Auto to manual swap?

SirDoopYJ

SirDoopYJ

YJ Enthusiast
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Joined
Oct 2, 2020
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755
Location
Stick Red, Louisiana
I have a 1993 4.0L, I assume 3 speed, automatic. I was looking patiently for a manual, but it seems they were non existent and the automatic I found was too huge of a deal to pass up since I was also looking for one with the 4.0L, which also seems was non existent.

I have never driven a manual before, but I have always been interested in learning. I have read that some people feel connected with their vehicle and that it is a great feeling. My Jeep is not a daily driver, I will maybe commute it an hour back and forth from work every once in awhile. I also drive it on the weekends to run errands. I do plan on taking it on alot of trails starting off with beginner trails and later on maybe to more intermediate trails.

The auto transmission works just fine and I still enjoy the hell out of this Jeep. I feel I got really lucky on the deal. My question is will it be worth it to do a swap? About how much will it cost? What other components need to change besides just the transmission? Can an automatic YJ still perform just as well as a manual on the trails? Is there much difference in torque that would be necessary to have?

If there really isn't a difference in performance or handling on the trails I will probably not worry about it depending on cost and labor. This will also be one of the last things I do to my Jeep during my restoration process and will be years from now down the road.

Thanks.
 
I don't have any experience with the auto in the YJ but much of what I've read over the last year says it's pretty good and each have something good or bad about them. Even for rock crawling the auto is good. So I've read.
 
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I really like the manual AX15 which is what all the manual 4.0L's came with. With a good clutch and properly working shift linkage, the whole setup just works really nice and smoothly. The 5 gears gives the 4.0 a lot of room to work with and you can gear the axles for power while really enjoying each gear and still be setup well for highway. The AX15 is still manufactured brand new in 2020, which is awesome for replacements and they are stronger by a little bit and shift better now than they did in the 90s. Especially if they are filled with a good fluid like Redline MT90 right from the beginning of their life.

The auto is a great transmission too, it's probably a better choice for really technical rock crawling, on the road I would say it works fine and it does, but will have a higher highway rpm (not such a big deal) but will feel a bit sluggish due to having only 3 gears to cover the spread. They are not still made new so you either have to find a replacement or get yours rebuilt somewhere you trust. Off road though the auto is definitely a better choice for really difficult trails, the manual serves little advantages there because it's just so much easier to focus with only two pedals and no chance of killing the engine when you really need it.

It will be a lot of work to swap, so it depends how badly you want it. The manual parts are pretty much all readily available so it can be done, you will need to do some wiring work in the neutral safety switch department, the rest is pretty simple, just a matter of collecting all the parts. If I had the auto, I probably would convert it, but I also don't really care about the $ cost and I just plain enjoy manual transmissions.
 
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machoheadgames said:
I really like the manual AX15 which is what all the manual 4.0L's came with. With a good clutch and properly working shift linkage, the whole setup just works really nice and smoothly. The 5 gears gives the 4.0 a lot of room to work with and you can gear the axles for power while really enjoying each gear and still be setup well for highway. The AX15 is still manufactured brand new in 2020, which is awesome for replacements and they are stronger by a little bit and shift better now than they did in the 90s. Especially if they are filled with a good fluid like Redline MT90 right from the beginning of their life.

The auto is a great transmission too, it's probably a better choice for really technical rock crawling, on the road I would say it works fine and it does, but will have a higher highway rpm (not such a big deal) but will feel a bit sluggish due to having only 3 gears to cover the spread. They are not still made new so you either have to find a replacement or get yours rebuilt somewhere you trust. Off road though the auto is definitely a better choice for really difficult trails, the manual serves little advantages there because it's just so much easier to focus with only two pedals and no chance of killing the engine when you really need it.

It will be a lot of work to swap, so it depends how badly you want it. The manual parts are pretty much all readily available so it can be done, you will need to do some wiring work in the neutral safety switch department, the rest is pretty simple, just a matter of collecting all the parts. If I had the auto, I probably would convert it, but I also don't really care about the $ cost and I just plain enjoy manual transmissions.
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On DeadJeep.com there is a AX-15 94-99 with the external slave cylinder for $700 and there is a PCM for 91 to 95 Manual Trans 4.0L engine for $300.

