Eagle

What's the diameter of the harmonic balancer? Figuring out the offset from TDC for 10 degrees isn't difficult. Let's say the diameter is 6 inches. The circumference is Pi x diameter, or 3.1412 x 6. That's 18.8472". The full diameter occupies 360 degrees, so divide 18.8472 by 36 and you have 10 degrees occupying 0.5235 inches. Substitute the actual diameter where I used "6" and go from there.

Nothing here ...

With an automatic and stock size tires you won't have any issues. As DesertRat already mentioned, you'll feel some loss of acceleration, but it would be worse with a 5-speed. He's spot on about the driveshaft. Figure on getting it shortened by 1".

I've been pondering whether there's an easy way to correct this for years. Can't make up my mind if it's easy, or impossible. What happened is that Chrysler reversed the polarity of the sender. On the Renix models, the fuel gauge range was 0 ohms, for Empty and 88 ohms for full. The Chysler sender's range is (IIRC) 105 ohms for Empty to 5 ohms for full. I think what would work is cutting the traces on the cluster printed circuit and connecting the two leads from the wire bundle to the "wrong" terminals on the back of the gauge. But I'm not certain about that. I guess the way to test would be to pull the gauge out of the cluster and connect it to the appropriate two pins on the wire header corrector, see what the gauge reads, then reverse the two wires and see if the gauge reads in reverse. For this to be most useful, you would want to do it with the tank either 3/4 or more full, or 1/4 or less. If you're good with connectors, it might be possible to remove the two wires from the header that plugs into the cluster and switch their positions. I don't think switching the leads at the sender would have any effect. The resistance would still be the same.

The timing mark isn't on the pulley, it's on the harmonic balancer -- and you can;'t swap that from the 2.8L to the 3.4L because the two engines are balanced differently. What you can do is manually rotate your engine until the #1 cylinder is at TDC (top dead center) on the compression stroke. To find that, remove the #1 spark plug and probe inside the cylinder with something like a length of solid (not stranded) copper wire while a friend turns the engine with a wrench. (It'll turn easier with all the spark plugs removed.) Use a toothpick and some bright white or yellow paint to mark a line on the damper and on the block. Then calculate how far away from the first line you need to be to get 10 degrees, mark a second line on the damper, then wipe or scrape off the first line. Now replace the spark plugs, attach the timing light, fire it up and set the timing.

The GM 3.4L isn't a bad engine, and it's a MUCH easier swap in an '86 MJ. If I had to do one, I would do the 3.4L before I would even consider trying to convert to a 4.0L. What I want to know is why, if this truck is so pristine and rust-free, were the wheels and both bumpers replaced?

Nope. My house was built in 1950 by (for) my parents. It was a low budget house. All the doorknobs are brass (plated), except the bathroom door knobs are brass on the hallweay side and nickel (or some shiny, silver-ish color) on the bathroom side. mjben's answer seems like the best explanation.

It's been done ... by one of our members.

Flywheel won't be the same. 1990 is still Renix -- 1991 is Chrysler. He'll have to use the old flywheel or flex plate.

Ten years ago, when I worked for the building department in a small town up-state, our mail carrier made her rounds in a late model, right-hand drive Cherokee. I would have loved to buy it, but it wasn't for sale.

That's good to know. I thought only Redline had the friction modifier.

You will have to make a custom bracket. Where are you going to mount the license plate and light(s)?

