Eagle

How much would the trailer and boat weigh? And how far do you plan to tow and at what speeds? Without specifics, my guess is a 23-foot boat on a trailer is probably pushing the envelope.

I thought you were referring to leaf pack thickness. It's deceptive referring to perch "thickness," because the perches aren't solid. What counts isn't their thickness, but the distance from the OD of the axle tube to the mating surface of the perch. That's why I expressed it as I did. Another way to envision it would be as if you had the same axle tube with both the old (under) perches and the new (over) perches in place. You would simply measure the distance/height between the upper and lower perch mating surfaces. Then add in the thickness of the leaf pack and you have the amount of lift. And then you can add or subtract as necessary if the axle tube diameter changes. I think we're saying the same thing, it's just a matter of expressing a visual image in words.

on the same note the sum of a lower (spring under axle of different thickness) is the [new axle OD minus the old axle OD] plus the [thickness of the new perch minus the thickness of the old perch] if i'm not mistaken...old thickness has to be taken into account as such. just an observation Nope. When the spring is under the axle, the thickness of the spring pack doesn't matter because regardless of the number or thickness of the leaves, the axle always rests on top of the main leaf.

"Evac" means to evacuate -- which in turn means removing any existing R-12 left in the system. R-12 is a serious greenhouse gas and can be serviced only by licensed technicians. Most states (and I thinkg the Feds) make it a criminal offense to just dump the stuff into the atmosphere. Besides, since the stuff cannot be manufactured any more, the only source for it is what shops can salvage. A tank of R-12 now sells for several hundred dollars. Most shops will at least evacuate your system for free in exchange for any R-12 they can recapture. Once in awhile they might even pay you for it. Once the remaining R-12 has been reclaimed, the next step is to "pull a vacuum," which is done to ensure that there's no residual moisture lurking in there to muck up the new gas. The new kits claim you can then just pump their contents into the system, but most sources I've seen recommend replacing the drier first. That would be done, of course, before pulling the vaccum and refilling the system.

That's sort of what I was thinking. As it stands, I now have no A/C. What's the worst that can happen, I won't have A/C?

Don't forget, when you go from spring under to spring over, the amount of lift is the sum of the axle tube OD plus the distance from the tube to the perch mounting surface (times two, once for under and once for over), plus the thickness of the spring pack itself. And if you're going from a D35 to a Chrysler 8.25, then you also add the difference in the tube diameters. I think that's going to add up to around 6"

Ummm, wrong. 1) The XJ spring perches are spaced differently from the MJ. You'll have to cut them off and relocate them. 2) More like 5" to 6" of lift. No way is it 3" for a SOA conversion. The 8.25 has larger tubes that either a D35 or a D44 so it's probably going to be at least 6" for you.

I'm looking at this conversion for both my '88 XJ and '88 MJ. I know the oil compatibility was a huge problem with the original RC134 conversions, but the kits they sell now imply that the oil in the kits is somehow compatible with the old oil in the R-12 systems. Is this true? Can I just evecuate and refill, or do I really have to pull the compressor and dump all the old oil?

Rear? I think they're 10mm but I don't remember the thread pitch. I'm sure they are metric.

Brakes are a good thing. You can take that to the bank.

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.