Some of the other things I will need are Clutch Pedal Assembly, Flywheel, Clutch Master Cylinder. Some one told me to do a slip yoke eliminator while I am at it.

For the Neutral Safety Switch I saw a thread where someone did a conversion in there 4.0L Cherokee and bridged the Park and Neutral connections to make the engine think it is in park/neutral all the time. Should I do this or buy the manual PCM instead? I do not mind spending the money.
 
SirDoopYJ said:
On DeadJeep.com there is a AX-15 94-99 with the external slave cylinder for $700 and there is a PCM for 91 to 95 Manual Trans 4.0L engine for $300.

Some of the other things I will need are Clutch Pedal Assembly, Flywheel, Clutch Master Cylinder. Some one told me to do a slip yoke eliminator while I am at it.

For the Neutral Safety Switch I saw a thread where someone did a conversion in there 4.0L Cherokee and bridged the Park and Neutral connections to make the engine think it is in park/neutral all the time. Should I do this or buy the manual PCM instead? I do not mind spending the money.
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That’s pretty good pricing for those parts. I would buy a pre bled master/slave assembly and probably wouldn’t use the plain slave that comes with the trans. The whole assembly can be bought for like $80 at rockauto, and not dealing with trying to bleed that system is a huge plus. It is more difficult to bleed than brakes, seems like it never bleeds properly. Luk flywheels are cheap, and I’m going to run the Luk 05-901 pro gold clutch. Have it all on my shelf just haven’t installed yet.

Slip Yoke Eliminator would be a good idea since you may have to swap the trans input gear too. It would be a good idea regardless though.

As for the PCMs, that part is a mess. Some people say they’re the exact same thing and you just unplug the Torque converter lockup relay on the firewall. On the manuals that harness just dangles with nothing plugged in. And of course I believe you’d have to ground out the park side of the neutral safety switch. You’d also have to redo the wiring for the reverse switch to hook it up to the manual trans. I believe manual and auto Jeeps have the Exact same harness down to the trans and then there is a different jumper harness for manual and auto based on the trans to make the connections. So you might even be able to buy the manual jumper, plug it in on yours, remove the TCC relay and call it good. Although if there is a difference between manual/auto PCM, then it might be looking for that park circuit to be grounded. I’m just not sure if there is a difference in PCMs or not. Wondering if installing manual wiring takes care of all that regardless of pcm.
 
Good to know it is a good price. It seems used the transmission is 600 to 700 bucks and rebuild used is about 1,000 to 1,200 bucks. I am sure deadjeep.com is trustworthy they said that the AX-15 shifts good and aren't any issues and the PCM came off a running Jeep.

As far as swapping the PCM, I only mentioned it because someone converted their TJ and changed the PCM and I told them about the NSS. He said if he was going to swap he wantes to do it right. I am not sure what that means and he never responded after that.

What would be different (operating the vehicle) about changing PCM vs bridging NSS?
 
So that's the thing, I don't know the differences between the auto and manual PCMs. I don't know if there is any timing curve differences or anything to help the engine have a bit more power for the auto. I know the PCMs lock the torque converter on autos and light the upshift light on manuals out of the same circuit. So I believe either PCM can operate with either transmission just fine. I do not know if running an auto PCM on a manual might cause code 37 to pop up which is related to the torque converter not being locked up. I would doubt it because it uses the speed sensor input and compares it to RPM to know if the torque converter is slipping. On a manual the clutch doesn't slip so I'd imagine it won't light the code. So my best guess is the auto PCM would still work. If I were you, I'd probably buy the manual PCM and try it and the auto one and compare. Good info for the forums, and you could always keep the other as a spare if it works, because they are getting hard to come by.

NOW, regardless of what PCM you run, you will have to do some wiring down at the neutral safety switch (PNP Switch). The harnesses between manual and auto are the same up until they get to the transmission. The starter relay is grounded by the PNP switch on autos. On manuals, there is a jumper wire feeding the starter relay ground directly into ground so that it starts no matter what. Basically the vehicle harness goes down to the trans and it's the same between all Jeeps. It terminates to a 6 pin plug and is populated by 5 wires:
-keyed power for backup lights
-backup light feed to tail lights
-torque converter lockup wire for autos
-starter relay ground
-ground wire for manuals

There is a jumper harness specific to your vehicle. On autos, the auto harness plugs in. It has 4 wires. Keyed Power to the PNP switch (for backup lights), and a tail light wire that feeds the backup lights. Put auto in reverse, it connects those two wires together to light up the backup lamps. Coming out of the 6 pin plug are also the starter relay ground wire (which is grounded when you put the trans in neutral or park), and the torque converter lockup wire.