Point of clarification: Your 4.0L engine does not have a PCV valve. PCV is an acronym for "Positive Crankcase Ventilation" -- the 2.5L engine has a PCV valve. The 4.0L system does not have any valve -- the flow is supposed to be controlled/regulated by the size of the rear (suction) tube. That's the one that gets clogged. There is no valve -- not in the front, not in the rear. In the old days, before emissions became a thing, engines just had an open tube out one side that turned down and vented to the atmosphere. That worked, but as the engines aged and developed more blowby, they pushed more and more oil out those tubes. Once we got into controlling emissions, the engineers decided to capture those oily fumes and recycle them through the engine to burn them. So -- no more dump tube in the side of the block. So now the inside of the engine was essentially sealed. But blowby still happens, so there has to be somewhere for those fumes to go. So they put a fresh air inlet in one end of the valve cover, and a suction tube in the other end. The suction tube led to the carburetor, throttle body, or direct to the intake manifold. Engine vacuum then pulled air out of the engine through the suction tube, and it was replaced by fresh air coming in through the inlet -- or by blowby. Unless an engine gets really bad, the system should suck out more than blowby puts in. The crankcase is under negative pressure. If the suction tube gets clogged -- which is what happens to the 4.0Ls -- there is no suction (or it's greatly reduced). When that happens, blowby pressurizes the crankcase. That pressure, which has oily fumes in it, has to go somewhere. I can't get through the skinny tube where it's supposed to go, so it goes out the other opening -- the opening that's supposed to be the inlet. That's when we get oil dripping into the air box. Rerouting the inlet hose to a catch can is essentially just reverting to the old, pre-emissions control system of leaving the crankcase open to the atmosphere. In theory (although it wouldn't be legal, but neither is the catch can) you could just put on a longer hose, run it down to the frame rail, and let it drip onto the ground while you drive.

True.

I think I remember someone in NAXJA doing a 3,1L swap "back in the day," but now? Why bother? The cost of a junkyard 3.1L is likely the same as a 3.4L so why get the smaller engine when you can get the bigger engine?

Yes. (Same answer I gave the first time you asked.) https://en.wikipedia.org/wiki/General_Motors_60°_V6_engine

Nope. I haven't noticed any deformity, but I wasn't looking for it. If it was there, it was very minor.

I get my U-bolts custom made from a commercial truck spring shop. They'll make them in any size I want (but SAE/imperial sizes, not metric). They all have thick washers and double-length nuts. I have to disagree with you on the appropriateness of the 5/8" U-bolts. Your truck isn't any heavier now than it was before you swapped the axle. If the factory thought 14mm was adequate for a pickup rated to carry a full ton, then a 9/16" U-bolt (which is already larger than a 14mm) would certainly be adequate for just about anything. What makes the 5/8" inappropriate IMHO is that you had to drill out the holes in the reinforcing plates. That means anyone wanting to replace the U-bolts with the correct 14mm U-bolts in the future would have a sloppy fit. Not the end of the world, but not right, either. I'm all in favor of strengthening beyond factory specs, but I'm not in favor of going farther than necessary, and generating other (otherwise unnecessary) modifications in the process.

60-degrees is the angle between the two banks of cylinders, it has nothing to do with the bell housing. But, yes, the 2.8L, 3.1L and 3.4L are all based on the same 60-degree block design. The GM 4.3L is a 90-dgree design, which is why those engines are so much wider.

Unless it has been removed, the MJ has a height (load) sensing proportioning valve located above the rear axle. The purpose is to reduce the braking power at the rear wheels when the truck is empty, to help alleviate the problem of rear brake lock-up causing a spin-out. There are TWO lines to the rear brakes, one for normal (proportioned) braking, the other is a bypass that sends full power to the rear brakes if the front brakes fail. One or the other of those lines often rusts out, usually where they run above the gas tank. Because of the safety bypass feature, there is a special procedure needed to bleed the rear brakes. The owner probably doesn't know that. My guess is that one or both of the lines to the rear brakes is/are rusted out.

^^^ This. That "carriage bolts" just jumped off the page at me when I read it. And I'm pretty sure 1/4" is too small. Check the size of the holes in the springs -- I think they're either 5/16" or 3/8". Factory MJ U-bolts are 14mm. Factory XJ U-bolts are 12mm. 14mm is approximately 0.55118". A 9/16" is 0.5625". Those 5/8" U-bolts are serious overkill.

Quarter window? MJs don't have quarter windows. Are you talking about the triangular front side window?

That actually could be repaired by chopping the roof off and splicing on a "new" roof from a rust bucket donor vehicle. It could possibly even be done using a roof and partial A pillar sections from an XJ. I hope it doesn't get sold for parts. It should be put back on the road.

Duty, hell. You're FAMILY, man. We (most of us, anyway) care what happens to our MJ brethren. That's definitely a bummer -- probably even worse than my two medical crises a couple/few years back. I'll add you to my prayer list. Let us know what the doctors figure out, and take care of yourself.

Yes.