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Old 07-07-2012, 12:28 PM   #1
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99 3 Spd Tranny option's ?

Got a 99 TJ, 4.0 w/ a 3 spd auto at the 1401k mark. It's bucking and dropping, and now is 'clicking', and, I suspect, on the way 'out'. That as a given, has anyone ever tried to swap a Jeep 4 speed auto in place of a 3 spd auto ? I'm up here in Northern Maine so mileage is a big factor. I've pretty much decided on swapping out the axle gear's for a set of 3.73's for both end's for the mileage as well. The engine is doing great as I switched to a 5W30 synthetic that has gotten the RPM down but the tranny is the issue. Any idea's would be a great help as I want to get this done before this winter's snow's hit.

retired04497@gmail.com

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Old 07-07-2012, 12:30 PM   #2
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If you want a jeep 4 speed auto, I would get the xj's AW4, look for a donor Cherokee. I'm not completely sure of all the work that is involved though

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Old 07-07-2012, 12:34 PM   #3
Knows a couple things...

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Your 3-speed automatic is a much better, reliable, and solid transmission than the newer TJ's 4-speed 42RLE transmission is. Not to mention the 42RLE would be nearly impossible to get working properly in your '99 due to it requiring a pair of computers to run it... not only the transmission's computer which is the easy part, but the main engine computer too... and your computer can't run it and you can't use an engine computer out of a TJ that is new enough to run the 4-speed automatic.

I'd just have your present transmission rebuilt. I converted my previous TJ to use the same transmission you have now and loved it. That TJ was stolen so I now run an '04 with the 4-speed automatic and I'd much (!) rather have my old 3-speed automatic back. The 4th gear drops the engine rpms WAY too low so the engine lugs and the transmission itself is not as reliable.

Edit: as Eagle233 suggests, the 4-speed AW4 automatic out of a Cherokee would be a good choice. I forgot to mention that very good option. The AW4 can be made to work with your computer and it's a very solid well-respected transmission. There is a writeup on getting one installed on Stu's site at http://www.stu-offroad.com/index.asp. One of those good writeups is at http://www.stu-offroad.com/engine/aw-4a/aw-4a-1.htm
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Old 07-08-2012, 06:05 AM   #4
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Thank you everybody. I'm just resigned to a re-build. To that end, anyone got an idea as to what synthetic tranny fluid to use ? I'm leaning toward Royal Purple but am more than open to other option's. The other thing here in Maine is it's ability to flow at L-O-W temp's. Take +15 degree's, add a 60 MPH windchill and you can see the problem. I've already given up on the idea of a 'tube'd' airflow since that's all but certain to have whatever fluid is used to turn to concrete with the windchill going thru it.
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Old 07-08-2012, 06:29 AM   #5
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Quote:
Originally Posted by Old Grunt View Post
Thank you everybody. I'm just resigned to a re-build. To that end, anyone got an idea as to what synthetic tranny fluid to use ? I'm leaning toward Royal Purple but am more than open to other option's. The other thing here in Maine is it's ability to flow at L-O-W temp's. Take +15 degree's, add a 60 MPH windchill and you can see the problem. I've already given up on the idea of a 'tube'd' airflow since that's all but certain to have whatever fluid is used to turn to concrete with the windchill going thru it.
I have always used Mobil 1 fluids, and never had a problem. I use them mostly because they are easy to find and are stocked by a lot of places that do fluid changes.
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