The manual has a different jumper harness that plugs into that 6-pin. Two wires come out of the plug and go to the manual trans backup switch (keyed power and feed to the backup lamps). The other wire comes out of the manual harness and feeds right back into that ground. This grounds the starter relay on manuals. So they are grounded no matter what.

If it would help, I could probably make you a harness that plugs into the manual backup switch. For the starter relay you would need to snip the ground wire and connect it to the ground wire in the 6 pin if that makes sense. Sorry, throwing a lot at you here but I do believe I understand how it works and can help walk you through it if you have questions.

I'm posting the diagrams I found in the FSM. It will make more sense than the rambling I'm doing here.

So if you look below, the blue circled plug is the body side. You and I both have that plug on both manuals and autos. If you look at the second pic, it shows the difference between autos and manuals. So for me, I have that blue T22 wire which is the output from the torque converter relay. But I don't have a relay in the plug, so nothing ever happens on that wire for me. You would need to ground your T41 wire (starter relay ground) by hooking it to the Z2 black/orange wire at your body side plug. And then you would want to snip off the PNP switch connector (the 3 wire plug) and run the G5 and L1 wires over to the manual trans switch. The third wire from that PNP switch plug would be the ground that you're hooking up to Z2.

Let me know which of that mess doesn't make sense. I can try to clarify further.

IMG_1026.jpeg
IMG_1027.jpeg
 
One thing you could maybe do, is ship me your auto harness, I could doctor it up to fit my Jeep, and then I could send you mine. Depending upon yours being in good condition. I have tons of electrical tools and can make it be nearly factory for myself. And it would be plug and play for you.
 
That is some awesome info. I really do appreciate the time you are taking to help me out. I am going to see if I can do the wiring myself first, it doesn't sound like it will be too hard of a project and my dad should have everything I need to not make it look like a hack job. If it does, I will send it your way lol.

For the PCM, I got two more confirmations on reddit saying that the only difference is that it locks up the torque converter and another guy said he is still using the same auto computer on his after swapping. I will still look into getting the spare. IDK what the lifespan is on PCMs.

Is this the pre-bled Master/slave assembly you are speaking of $88.79?

Capture.PNG

And then the Flywheel $49.79, does price make a difference in quality, or is a flywheel a flywheel?

Capture2.PNG
 
SirDoopYJ said:
That is some awesome info. I really do appreciate the time you are taking to help me out. I am going to see if I can do the wiring myself first, it doesn't sound like it will be too hard of a project and my dad should have everything I need to not make it look like a hack job. If it does, I will send it your way lol.

For the PCM, I got two more confirmations on reddit saying that the only difference is that it locks up the torque converter and another guy said he is still using the same auto computer on his after swapping. I will still look into getting the spare. IDK what the lifespan is on PCMs.

Is this the pre-bled Master/slave assembly you are speaking of $88.79?

View attachment 116794

And then the Flywheel $49.79, does price make a difference in quality, or is a flywheel a flywheel?

View attachment 116795
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Sure thing. The wiring is really much easier than it sounds. Terminate the keyed power (for reverse) and the backup light wire to a 2-pin male weatherpack. They will then plug into the female weatherpack on the manual transmission backup switch. Take the brown and yellow starter relay ground and ground it to the orange and black Z2 wire. Cut and heat shrink the blue Torque converter wire. Pull the TCC relay from the harness on the firewall.

Yes, I have been researching since yesterday as well. Basically an auto can be used to run a manual, the manual PCM can not be used to run an auto is what I've seen. So you should be fine. The PCMs have decent life, the only things I really see fail are the alternator voltage regulator (built into the PCM) which can be solved with a new PCM or an external voltage regulator kit that you splice in. The other thing I see fail are the capacitors, which can be repaired DIY or through an ebay service that you send off and wait for repair and they send it back. I do keep a spare PCM just in case. However if one is needed, they can be obtained from XJs in the junkyard somewhat easily, so you're not screwed necessarily.

