wheel cylinder replacement

How tough, I've not yet torn into the MJ's rear drums except to inspect and adjust. I just snapped a bleeder off at the threads on the passenger side. Drivers side went smooth, I thought I was golden all the way round after the requisite PB soaking. Not so...

I don't even take off the shoes if they have had a recent service. The tricky part is getting the compression nut for the hard line off of the wheel cylinder. Just my methode, works for me. I've had half a dozen sets of line wrenches over the years, none seemed to work well for the initial loosening of the nut. I use a good set of vice grips, adjustment is critical. Too tight and they deform the nut, too loose and they slip. A little oil and wiggle the nut back and forth until it loosens a little, then switch to the line wrench or a good open end. if you take an extra minute or two and clean the area where the hard line goes into the nut, clean, scrape and oil, you may be able to avoid turning the hard line with the nut. Sometimes it hangs pretty tight, sometimes it doesn't. You can compress the cylinders pretty far with the line (or bleeder loosened). You may have to take off one hold down spring for the shoes to spread them a little. The two bolts holding the cylinder in haven't caused me much trouble, but I've heard where other people have had problems. A carefull tap on the end of the bolts, may help loosen things up a bit. I most always use a six point socket and turn with feeling. if the bolts have been in there for awhile, enough material could have rusted off to make them a loose fit for a standard socket.
Having a plug ready to stick in the end of the hard line, will help avoid more of a mess than necessary. Gravity will often keep the hard line flowing somewhat, the less air in the system the better.

well, this was all for instlling my speed bleeders anyway. I got air in the system on a steep hillclimb@ WF. Air was in the fronts, I got them bled, I decided to just do a whole fluid flush and when I got to that one I broke it right off. Wasn't even applying too much pressure, was using a 1/4 drive 3/8 6 point to break it free. Thanks for the info, good to know that I don't even have to take off the shoes. I'm off to go and get a new wheel cylinder.

I have a good set of K-D flarenut wrenches, and usually have not had the problem 8mud has, even on rusty nuts, if they aren't already mashed up. But the vise grips trick works too if you don't have extra-good wrenches with no spring at all in them. Even "good" wrenches won't do it. What I do often have trouble with here in rust country is the nut seizing over the line and twisting that and breaking it. If you don't want to have to replace the line, follow the advice to wiggle back and forth. Don't start really unscrewing until you see the nut move relative to the line itself. Usually it will break free without damage, if you're patient.

If you need to install new rear cylinders (@$15 each new at NAPA) then get ones for an '84 AMC Eagle. The bore is slightly bigger and gave me a LOT more rear braking with my 33" tires!

A different size/diameter/bore wheel cylinder will change the brake proportioning front and rear. If thats what you want, than your fine, but just because you got larger tires, I'd think you'd want to increase brake pressure equally front and rear, not just a greater amount at the rear.

Rick Anderson said:

A different size/diameter/bore wheel cylinder will change the brake proportioning front and rear. If thats what you want, than your fine, but just because you got larger tires, I'd think you'd want to increase brake pressure equally front and rear, not just a greater amount at the rear.

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The MJ has an extra proportioning valve, to acutally cut down on the pressure to the rear cylinders when the bed is empty. At least that is how I'm quessing it works, haven't researched it. Locking up the rears can/will cause the rear to swing out left or right, especially on wet/snowy/ Icy roads, even swap ends pretty quick sometimes. Locking up the rears or even overbraking is to be avoided and with the light rear of a P.U. even more important.
Too much braking in the front and you loose steering, to much in the rear and the rear swings out/doesn't track straight. Kind of a trade off between stopping in a straigt line, with possibly some steering control and braking as quickly as possible. I guess that's why ABS is all around, a good deal, most ways.
With the larger tires, larger rear cylinders may work better, or may cause problems. My best guess (like mentioned before) is a balanced approach, fronts and rears. With the fronts actually being much more important.

I have plans to run Mopar 1/2 ton front brakes (same 5 on 4.5" pattern, but on a Dana 44 cut down to fit) The front pads were already upgraded to brute force brakes, but it seemed like they were working by themselves (even after I bypassed the rear valve) Later I'll be putting in an adjustable proportioning valve. I've had to lock up my brakes numerous times on the highway this winter, and there is a slight kick out on the back, but front's only would've had me parked into the trunk of the &^%$#@!! that cut me off!

carnuck said:

Later I'll be putting in an adjustable proportioning valve.

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I was going to suggest that, sounds like a good plan.

For others, unless your doing brake upgrades both front and rear, and installing an adjustable proportioning valve, I'd say stick with the stock wheel cylinder.

If you've got big tires, but stock brakes and trouble stopping the big tires, at the very least, I'd get aftermarket pads/shoes that have greater stopping force than OEM and direct replacement pads/shoes.

If your getting into swapping in bigger brakes not designed for your particular application, then you most likely will need an adjustable proportioning valve.

8Mud, what I've read on P.U. extra proportioning valve, I agree with your assesment. My mini-vans have had the same thing and I've dealt with them before. You may know this, but that 2nd proportioning valve (connected to the rear suspension to change rear brake proportioning according to the load on the rear suspension) is designed to work with a specific 1st proportioning valve.

Basically the 1st proportioning valve has a much higher ratio biased toward the rear, than most single proportioning valves. The 2nd proportioning valve is designed to step down that higher pressure even more. So, if you eleminate the 2nd proportioning valve, you have to replace the 1st proportioning valve with the appropraite proportioning valve that provides the correct step down in pressure. Vice-a-versa, you add a 2nd Proportioning valve, you got to swap in the appropraite 1st proportioning valve.

Some people rig up their Adjustable Proportioning valve so that its in the passenger compartment, or it sticks thru the firewall with the knob in the passenger compartment. So that you can adjust the brake proportioning easily at any time, including while driving.

well I got three wheels bled. I think my air was in the fronts. I can lock up all 4 wheels now on a wet road pretty easily.
I'll be sticking with a stock wheel cylinder, as I don't want or have time to do both, and I can't have two different wheel cylinders. Not to mention that it's a pickup, and the rears lock before the front's anyway.