Eagle

What is the vehicle behind the Comanche? It's difficult to make it out, but it sort of appears like it might be the roof line of an early 1950s Willys station wagon.

Back to swapping in an XJ proportioning ("combination") valve. Somewhere on this forum, a long time ago, I or Pete posted a photo I took of an MJ front metering block (I'll call it that since it doesn't have any proportioning function) that I sliced in half to be able to see how it worked internally. It was that exercise that showed me the "extra" rear brake line for the MJs isn't a "return" line, as I had always been told (even by the techs at the dealership), but an emergency by-pass line. It was a worthwhile sacrifice. I haven't got a photo, but since doing the MJ combo valve I have more recently sliced up an XJ combo valve. And having done so, I still cannot figure out just what it's supposed to do. The best I can figure, what it actually does seems to be that it prevents any fluid from getting to the rear brakes until you really stomp on the brake pedal ... at which time it would allow full pressure to the rears. That's the only way the spings and plungers and O-ring inside the thing can work, but it doesn't make any sense to my understanding of what a brake proportioning valve is supposed to do -- which is limit the pressure to the rear under conditions that might cause a spinout if the rear brakes lock up before the fronts. That doesn't happen under normal driving -- it happens under heavy braking and in panic stops. The other problem with XJ combo valves is that they get gummed up internally. I know of numerous people in NAXJA who found they had NO rear brakes. My own '88 XJ is that way -- if I stomp on the brakes in snow, the fronts lock up and the rears keep rolling. One of these days I have to open that combo valve up and either clean it out, or just gut it. For that reason, although I've explained the downside to keeping the MJ combo valve and removing the rear height-sensing valve, I also don't see swapping in an XJ combo valve as much (if any) of an improvement. Personally, I would rather know that I have rear brakes, and then deal with how to limit the rear braking force if the rear wheels lock up too much. I can deal with too much rear brakes a LOT better than I can deal with no rear brakes. I have a box on my bench with 5 XJ combo valves in it and one MJ combo valve. Those 5 XJ valves are NOT slated for installation in any of my MJs.

What's the problem? You haven't provided enough information to show that you have a problem. If your truck is lifted, you don't have a problem. The actual difference in length is less than an inch. Check your driveshaft to see how much is engaged on the transfer case output shaft when the yoke is in as far as the wear marks show that it normall goes. If you have an additional 3/4 of an inch before it bottoms out, you should be okay. If it bottoms out, running that driveshaft with the 8-1/4" axle could destroy your transfer case. One shade tree solution (which I would try to avoid, as it isn't reversable w/o infusions of $$$) would be to take a cutoff wheel and chop a little bit off the end of your output shaft to provide clearance. But that will provide the answer only if the yoke is bottoming on the shaft before the outer portion hits the tailshaft housing. Another partial solution would be to install taller rear bump stops. As the suspension compresses, the driveshaft gets pushed forward. Limit the amount the suspension can compress and you limit how much the front yoke can get shoved into the transfer case. You probably have enough clearance to bolt in the new axle and have the drive shaft mount up. What you need to be concerned about is ensuring that there's anouth clearance for the yoke to move forward as the suspension cycles.

For a 3" lift in an MJ you probably wouldn't need a new drive shaft even if you did nothing to the axle, but swapping in a D44 or an 8-1/4 would put things back just about to stock engagement. In fact, you should probably cycle the suspension with the new axle in place to be sure the front yoke doesn't bottom out at the transfer case.

Is this where I get to say "I told you so," or didn't I told you so? There is NOTHING wrong with an AMC Model 20 axle. It's a huge, beefy axle that has been used reliably for many years in vehicles much larger and heavier than the MJ. The only problem with it is weight and ground clearance.

Actually, it may be a problem precisely because you don't carry heavy loads. When you eliminate the rear height-sensing valve, you get full braking force to the rear wheels at all times. When a pickup is unloaded, the back is quite light and heavy braking or panic stops usually result in the rear brakes locking up long before the fronts. The purpose of the valve is to reduce the amount of rear braking when you're running light, and to give you full brake power to the rear when you're loaded down. This is a non-issue for me because I'm an olde pharte who grew up and learned to drive a couple of decades before they invented proportioning valves. I expect the rear brakes to lock and the vehicle to try to switch ends on me under some conditions, so it's not something new, different, and scary. Those of you who have never gone through a brake-induced spin-out should take this into account. Under most conditions it'll never be a problem. Where it could be a problem is rain, snow/ice, and when you're heading down a steep hill so that even more of the vehicle weight is on the front wheels rather than the back. A true panic stop isn't an issue because when you REALLY stomp on the brakes all four wheels lock up. At that point you're no longer driving, you're just along for the ride in a pre-aimed cruise missile. (No, you really can't steer when the front wheels are locked up. Trust me on that.) Try it with the rear valve out of the circuit, but drive easy until you know how your brakes are going to act. And if you're a really heavy-footed driver I would suggest that you do this only in conjunction with a Mopar or Wildwood adjustable proportioning valve in the rear brake circuit. For the rest of us, and especially if you're due to freshen up the rear brakes anyway, a partial offset is to look for rear wheel cylinders that have the same length as the factory ones but a smaller piston diameter. If your axle is a D44 this is easy -- buy wheel cylinders for the D35. They're smaller. Using smaller diameter wheel cylinders reduces the amount of force actually transmitted from the hydraulic circuit to the brake shoes. It's not perfect, but it helps.

Correction -- The D35 snout is about 3/4" SHORTER than either the D44 or 8-1/4 (which are the same length)

The special tool is the folding handle for the factory jack. It's probably still behind your seat because most previous owners never, ever bothered to winch down the spare or jack up the truck.