Yes, that pre-bled assembly should work fine. They're all pretty much the same thing. Just don't buy one from O'Reilly. I had their powertorque brand for went through like 4 of them in 4 years. Very obnoxious.

Yeah the flywheel is fine too. I've been running Luk flywheel for 6 years. No issues whatsoever. It is even shaped properly with the appropriate domed surface for smooth clutch engagement. I have another Luk FW on the shelf waiting to go in when I install the pro gold clutch.
 
SirDoopYJ said:
Would you recommend updating the other clutch parts like pressure plate or disc? Or should these still be good to go?
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Not sure what you mean by updating. Are you receiving a clutch with the transmission?

Either way, I would buy the Luk pro gold clutch which is 05-901. I prefer the Mopar throw out bearing as well. Everything else should be fine. Not sure if the transmission comes with a new clutch fork, pivot ball, fork retainer spring, etc. So once you get the trans you can post up pics and see what you need to buy in addition. Pro gold clutches are relatively cheap.
 
machoheadgames said:
Not sure what you mean by updating. Are you receiving a clutch with the transmission?

Either way, I would buy the Luk pro gold clutch which is 05-901. I prefer the Mopar throw out bearing as well. Everything else should be fine. Not sure if the transmission comes with a new clutch fork, pivot ball, fork retainer spring, etc. So once you get the trans you can post up pics and see what you need to buy in addition. Pro gold clutches are relatively cheap.
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I think it is just going to be the transmission by itself. The pictures didn't show a shifter either.

For updating, I mean should I buy a whole new clutch kit that includes a new disc and pressure plate or just the flywheel by itself? I didn't know if it would make a difference while everything was off. I am assuming Autos have pressure plates and clutch discs too.

This is what I bought:
deadjeep.com

94-99 Wrangler YJ TJ 4.0L 6 Cylinder 4WD 5 Speed Manual AX15 Transmission

94-99 Wrangler 4.0L 6 Cylinder 4WD 5 Speed Manual AX15 Transmission, thoroughly tested and shifted nice, fluid was also clean. Standard handling time on this part is 15 business days.
deadjeep.com deadjeep.com
 
SirDoopYJ said:
I think it is just going to be the transmission by itself. The pictures didn't show a shifter either.

For updating, I mean should I buy a whole new clutch kit that includes a new disc and pressure plate or just the flywheel by itself? I didn't know if it would make a difference while everything was off. I am assuming Autos have pressure plates and clutch discs too.

This is what I bought:
deadjeep.com

94-99 Wrangler YJ TJ 4.0L 6 Cylinder 4WD 5 Speed Manual AX15 Transmission

94-99 Wrangler 4.0L 6 Cylinder 4WD 5 Speed Manual AX15 Transmission, thoroughly tested and shifted nice, fluid was also clean. Standard handling time on this part is 15 business days.
deadjeep.com deadjeep.com
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Yeah that's just a transmission. They cut the weatherpack plug off of the backup light switch so you'll probably want to buy a new backup light switch.

www.transmissionpartsdistributors.com

AX15 AX5 AX4 TRANSMISSION BACKUP LAMP SWITCH FITS JEEP '84-'02 MOPAR 83500629

AX15 AX5 AX4 TRANSMISSIONS REVERSE LIGHT SWITCH FITS '84-'02 MOPAR 83500629
www.transmissionpartsdistributors.com www.transmissionpartsdistributors.com

Can use that Mopar 8350029 to try and find a genuine Mopar somewhere, or cross reference it. You can buy them Standard Motor Parts at pretty much any parts store as well. Simple bolt on install.

The shifter you can get on eBay. You can still buy Mopar branded shift boots if desired. I bought one just this year, it's nice quality. The shifter stick is different from YJ to TJ, so make sure to buy one for a YJ. They're usually around 100 bucks.

As for the clutch, it comes with a pressure plate, friction disc, lineup tool for install, and a throwout bearing. I discard the throwout bearing from the kit and buy Mopar instead. Not a must, just my preference. The aftermarket throwout bearings seem to be trash. Mopar 53008342 is the part number for the TOB I use.

