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Just finished up the re assembly. It shift so smoothly. Really happy with how it turned out. It’s worth noting that the synchros that come in a rebuild kit will typically give you the wrong rings for 3/4 gears. The part you need that has the “house” shaped teeth is the same as the 5th gear synchro. One could just order up a couple more 5th gears synchros to compete the kit. I ended up re-using my 3/4 synchros as they were if like new shape with almost zero wear. Evidence of the relatively low mileage on this Comanche (90k). First and second synchros were a bit more worn but everything is new now. One particular aspect to pay attention to on a transmission rebuild are the springs and keys that are inside the synchro hubs. They play a crucial role in shift performance and keeping you in gear. They aren’t difficult to assemble but are a bit finicky. Still need to finish prepping and painting the case. On to complete the engine work tomorrow.

Transmission internals are all finished and the upgrades are in place. Very satisfying project. Really came to appreciate the way this thing is engineered.

So the 5th gear update difference is in the gear hub design. The new style uses different keys and springs for the synchro hub. Looks like a better design to hold it in gear better. The gear itself looks identical.

I’ll be installing it tomorrow. I think the difference is with the 5th gear shift hub or possibly the blocking rings “slipper clutch” but don’t know for sure yet. I ran into the same issue that many people do when rebuilding the ax15. The new 3-4th gear blocking rings have different shaped teeth than the originals. I see a lot of people reuse originals as you can’t really find the “house” shaped teeth versions for 3-4 rings. You’ll notice a comparison pic of the new vs old above. Supposedly, the adjustment in tooth design was designed to improve 4-3 downshifts and 3-4 upshifts. I researched it quite thoroughly and others have used the newer “ramped” style tooth blocking rings on the older synchros with no issue. It doesn’t seem like it would present an issue since ultimately, the tooth width is the same at the base, the blocking rings will still engage the slider teeth and the slider and synchro still have the same pattern.

Interesting project. Never delved into the ax15 this far. Was able to do a full rebuild and upgrade to the newer synchros, Marlin HD thrust washer and billet retainer plate. Fun project. Tested all the gears and it shifts great.

Rear half of the case disassembled

Tapped the passenger side coolant port to 3/8 npt to use a decent quality 3/8 to 1/8 reducer to run the Jeep gauge sensor. Lots of cleanup and assembly. 100% genuine GM parts used, none of those copy lifters, trays, gaskets etc. Also am swapping to an ls2 water pump as it looks much cleaner under the hood vs that giant ls1 water pump pulley. Awaiting a replacement set of Che bronze trunions that will complete the heads. Went with remflex header gaskets also to ensure zero leaks on the Sanderson headers. Coated all new parts and cylinders/pistons/valves in a light coating of assembly lube. Tranny work coming up next. The last picture is of the ax15 5th gear upgrade kit. Since I don’t have the original gear out yet I can’t say what the difference is but I’ll document it and compare some of the upgrades with the original parts.

Should be just fine. I doubt it damaged the inner roof skin. In order to affect the a pillars both the inner and outer roof structure would need to be damaged enough to pull the pillars in. For additional peace of mind, check your door gaps against the a pillars and see if you see a significant difference from before

Engine tore down to a short block. Doing a full cleaning and inspection. Crosshatching on the cylinder walls is fully visible. Everything looks great overall. Removed any carbon buildup.

Good to know. I’m going to measure the thickness of the material and see how much could be safely ground before I slice it open for a plate. If it doesn’t have to be structural and if the material is thick enough, I may make an actual access plate.

Engine is out. Transmission has it own workspace prepped for the upgraded parts and rebuild. I’ll need to add the washers to the pivot ball side of the throw out bearing fork to space it a little closer to the clutch. Also marked the offending areas of the quick draw bell housing where it makes contact with the firewall. Going to remove some material there and make a flat surface. Possibly by welding in a plate.

Makes sense. Lots of factors at play when it comes to handling and an ifs MJ would have a whole new set of equations I’m sure.

This . Rear axle width doesn’t play into the equation. Front axle pivot points and wheelbase are the factors here. It is perfectly acceptable to have a slightly wider rear axle or front axle. It will be one of a great many factors that determine the handling characteristics of a vehicle.

The 8.8 housing is a decent bit larger than the ring gear and, compared to a D35, will loose significant clearance. Normally in the order of two tire sizes. So if you’re getting an 8.8 to run 33’s, vs 31’s on your existing d35, it’s a zero sum game. The 8.25 is also larger than it needs to be but does provide more room to shave the bottom of the pumpkin than the 8.8. Other than that, they tend to be higher priced and harder to find now than liberty axles. They are narrower and can rub on the frame rails of an MJ, the tubes are prone to spinning with large tires, they max out at about a 35 in stock form, still have c clips, still need shims to setup the gears. They’re not horrible axles but they just aren’t as good of a swap candidate for an MJ. And they come with a hefty weight penalty. If you’re running 31’s there’s a solid argument for keeping a d35. Up to 35’s and there a solid argument for the 8.25. The argument for the 8.8 just isn’t as convincing as it was 10+ years ago and more so for an MJ.

I just picked up a nos module. Wondering if it will work correctly . Any idea to keep a good one from failing? Does it need to stay cooler? Or is moisture killing them?

KJ 8.25 is about 2.5” wider than the XJ model. Fits the rear of an MJ very well since it is a bit wider at the bed. Lots of brackets to remove but that’s not any real issue. Fairly easy to re-gear since it has side adjusters and a crush sleeve. That being said, rock auto has your bolt in d35 1541 axles around $150/ea. Also check with revolution axle and gear. They still had them last I checked. I’d stay away from an 8.8 for only 31’s. Too narrow on an MJ and with its large pumpkin, you might as well run 29’s on a d35. As for what ratio to run, plug your numbers into grimmjeeper gear calc and see what your rpm’s will be. And measure your actual tire size to use as your number. It’s likely 29”-30” true size

Happy to help. Can't tell you how many other builds have been inspirations to mine as well. Looking forward to your build thread

Mine was about 2k. There are some pics in my build thread of it installed. I think I got some extra options on mine but don’t recall what they were. Haven’t seen my truck for a long time.

Just to follow up on this, @Pete M can we move this to the DIY section for easier lookup?

An excellent option is the truck covers USA cover. It’s a retractable aluminum setup. They have custom made an MJ specific cover for at least a couple of us here on CC. It’s definitely not the cheapest option but it is phenomenal.

Sounds great!

Definitely

Nice! Just sent you a PM

Value you it at what it would cost you to replace it along with your time and investment. The market just isn’t what it was even 5 years ago so a decent replacement will be costly. With insurance, that shouldn’t be your cost to bear. It’s nice to have a cash value that would make it easy to find another vs having to scour and haggle to find one.