42RLE overheating, overdrive, mountains, manual shifting, and big tires discussion

JP761

JP761

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Joined
May 20, 2019
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Dahlonega, GA
Alright, so maybe I don't know what I'm talking about, maybe something is broken (I don't think so anyway) or maybe I might be tearing something up, either way, I'm curious. I've never owned anything automatic. I didn't want an automatic Jeep either, but my wife did, and then I found a LJ with relatively low miles for the price with an auto. I went with it, no biggie.

Then I moved up into the mountains- and good grief this thing wants to shift in and out of overdrive all the time. First I turned OD off and that helped, but I would still get that chocolately smell whenever I would go up in the hills. I bought and installed a Derale trans cooler (thanks for the write-up Jerry) and I definitely needed it because it runs pretty often. Then I just started dropping the thing out of D and into 2 and everything works so much better. It doesn't shift constantly and for no reason. I was wanting to re-gear, but I'm not so sure anymore because I would lose the ability to run 35-50mph in second on those steep mountain roads without winding the engine up too much. I know the re-gear will help literally everywhere else, I just don't want to burn the clutches up. Any thoughts on this? Feel free to tell me to shut up and stop complaining about automatics if that's all the advice I need haha.
 
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Simple question... what size tires are you running and have you regeared your axles? Don't worry about burning the transmission's clutches up.

Automatics work great when you're geared properly. Same as with manual transmissions.
 
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If you regear deep enough, it might actually prevent transmission overheating.
If you're not familiar with them, look up how a lockup torque converter works. In short, most of the time the transmission allows a certain amount of slippage, much like allowing your clutch to slip. It uses fluid instead of friction material, so it rarely overheats and doesn't wear out. In certain conditions, the torque converter locks and causes the gearbox input shaft to rotate at the same speed as the TC input. This reduces the amount of energy loss due to slippage.

Old automatics used to get worse fuel mileage because the torque converter was always slipping, and wasting a portion of the engine power as heat. Locking it up gives it the same efficiency as a manual transmission.

In all but 4th gear (3rd with OD off), the torque converter remains unlocked. This is where much of the transmission heat comes from. So when you're hauling up the hill in 2nd, the torque converter is unlocked, and a significant amount of engine power is lost as heat in the transmission.

If you regear deep enough, you can climb the same hills in 3rd with the torque converter locked most of the time (assuming you turn off overdrive). This means much less engine power is dissipated as heat in the transmission, and a higher proportion of engine power makes it to the wheels.
 
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Jerry Bransford said:
Simple question... what size tires are you running and have you regeared your axles? Don't worry about burning the transmission's clutches up.

Automatics work great when you're geared properly. Same as with manual transmissions.
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I've got 3.73s now, and 33" tires. I was planning to go to 5.18s.
 
JP761 said:
I've got 3.73s now, and 33" tires. I was planning to go to 5.18s.
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That should significantly improve performance. In 3rd gear with the torque converter locked at 70 mph, you'll be turning 3800 rpm, and higher when the torque converter unlocks. That's easily high enough to climb hills.
That regear is definitely worth the money in my opinion. Short of bolting on a supercharger or turbocharger, that will be the biggest improvement you can do for hills.
 
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Gears and a good program for the PCM is my answer. I retuned first which helps a lot. Changing gears helped too, but I don't like the rpm at 70 mph in 3rd with 5.38s and 35s. With 4.10s it had power to spare in 3rd at 70 mph and 2800 rpm. With 5.38s in OD it struggles on long hills.
 
Brianj5600 said:
Gears and a good program for the PCM is my answer. I retuned first which helps a lot. Changing gears helped too, but I don't like the rpm at 70 mph in 3rd with 5.38s and 35s. With 4.10s it had power to spare in 3rd at 70 mph and 2800 rpm. With 5.38s in OD it struggles on long hills.
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That's always the dilemma with the POS transmission. Gear it for drive or try to make it work in OD. It needs to be something other than screwed up in both.
 
I'm sure it will drive much better with the lower ratio. I just didn't want to end up with the thing shifting all over the place still and not having a decent way to control it. It sounds like the ratio is still the root of the problem here, not the transmission control.

The mention of the PCM is interesting though Brian- I didn’t think you could do much with the PCM in these things.
 
I don't think there has been any tuners messing with Jeeps TJs. The only one I am aware of is Flyin Ryan. I think he is a little bit too expensive for a canned tune, but I don't know of anyone else doing it. HP Tuners is available for your year Jeep which is much better than my 04. The difference is obvious.
 
Brianj5600 said:
I don't think there has been any tuners messing with Jeeps TJs. The only one I am aware of is Flyin Ryan. I think he is a little bit too expensive for a canned tune, but I don't know of anyone else doing it. HP Tuners is available for your year Jeep which is much better than my 04. The difference is obvious.
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Josh Pearl with Performance Dyno tunes Jeeps, though he only does the 05-06 models (to my knowledge) for which HPTuners is available .
 
@JP761 Looks like you have at least 2 choices. I have a friend that has an 05 6 speed that I am trying to convince to get HP Tuners. The stock tune is pretty good until you get to about half throttle. Just when you need more power the tune gets overly cautious.
 
Doesn't matter how much horsepower you have if the gearing isn't correct. If your Jeep was geared correctly you would not need to run around in 2nd. The 4 spd auto is a turd of a trans, unfortunately. The super deep overdrive is the biggest issue. The jump from 1:1 to .69:1 is too far of a spread.
 
Chris said:
Get a transmission cooler too, it certainly won't hurt.
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Done. It runs way more than I thought it would. I'm really glad I did it. Tougher job than it should have been- ever heard of a jiffy fitting? Apparently none of the auto parts stores around here have either. I had to use the tubing cutters and flaring kit to get the lines together haha.

I started this thread to reassure myself to spend the money on a gear install and it sounds like that will remedy a lot of my concerns. I could manage it with manually shifting the thing to keep from cooking the trans, but it's still a dog around town (HWY is limited, work truck does all that). I've got a go fast toy. I want the Jeep to be more reliable than fast. If a tuner can make it run better I don't mind doing it, but I'm not racing the thing. I just don't want stuff breaking because I'm ignorant.
 
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