The clutch kits don't come with a flywheel, so you'll need that and a clutch kit regardless. Luk 05-901 and LFW193 can both easily be sourced on Amazon or RockAuto for a decent price.

Automatics don't have a clutch at all, they use a flexplate which is what the starter spins (as opposed to a flywheel's teeth), and then they use a fluid filled torque converter that is viscous. So you will not have any of the parts needed as far as the clutch goes. But, no big deal, they can all be had for a fair price and will work like new. So, no biggie. Buying the transmission is the worst part.
 
I am emailing deadjeep to make sure what it all comes with, because it looks like they are using the same photos on one I saw on ebay that is a 90 to 93 AX-15 and it is being sold from deadjeep.

There is another one I found on Facebook market place for $750. The guy told me he bought it from someone else that was swapped into two different TJ's when he bought it. From what he knows is that it was recently rebuilt. It includes the shifter, throw out bearing and clutch fork. He is selling it because he is swapping in an auto into his LS. It is near where I live, but I won't be back in town until a week from now.
 
SirDoopYJ said:
I am emailing deadjeep to make sure what it all comes with, because it looks like they are using the same photos on one I saw on ebay that is a 90 to 93 AX-15 and it is being sold from deadjeep.

There is another one I found on Facebook market place for $750. The guy told me he bought it from someone else that was swapped into two different TJ's when he bought it. From what he knows is that it was recently rebuilt. It includes the shifter, throw out bearing and clutch fork. He is selling it because he is swapping in an auto into his LS. It is near where I live, but I won't be back in town until a week from now.
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That deadjeep one is 94+. I can tell by looking at the hollow sleeve going over the input shaft. The 93 and earlier models don't have that. Their "bearing retainer" plate is relatively flat. The 94+ has the sleeve built in for the external slave throwout bearing to ride on. I just noticed that dead jeep trans doesn't have a bell housing though, so you will need to buy one. The automatic's is built in so there is nothing to save and reuse.

The Facebook one doesn't seem bad, if it shifts decently. At least it comes with good parts like the shifter, but if it's from a TJ you likely won't want that shifter. The TJ console setup is much different. If I recall, the TJ shifter rod puts the ball in a really weird spot for the driver in a YJ and ends up hitting either the seat or the console or something. Could always give it a try, but plan on buying a YJ shifter. If you send pics of the shifter I can recognize what it came out of. I would buy a new throwout bearing, I would never reuse an old one. Too much work to replace if that old one for some reason decided to kick the can. Clutch fork is nice though, one less thing to buy. Nothing wrong with reusing that.
 
machoheadgames said:
That deadjeep one is 94+. I can tell by looking at the hollow sleeve going over the input shaft. The 93 and earlier models don't have that. Their "bearing retainer" plate is relatively flat. The 94+ has the sleeve built in for the external slave throwout bearing to ride on. I just noticed that dead jeep trans doesn't have a bell housing though, so you will need to buy one. The automatic's is built in so there is nothing to save and reuse.

The Facebook one doesn't seem bad, if it shifts decently. At least it comes with good parts like the shifter, but if it's from a TJ you likely won't want that shifter. The TJ console setup is much different. If I recall, the TJ shifter rod puts the ball in a really weird spot for the driver in a YJ and ends up hitting either the seat or the console or something. Could always give it a try, but plan on buying a YJ shifter. If you send pics of the shifter I can recognize what it came out of. I would buy a new throwout bearing, I would never reuse an old one. Too much work to replace if that old one for some reason decided to kick the can. Clutch fork is nice though, one less thing to buy. Nothing wrong with reusing that.
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So he bought a Jeep from someone with it already attached. The previous owner blew the rings in the motor, he was able to drive it for a little while and said that it shifted fine. He is doing an LS swap (idk what that means) and doing an auto trans which is why he is selling it.
 
SirDoopYJ said:
So he bought a Jeep from someone with it already attached. The previous owner blew the rings in the motor, he was able to drive it for a little while and said that it shifted fine. He is doing an LS swap (idk what that means) and doing an auto trans which is why he is selling it.
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Makes sense. If he was using it in a TJ it’s probably not going to be the shifter you’ll want but we’ll see.

LS Swap just means he’s swapping in an engine from GM’s LS series into his Jeep. And obviously no longer needs the manual since he’s going auto.
 
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