89 YJ 4.2 auto to manual swap help

v8haha

v8haha

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Joined
Sep 9, 2024
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4
Location
Pennsylvania
Good afternoon Jeep folks. I am enlisted to help a friend replace the engine and transmission in his 89 YJ with a 4.2l 6 cylinder automatic with an 89 YJ 4.2l 6 cylinder and 5 speed AX15 transmission. I am looking for any resources that might be helpful in this endeavor. I'm jeep literate but haven't done a swap before.

We have the complete running assembly from a rotted out wrangler. It's appears complete from carb to transfer case, so a lot of the "need to source" components are there. We did not pull the set, so I don't know if it might be missing a sensor or two, but it has a lot of the vacuum lines, wiring etc. with it. We replaced the clutch and flywheel along with the internal slave cylinder (I know, I know, the external is better).

We also have the shift boots and plate, shifters, new master cylinder and hydraulic line, clutch pedal assembly, transmission mount, new motor mounts, and fluids

What I'm looking for is guidance or confirmation on the little things I'm thinking about;

Neutral Safety Switch
Reverse Lights
Auto Steering Column - disconnect and leave?
Driveshafts (different lengths, same between auto/manual?)
Any sensors needed or swapped, ie crank position etc., for an 89?

Thanks in advance!
 
Evening...I've got a '90 4.2/AX15 that's 45k miles from new and never butchered. Motor still has all of the vacuum hook-ups, etc....I'm not bragging here, but as an original example to go by I can tell you a couple of things:

1.) I'm not sure about driveshaft lengths
2.) As far as I can tell I don't have a neutral safety switch...my YJ will start without the clutch pedal depressed
3.) The back-up light switch is located on the passenger side of the AX-15 if memory serves, but I'm not sure if the harness from an auto trans will mate up to it
4.) If aesthetics are an issue, recommend swapping the steering column from your donor, other wise your have the auto shift lever mount range and PRNDL indicator still attached to your colu.n
5.) Carbed 4.2s are pretty straight forward, I don't believe sensor swap will be necessary...there are no crank sensors installed that I'm aware of
6.) The transmission cooling lines go to a closed loop circuit inside the radiator. Once you disconnect them and drain the fluid from the radiator you shouldn't have to worry about plugging the holes


I defer to the Forum members to cross a check my math, but hope I've helped a bit...good luck with the swap...
 
You will need to modify your auto trans crosmember to bolt the manual trans mount to it, the ax15 is longer then the auto so you will need to shorten your rear drive shaft, as for the front drive shaft it will fit but it will max the slip yolk out so i wold advise geting a ax15 front drive shaft, i just did a auto to ax15 swap a couple weeks ago so dont be afrade to ask anything!🙂
 
Yj'srule said:
You will need to modify your auto trans crosmember to bolt the manual trans mount to it, the ax15 is longer then the auto so you will need to shorten your rear drive shaft, as for the front drive shaft it will fit but it will max the slip yolk out so i wold advise geting a ax15 front drive shaft, i just did a auto to ax15 swap a couple weeks ago so dont be afrade to ask anything!🙂
Click to expand...

Thanks! What did you do about the PCM and neutral safety switch wiring?
 
My jeep is a 89 yj with the 4.2 and a nutter bypass so no pcm or computors to deal with, in the past somone had already by past the neutrual safety swich so i didnt have to deal with that ether.
 
Im runing the auto steering colemn til i can find a replacment, i fabricate'd my own cluch/brake pedal assembly, yj parts are hard to find in my area, so i have done lots of modifing xj parts to fit
 
v8haha said:
Thanks! What did you do about the PCM and neutral safety switch wiring?
Click to expand...

I swapped my auto for a new AX15 in my 95. I am still using the auto pcm in my Jeep and it runs without any problem. I picked up a manual pcm for it just in case but didn't need it. The wiring was pretty easy. For the reverse light, I just purchased a 2 pin weather pack connecter and spliced it in to the harness. It was just plug and play after that. The neutral safety switch wire can just be grounded. My swap thread was posted above that talks about it in more detail. I wound up using the neutral safety switch wire as a kill switch with a toggle in a hidden location and grounded. It's worked very well.
 
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