I'm thinking the same thing. At this point I think I just want to push the easy button. I have a few possible paths.

1. Novak new production. $2200 plus tax and shipping for a brand new unit with the redrilled XJ t-case clocking.
2. Novak reman. $1700 plus tax and shipping. Upgraded over a standard rebuild.
2. Allstate gear or some other reputable vendors reman unit. $1400 plus tax and shipping. The $400 core charge means I still am ahead for having bought this transmission and bellhousing for $225.
3. Rebuild and kitbash the 2wd and 4wd transmissions together. Fraught with peril, might need hundreds of dollars more of new parts, and I might screw up assembly or miss an issue and break it soon after, with no warranty.

I've got $225 in the 4wd trans, plus about $400 in rebuild parts. I could sell the rebuild parts at a loss and just move on with my life. I've been dragging my feet on this manual swap for years now. This transmission was likely thrown together for a beater Jeep. I'd be fine with that, if this was a beater Jeep.

A quick win would be worth the extra cost. I just need to decide if I want reman or new unless a known good AX15 pops up for sale locally in the next few days.

 

I came to my senses and realized there was no loss to cracking open the 2wd transmission. It's either going to donate the parts I need, or all of this is scrap to be used as a core.

First I tore deeper into the 4wd transmission and disassembled the output shaft gearset You can tell it's a used part, but it'll do. The 1st gear bearing surface isn't perfect and the 2nd/3rd thrust flange has a small lip, but everything measures out to be within spec. The part of the shaft that looks really ugly is where a cartridge bearing presses on, so no worries there.





I had to get some 4x4 sections cut to support the bearing splitter, as shown in the ucandoit2 video series.



Sir, a second transmission has hit the workbench...



Our first glimpse into the health of this 2wd transmission that came out of an absolute beater. The drain plug looks surprisingly okay.



Output shaft the looooooong way.



Mounting the intermediate plate in a vise, on your own, is a pain. I used some thin wood pulled from the scrap bin at Home Depot as soft jaws. So that I could free up a hand and not worry about holding the plate at the correct height and angle while tightening down the vise, I used some sockets to raise the "floor" the gears sat on. That made stabilizing the plate a one hand task. Just make sure whatever spacer you use gives you enough clearance to pull gears off and rotate things for inspection.



And now I have a lot of random gears laying around on my desk. I'm pretty pleased with what I've found, given the state of the Jeep I pulled this 2wd trans from. Everything appears to be in much better condition than the 4wd trans, and I feel confident I'm the first person to open up this unit.



Here are the clearances I've measured so far. Parts highlighted in yellow are what I intend to move forward with - as many internals as I can get from the 2wd all fitted to the 4wd output shaft. The countershaft gear and input shaft will be the 2wd parts as well.



3rd gear clearance is just outside spec. The factory service manual says if it's outside of spec, there are two possible causes - the gear thrust face, and the output shaft flange thrust face. The FSM says if the flange is in spec, to replace the gear.

I am taking off for another long weekend, but I plan to put in one more parts order so that I can start reassembly when I return.

• 4th gear synchro - A definite buy. 3rd, 4th, and 5th synchro are identical in some years of the AX15. While I've seen some people say 4th and 5th are functionally interchangeable, they are obviously visually different in my transmission. Might as well buy the most bestest one for my application.
• 3rd gear? A new bearing might tighten up the clearance here to be back within spec, but for $45 I can get a brand new one and have followed the FSM to the letter.
• Retainer plate? The 2wd retainer plate is in better shape than the 4wd unit, but also has wear marks. It's a pretty affordable upgrade ($67) to get the billet one from Marlin Crawler.

As a friend of mine said "Well, this is where you gotta decide if it's good enough. It's going in an old Jeep, if it looks like normal wear and tear for the age then oh well." I need to keep that in mind and not chase perfection.

I can't wait to get back in town and get this thing back together.

 

Last night I prepped the input shaft and counter gear shaft. Old bearings pressed off, new ones pressed on. The main gear set will have to wait.

I also went ahead and cleaned out behind all four of the shift detent plugs. I pulled the caps, cleaned the spring and ball, then used brake clean and compressed air to get any remaining schmoo out of the intermediate plate, and reinstalled the plugs with Loctite Orange. This should get everything in the shift lockout system 98% as clean as a full teardown like shown in most rebuild guides, with much less work. I cleaned out the three on the side first, then the top one. Before reinstalling the top cap, I filled the hole with oil so that it would drain down into all the other detents.



Something got me thinking about all the work I haven't done to the Jeep since the trip. And how I haven't looked into the overheating at all, and just assumed that it definitely was the fan clutch. I popped the radiator cap to see if boiling over had reduced the coolant level. Nope.

But I found this brown goo in there.



