pedal, you can force fluid through them but fluid is not able to flow back out from the calipers. Just one thing to check.
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post #6 of (permalink) Old 06-15-2004, 07:26 AM
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Re: CJ7 Brake Problem

In '78 there was an optional heavy duty brake package. It included the thicker rotors, different calipers and caliper brackets and, I think, the 11" drums instead of 10". You seem to have a mismatch of components; possibly HD calipers, standard rotors and pads.
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post #7 of (permalink) Old 06-15-2004, 07:50 AM Thread Starter
 
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Re: CJ7 Brake Problem

Thanks for the replies. So up to 78.5 used a 6 bolt caliper bracket and 78.5 and later used a 2 bolt bracket. I am almost positive the bracket I have is the 6 bolt version but I'll double check it. I'll check the part numbers on the calipers and rotors and make sure they match the bracket.

The soft lines on the jeep are braided steel and brand new so I don't thik I have a problem with them swelling shut. The hard lines are new also. Both sides bleed perfectly so I would rule out any restrictions.

I'll let you know what I come up with.
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post #8 of (permalink) Old 06-15-2004, 07:54 AM
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Re: CJ7 Brake Problem

I'd have to agree with the above but just to throw another thought in the pot...

I had the same issues with my CJ once. but my problem ended up being that i swapped out a new MC, and the push rod for it was a different length. It was about 1/8" too long. doesn't seem like much, but that added length made it so that the brake lines wouldn't bleed back into the MC and thus each time I presed the brakes they got tighter and tighter. until I was smoking the brakes. I pulled teh rod out, cut it down, smoothed it off, threw it back in and all is well.

But again, I think you have a mismatched brake set-up.
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post #9 of (permalink) Old 06-16-2004, 08:38 AM Thread Starter
 
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Re: CJ7 Brake Problem

I checked again and the caliper brackets are 6 bolt. However, the rotors are 7/8" thick. I checked all my part numbers and they match a 77 model, none match the 79 model.

I made sure all the parts were for an 11" drum when I purchased them because I was returning the parts for a 10" drum. It appears Advance Auto Parts lists the wrong rotors for the 11" drum package. Whether the calipers are correct for the application is a moot point because they're ruined now. I guess I'm returning the rotors, calipers, and pads and trying a different parts store.

Thanks again for all your help guys. I'd probably still be scratching my head if not for you.
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post #10 of (permalink) Old 06-16-2004, 10:03 AM
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Re: CJ7 Brake Problem

Now that you mention it, I think that someone else had the same problem - one of the chain parts stores had bad data in their computer system.

Ask for parts for a '78 with the heavy-duty brakes option. If they don't have one set of numbers for calipers, rotors and pads, and completely different numbers for standard-duty parts, you're wasting your time and theirs.

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