: AX15/GM bellhousing

10-17-2009, 01:35 AM
I am trying to decide which method to use to mate an AX15 to a GM pattern 4bt.
Option 1 is; use a Novak adapter between the AX15 and a GM bellhousing, need to buy a GM bellhousing.
Option 2 is; Use a Advance Adapters custom bellhousing that bolts directly to the AX15 and has a GM pattern.
The price difference between the two after buying a GM bellhousing in option 1 is negligible.

M715 tow rig
10-17-2009, 03:28 AM
I have used Advance Adaptors bellhousings before, nice castings, thick and beefy. Wasn't overly happy with thier idea for the slave cylinder, I had to modify the mounting position to get it to work right in the end.

The AX/15 is a moderately strong light duty 5 spd but won't take higher power numbers and abuse for very long. In my buddies YJ we run a mild built AMC 360 engine and the AX/15 with a Rubicon 241OR Tcase and he goes through trannies about every 1 1/2 - 2 years. But we 4 wheel very hard in our rigs, those trannies see alot of abuse in his truck.

They are easy trannies to overhaul though. Not requireing any specialty tools, just your typical snap ring pliers, bearing pullers and a press.

10-17-2009, 01:21 PM
Have you guys considered a nv3500/3550?
I am very much a finesse type of driver rather than a pedal to the floor type, so I hope I can make it last. I had heard the AX15 was an easy rebuild, thats good.
I do have a few other trannies as replacements. This is not a DD rig and I don't do any rock crawling like they do in the southwest.

10-17-2009, 01:25 PM
i've ran a nv3500 for the last year and i am a very much pedal to the floor kinda driver[oh and free pump mods] and it has held up nicely so far no problems other than the tranny likes to slowely leak oil out of where the shifter attaches.

M715 tow rig
10-17-2009, 06:14 PM
Our specialty at my shop is Jeeps I have done lots of work on both the AX/15 and the Jeep NV3550 and I have not found any significant difference in strength or reliability in either of the trannys. The 3550 I have found to be a little noisier and a little more clunky to shift than the AX/15. The AX/15 is a little easier to find replacement parts for as well.

10-17-2009, 08:24 PM
All the more reason to try my AX15 then. Some people were telling me to use a nv3500 in place of the AX15. I thought they were pretty close in strength but couldn't find the specs on both to compare.

M715 tow rig
10-18-2009, 01:33 AM
If you do wind up using an AX/15 to Chev 4bt swap, some little tidbits of info for you. The early version Jeep AX/15, 89 to 91 IIRC, uses an input shaft with the same pilot bearing size as the standard Chev V8, the later version has a larger pilot size. The 94 and later AX/15s with the external slave cylinder use an input bearing retainer with the correct size sleeve for the standard Chev short throw out bearing.

The Cherokee/Comanche AX15 has a different rear extension housing and shifter pivot tower/shifter handle assembly than the YJ/TJ AX/15. The Cher AX/15 clocks the Tcase slightly more counter clockwise when looking at the back of the tranny than the YJ/TJ AX/15. The Cher shifter tower pivot and shifter is shorter than the YJ/TJ tranny.

Most of the Jeep transfer cases from 1980 and newer used the 23 spline input and standard New Process style 6 bolt round flange.

10-18-2009, 11:49 AM
The vehicle is a 98 Jeep TJ which is what the AX15/231 came from, 180,000 miles on the odometer. Axles are 1996 Ford 1 ton, detroit locker in both.
BTW M715 thanks for the info.

11-06-2009, 10:43 AM
I have a question for those who have done this swap.
Novak has a new adapter that has not made it on their website yet. It is a 1/2" plate that goes between the GM pattern flywheel housing and the stock Jeep bellhousing. This will allow the stock Jeep hyd. throwout assembly to be retained. No GM bellhousing used, or special adapter belhousing such as what AA offers which requires a few other parts to make it work.
1. What clutch will fit into the Jeep AX15 bellhousing and hold the power?
2. Will the stock Jeep hydraulic throwout assembly handle such a clutch? Assuming of course this is a diaphram style pressure plate not a Borg & Beck style.
Yes I did search a few times in the trans stickies.

I too would like to know some more info on this


11-06-2009, 01:51 PM
As long as Andre allows me cross posting this info. Here is a cut and paste from my TJ build thread.
(part #721567) Is the AA custom bellhousing, it puts the clutch fork and slave cyl on the passenger side which gets in the way of the down pipe. Also you will need a Toyota slave, a custom hydraulic hose, and long style throwout bearing to make it work, all of which AA sells, of course adding to the cost.
(part #GMAX15) Is the Novak plate adapter which goes between the AX15 and a GM bellhousing. I believe it requires the longer throwout bearing as well, and a GM belhousing with the external slave mount which in my area are very hard to come by and demand a premium ($150+).
(Novak part #375-1, $368) Is the new adapter, it retains the jeep belhousing, hydraulic throwout assy., and throwout bearing as well as keeps it all on the drivers side. If the Jeep hydraulic throwout assy. is strong enough that is one less item to modify. Neither of these adapters were designed for a 4bt swap. They were all designed for a Chevy V8-V6, I6 to Jeep AX15 swap.

11-06-2009, 03:09 PM
Well I just ordered my Novak 375-1 adapter. I talked at length with them about the clutch and they know for certain that an 11" clutch will fit as that is what they recommend in a V8 swap. So that is the size I will run.
I am very familiar with the cnc process it takes to make these adapters and talked with them about the 8* passenger side engine tilt. They said it was entirely possible to machine the bellhousing bolt pattern at a 8* rotation effectively removing the engine tilt, they said there would be an extra cost involved of $84, as well as a slight added lead time for setup out of the ordinary. I figured that was dirt cheap compared to other options I looked at, and I understand the lead time issue.
Novak restated aside from a larger clutch the rest of the stock clutch assembly is retained, i.e. fork, T.O. bearing, master, slave, & line.

