Jeep trans issue - please help

[joe8918]

I have a '96 4.0 4x4 with an automatic trans and was driving at highway speed (~65mph) yesterday and the transmission downshifted from 4th to 3rd. It was on cruise control and never upshifted back to 4th. I noticed earlier in the day driving at highway speeds that there was a sudden downshift but it ended up going back up to 4th. I was driving on a level surface (no need for the trans to downshift). Anyone ever had this issue? Possible culprits?

Also, when I got home I put it into part and when I dropped it into reverse the shift seemed a little more violent than usual but that could have just been me being that I was concerned already over why the Jeep never went back into 4th that day. Please advise.

[fredjacksonsan]

I think the trans shifts from o.d. to 3rd when it's getting too hot. Were you towing or doing anything heavy duty?

If you have a trans cooler, check to make sure the cooling fins are clear of mud, bugs, etc.

A fluid change may be in order, since it got too hot.

How many miles on the Jeep?

[joe8918]

Hello Fred,
Thanks for your reply. Please see additional information...

1996 4.0L 4x4 62,000 miles

I was not towing anything and not going very fast (not a real chance for engine overheating). Also, I got the Jeep 1 year ago and have to admit that I have not changed the trans. fluid yet, I should do that. I have checked the trans. fluid level and it was acceptable but as you said that old fluid may not descipate the heat.

I will check to clear the fins and thing like that. Please provide any further detail. I'm not really concerned with the severity of the shift to reverse from park because I was probably just all worked up over why the trans did not upshift back to 4th. It's a Jeep...it shifts into gear pretty hard anyhow, right?

thanks again and provide any other feedback

[fredjacksonsan]

I was thinking that if it got that hot, that you may have burned your trans fluid, and at 62K you're probably due for a change.

The trans cooler is a small radiator looking thing near the main radiator. If you've done some offroading it could be covered by mud. You should be able to find it by tracing the lines coming from the transmission.


Further, you may want to see if the computer is throwing any diagnostic codes. There are numerous posts here about how to get the codes and what they mean, have a look around and check them. If there's an issue with the computer, that could also cause a shifting issue.

-edit- The hard shifting issue. My auto Jeeps have shifted firmly, but not harshly. I'd change the fluid over and see if that changes it.