Eagle

I think rebuilding the Trac-Lok is a good choice, given that your driving is 80% pavement. I definitely wouldn't go with an auto-locker. Second choice would be a TrueTrac, which is a limited slip but doesn't use clutches.

No, the early ones didn't have the potentiometer. That didn't come until the "new" instrument cluster design, in 1988. And it wouldn't make it 6,000 RPM high, anyway.

They are.

Back to the original post -- I hope your planned build is mild, because that MJ is far to nice to hack up. It should be preserved.

To me, "clutch out" means the clutch is disengaged. I think you're saying it makes noise when the clutch is engaged, and the noise stops when the clutch is disengaged. That, plus popping out of gear, says to me that the synchronizers are shot. Possibly due to using the incorrect gear lube in the transmission. Unfortunately, the factory initially said to use GL-3, but GL-3 was replaced by succeeding numbers. GL-5, which is what's generally available, has a lot of sulpher. The sulpher attacks "yellow metal" (brass and bronze). Guess what the synchronizers are made of.

Why does the fuse panel need to be replaced? Why not replace with another Cherokee/Comanche fuse panel? And who swapped in the AX-15? Is the transmission change related to the fuse panel issue?

7,000 RPM? I thought in-line sixes had a destructive harmonic at 6,000 or 6,500 RPM. There was never any reason to push an AMC (or Jeep) I-6 even to 5,000 RPM. They're long stroke engines, designed and built for torque, not high-RPM horsepower. Long stroke engines don't particularly like to rev. Among all the Cherokees and Comanches I've owned through the years, completely ignoring the AMC cars, I've easily put over a half million miles on the 4.0L engine -- probably closer to a million. I don't think I've ever taken one above 3,500 RPM, and I rarely go over 2,500. My usual shift point with the 5-speeds is between 2,000 and 2,200 RPM.

I was thinking of "around town" as being generally 45 and under -- mostly under. Going back to the root of these engines, my family was a Hudson ==> AMC family. Between my parents, my brother, and myself we've owned a number of the old AMC versions of this engine, ranging from 199 c.i.d. to 232 c.i.d. to 258 c.i.d. Also owned any number of Javelins and AMXs with V8s. All were standard transmissions, from before the days of overdrive (except as an expensive option, which we never opted for). Regardless of gearing and tire size combination, the end result was always 24 MPH per 1,000 RPM in top gear -- so 60 MPH was exactly 2500 RPM, and 3,000 RPM gave a nice, slightly extra-legal 72 MPH cruise. I know for those accustomed to newer vehicles with 5- and 6-speed transmissions the idea of running around at 2500 RPM seems like "burning up the engine," but it isn't. Don, with your tire and gear combination 50 MPH in 3rd gear should be 2323 RPM. Overdrive at 50 should be 1743. I'd probably let it go into overdrive at 50, but I'd certainly try keeping to 3rd below 50 just to see what happens.

I know he has the numbers, but I don't have them. I don't really care what the actual numbers are. The point is that his around-town gas mileage sucks. If it turns out that he's operating well below whatever his torque peak RPM is, it's very possible that his fuel economy might increase if he stays in a lower gear, to keep the engine running closer to the torque peak RPM. The AW4 likes to shift into 4th gear (overdrive) at a much lower speed than where I would choose to shift a manual transmission into overdrive, so it's worth a try. Don said he's running 31" tires and 4.10 gears. By my chart, at 40 MPH in overdrive the engine would only be turning 1394 RPM. And I think the AW4 will go into 4th at 40 MPH. At 45 MPH, it would be turning 1568 RPM. Still WAAAY below the torque peak, and probably not even sneaking into the "fat" part of the torque curve. Keep it in third gear (direct, 1:1 ratio) and the RPMs become 1859 at 40 MPH and 2091 at 45 MPH. I would think that's getting into a more useful region of the torque curve.

All things being equal (which they never are), the torque peak is the engine speed at which the engine is operating most efficiently. In a motor vehicle, other factors mess that up, such as mechanical drag and aerodynamic drag, both of which increase exponentially with speed. Nonetheless, it's worth a try. I know that here in Connecticut for many years the maximum speed limit on any highway was 55 MPH. (They've now gone back to 65 for a couple of Interstates.) My '88 Cherokee 4.0L 5-speed (stock tires and gears) only turns about 1540 RPM at 55 MPH. That's far below the torque peak, even for a Renix-era engine. The torque peak for the '88 is at 2400 RPM. I found by actual testing that my highway gas mileage was the same in fourth gear as it was in fifth. In fourth, 55 MPH is 2054 RPM. That's still below the torque peak, but at least it's getting closer. There wasn't enough difference to make me always run in fourth. I used fifth because it was there, and because it might result in less wear on the engine. But fifth was so far under the torque peak that, at 55 and even 60 MPH, most long upgrades required a downshift to fourth. So I think it's worthwhile for Don to at least try it.

Mea culpa.

That's because there ain't no other 4.0L, AX-15 ZJs out there. That's almost as rare a bird as my 2000 XJ 4.0L with 5-speed.

It could be bad synchronizers. Does it sometimes pop out of gear when you're coasting? By the way -- did you swap the transmission? Because an '88 should have a BA 10/5, not an AX-15.

Don, you had your stroker dynoed, didn't you? Do you have a torque curve for it? Is it possible that you might do better around town if you put the shifter in "3" to lock out overdrive? If that would put your RPMs closer to the torque peak, it might make a difference.

Incipient CPS failure. I had that in an XJ (the original '88) a number of years ago. Had been running fine. Drove a few miles from a Subway restaurant down the road to Walmart. Noticed a skip under power on the highway, but no other issues. came out of Wally World and it was dead as a doornail. Another possibility is failing spark plug wires but, with a Jeep 4.0L, I now tend to suspect the CPS before I look at ignition wires.

Using the rotary switch takes care of that. It only locks it in third or fourth, and the shift from third up goes to UNLOCKED fourth. Then it's another switch position to lock it in fourth.

Don't know if it matters, but what year? Torque specs sometimes changed from year to year.

I don't know how Frank did it, but he did it. It was his daily driver, I believe. And I'm quite certain he was using a rotary switch. I remember because at the time I thought it was a terrific solution. Since I'm not an electrical engineer, don't know protected diodes from unprotected (first time I ever heard of protected diodes), and don't know what "iso" is, I'm afraid I can't offer anything useful other than the concept (which isn't mine).

When you shift manually, you lose first gear. Frank did it with a rotary switch. That made it progressive -- just move one position for each gear you want. I believe he said he used a six position switch. The way I think that would play out would be: First Second Third Third - locked Fourth Fourth - locked

I have a question that I've often wondered about, but never pursued since I mostly drive standard transmissions: Exactly how does an automatic tranny shift? If you add a toggle switch to control torque converter lockup on the AW4, can the tranny shift from fourth to third or second with the converter locked (as long as you're moving at an appropriate speed)?

Back in pre-NAXJA days, on the old XJ forum, Frank Swigert posted details of how he wired an AW4 with a rotary switch in an AMC Hornet. Someone on the strokers forum may know how to contact Frank -- I believe he's still around.

Only "sort of " close. 31x10.50-15s through 3.73 gears are almost exactly equal to 225/75-15s through 3.55 gears.

Add a toggle switch to manually control torque converter lock.

Agreed. Two things that terrify me are spiders and snakes.