I'm not sure what the goo is from - cracked 0331 head? Rust in the cooling system? Blown transmission oil cooler?

As background for anyone just dropping in, this is a '00 engine, 0331 head and all, in my '99 with 195k miles, all original.. The engine was flushed multiple times when it was still installed in it's first home, my old green 2000. During the engine swap (Winter 2020-2021), I removed the freeze plugs and scrubbed every bit of rust away that I could. The water pump was replaced in 2018 and was still looking great at swap time. I installed a new radiator, and I ran a coolant filter for an entire summer after that to try and clean it out more. I think I replaced the coolant during my dash off clutch pedal install and blend door repair back in January 2024, but I don't have record of it. At most, the coolant is 4 years old.

Coolant levels in the overflow tank are normal-ish. It's needed a top off every few months since the swap, I assume due to a leaky freeze plug on the back of the engine. I don't see any of the telltale 0331 cracks under the oil cap, which doesn't have any milkshake on it either. Admittedly I haven't driven the Jeep in a few days.

I'll add a coolant flush to the to-do list and keep an eye on it. If things get worse I'll test for combustion gasses in the coolant.

 

I wasn't feeling too motivated for transmission work so I spent this evening catching up on some of the Jeeps actual problems.

First up, that overheating and gross coolant. Let's find out if they're related. I did some research on coolant flushes, figuring that there had to be a more effective and economical approach than the generic bottles of radiator flush. Bob Is The Oil Guy had some threads about using citric acid, so I went with that.


This was $7 for 12 ounces of powder, I found it next to mason jars used for canning. The Prestone radiator flush is sodium citrate and was $5... close enough to the same thing. My bet is on the citric acid being more concentrated and powerful.

I drained the radiator and it came out fairly clean.

This is what was left in the lower radiator hose after draining the rad.



With most of the coolant caught in buckets, I used a hose to flush the rest of the block, radiator, and heater core. I also pulled the block drain plug to be thorough.

With everything put back together, I used a magic fill funnel, dumped in the citric acid powder, and filled the remainder with water until the thermostat opened. Once the coolant began to expand and backfill into the magic funnel, I raised the revs to suck in more coolant with one hand, and quickly swapped rad caps with the other. Boom, good enough of a fill.

The grill got partially blocked off to increase flow through the radiator and thermostat. Plus, by getting it into the 210-220* range, I figured the acid would be even more effective.

This is what came out.



So tomorrow, I'm going to go buy more citric acid powder and run yet another coolant flush.

I'm pretty disappointed with how badly this engines coolant jacket has rusted. Again, this engine has been flushed multiple times over the past few years, physically cleaned out by removing the freeze plugs and scrubbing everything I could reach, and flushed again after that back in 2021.

 

Four years ago I cleaned the crap out of this engine block while it was on the stand before swapping it into this Jeep. I pulled the freeze plugs, removed the rust scale, scrubbed everything I could reach with wire brushes and rifle brushes to get between the cylinders. I replaced every single part of the cooling system. I filled it with coolant I mixed myself - 50:50 of concentrate and distilled water. The fact that it didn't crack the block back in January when I took it into the mountains and the temp dropped to -4*F should be proof enough that this had coolant and not just straight water. This engine got PAMPERED.

Here are samples of the four coolant flushes I've done in the past week.



What do I have to show for it? Here's a borescope view of the block drain plug hole.



The black pool to the left is water that remained in the block. The lumpy crud above and to the right of it appears to be rust scale.

What sort of junky pot metal are these engines cast out of?? I have completely ignored the cooling system in my other vehicles for years and never had an issue with rust. This thing gets babied and maintained almost perfectly and it still rusts out.

I put the block drain plug back in, poured another bottle of coolant flush into the heater core outlet on the thermostat housing, and walked away. I'll just leave it to work at full strength on the bottom of the cooling jacket for a while.

__________________________________________________ __________________

So let's go work on the transmission! Time to reassemble after giving every part a deep clean. This has taken forever to get back together because I keep finding new issues on part inspection. I had been waiting a few days to get in the correct 4th gear synchro.

What's that? The new bearing I bought is missing a roller!



I got mad, thought about seeing if the seller would send me a new bearing, then decided to just go ahead with the rebuild using the original bearing that still looked great.

The main output shaft went together smoothly.



There were no problems until I installed the whole thing into the midplate and did a function test after complete assembly with loctite. Shifting into 4th and doing a spin test resulted in the clatter of synchro teeth as the transmission slipped.

The 4th gear synchro doesn't fit and wouldn't fully engage 4th gear. I double checked the part number both before purchase, and after seeing this, and it is indeed the correct part number for the 3/4 "home plate" synchro.



The original fits right into place, obviously.



A comparison of the two. The new part is ever so slightly larger in diameter on the faces that are touching, so it won't slide into the synchro hub. It's also thicker, for some reason.