11-06-2009, 04:26 PM
hey, that sounds great. bounce

got a question.... I currently have the auto setup

yes I know that I need the elusive manual flywheel.... :confused:

but will the motor adapter that I have work with the new flywheel and this new 375-1 adapter?


11-06-2009, 04:33 PM
The flywheel housing is the same for auto and manual transmission. The starter is the same too.

M715 tow rig
11-06-2009, 07:20 PM
There are to versions of the clutch hydraulics for the AX/15 trans

89 - 93 used an internal slave cylinder. The internal slave for the Jeep is a known problem, they are very bad for leaking.

94 - 98 used an external slave with a throw out bearing and fork

Both systems use the same dimension bore and stroke for the clutch master.

the parts from both set ups are interchangeable. The input shaft length did not change on the Jeep AX/15, so you can take the bellhousing, bearing retainer, throw out bearing and fork, and slave from an external setup and swap it onto an internal slave tranny or vise versa.

I have run the AX/15 hydraulics with good aftermarket 10 1/2 in diaphram type clutches, McCloud, Centerforce, with good success. The 11 in clutch shouldn't be much harder on the hydraulics. As I said the only real issue I have found with the Jeep setups is the leaky internal slaves, pretty much count on only getting about 25,000 miles out of an internal slave.

Russel fittings also makes an A N adaptor for the Chrysler O ring hydraulic clutch fittings so you can use a -3 braided line if you are doing a retrofit of these parts into something else.

11-06-2009, 07:29 PM
My TJ is a 98 with the external slave.

M715 tow rig
11-06-2009, 07:38 PM
The only issue I have ever run into with the external slave clutches on the Jeeps is, on a couple of them I have seen the throw out fork crack. The fork setup on the AX/15 mounts the slave on the drivers side of the input shaft and the pivot on the passenger side of the input shaft and mounts the throw out bearing in the middle of the fork. I have replaced a couple of forks for cracking right where the bearing mounts. The fork cracks then it flexes to much and won't fully release the clutch.

11-25-2009, 11:03 AM

I'm closely monitoring your progress. I plan to put a 4BT into my 1990 wrangler they way you are doing it 4BT-AX15 direct mating if possible. I did some research on the AA AX15-GM bell housing adapter and I think that's they way I'm going to go at the moment. The kit (P/N YJ002 -Asin AX15 Package Option 2) advanceadapters.com/product/5121/CP-YJ00X.html appears to have the correct parts, minus the things I don't need, like radiator and such. Basically I'm basing my swap off of yours. Any helpful and cost effective info is much appreciated. I'm intermediate in my experience with ground vehicle maintenance but I'm a veteran helicopter mechanic. Hopefully this won't prove to be beyond my capabilities. Keep up the good work. Any tips and tricks from you will come in handy I'm sure.

11-25-2009, 04:58 PM
Thank you for the compliment and I saw and responded to your PM before seeing this post. So your questions were answered there.
I do not remember which adapter it was, but one of them put the slave on the passenger side, which I thought would get kinda tight with my starter, and down pipe already on that side.
Like I mentioned in the PM call them and ask lots of questions, both companies were very willing to answer all my questions. Remember none of these adapters were designed for the 4bt or any diesel for that matter. They were designed for the gas engine of whatever bolt pattern flywheel housing you have. We just happen to be able to utilize the gas engine bellhousing bolt pattern via our flywheel housing.

11-26-2009, 01:14 AM
I'm just curious here, but... why do you want to use the AX15? I ask simply because it isn't any more work to do a trans swap when doing an engine swap, and there are plenty of beefier transmissions out there (like the Ford 5 speed ZF's)?

11-26-2009, 08:12 AM
I'm just curious here, but... why do you want to use the AX15? I ask simply because it isn't any more work to do a trans swap when doing an engine swap, and there are plenty of beefier transmissions out there (like the Ford 5 speed ZF's)?

I can't answer for Ggg but it certainly can be more work.

My swap (GFs jeep actually) was a 2.5 with an ax5. I went out and bought a used Ax15 even though there were beefier options for similar price because it was going to be much easier.

transfer case bolted right up in the exact same spot (did have to convert to a 23 spline input on it but no big deal). Which meant driveshafts were exactly the same. Which meant shifter location was exactly the same, which means TC select was in the exact same spot. Which meant no modifying the skid or building a new one to mount the TC to. That's a lot that remained unchanged that wouldn't necessarily have with a different transmission.

There are others using the Ax15 behind 4bts and turbo'd/supercharged 4.0s without any problems so it can hold up. For my (our) purposes this jeep never goes off road in the ~10 years she has owned it she has not once put it in 4wd that she remembers. She doesn't race it or launch it at every traffic light (Although I may be a few times :) ) she just drives fast on the highway and the ax15 will hold up fine. So using a trans that bolts right up to everything she had with no questions or extra work saved me hours and hours of time.

Just my reasons.

11-26-2009, 10:30 AM
I chose mine for many of the same reasons as chris, lots of stuff that didn't need to be changed plus even in rock crawling situations it has proven itself capable of handling the power.
The biggest thing was it was free as in my Jeep already had it, and no other adapters except for the bellhousing adapter were needed to make it work. If I break it I am not out any money, just buy a beefier trans at that time, or swap in my th475.