Eagle

If you mean as a direct replacement for the MJ bench seat, the answer is no, it won't fit.

Yes, the alignment specs may be different with a lift. You didn't list all the components you used to get your 4.5" lift. In the XJ/MJ front suspension, caster angle is adjusted by adding or removing shims at the rear end of the lower control arms, to push the LCA locations forward or back, thereby rotating the axle tubes and changing the tilt angle on the Cs and steering knuckles. That's what caster angle is -- the tilt in the forward-to-aft axis of rotation of the ball joints. Positive caster is when the lower end of this axis is forward of the upper end. Positive caster is what helps generate good tracking at highway speeds, but it is also important in preventling death wobble. So HOW you achieved your lift and what alignment specs were used is important. The effect of just adding a lift, without replacing the LCAs with longer or adjustable LCAs or adding a lot of shims, is to reduce the caster angle. If you reduce the caster angle significantly, you greatly increase the probability of experiencing death wobble. This is why so many aftermarket companies sell adjustable LCAs. Even then, you get into a delicate balance. With taller lifts, you're also messing with the U-joint angles in the front drive shaft. Trying to put the caster angle back to within factory specs with a significant lift results in excessive U-joint angles. Consequently, you have to search for the sweet spot between a caster angle that won't kill your U-joints and a caster angle that will be enough to prevent death wobble. There has been a lot written on this topic, both on this forum and on NAXJA.

Why "must" it be a design flaw? I currently own three XJs and three MJs that I have personally driven significant distances, plus a 2001 XJ that I sold to a friend awhile back. Among all of them, I probably have close to half a million miles racked up. I bought my first XJ in early 1988, so that's more than 30 years ago. The original '88 XJ alone has 287,000+ miles on it. Out of all those miles, the only one that ever experienced death wobble was the red '88 MJ. The death wobble occurred when it had the 4" lift installed (later removed) and when I had it on 31-inch tires. The cause was tire balance, and the cure was to put a different set of tires on it. Solid front axle vehicles are inherently more prone to death wobble than independent suspension designs, but that doesn't mean there is a design flaw in the Jeep solid axle design. It just means we should not make a bunch of changes without being aware that changes may have consequences.

Then the tires are probably the cause. I've been through this twice on my XJs. New tires, mounted and balanced at the tire shop, get on the highway at about 55 MPH and the front end starts to shimmy. Never gets to full death wobble, and if I speed up to about 62 MPH or faster it smooths out again. Take them back to the shop, they balance them again ... same issue. I have a friend (former XJ and MJ owner, currently has a ZJ) who works as a shop foreman at a VW dealership. Both times, he took the tires and balanced them for me and they've been perfect ever since. Too many techs these days don't know how to use the tire machines. I had one shop tell my my Jeep factory alloy rims were bent so they couldn't be balanced. My friend put them on his shop's Hunter machine and he said the wheels were perfect. The "technicians" at the other shop didn't even know how to attach a wheel the the machine, why should I expect them to know how to balance a tire? Here's a clue: This has been true ever since I can remember, going back to my mother's 1958 Rambler station wagon: for some reason, tire balance issues ALWAYS manifest at 55 MPH. If you can drive through it and it smooths out above 62 (or so), it's not a death wobble or suspension issue, it's a tire balance issue.

To expand on Hornbrod's response -- "it depends." That grille won't directly bolt onto your header panel (that's the fiberglass section in front of the fenders, to which the grille attaches). However, it's really not a big deal to just swap the entire header. That vehicle has the older, 10-slot grille, which is less common than the 8-slot grille, which then became a liability for Jeep when they found themselves trying to claim copyright (or trademark) infringement on other makers who had the temerity to put seven vertical slots in their grilles. Nowadays, every Jeep vehicle has a seven slot grille, even if it looks stupid. That bumper is in nice shape, too. And it has the steel license plate holder, which is much more durable than the plastic ones used in later years. (I don't know what year they switched, but my 2000 XJs have plastic, and it sucks.) So, if you're willing to do a bit more work, putting that nose on your truck is a bolt-on swap.

Liar, liar, pants on fire! [See my signature!]

Then you should be able to sell them for what you paid for them, or more. The problem is, the helluva deal on the tires is going to cost you a helluva lot of money. To run those things, you need new lower control arms just for turning clearance. You need at least a 4-inch lift, and a 6-inch lift would be better. When you get into that much lift, you need: An adjustable track bar Adjustable lower control arms Adjustable upper control arms A rear lift, either a spring-over conversion, new springs, or an add-a-leaf plus shackles Longer shock absorbers on all four corners New, longer flexible brake hoses A major wheel alignment I'm sure there's something I've forgotten, but you get the idea. Whereas, you can run 31x10.50s on factory Jeep wheels with NO lift at all, or maybe a 2-inch budget boost if you feel you just have to do something to it. But a stock MJ is a very capable off-road truck even at stock height.

