Eagle

Going back a decade, the "hot" trick in NAXJA was to just remove the cup washer and spring, and leave the plunger/piston in the forward position (pulled into the cap nut, leaving the orifice open). I never heard of anyone having a problem doing that. After following Shelbyluvv's link, that led me to another video in which an older gent with a southern accent discussed proportioning valves. He claims they are all just pressure limiting valves. Dunno. It was a long video, at the end of which I knew nothing more about how they actually work. Or if they're really needed. The first car I had with front disc brakes was my first 1968 Javelin. Disc front/drum rear, and it did not have a proportioning valve. However, the 1968 AMX (which was the shorter, 2-seat version of the Javelin) did use a rear proportioning valve. Shorter wheelbase ==> more tendency for weight transfer to the front, thus greater tendency to spin out under heavy braking. One of my friends bought a used AMX. Drove it home a few miles from where he bought it, and all the brakes locked up and burned up the linings. Turned out the previous owner had used ATF in the brake system, and the ATF caused all the seals to swell up. Most of the parts were available or rebuildable. What we could not find (or figure out how to rebuild) was the rear proportioning valve. So we just eliminated it. We knew what it did, so we took an alternate approach to reducing the braking at the rear wheels. His AMX was a 343 c.i.d. V8. We used wheel cylinders from a 6-cylinder Gremlin. They were smaller in diameter, and we calculated that would reduce the rear braking power by about 25 percent. He drove that car for twenty years or more like that, including autocrossing it, and never had a problem. I wish there was a new manufacture ( or quality rebuilt) source for the MJ height sensing valve, because they way they operate makes a lot more sense to me than the black magic of the XJ combination valve.

Here's a closer view of just the proportioning valve segment of the XJ valve. The upper vertical passage to the left is a full-pressure by-pass for the rear brakes in case the fronts fail. Under normal conditions, the shuttle valve blocks it off (as shown). If the front circuit loses pressure, the shuttle valve moves to the left, opening the straight-through path to the bottom output passage. That much is easy to figure out. What's less easy is how it works under normal conditions. The input is the vertical passage at upper right. The fluid (and pressure) come down that passage and into the chamber the right of the cup washer on the piston. Then somehow the fluid and pressure have to get past that cup washer and into the lower vertical outlet passage at the lower left. I don't get it.

Interesting video, but IMHO useless. The XJ proportioning (or "combination") valve and the MJ distribution block don't have what he referred to as a "metering valve" in the rear of the block. His explanation of how the proportioning spring works doesn't at all correspond to how it seems to work based on what we can see by cutting one open. His explanation of the shuttle valve operation is backwards. I'd like to see an example of the valve in that video sliced open to show how it works.

here's a photo from an older thread on this site: The 2000 and up TJ bearing is on the right, its got longer studs and you can see how the WMS is shorter. Source thread: http://comancheclub.com/topic/39809-wj-knuckles/?hl=hubs

A couple of people have commented on the way the leaf retainer bolt in the rear springs can start to wear a groove into the upper surface of the main leaf. I've seen that myself. Awhile back I took apart two pairs of broken MJ leaf packs, mixed and matched parts, and managed to put together two complete springs out of the parts from four. In the process I was reminded that not all MJ leaf springs have the retainer bolt in contact with the main leaf. On some there's about a quarter of an inch of clearance, as shown in this photo. Does anyone know which springs got the extra space and which didn't? These were all standard 3+1 MJ springs, no metric ton stuff here.

XJs don't need any special tools. Bleed normally (start at right rear, progress to left front last). If the shuttle valve hasn't reset to cancel the warning light, stomp on the peddle a couple of times to reset it.

That's the horizontal plunger across the top. Both the XJ and MJ units have that. It's cleverly called the shuttle valve, and it also actuates the brake system warning light. You can see how the plunger for the switch is down in the narrowed "neck" of the shuttle plunger. If the valve moves in either direction (caused by a failure of either the front or rear cirsuit), it'll push the plunger up and turn on the light. It's how that lower, proportioning plunger in the XJ valve works that has me puzzled.

The problem is that the hubs have slightly different offsets for different years. I'm pretty certain that the YJ and the TJ did NOT take the same hub, so whatever year front axle you have, there's a good possibility these hubs won't fit. The above is from my manuscript, which is copyrighted to me. Please do not disseminate by any means.

The stars finally aligned, my camera batteries weren't dead, and my Internet connection was functioning. I found the XJ proportioning valve I had sliced and diced, so I can now post photos to show how the XJ proportioning valve is different internally from the MJ front distribution block. First up, the MJ distribution block. I've posted a photo of this one before -- this photo is touched up to show how the emergency bypass circuit is supposed to run: And now the XJ proportioning valve. Notice the plunger, spring, and rubber cup washer. That's the proportioning mechanism, but after studying it I can't figure out how it works. If you look closely, you'll see that the outer surface of the rubber cup washer has ribs, so perhaps the ribs allow brake flow until the pressure gets high enough to compress the ribs and allow the cup to seal against the bore? Dunno. I also realized that the XJ valve has a bypass, similar to the MJ, so if the front brakes fail the rears will get full flow and pressure, not proportioned.

