zanderman111

I just bought a 1999 Grand Cherokee I6. When its cold it seems to slip out of gear when shifting between 2nd and 3rd. When its warmed up (after 2-3ish minutes of driving) it shifts perfect. Any idea what would cause this? Solenoid pack? TCM? Any possible ideas as to a solution would be greatly appreciated!

Thanks in advance!

ol"blue

Have you checked the trans fluid? What color is it? Does it look or smell burnt? Is it full or low?
And Welcome to CF.

zanderman111

Thanks for the welcome!

The trans fluid color is actually of similar color to engine oil. Level is ok. It doesnt smell burnt, but it should be cherry red correct? Is this an indication of something gone wrong internally or just old fluid in need of replacement?

PS: thought I should mention that it has 102000 miles.

ol"blue

Yes it should be reddish in color. I'd change the fluid and filter but wouldn't flush it.
Read this. http://www.wjjeeps.com/service/transmission.htm
That's a good site full of useful info about the WJ's.

zanderman111

What exactly is the difference between a change and a flush? Thanks for the link, I had already been reading that page. I am planning on doing this myself, as I am pretty mechanically inclined, but I do not have much experience with transmissions. Supposing I took it to a shop, how much should I expect to pay to have this done? Or any general instructions as to how to do it myself would be appreciated.

Thanks again!

ol"blue

Fluid & filter change is just that. You remove the pan & filter and drain what fluid comes out by gravity, leaving old fluid in the torque converter, lines, and cooler. Flush forces out all the old fluid but sometimes gets particles stuck in the small passages causing major problems.
On that link, at the top, it has an icon for Fluid & Fluid service (on the right), among the other options in Blue writing.

zanderman111

I have read that this only changes out roughly 30% of the fluid. Wont my old "brown" fluid contaminate the new fluid that I would put in thus making the change almost meaningless?

ol"blue

Then either do it twice (or more), or take it in and have it flushed.

zanderman111

Thanks for all the advice! Ill do that asap and hopefully that will fix my problem.

candymancan

I would just have it flushed if it was brown like that, how many miles do you have on the transmission ?

Most Jeeps have that i have seen had tranny's flushed around 60-100k miles. The 5.9 i just bought had it flushed at 60k by the previous owner, and my mom had hers flushed at around 100k because the fluid was very dirty..

Or you could just drain the fluid, fill it up, drive it around and drain it again, and maybe do it a 3rd time. You'd still be spending about the same amount of money either way if you do it yourself and change it 2-3 times your going to spend around $130 on all those bottles of atf +4 cause each time you drain the fluid it takes about 5-7 bottles to refill it, and to flush it and refill it completetly would probably cost about the same or more

zanderman111

The tranny has 102K on it. I would prefer to do everything myself, but do you think a flush would give me better results?

Also, I am just trying to understand here, but why exactly will changing the fluid fix my problem? I am hoping it will, but again, I am just looking to understand what all is going on inside there. My problem appears to only happen between 2nd and 3rd, which would make me think it would be more of a problem with the TCM or something like that. To more specifically describe what happens:

Put it in drive. First gear works flawlessly, great pickup and response. Shifts to second fine. Then when I am in second, it seems to want me to rev past 3k to make it shift to 3rd. When I let off the gas (in second) before it shifts to 3rd, it appears to disengage, allowing the engine to rev seemingly in neutral. When it revs back up to roughly 2500-3k, it pops back into gear and then will shift to third. Downshifting seems to work fine, it just hesitates like I said before shifting to third. After really no more than about a mile or so of driving, it smooths out and runs like the day it was made.

My uneducated guess would be that something with the TCM or solenoid pack just isnt telling the tranny to shift, but again, I am very uneducated in this area.

I hope this may add some insight to my problem. Thanks for any and all information. I am an engineering student and like to learn about what is happening, not just a quick fix.

2000xjcherokee824

I had an Audi with the same problem it actually advanced to the point I'd be at a stopsign and it would rev then lock and the car would essentilly neutral drop itself that's y I went to standard btw it's probably ur second and third gear solenoids in the trans I replaced my entire trans might be able to find just the solenoid hope this works goodluck

ol"blue

The fluid changes when it gets warmer and your problem goes away. If it did it all the time I'd say the solenoids or the PCM. The WJ doesn't have a separate TCM, it's controlled by the Powertrain Control Module. That can be "Re-flashed" by the dealer service dept. to correct some issues w/ the trans shift points.

zanderman111

ol''blue, so are you in agreement with the other that I need a fluid change + filter or flush? I took it to a monro muffler shop just to have them look at it and see their opinion. They actually refused to change/flush the fluid because they were thinking that it would only worsen my problem. They did think however that the fluid had been flushed at some point in time prior to me taking it in. The fluid was dirty, but still in decent condition, too good to be factory original. Does anyone think there is any truth to what the monro muffler guys were saying?

Thanks!

ol"blue

Yes it's probably been changed before.

And I made a mistake about the TCM. I was thinking of my ZJ and not my WJ. The WJ does have a separate TCM. See here: http://www.wjjeeps.com/modules.htm
Click pics to enlarge.