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serious brake problems - please help!

I recently hired a guy to convert the rear brakes on my 82 CJ from drum to disc. (There was nothing wrong with the drums, I just had some spare cash burning a hole in my pocket.)

However, after the job was complete, the disc brakes stop the vehicle MUCH more poorly than the old drums. In fact it's now quite dangerous to drive. There is now absolutely no resistance in the first 2/3 of the brake pedal. There is finally some resistance and grab in the last 1/3 of the pedal, but even mashed all the way to the floor, the brake pedal only gives me a moderately effective stop. If I get into a freeway situation requiring quick braking, I will be in very serious trouble.

I do seem to be able to get more resistance by quickly pumping the brake pedal a couple of times; on the 2nd or 3rd pump the pedal gets noticeably harder, but it still isn't super great for stopping.

The guy who did the work said that he suspects the problem is the master cylinder. He claims that the stock master cylinder on CJs is probably just not high enough capacity to handle the additional demands of the rear disc brakes, and that I could fix the problem by upgrading to a higher capacity master cylinder. I don't know nearly enough about mechanics to know if this is good advice or not (otherwise I would have done the job myself...) so can anyone here tell me if this is a reasonable answer? If so, any suggestions on what master cylinder to use as a replacement? If not, any other ideas?

The guy who did the work came highly recommended by many local jeepers and has been popular with local jeep clubs for 20+ years, so I tend to think it's not just a case of him doing shoddy work or rippig me off. ( He assured me that he topped off the brake fluids, bled the brakes, and did everything else properly.) Unfortunately I can't take it back to him since I moved 1100 miles away immediately after this work was done.

Reply to
sm3gurpal
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I'd tend to think he's right or there's still some air in the lines. I've had several MCs go out immediately after brake jobs, particularly on older cars, so it could be a case of that instead of it just being too small. I'd try having the lines bled again just to be sure, and if that doesn't fix it, upgrade the MC.

Reply to
Ichabod Shagnasti

I would properly bleed the brakes first:

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As indicated in this guys method, start from the longest line.

-- JimG

80' CJ-7 258 CID 35" BFG MT on 15x10 Centerlines D44 Rear, Dana 30 Front. SOA 4.56 Gears, LockRight F&R Dana 300 w/4:1 & Currie twin sticks Warn X8000i w/ dual batteries
Reply to
JimG

I may be wrong, but I thought the rear disk brake conversion required a different proportioning valve. Anyone?

Tom

Reply to
mabar

You could be right:

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JimG

Reply to
JimG

Reply to
L.W.(ßill)

If you pump up the brakes and then keep a slight pressure on the pedal does it hold or slowly drop to the floor? If it drops in pressure you probably do need a new master cyl. and it would be a good time to try a bigger master cyl.

I have done some reading and it seems you are not the only one with this problem. They mention some of the same thoughts like a tougher master cyl also mentioned is adjustments to the proportioning valve.

I suspect this guy has bled the brakes a few times just to be sure you don't have some trapped air in the system, maybe they need to be vacuum bled in the new configuration.

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Reply to
Jeepster

Didn't think about that one, but seems logical. I'd start with bleeding, then the proportioning valve, then MC.

Reply to
Ichabod Shagnasti

Disk brake calipers use much more fluid to stop a vehicle than does a cylandar a new MC schould be part of EVERY disk brake upgrade.

Jeremy

Reply to
Jeremy Hupe

I did the same swap this fall, and had the same problem. I had the hardest time getting all of the air out of the lines. As a matter of fact, the brakes were "professionally" bled, and STILL had air in the lines. The trick:

- pull the rear calipers - put a block of wood (or something similar) between the pads. I used a socket that was the same width as the rotors. - rotate the caliper until the bleeder is at the top - hold down the bypass button on the proportioning valve (I think Jeep has a little clip for this at the parts counter). Otherwise, you just push the air back to the front. - bleed away.

I still have the stock proportioning valve, and it works fine. I did upgrade to a larger master cylinder (for a '79 Firebird with manual

4-wheel disk), but only because the old one was leaking anyway.

My suggestion: Bleed 'em again. When the air is gone, it will stop on a dime (well, for a jeep).

Check out

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for some good info aswell. For a visual of why the pedal is falling 1/2 way before itgrabs, see:
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Good luck! Ryan snipped-for-privacy@earthlink.net

Reply to
Ryan

I will second what Ryan is saying. Especially getting the air out of the valve.

If the calipers need moving to get the bleeder up top, then they are on right left backward and need to be changed over.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Ryan wrote:

Reply to
Mike Romain

Thanks guys. Can someone please suggest a model or part # for a bigger, badder master cylinder that will easily fit right into a CJ7?

Reply to
sm3gurpal

Reply to
Jeepster

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