This isn't a private conversation between you and Don, this is an open discussion. All you said was that your '89 has "them." You're apparently referring to the side body moldings, but this thread started out about the underbody fairings/rails.

I have to disagree. Someone earlier in this thread already noted that there were fewer than 1,000 '92 MJs built. It certainly IS super rare, and IMHO for that reason alone it should be preserved in original condition rather than hacked to put on bigger tires that probably aren't necessary for the limited wheeling Mancheflo will be doing. Value is a different matter, but if it's preserved in original configuration and taken care of, the value will only go up. As soon as the sheet metal gets cut, the value plummets. It is his truck, and it's his decision. That said, I still think it's a very bad idea to start cutting up a pristine example of a very rare Comanche. Especially since it's a longbed, which isn't a good candidate for wheeling anyway. The shortbed MJ is much more nimble on the trail. The shortbed has a better breakover angle and a better departure angle.

Look underneath. The transfer case and drive shaft are below the "frame" (unibody) rails. A flat belly pan isn't possible.

NOOOOOOOOOOOOOO!!!!!!!!!!!! That truck is MUCH too nice to be cut into.

What are "running lights"? Headlights? Parking lights? Taillights? All of the above? It sounds to me like a bad headlight switch.

Not that I want to do an IFS swap, but keep in mind that the MJ is an AMC design, and AMC was building unibody cars that were around the same size as the XJ/MJ for decades before the XJ came out. I would look at adapting the front suspension out of a Javelin, Hornet, or Concord. Avoid Rambler Americans -- they had a very strange coil spring/trunnion setup that had some problems, and would likely be impossible to find replacement bushings for today.

Oops.

The problems are that (a) the glass is curved, not flat, and (b) the rear glass is tempered, not laminated. You can't use epoxy injection to repair tempered glass like you can with laminated windshield glass. Your options are to find another factory MJ window, install an aftermarket slider, or use plexiglas to make a replacement panel. If there are any old-school glass shops in your area, you might find one that will cut a flat replacement for you using laminated safety glass, and that would be better than plexiglas, bit it'll still be flat and not match the original.

What upper piece? I thought 1990 was the year they changed the grille to incorporating the upper trim strip into the grille itself rather than having it as a separate strip like on my '88s.

Like most of the other votes, I vote to keep the nice one nice, and use the rust bucket as the off-road project. It's going to get beat up anyway, so why bash up a nice, solid, straight MJ when you have a beater candidate already?

Anticipating the next question: No, they are not the same as 2-door XJ rear flares.

I'm still thoroughly confused because Dzimm refers to the tires by what he thinks the diameter is rather than what the actual size is. He did mention a 225/70 (15?), but (a) I don't know which truck those are on or if those are the tires he used to get his speed and RPM readings for, and (b) that wasn't a size that was offered by the factory, so the speedoemter can't be accurate.

I think I got the updated version uploaded to Google. If the top says copyright through 2018 ... it's the new version. It's as correct as I can make it from the limited real-world revolutions per mile I could find. When I first made up the spreadsheet, almost all the tire manufacturers gave that data. Now almost none do. For tire sizes not listed, I did some comparisons. I spot checked a number of entries in another spreadsheet I have, of tire specs. For ten entries for which I had actual revolutions per mile, I compared those to the revs/mile calculated based on nominal tire size. The difference ranged from 2.64% to3.53%. So, to get in the ballpark, if all you have is the calculated revolutions per mile ... just add 3 percent and you should be close enough for most purposes. I'm not sure if you lads can just view the spreadsheet, or if you can edit it. If you find that you can edit it -- PLEASE DON'T! If you want to play, download your own copy, don't change the one I uploaded. And, please respect my copyright. A fair amount of work went into that spreadsheet. It says it's copyrighted because I am not releasing it into the public domain. Please don't pass it on to anyone else.

Cooper Tire still publishes revolutions per mile in their specs. For anyone wishing to accurately figure out RPMs relative to speed, that's the number to use. https://tiresize.com/tires/Cooper/Discoverer-AT3.htm For some sizes, they list three different tires, I guess based on load rating (or speed rating), and the numbers are different. I'm going to have to update my spreadsheets. I'm not going to list three of the same size, because if you look at another manufacturer's tires of the same size, their numbers will be different. A difference of 5 or 10 or even 25 RPM doesn't matter, so where they list multiple entries for the same nominal tire size ... I averaged them. Now I have to get a good night's sleep and come back to triple check my work. And then I have to try to remember how to update the document on Google Docs

Here ya go -- a 195/60-15 has a theoretical diameter of 24.2 inches. I have a spec for that tire -- 833.1 revolutions per mile. You can run the math on it and see what kind of RPMs you get.

2600 RPM would be about right (2636) for 1:1 transmission ratio -- which is 4th gear, not fifth. Then you factor in the overdrive ratio. 2636 x 0.75 = 1977 RPM at 70 MPH. Are you not using fifth gear?

I have no idea whatsoever. Find me the revolutions per mile for the tire you have in mind and I'll have an answer for you.