Eagle

I don't know how fast you drive, but even with 205/75 tires and 4.10 gears 70 MPH would only be turning 2750 RPM. 3350 would be an 85 MPH cruise. Personally, I wouldn't drive any MJ (or XJ) that fast, even if it were legal (which, of course, it isn't).

My guess would be that the more expensive one has more "meat," which would allow for the drum(s) to be turned two or three times before going out-of-spec, which the cheaper one may have only enough thickness for one turning before going oversized.

Where's the "mature" part? And where's the "humorous" part?

The right side horn. If your truck is a base model, it doesn't have dual horns.

Correction: Its torque PEAK is 2250 RPM. The torque curve below that is ramping up, while beyond that it's pretty flat all the way to about 4,000 RPM. At highway speeds, when you're pushing that flying brick through the headwind, you'll get better gas mileage running 2500 to 2600 RPM than you will running 1700 to 1800 RPM. As I wrote, the basic engine was designed to run all day at 3,000 RPM. Aside from EFI, the only basic difference in any of these engines, all the way from the original 232 c.i.d. to the 199 to the 258 (4.2L) to the 4.0L is the stroke. The 4.0L is the only one that used a different bore, and it's not different enough to affect reliability at a sustained 3,000 RPM cruise.

That depends on how heavy the draw is. For example, the clock is a constant draw, but how many dead batteries have ever been caused by the clock?

GM's later 3.1L and 3.4L V8s use the same block as the 2.8L that was optional in the '86 MJ. That would be an excellent candidate for a swap. In fact, the later 4-cylinders ('91 and up) with the multi-port injection produced significantly more power than the throttle-body version. Not in the same class as the 4.0L, but a late-model 2.5L would require no physical changes to your truck, you would just have to graft in the engine room wiring and ECU to make it a complete conversion.

If I were a betting man, I would be willing to bet that with two otherwise identical MJs, one that ran 3,000 RPM at 70 MPH would deliver better gas mileage than one with stock gears and a 5-speed, that runs 1960 RPM at 70 MPH. There's just nothing like running UNDER the torque curve to boost your gas mileage ... NOT. 3,000 RPM is not "@#$% ridiculous high rpm's" for these engines -- it's the speed they were designed to run at.

Redlining it? How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150? Eagle, it was a figure of speach. I didn't say that I DO redline it...just that I don't want to. No, you said you were worried about redlining it. And I was pointing out that with 4.10 gears you would be a LOOOOOOOOONG way from ever approaching redline even at extra-legal highway speeds. Remember these engines were designed before most people had overdrives. The standard setup from AMC typically was 3.08 gears for the I6s and 3.15 gears for the V8s, and on stock tires we cruised at 3000 RPM at 72 MPH -- all day, for hundreds of miles. Y'all (not just you, Pat) have gotten so accustomed to the ridiculously low engine speeds the factory pushed out the door that you think anything over 2,000 RPM is going to blow up the engine. Not so.

Redlining it? How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150?

And don't forget that if you are regearing, the new pinion gear has to be set for depth, and that is controlled entirely by shims. It is possible that the old shims might be right ... but highly unlikely. You need a shim kit.

The 5-speed overdrive ratio changed a few times but, in the overall scheme of things, none of them are enough different from that of the AW4 to indicate a different choice of ratio based on the transmission. As I have posted a number of times, I ran the lifted '88 MJ on 31s with 3.73 gears the entire time it was lifted and used for wheeling. 31s and 3.73s results in exactly the same overall final drive ratio as stock tires with 3.54 gears. It's very drivable on the street, but could use a bit more gear for a better off-road crawl ratio. IMHO 4.10s are the optimum gear ratio with 31" tires.

His post did not stipulate that the '89 has an automatic transmission. Also, given the frequency of the flex plate cracking, I would not do a tranny swap without replacing the flex plate. I don't want to pull a tranny and transfer case that I just installed three months ago.

Check your battery cables where they go on the battery.