I bought a 5th gear thrust washer not because it was needed, but just to tighten things up a bit, and it wasn't too expensive. Look how much less shiny and reflective it is. It looks like they never bothered to do a precision grinding of the thrust faces and just did a standard machining pass. I'll be returning this. It's another Crown part, but I didn't know that when I bought it.



So here's a complete list of all the issues I have had with new parts on my AX15 rebuild.

1. Rebuild kit has two 3rd gear "triangle" synchro and no 4th gear "home plate" synchro. This is a known issue encountered by everyone that buys the kit. The root cause appears to be a confusion in the fact that older AX15s shared the same "home plate" synchro for 3rd and 4th, before 3rd was updated to the "triangle" style. Well, the rebuild kits include two matching synchros for 3 and 4, but of the updated "triangle" style for 3rd gear. By the way, if you go to buy a new 3rd gear, it will have the older style "home plate" pattern on both 3rd and 4th, so you'll need a new hub and synchros as well. The rebuild kit is appropriate for no transmission ever made, and doesn't match the other new parts available for sale FROM THE SAME VENDORS.
2. Rebuild kit has a bearing that is bad out of the box and never should have passed QC.
3. 4th gear synchro purchased from Crown, a specialty Jeep parts supplier, does not fit.
4. 5th gear thrust washer made by Crown has worse surface finish than the original parts, such that I'd rather use the old part.


I am so close to crashing out and giving up on project cars. This crap I'm dealing with isn't worth it.

I have another old project car, a 2001 Miata. After 200k miles and who knows how many track days, the original engine was tired. I bought a used engine to get it back on the road quick and found that it most definitely was not the 60k mile JDM takeout that it was advertised as, with obvious crankshaft damage. So, I returned it and decided I'd be happier rebuilding my original engine, using a machine shop I've worked with before. He told me it would take a month to bore the block and rebuild the head. That was for 4 months ago. I've checked in a few times and keep getting excuses. Now, normally I would have grown tired of this and taken my parts and business elsewhere, but I busied myself with the accident repair and this transmission rebuild.

Why do I feel like I'm having to cobble 30 year old used parts together, zombie Mad Max world style, to keep one of the most popular cars ever made on the road? Why are corners cut everywhere, by everyone? What is the point of all this? WHY IS EVERYTHING GARBAGE??

Don't buy Crown parts if you can avoid it. But don't expect quality even from the original OEM Tier 1 supplier! In fact, just don't buy new parts if you can avoid it.

 

Corrosion in the cooling system??
Rule out the bad kind of electrolysis by cleaning every single engine electrical and chassis electrical ground connection.
When it's easier for any electrical circuit to return ground through the cooling system, they will and they do.

Also never underestimate oils ability to migrate under pressure to places of less pressure.

UV dye and flashlight are your friends.

 

Good point on the grounds. I've replaced the main block ground cables, but I'll go ahead and clean the contact points on the engine too. Maybe I'll upgrade that interference strap at the back of the head as well, or ground the alternator body itself as well.

As for oil, so far I think the 0331 head is doing okay. There's no milkshake under the oil cap, or any crack line under it where they so commonly fail. The coolant doesn't have a sheen of oil on top. Of course, it could also be the ATF cooler leaking, but I'm working on deleting that!

Speaking of... I reassembled the manual transmission. It's pretty much ready to install. I'm considering if I want to try to get it in this weekend. Probably won't, but it's tempting.







Everything shifts nice on the floor. Fingers crossed that it works well in the Jeep!

 

I finally got around to dealing with the u-joint and realized how long overdue this was. It went much smoother than expected.

The pictures should speak for themselves, but it looks like the seals failed and let water in, rusting out 2/4 of the bearings. These were installed by me 5ish years and 50k miles ago and apparently should have been changed out long ago. I'm so tired of junk parts failing long before they should.








All buttoned up and back together with a new Moog u-joint. Maybe I'll have to use that lifetime warranty.



I did another coolant flush with Prestone and dishwashing detergent.



I drove it in to work today with just water and Cascade dishwashing detergent for coolant. I'm getting tired of $5 a flush and want to see if I can't get the scale to come loose just with time and detergent.

I'm getting leaks at all the hose joints that have been removed. New radiator hoses and water pump are on the way as I figure constant removal and acid treatment this isn't doing them any favors.

 

I had a free weekend, rare these days, and decided to finally get at it on Saturday after years of hoarding parts and prep. The pedal box was installed back... almost two years ago. I haven't gotten it done though. I'm not the fastest worker, and I inevitably fall prey to overthinking. Last night I pulled the transmission and transfer case. But first, let's recap.

I was still doing flushes since my last post. Many flushes. So many. I got tired of it all and felt like acid based treatments were putting the head gasket at risk. So, I went nuclear and got Evaporust Thermocure like a few people had recommended to me, and drove with it in there for three days. Stinky crap. It came out black.



