Is there a way to make the 42RLE overdrive switch off by default?

Rubicon John said:
I was under the impression that one can feel the tq converter locking when the rpms drop while cruising in 3rd. (Almost feels like a shift in to 4th) Is this true? If so, mine does that no matter when I turn the OD off.
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O/D On = TCC lockup in 4th gear
O/D Off = TCC lockup in 3rd gear

You should be able to feel each shift. TCC lockup is more subtle because the torque converter clutch engages similar to a clutch in a manual transmission and the RPMs slowly drop, whereas with a gear change the RPMs drop quickly and you feel the gear engaging.

I'm not suggesting that we leave overdrive on, simply that it's best to turn it off after the 2-3 shift because the PCM will otherwise lock the TCC as soon as the 2-3 shift occurs. This locking and unlocking of the TCC both kills power and causes wear on the TCC.

I'd encourage anyone with a 42RLE to test the transmission shift behaviors from 0-60 with O/D off, then with O/D on, then with O/D on until after the 2-3 shift occurs (at which point you turn it off). You'll find that if you start out with O/D off there will be a momentary loss of acceleration after the 2-3 shift as the TCC locks up then unlocks. If you turn O/D off after the 2-3 shift, but before the 3-4 shift, you can continue to accelerate in the 3rd gear 1:1 ratio and the TCC will lock up at a much higher RPM, generally as you ease off the accelerator, and you won't feel that loss of power.
 
Chris said:
Yep

I love driving the manual on-road, but with the technical wheeling I am doing out here, I've come to realize just how beneficial it is to have an automatic :LOL:
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Oh I totally get it, I just love the mods you have been willing to do over the years no matter how extreme 🤣
 
AjRagno said:
O/D On = TCC lockup in 4th gear
O/D Off = TCC lockup in 3rd gear

You should be able to feel each shift. TCC lockup is more subtle because the torque converter clutch engages similar to a clutch in a manual transmission and the RPMs slowly drop, whereas with a gear change the RPMs drop quickly and you feel the gear engaging.

I'm not suggesting that we leave overdrive on, simply that it's best to turn it off after the 2-3 shift because the PCM will otherwise lock the TCC as soon as the 2-3 shift occurs. This locking and unlocking of the TCC both kills power and causes wear on the TCC.

I'd encourage anyone with a 42RLE to test the transmission shift behaviors from 0-60 with O/D off, then with O/D on, then with O/D on until after the 2-3 shift occurs (at which point you turn it off). You'll find that if you start out with O/D off there will be a momentary loss of acceleration after the 2-3 shift as the TCC locks up then unlocks. If you turn O/D off after the 2-3 shift, but before the 3-4 shift, you can continue to accelerate in the 3rd gear 1:1 ratio and the TCC will lock up at a much higher RPM, generally as you ease off the accelerator, and you won't feel that loss of power.
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Thank you for the info, I’m going to try it out just out of pure curiosity. You’re saying when you hit the switch after the 2-3 shift, the transmission stays in that locked up mode full time until you shut the Jeep off?
 
Rubicon John said:
Thank you for the info, I’m going to try it out just out of pure curiosity. You’re saying when you hit the switch after the 2-3 shift, the transmission stays in that locked up mode full time until you shut the Jeep off?
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Keep in mind that the O/D switch is there to let you decide if the transmission should shift into 4th gear (overdrive) or if it should stay in 3rd gear (direct drive 1:1 ratio). The point of my post was to point out that starting off with O/D off is not a solution to our transmission quirks because of how using that switch also determines TCC lockup behaviors. Starting off with O/D off guarantees TCC lockup as soon as the transmission shifts into 3rd gear.

The TCC will still lock and unlock depending on speed and engine load. You will still need to turn overdrive on and off depending on the speed you're going. If you pay attention, over time you'll always know what gear you're in, whether the TCC is locked, and whether or not O/D should be on or off.
 
