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42RLE Experts

lt1yj

Well-known member
Joined
Jul 6, 2020
Member Number
2258
Messages
179
Two questions:

1. What's the physical difference between 2003-2004 vs 2005-2006 TJ/LJ 42RLE transmissions? Online and local shops says they are not interchangeable, but it appears they run the same valve body and solenoid pack. I want to build a spare trans to have for both my 2004 and 2006 LJ's.

2. Does anyone have a way to improve/program the shift points and pressures to eliminate the funky shifting from the factory 2004 separate trans controller? Or a completely different trans controller. In high range my LJ takes shifts from 1-2 really early and hard, 2-3 is better but 3 to overdrive is incredibly slow. In low range it seems to get confused on downshifts from 2-1 and will shudder and even stall the engine on occasions unless I manually shift before every climb.

It seems the 2005/2006 with the trans control built into the engine computer is better but still not great. The shifts are smoother and it doesn't stall in low range but it's still shifting way too early for 1-2 and still takes a long time to shift into overdrive.
 
Wish I could help but I would like to know the differences also. I have an 04 LJ and want to find a spare in case mine goes also.
 
Not an expert by any means but I have been all up in the guts of my 06. If there are any differences they are probably to do with the controller being separate / combined maybe wiring on the sensors or something? I know for a fact that there were a couple of components and connectors added in 07 for the JKs.

It is generally accepted that these shift funky no matter what, It almost refuses to downshift unless you mash on the gas, and if your axle gearing is too high the tall .69 overdrive is unusable.

You can take it to a trans shop and they can scan it for wear, it keeps track of the time it takes to engage the clutch packs and extrapolate wear from that.
 
Anyone have the trans wiring diagram for '04 and '05? My google skills are lacking today.
 
Hptuners allows playing with shift points and line pressure, at least in my 05. I haven't actually started messing with mine though because I haven't had the time to spend to get it dialed in.
 
I am not an expert but ....

I second the HP tuners ability. I have asked on a few forums and I cant get feedback from some one who has done it, I would love to hear one person say YES it worked and my 42rle holds 3 a little longer!

04 LJs were offered in auto only, no manuals offered and TCM is a separate module from PCM. This reflects true for my 04 LJ.

05 and 06 integrated the TCM into the PCM and they started offering manuals.

The 42RLE gets a bad rap due to the .69 overdrive. As soon as you increase tire size it becomes a dog. Most want to run 35's and you really need to run 5:38 gears to make 42rle happy. The issue becomes you cant get 5:38 gears for the dana 30(or at least not when I built mine). So most go 5:13's thinking its not a big enough difference to matter. But it does, I have driven both.

All LJ's have dana 44 rears and 5:38 gears are available, whohoo!

The front is where you run into issues. No one makes 5:38 dana 30 front gears. You either source a rubi dana 44 front or swap the axle. I would recommend swapping the axle. It seems drastic, until you drive a LJ with 35s and 5:38s and don't have to switch off the overdrive every time you drive it.

I know you are asking about the 42rle and I am talking about front axles but I think its relevant.

Rule#1 keep it cool. ALL 42rle's need some kind of external cooler to keep them alive and happy for the long haul.

Rule#2 run the correct gears for your tire size.
 
I should have given some specs on the Jeeps.

#1 '04 LJ 4.0L 42RLE rubicrawler rubi tcase sterling rear narrowed 2009 HP60 5.13's yukon zip lockers 40" treps or 40" Mickey Thompson

#2 '06 LJ 4.0L 42RLE rubi Tcase Rubi dana 44's, 4.10 gears, 33" tires.

On mostly flat level roads I can be in overdrive over 70Mph with the Mickey Thompson's. Hills it will downshift and rev. No OD with the treps on. The treps get 1-2Mpg lower fuel mileage as well.
 
FLUX said:
The front is where you run into issues. No one makes 5:38 dana 30 front gears. You either source a rubi dana 44 front or swap the axle. I would recommend swapping the axle. It seems drastic, until you drive a LJ with 35s and 5:38s and don't have to switch off the overdrive every time you drive it.