I let it sit, and about 3/16-1/4" of iron powder was sitting at the bottom of the bucket I caught most of it in.



I piled it all up. Maybe I should weigh it and see if I now have a lightweight block.



I decided to replace the water pump and thermostat out of an abundance of caution.

The thermostat... Well, I bought a Motorad High Flow unit, since that is what most of them are now anyways. The one I pulled out has always been holding temperature well, and has USA stamped on it. The old one measured at about 29mm, and the new high flow one at about 32mm. Plus, the old one has the true Stant style V-notches in the piston that make the transition from open to close less abrupt. That's not enough of a size increase for me to justify removing a part I know the history of after so much bad luck with parts lately. So I put the old one back in. For $4 I'll keep it as a spare - I've verified it worked in boiling water.



Look at how eaten away the iron is under the thermostat housing. And look at how yellow tinted the internal casting features are.



The old water pump felt to have stiffer bearing, but the new one had a noticeably smaller gap between impeller and housing. And with signs of fluid leaking out of the weep hole, there wasn't much of a choice. The new one is obviously manufactured differently - casting, impeller, bearing stiffness, all of it. Both are Gates units, one from 2018, one from 2025.





Oh look, what an unexpected surprise, this freeze plug was leaking like so many of the others when I first did them for the motor swap. While I'm in there...



Holy crap. How is this engine still held together. How is the head gasket still holding.



Admittedly, a lot of that is sand. I'm assuming it's casting sand, but I'll check to see if it's from all the Cascade dishwashing detergent.

The freeze plug has been replaced, flywheel and clutch installed, the manual transmission is in, as is the transfer case. I'll compile a few lessons learned from both endeavors and share them with the group here in the next few days. It started coming down hard with rain and cut me off early tonight. Wouldn't it be nice if my other project car hadn't been sitting on jackstands, hogging the garage space for the past four months waiting on other people to do their job.

 

Sweet update and solid progress! You're making me paranoid about one of mine though - it too has brown coolant at the moment... looking forward to your learnings ha!

At least these things can put up with such conditions and still run normalish. It's one of their "party pieces" if you ask me.

 

I'm convinced now that once the rust has truly taken hold, only way to fully clean out these systems is to pull that freeze plug. There simply isn't enough coolant flow there to stir up the crap that falls out of suspension Anything else is a half measure. I'm thinking that the remaining rust still on the walls and that's loose in the system "eats up" a lot of the anti corrosion chemicals when you pour in fresh coolant, dramatically shortening coolant life.

That said, I'd like to look for any other potential cause for things to get this bad. I'm not convinced this is a reasonable amount of rust for 4 year old coolant, some of which was replaced when I worked on the heater box back in 2023.

Here is what the inside of the block looked like before I put in freeze plugs back in 2021.

 

My gas powered leaf blower blowing in the head at the thermostat recess and exiting at the water pump mounting face does a fairly good job of blowing the crap out the block for me.

An old trick from the days before overhead valves was a strip of zinc on a few links of brass chain soldered the bottom of the radiator cap to hang in the coolant as a sacrificial anode.

Today we have coolant filters with Supplemental Coolant Adative cartiges (donut shaped) inside to do do that plus balance the PH and replenish the pump seal lubricant.

NAPA is one source for the spin on coolant filter base and filters. They're plumbed into one of the heater hoses. TractorTractor trailers all have them. That might be something worth looking into.

Iirc someone on this forum has one mounted behind the front bumper of their dark green Cherokee.

 

I ran just such a coolant filter for an entire summer after installing the engine and it didn't catch that much. Maybe it's because the system was still clean then, but my suspicion is that the large screw on coolant filters simply don't allow enough coolant flow to keep rust chunks in floating in suspension a lot of the time.

Captain Jerry - '99 Restoration/Modification - Page 3 - Jeep Cherokee Forum

It's post 38 if the link doesn't work.

The coolant filters have a 5/32" hole that all the coolant has to flow through, I assume to ensure the filter media isn't overwhelmed and blown out by the water pump.

 

Well, with yesterday being a day off from work I got the manual transmission install finished!



There are lots of loose ends to wrap up, but it is running and driving. I've only put 70 miles on it so far, but I've already felt an improvement in shifting and clutch action in that time. I'm running Mobil1 10W30, not anything fancy, and it's a bit notchy. Overall though, I'm happy with it and only getting more so as I keep putting on miles. I don't have the front driveshaft in it yet, so the transfer case is disconnected. I'm looking forward to testing Full Time mode with a manual trans!

 

High five my five speed clutch kicking brother! I can't wait to hear how the NP242 goes with the ax15. I want to swap that t-case into my factory manual commuter XJ soon.