I thought I seen a how-to on doing that before. I thought on this site, but maybe not.
 
AjRagno said:
Keep in mind that the O/D switch is there to let you decide if the transmission should shift into 4th gear (overdrive) or if it should stay in 3rd gear (direct drive 1:1 ratio). The point of my post was to point out that starting off with O/D off is not a solution to our transmission quirks because of how using that switch also determines TCC lockup behaviors. Starting off with O/D off guarantees TCC lockup as soon as the transmission shifts into 3rd gear.

The TCC will still lock and unlock depending on speed and engine load. You will still need to turn overdrive on and off depending on the speed you're going. If you pay attention, over time you'll always know what gear you're in, whether the TCC is locked, and whether or not O/D should be on or off.
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Gotcha, I’m planning a re gear soon so I’m not trying to use it as a solution. That ship has already sailed. The engine simply needs more RPM in all gears if you ask me.
 
Andy-WhiteTJ said:
fireman3 on another forum:

42RLE overdrive solution
​
Been searching for a solution to shut the OD off in my LJ instead of having to flip the switch every time I start it.
Have read a few suggestions but never found anyone who actually did it so today I decided that I'd give it a try.
This solution works great and leaves your overdrive off switch functioning like factory, the only difference is that the overdrive is now in the off position normally instead of the normally on position. View attachment 221887

For anyone who wants to do this it is simple if you have a little mechanical experience.
What I did was use a relay which is hooked into my backup lights to shut the OD off. Since you have to go past the reverse position to put your Jeep into Drive, the backup lights always blink on for a split second and that is what turns the OD off.
I spliced into the backup lights by using the white and lt green wire under the c drivers side kick panel cover.
Then I spliced into the green and orange wires on the back of the OD shut off switch.
I ran these wires to a relay that I tucked behind the glove box, added a ground wire, and it works !
If I want overdrive, I simply flip the original switch and presto, I have overdrive.
The light in the switch still works so you can see if it is in OD or not.
I believe the relay was wired like this:
Ground-85
BU light wire-86
Orange wire-87
Green wire-30
The numbers are usually printed on the little relays

Hope this helps someone View attachment 221888
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Thank you! I will do this when I recoup fro my hip replacement a couple days ago. In the meantime please let me know if you run into any issues regarding your setup.
 
As @Clocktower07 mentioned a PAC module should do the trick. I use one in my F-150 to have it automatically go into sport mode on startup. I don’t have an auto TJ so I can’t give you specifics but you can see what I did here: https://www.f150forum.com/f118/default-sport-mode-yes-please-439320/
to get an idea of what the module does. There is a link to the module in the write up as well as a link to the module instruction that might help.
 
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I'm unsure if it makes sense, but I keep my OD on when I'm driving in the hills around my house <50 mph. It seems to shift quicker and keep higher RPM's. I typically only turn the OD off when I'm on the highway or a long, flat stretch. Running 33's with 3.73's too.
 
Ron505 said:
I'm unsure if it makes sense, but I keep my OD on when I'm driving in the hills around my house <50 mph. It seems to shift quicker and keep higher RPM's. I typically only turn the OD off when I'm on the highway or a long, flat stretch. Running 33's with 3.73's too.
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That seems exactly backwards. :unsure:

I don't always turn mine off (4.10s & 33s), but the Pac module seems cheap enough to experiment with.
 
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1612245128318.png
 
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LONGJP2 said:
That seems exactly backwards. :unsure:

I don't always turn mine off (4.10s & 33s), but the Pac module seems cheap enough to experiment with.
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I know it seems backwards. But mine seems to have different shifting points when OD is off compared to on. I guess the TCC is doing that? My brain currently doesn't have the capacity to follow all of the TCC conversation I guess.
 
With OD on, transmission shifts way too soon into OD.
With OD off, transmission shifts way too soon into 3rd.
What idiot setup these shift points and why didn't Jeep come out with a TCM or PCM update to fix them?
 
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