Why Not Just Use The 32RH?

[That'll Buff]

I'll start this off by saying I know very very little about what goes into a transmission swap. I also do not know the major differences between the 42RLE and 32RH other than they are controlled differently (electronic vs hydraulic) and that the 42RLE has OD. That being said, I have read a few threads about forum members swapping to automatic transmissions and read through the "8HP70 and 4.0?" thread, with all of them having the same conclusion that the 42RLE requires very deep and specific gearing in order to be bearable.

My question is, why is it that later models can't use the 32RH instead? With the TJ being such a popular platform for so long, I would think that an adaptor plate would be made if it's a bellhousing mounting difference, along with a skid plate adapter if there are transmission mount differences. For those swapping from a manual to an automatic, I would think the level of work required would be similar enough that a difference in shift controls wouldn't be an issue like an automatic to automatic swap. So now I wonder, what are the major reasons this swap doesn't happen despite the issues people have with the 42RLE?

 

[Tronner]

 

[freedom_in_4low]

I'll start this off by saying I know very very little about what goes into a transmission swap. I also do not know the major differences between the 42RLE and 32RH other than they are controlled differently (electronic vs hydraulic) and that the 42RLE has OD. That being said, I have read a few threads about forum members swapping to automatic transmissions and read through the "8HP70 and 4.0?" thread, with all of them having the same conclusion that the 42RLE requires very deep and specific gearing in order to be bearable.

My question is, why is it that later models can't use the 32RH instead? With the TJ being such a popular platform for so long, I would think that an adaptor plate would be made if it's a bellhousing mounting difference, along with a skid plate adapter if there are transmission mount differences. For those swapping from a manual to an automatic, I would think the level of work required would be similar enough that a difference in shift controls wouldn't be an issue like an automatic to automatic swap. So now I wonder, what are the major reasons this swap doesn't happen despite the issues people have with the 42RLE?

both transmissions have at least some electronic controls and they are implemented differently in the PCM. I don't know all the details but it seems that in itself makes swapping a 32RH into a late TJ a nastier proposition than swapping in a 42RLE along with its compromises.

 

[Lou]

It can be done on 03-04 by converting the pcm and “some” wiring to match a 2002. 05-06 isn’t worth the hassle as it’s a completely different pcm and harness.

The floor shifter plates are totally different as the hole in the floor of the tub is totally different. Shifter assemblies are not interchangeable so some fabrication is required to get the early shifter in an 03-04 but not bad at all.

The standout sensor different is the oil pressure sensor. 03-04 is a single wire switch, 02 is a 3 wire sensor. So you need a 2002 sensor and need to wire in 5v supply and return to the correct sensor supply on the harness.

Minor wiring modification was needed to convert an 03 manual harness to the 02 NSS stuff. In addition, a single wire and terminal was needed to run to the pcm for TCC lock up.

Alternative method would be get an 02 engine harness and potentially pdc harness and it’s likely plug and play.

 

[Lou]

You’ll also need to make a standalone transmission mount crossmember as the trans mounts are in completely different spots. Beyond what I mentioned I can’t recall any other differences… may have missed a detail or two.

 

[That'll Buff]

Alternative method would be get an 02 engine harness and potentially pdc harness and it’s likely plug and play.

Ok, im mostly following. If this is true though for 03-04, why is it not true for 05-06 if you also swap the PCM? Sounds to me like the same work just with the addition of an older PCM, so I know there's something I'm missing there that makes it more trouble than it's worth. Along with transmission swaps I also don't know much if anything about the wiring and computer differences over the years. I assume something significant changed in the 05-06 models that make it less simple than telling the computer "you have a 32RH now" that the 03-04 seem to be able to do (gross simplification)?

 

[bbaldwin237]

The 32RH is durable and often considered the better auto in TJs. That does not make it the best auto. Ask yourself if an engine could maintain ideal RPMs better with 3, 4, or 8 gear choices? Any swap is going to require modification and customization. There is no single answer for what is best, because everyone's wants, needs, and uses may vary.

There are times driving the 32RH where I really wish there was an overdrive. But I really find myself wishing there was something between 1 and 2 or 2 and 3. Especially on connector trails in 4L.

And as far as gearing, you always have to gear the axles appropriately for your setup, so that's kind of a moot point.

 

[mrblaine]

It can be done on 03-04 by converting the pcm and “some” wiring to match a 2002. 05-06 isn’t worth the hassle as it’s a completely different pcm and harness.