The original post doesn't say what engine or tranny are in the '89. The '94 AW4 will work with an '89 4.0L, but it will require buying a new flex plate because the flex plate teeth are what trigger the CPS, and the Chrysler HO system is completely different and not compatible. Ditto if the engine in the '89 is a 2.5L, except that there you'll also need the appropriate bell housing and torque converter for the 4-cylinder engine.

Seems to me if he was a real friend he'd let you have it for $50 less than what a scrap yard would give him, or at least the same amount. I could understand a stranger holding you up for more, but a friend? That ain't right.

An internal combustion engine requires three things in order to fire and run: fuel (gasoline), air, and spark. We'll assume that you have air, so you need to verify that you are getting spark and gasoline. Gasoline can be introduced as simply as dribbling gas into the carb opening, so first you need to find out if you have spark.

The factory spec is 13 psi (minimum) at idle, and 37 - 75 psi above 1600 RPM. That's for all the engines. In reality, most tend to idle around 25 to 30 psi and run at 50 to 55 psi at normal highway cruise (60 to 70 MPH). There should be a distinct drop when you stop and the engine speeds goes down to idle. But ... the factory gauge in my '88 XJ basically sits at 40 psi no matter what speed the engine is turning. It has to be the gauge, because I've replaced the sender three times and it made no difference whatsoever. It drops to zero after the engine has been shut off, but once started it's more of a GO - NO GO gauge than a pressure gauge.

They are completely different in size and shape. I very much doubt that an XJ tank would fit unless you hung it below the frame rails, which would be a VERY bad idea.

The box is bolt-in but the pitman arm is different and should be replaced with an XJ/MJ pitman arm. As to whether the ZJ box is an "upgrade," it depends on your usage. The ZJ box has a faster ratio. That's a good thing for street driving on stock or near-stock size tires. But the ZJ box is not any bigger or stronger than the XJ/MJ box. Running a quicker ratio with large tires, especially if you do rock crawling, is very hard on the box. If anything, a rock crawler on very large tires should be going to an 18:1 ratio box rather than a quicker ratio box.

Not my problem. I don't regard that as a viable excuse. The bottom line is: If I can't read the post, I can't understand the question. If I can't understand the question, I can't provide a useful answer, so I don't even bother to post a response. The common language on this forum is English, not TXT. And, BTW, a tech question should be posted in the tech area. Posting a technical question in the Pub because you think more people might see it is a violation of the forum rules, plus it's just plain rude. Also, BTW BTW -- the seats and console from a new body style Cherokee will not fit into a Comanche without custom brackets for the seats and a bunch of carving on the console.

As CW mentioned, 3:10 was not a Jeep ratio. I had a difficult time understanding your post, until I realized that wasn't a typo but an incorrect ratio. 4.0L engine w/ 5-speed, the stock ratio was 3.07. That ratio, IMHO, was a factory mistake and should never have been used. But ... they didn't ask me. My rule of thumb for ratios, based on the vehicle being used for a mix of daily driver and moderate wheeling: 3.54 for stock tires 3.73 for 30" tires 4.10 for 31" tires 4.56 for anything larger than 31s 3.73 gears with 31x10.50 tires is EXACTLY the same final drive ratio as stock tires with 3.54 gears. (Equal final drive ratio = equal power.) There is no way 35s with 4.10s would come even close to matching the stock final drive ratio. BTW, 4.88 is an available ratio. Dana-Spicer doesn't offer 4.88 gears for the Dana 30, but some aftermarket companies do. BUT -- you have to be brave to use then, and not have a heavy right foot. The problem is that the pinion gear gets very small with the 4.88 gearset, so the differential isn't very strong. Which, of course, is the opposite of what you want when you're moving to tires so much bigger than stock. I can't imagine why you might want to put 35s on a Comanche. The front Dana 30 is a decent axle, but it's not equal to 35s. Plus, you'll have to do so much chopping that you won't have a Comanche when you're done.

XJs are spring-over, MJs are spring under. The XJ springs have less native arch than MJ springs. Using one leaf (any leaf) out of an XJ pack to replace a broken leaf in an MJ pack cannot possible duplicate the original spring's characteristics.

Oxygen sensor? Runs okay cold but goes nuts once it gets warm?

The bottom got slightly chopped off on the last version.