I hope y'all stay safe and (comparatively) sober. If any of you or your parents are or were veterans, God bless 'em all for serving.

I agree. The wisdom of dumping the rear height-sensing valve was brought home to me when I lost my brakes as a result of a panic stop when I was cut off by an errant senior citizen (more senior even than me, if you can imagine that). Not only did the rusty hard line pop over the gas tank, the rear valve also exploded. Now I don't trust them. At all.

They will stick out beyond the flares, they will hit the flares if the suspension compresses, and if your state requires that the bodywark cover the entire tread portion of the tire -- it won't. Stock backspacing is 5-1/4" and 30x9.50s work great with that ... just slight rubbing on the lower control arms at full steering lock. You'll be pushing the tires a full 2" farther outboard.

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

Windshield? On a scale os 1 to 10 ... about a 12, maybe 13

The decal just means that AMC/Jeep was a sponsor of the Olympics in 1988. My '88 XJ has an Olympic 5-ring decal in one of the back side windows. It's a Pioneer -- not to be confused with something called an "Olympic Edition" that was offered in some other year.

Yep. Log onto NAXJA and contact the guy in the North Atlantic Chapter who posts as Magoo. (Actually, I think there may be some numbers in his screen name, but you should be able to find him). He did what you're talking about maybe two or three years ago. I haven't seen the finished product but, knowing Mitch, I'm sure it's pretty sick.

The guy who used to run a Jeep & off-road shop down the road (he's now doing heavy equipment repair ... better money because the customers pay their bills ;) ) told me there's a special anaerobic sealant for that. I think I recall seeing confirmation in a FSM awhile ago. Plain old RTV may work but I don't think it's the right stuff.

This is a question with no answer. Look at a parts book. The ZJ was available with averything from a 6-cylinder engine with standard (soft) suspension to a 5.9L V8 with optional off-road suspension. Unless you know which ZJ springs you're dealing with, the question cannot be answered.

Yes

3.73 is good for 30" tires 4.10 is good for 31" tires 4.56 is good for 32" and 33" tires You might be surprised to know that 31" tires with 3.73 gears is actually the exact same overall ratio as stock tires with 3.54 gears.

You can, but it's not a good idea. Old steel brake lines may be rusty, and when you try to straighten out the neds to lower the end they often crack at the bend. On an MJ the original rubber brake hoses are probably overdue for replacement anyway, so it's preferable to do it the right way and just buy longer hoses.

The factory limited slip for the D35, D44, and Chrysler 8.25 was the Dana Trac-Lok. It's a clutch-type limited slip, and if you find one in a junkyard you should assume that it will need to be rebuilt, so factor that into the cost of a junkyard axle. For an old MJ with 2WD, I think I'd just throw in a lunchbox locker and drive it 'til it breaks. The Dana 35 is fine for street use unless you abuse it (although it does sorta sound like you're planning to abuse it).

The old ones were supposed to use 10W30 or 10W40 (both were listed in the FSM). The newer ones are supposed to use 5W30 How's your oil pressure? If you're getting 40 psi or better at highway speed with the 10W30, it's okay. Personally, on a high mileage engine I would be using 10W40 or a wider range synthetic. In my '88 XJ I'm at 265,000 miles and I run Castrol 5W50 in the winter, 20W50 in the summer. And you shouldn't be running a 4.0L above 3,500 RPM a lot. Especially not an '88. The torque peak is WELL below that. You're just beating up the engine for no purpose. I doubt that mine ever goes above 3,500 RPM. My normal shift point is 2,200 RPM.

That would be correct. The knock sensor goes into a dry hole in a boss just above the oil pan flange. So you killed your computer's temp sensor. As I wrote, it should still run, but it'll most likely always be in open loop mode, meaning it won't know when the engine has warmed up so it will constantly run according to the pre-mapped fuel curve (i.e. rich) that's used for warming up. I don't think it'll hurt the engine, but it sure won't do wonderful things for your fuel mileage. I don't think that sensor interchanges with the one for the gauges in the head, due to a vastly different ohm range. So you are wise to bite the bullet and go to a dealer. The parts chains may not even be aware that the Renix era XJs and MJs have two (different) temp sensors.

NAXJA is an interesting critter. I should know -- I'm a charter member, and a lifetime member. And I haven't visited the forum for probably at least six months. I am and will be forever grateful to Pete for getting this forum started, because it gave me a haven when I threw in the towel at NAXJA. The thing is, the club promotes itself and its forum as "family oriented." I don't know if the rules have been changed since my term as a Director and moderator ended, but when I was a moderator the rules were rather clear about both language and flaming. But when I had the audacity to moderate some posts by one of the favored sons, the then-president shut off my moderating privileges with no discussion, no vote of the board of directors, and no notice. At 10:00 a.m. one day I was a moderator, at 3:00 p.m. that day I wasn't. All because I enforced a written rule. When NAXJA was young and small, it was a good group with which to be associated, and the members tried to help one another. Recently, the forum has become a rather unpleasant experience. I am still friends with most of the same NAXJA members I made early one. The curious thing is that, except for one or two others who are also lifetime members ... none of them are NAXJA members any more. Let us hope this forum never sinks to the same depths.

UH-OH indeed. That is the temperature sensor that sends data to the ECU. Without that, your ECU will be running in open-loop ("warm-up") mode all the time. It'll run ... but it'll be using a pre-set fuel map that's richer than optimum and your fuel economy will suffer. Either that, or you just cut the wires off the knock sensor. Both are located on the driver's side of the block.