Not legal. Federal regulations require that fog lights MUST NOT operate when the headlights are on high beam.

First, what kind of hitch do you have? Second, your truck is still an MJ and it still only weighs around 3,200 or 3,300 pounds. You have to watch out for the trailer pushing the truck around. Third, you need more gear. 31x10.50s with 3.73 gears work out to exactly the same overall final drive ratio as stock tires with 3.55 gears, so your final drive ratio is closer to a stock 5-speed with stock tires.

But they charged you for a complete alignment? IMHO that's fraud. The same method applies to all Cherokees through 2001, and to Grand Cherokees at least through 1998 (I don't recall about the WJs). There are hundreds of thousands of those vehicles on the road. An alignment shop that doesn't know how to align them shouldn't be allowed to have a repair license.

How can you have 9 degrees of caster if you had an alignment done? That's way out of spec. (Although positive caster should help prevent death wobble, not cause it.) Tie rod ends cannot cause death wobble. New ones can (maybe) mask death wobble to an extent, but sloppy ones cannot cause death wobble.

BA 10/5 = Internal

To replace the rear main seal, you have to remove the rear main bearing cap. That's the part for which torque is critical. You have to do it right -- I've never heard of anyone dropping an oil pan to re-torque a main bearing cap. That's nuts.

This is invalid, because the measurement can change depending on tire size, and even tire pressure. Either use the hub-to-flare method already discussed, or crawl underneath and use the method Pete referred to. Hornbrod posted a link to that in a recent thread abut lifts and suspensions.

The hub-to-flare measurement for a stock suspension should be 17-1/2" for the front. So the XJ is a 2-1/2" lift, and the MJ is riding 1-1/2" higher than stock.

Update: I found the dissected XJ proportioning valve. And, I'm ashamed to admit, it does NOT appear to work the way I thought it did. In fact, after studying it more closely, I find it's a bit more sophisticated than I thought, and ... I have no clue how it works at all under normal braking. (Which may be why the hot tip in NAXJA was to remove the cup washer and disable the dang thing). I'll post photos in a day or two.

Nope -- that's the MJ distribution block. It has no proportioning function. I did the same surgery on an XJ proportioning valve, then I misplaced it before I could photograph it. I guess I'll just have to do it again, because the question keeps coming up.

They're all the same. Just unscrew the bolt-like thing in the "nose." Be careful -- there's a strong spring inside. Once it's open, you'll see the plunger and the cup washer.

It does mean that the axles are out of square, but that doesn't mean the frame is bent. It could be caused by one of the rear spring locating pins shifting in the spring plate. It could be caused by uneven shims on the front lower control arms. And, of course ... if the front axle is off center it's impossible for axle-to-axle diagonal measurements to be equal.

The line is the hydraulic line from the clutch master cylinder. The fitting with the bleeder screw in it is the bleeder for the clutch.

So ... 2-1/2" lift. 2" is what I consider the maximum lift for staying with the stock track bar. If you add 1-3/4" coil spacers, you'll be at 4-1/4". My '88 had a 4" lift when I bought it, and the axle was about 5/8" off-center. I installed an adjustable track bar to correct that.

Bleed again for the low pressure. To cancel the light, once you have a decent peddle, stomp on the brakes HARD. That should reset the shuttle valve in the front distribution block.

I understand what a brake proportioning valve should do. And that's not how the XJ proportioning valve works. It works exactly the opposite of the way you say a proportioning valve should work. I agree that's how they should work -- but that's NOT how the XJ proportioning valve works. I've had them apart, and I cut one in half to verify how it works. It completely blocks flow (and pressure) to the rear brake circuit until the pressure in the system gets pretty high, at which point the plunger overcomes the resistance of that big spring in there and allows the rubber cup seal to move forward and open the inlet to the rear circuit. In normal, day-to-day driving with light to moderate brake pressures, the rear brakes on an XJ do not do anything. With the XJ proportioning valve, once the plunger moves forward and the rear circuit opens, the pressure to the rear is the same as the pressure to the front. Always. And that's why I don't like the idea of the XJ proportioning valve in the MJ. If the bed isn't loaded, the tail of an MJ is relatively lighter than that of an XJ. You drive it around empty, and you get used to the rear always staying where it should be -- following the front. Then one day you get into a panic stop situation, you stomp on the brakes hard, the rear circuit opens up, and the rear wheels lock up. Spin-out. Yes, the same braking with NO proportioning valve would also lock up the rear brakes. But -- if you don't have any proportioning valve, you know how the brakes are going to react so you're not taken by surprise when all of a sudden you have rear brakes.