The floor shifter plates are totally different as the hole in the floor of the tub is totally different. Shifter assemblies are not interchangeable so some fabrication is required to get the early shifter in an 03-04 but not bad at all.

All 97-04 floor plates and auto shifters are interchangeable forward and backward. I suspect you may have wound up with a 42 shifter for the 05-06 which is different than the 03-04 42 shifter. The front half of the console is also different to account for the different shifter handle locations due to the bullshit needed for the NSG 370.

 

[mrblaine]

I'll start this off by saying I know very very little about what goes into a transmission swap. I also do not know the major differences between the 42RLE and 32RH other than they are controlled differently (electronic vs hydraulic) and that the 42RLE has OD. That being said, I have read a few threads about forum members swapping to automatic transmissions and read through the "8HP70 and 4.0?" thread, with all of them having the same conclusion that the 42RLE requires very deep and specific gearing in order to be bearable.

My question is, why is it that later models can't use the 32RH instead? With the TJ being such a popular platform for so long, I would think that an adaptor plate would be made if it's a bellhousing mounting difference, along with a skid plate adapter if there are transmission mount differences. For those swapping from a manual to an automatic, I would think the level of work required would be similar enough that a difference in shift controls wouldn't be an issue like an automatic to automatic swap. So now I wonder, what are the major reasons this swap doesn't happen despite the issues people have with the 42RLE?

If you have to regear for your tire size, the only problem is the preference to go 5.38 for 35's and that doesn't happen unless you have a front 44. Other than that, you will rarely not need to gear for your tire size so what difference does it make?

 

[That'll Buff]

The 32RH is durable and often considered the better auto in TJs. That does not make it the best auto. Ask yourself if an engine could maintain ideal RPMs better with 3, 4, or 8 gear choices? Any swap is going to require modification and customization. There is no single answer for what is best, because everyone's wants, needs, and uses may vary.

There are times driving the 32RH where I really wish there was an overdrive. But I really find myself wishing there was something between 1 and 2 or 2 and 3. Especially on connector trails in 4L.

And as far as gearing, you always have to gear the axles appropriately for your setup, so that's kind of a moot point.

I don't deny that more gears is often better, and that having an OD seems like a nice addition if done right which wasn't done in the 42RLE from what I've read. I'm not looking for the best transmission, I'm just curious as to why it seems to be common in later models to go with the 42RLE and make compromises around it if the work seems relatively the same in the big picture to choose the 32RH instead. This forum has plenty of members that are able to get as custom as it gets, so I don't feel like that is the limiting factor in any capacity. If you are converting from a manual to automatic, you're likely well prepared for the effort it takes.

As for gearing, I'm more so talking about how it seems like even on 5.38's with 35's I've seen some people complain it's not low enough. Maybe I misread or am misremembering or it was just one person's preference but that comment is the whole reason I have the question.

 

[That'll Buff]

If you have to regear for your tire size, the only problem is the preference to go 5.38 for 35's and that doesn't happen unless you have a front 44. Other than that, you will rarely not need to gear for your tire size so what difference does it make?

This is kind of the reason my question exists. If the person doesn't have a 44 in the front, how does the future of their build change then. Does it just become a "sucks, deal with it" moment and they're limited to either swapping/keeping a manual or staying at 33's if they can't find a front end? Obviously a lot of "What if's" in that scenario, but I'm trying to see if there is a reason someone in that situation who wants/has a 42RLE can't instead use the 32RH to fix that bottle neck and allow themselves to be properly geared for 35's.

 

[mrblaine]

I'm just curious as to why it seems to be common in later models to go with the 42RLE and make compromises around it if the work seems relatively the same in the big picture to choose the 32RH instead.

Given a choice, I will always keep the same generation by year when doing a trans swap. My preference is to make it look as factory as possible when doing those type things and since the factory already did it, all I have to do is hunt down the parts and use them.

 

[Ashim]

Years ago, a younger guy in our local Jeep club put a 32RH into an 03 Rubicon that he just bought. The Rubicon had already been hacked up by the previous owner (Dodge truck manual with granny gear, Atlas transfer case, air suspension, etc). He pulled the tub off the frame, cleaned and painted frame, replaced suspension, replaced engine and trans with low mileage 4.0 and 32RH from rusted out donor vehicle. Also transferred over the harness and pcm. I'm sure there was much more involved, but he ended up with the rig he wanted, running 37's.