I know you are asking about the 42rle and I am talking about front axles but I think its relevant.

Rule#1 keep it cool. ALL 42rle's need some kind of external cooler to keep them alive and happy for the long haul.

Rule#2 run the correct gears for your tire size.
Click to expand...
Can confirm, 5.38's and 35's in a light TJ seriously feels like the way it should have been from the factory.

A little buzzy rpm wise above 75 or so but I really shouldn't be driving this little thing that fast anyway. :laughing:
 
lt1yj said:
I should have given some specs on the Jeeps.

#1 '04 LJ 4.0L 42RLE rubicrawler rubi tcase sterling rear narrowed 2009 HP60 5.13's yukon zip lockers 40" treps or 40" Mickey Thompson

#2 '06 LJ 4.0L 42RLE rubi Tcase Rubi dana 44's, 4.10 gears, 33" tires.

On mostly flat level roads I can be in overdrive over 70Mph with the Mickey Thompson's. Hills it will downshift and rev. No OD with the treps on. The treps get 1-2Mpg lower fuel mileage as well.
Click to expand...
I'd be thinking about 5.89 or 6.17 in the 60's if you drive that thing on the street much. The OD in these 42rle's is really crazy high, I'm not sure they make gears deep enough to overgear on a 40 IMO.

Think about chucking some 4.88's in the 06? I'd bet you'll be surprised.

I know we went off on a gearing tangent but the 5.38 swap is one of the reasons I haven't spent much time messing with HPTuners yet. My jeep on 35's is a completely different animal and the trans feels so much better after the re-gear.
 
crazybluerider said:
I'd be thinking about 5.89 or 6.17 in the 60's if you drive that thing on the street much. The OD in these 42rle's is really crazy high, I'm not sure they make gears deep enough to overgear on a 40 IMO.

Think about chucking some 4.88's in the 06? I'd bet you'll be surprised.

I know we went off on a gearing tangent but the 5.38 swap is one of the reasons I haven't spent much time messing with HPTuners yet. My jeep on 35's is a completely different animal and the trans feels so much better after the re-gear.
Click to expand...
5.38's are the tallest gears available for the HP60. 5.38's would probably allow it to hold OD much better with the Mickey Thompsons. I don't think it would help a lot with the treps.

But I'm not changing gears. The '04 is driven to and from trails and I drive it around several times a week spring-fall. I put almost 7000 miles on it in the last 2 years. The '06 does ok with the 4.10's. If I bump up the tire size I'll regear it to 5.13's.

I think updating the 1-2 shift and the 3-od shift points and playing with the line pressure and timing would make a world of difference on both Jeeps. I'm assuming the line pressure can be modulated electronically. But I know almost nothing about the 42RLE.
 
Ahh makes sense, your ribicrawler and rubi transfer case make up the difference off road. On road with the O.D. off the 5:13 might be better for road driving.

With O.D. off the 42rle does lock the torque converter in 3rd, almost feels like another gear.

Talk to HP tuners. They claim you can adjust shift points. I assume its a rpm or load resistance thing. You would also be able to squeeze a little more power out of the motor. You could borough a MVP module from a friend and get the tokens to tune your rig.
 
I run 4.88’s on my TJ rubicon on 35s. Cruises good enough, the OD works fine just a little reluctant to downshift. I DD it and have Driven It to Moab and SW Colorado going 80mph across Nevada.

We have to remember that these are FWD minivan transmissions turned sideways and put in a Jeep. With rigs as heavily modified at the OPs there may not be any way to really make them work right.

I have heard of the input and output speed sensors causing drivability issues without throwing codes. If the hard 1-2 shifts are being caused by the computer you can sometimes get them to act right with a hard reset, At least on the 06.
 
Hell I have to drive with OD off if I'm not above 50mph or it shudders like its having a damn seizure in my project LJ and that's still on stock tires since I'm collecting ton and 3/4 link parts
 
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