42RLE shifts hard

mahshall

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Dec 4, 2015
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Tallahassee, FL
I've got a 2004 TJ with a 4.0 & 42RLE. About a month ago I replaced the original 42rle at 125k with a reman unit from Powertrain Solutions. I also added a Derale TJ transmission cooler to keep things cool and bypassed the radiator cooler as per the reman companies request.

Most of the time the transmission will shift fine through all the gears but sometimes it likes to rev before a shift and shift hard. The fluid is ATF+4 at the correct level. I've read about relearn procedures to reset the shift points but haven't tried anything yet.

Any ideas what might be causing the sporadic hard shifts?
 
I had a similar problem. While replacing the valve cover gasket. I cleaned the ground connection on the back of the head. That ground also goes to the transmission. Ever since that was done the hard shifting has disappeard. It may be just anecdotal evidence. But it wouldn't hurt to try it.
 
I've got a 2004 TJ with a 4.0 & 42RLE. About a month ago I replaced the original 42rle at 125k with a reman unit from Powertrain Solutions. I also added a Derale TJ transmission cooler to keep things cool and bypassed the radiator cooler as per the reman companies request.

Most of the time the transmission will shift fine through all the gears but sometimes it likes to rev before a shift and shift hard. The fluid is ATF+4 at the correct level. I've read about relearn procedures to reset the shift points but haven't tried anything yet.

Any ideas what might be causing the sporadic hard shifts?

I'm curious as to why you would bypass the radiator cooler. I have a rebuilt 42rle and the radiator cooler wasn't bypassed. I also have a derale cooler in the line. I don't have a solution but don't like the idea of bypassing the radiator cooler and depending only on the Derale.
 
I'm curious as to why you would bypass the radiator cooler. I have a rebuilt 42rle and the radiator cooler wasn't bypassed. I also have a derale cooler in the line. I don't have a solution but don't like the idea of bypassing the radiator cooler and depending only on the Derale.

I should probably add the radiator cooler back in line with the Derale. The transmission company said for the warranty to be valid I needed to provide picture evidence that the radiator was either replaced or bypassed with an aftermarket cooler.

I’ve replaced the radiator recently and have nothing going through the radiator trans cooler so I guess it would be wise to connect it back up.

My 42RLE still shifts hard randomly and I haven’t found a solution, I might try having the PCM reflashed with the newer transmission update but I doubt it will change anything.


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Was the engine running when checked the ATF level? You won't get an accurate ATF level on the dipstick if the engine isn't running.

That rebuild shop was wrong to recommend the radiator cooler be removed from the cooling circuit. Reconnect it and connect the Derale after the OE cooler.
 
Was the engine running when checked the ATF level? You won't get an accurate ATF level on the dipstick if the engine isn't running.

That rebuild shop was wrong to recommend the radiator cooler be removed from the cooling circuit. Reconnect it and connect the Derale after the OE cooler.

Yes, I’ve checked the ATF level hot/cold running/not running and it all seems to be correct. I’ve got a Warn 8274 in front of my radiator but I’ll reconnect it before the Derale cooler


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That you have the tall Warn 8274 or any big winch in front of your radiator is not causing the engine or transmission to run hotter than normal, the OE cooling system has way more excess cooling capacity than is required so those types of items are not a factor at all. Good decision to reconnect the OE cooler, I'm running both myself (with Derale) without problem.
 
I agree with plumbing the OE cooler into the circuit along with the Derale cooler.

The only reason I can think that the rebuilder wanted the stock cooler out of the system is that they don’t want to deal with the possibility that the cooler is clogged with debris from the failed transmission. The debris would either hinder the performance of the cooler circuit or flush out and cause a problem in the new transmission.
 
Any luck? Just bought an 06 TJ with 94k, 6 with auto trans- I’ve read all the treads saying the PCM needs updated, but no one has updated long term results.
Only very rarely does it shift hard since I took care of the ground. It seems to be a software/sensor issue. I've been a electronics tech for the past 25 yrs. I currently am employed as a radar tech. I've seen this stuff for quite a few years now. It's amazing what simple signal path grounding will do.