Possible consequences of not changing your tranny fluid?
 

Disclaimer: I'm not the one in this situation.

I know someone who's got a Jeep Grand Cherokee of unknown cylinder number and unknown wheel drive. I was told that in the 2.5 years of vehicle ownership that the owner has been doing oil changes but has never done a tranny fluid exchange.

Questions:

1. Is the worst case scenario that the whole tranny breaks and needs to be replaced or are there other system(s) that may be affected by a tranny failure?
2. I mentioned to the owner of the GasSavers method of popping the gear from D to N while idling at a red light but was told that the owner was concerned that the gear may not shift from N back to D when the light turns green. Should I raise the tranny fluid exchange issue to emergency level or not yet?
3. What is the mileage frequency for tranny fluid exchange for a Jeep Grand Cherokee?

Thanks in advance for your time in replying.

If he is having symptoms like wondering whether or not the car will go to D when he wants, he should change the fluid. No question. No matter what the factory says the interval is.

Factory interval for a Jeep Grand is somewhere between 30K and 50K (like most auto trannies)

A major word of caution!! If there are no records of tranny maintenance, DO NOT take the Grand to get a tranny flush/treatment. I don't know what it is about those transmissions...but they do not like it. (case in point....have a friend with 98 Grand. He flushed the tranny, added 1/2 quart Lucas ATF. 2 days later, he lost 1st gear and reverse. Now, new tranny time!!)

In my 89 Jeep Cherokee, I've not changed the fluid since I got it....and I'm reasonably sure it hasn't been changed in the past......2-5 years. The fluid is still in good shape, and hasn't been burned or scorched. I'm just going to leave it in there for the time being. When I do go to do maintenance, I'm just going to replace the tranny filter, then will *probably* put the old fluid back into the tranny, if it's still in good shape.

There should be zero concern that the transmission won't shift back into D at a light. If the owner needs proof, try it in a parking lot. Just make sure that they keep their foot off the skinny pedal, as throttle input will shock-load the TC, and possibly shorten the life of the drivetrain.

(and your worst case scenario?? It depends on how spectacular the tranny failure is.....I suppose it could damage the t-case (if equipped with 4WD), as well as engine damage (not likely at all, but possible) If the tranny locks up at highway speed, there's a big problem. Could throw a driveshaft, which is pretty cool to see from a distance, but incredibly dangerous/scary to see in person.)

What generation of Grand is it? From what I've heard from my friends with the 1 gen Grand (ZJ) most auto don't make it to the 100k mark without needing a rebuild. And thats just normal usage. The 2nd gens (WJ) are apparently better.

If it uses the original Chrysler 7176 tranny fluid, you don't want to do anything to it in my experience. Even a filter change. For some reason using any fluid other than 7176 destroys the torque converter and taking the tranny along with it. I haven't had any problems flushing trannys that use ATF+3/4 but YMMV.

My son bought an Acura with an A/T recently. About half way home it seemingly slipped into neutral. He ran the shifter through the gears, but it still wouldn't go. He shut the engine off, restarted, and it drove about 1 mile before slipping out of gear again. He repeated this behavior and limped home on side streets.

Bummed at the thought of buying a new trannie, I suggested he replace the fluid. I went to the parts store to get 10 qts of fluid, and was explaining the situation to the salesman. He warned me against the full change and flush, just as racoonjoe stated above. So we just changed the fluid in the pan and the filter. It has run fine since then.

OMG. I've never seen such thick, black trannie fluid in my life! With 1000 miles on it now, my son is about to do another partial fluid change. The thought of that black goop in there is too much for either of us :-P

I believe regular trannie fluid changes will extend the transmission's life dramatically. However, it appears you can have too much of a good thing in old, abuse A/Ts.

I'm not sure exactly why the new fluid kills these autos. I've heard of guys that keep the old fluid, and dump it in when/if they start having problems. I would *not* recommend using any kind of additive at all in your auto transmission.....

If it's slipping badly, it's probably toast anyways. You may be able to limp it along for a while, but slippage is not good. Either you're out of fluid (kills trannies), the fluid is burned and thick from overheating (dead trannie soon!!), or the internals of the transmission are already FUBARed.

From my research on the AW4 transmission in Jeeps, particularly, I've been hesitant to change my tranny fluid/filter. I just can't afford a new one. My fluid is still nice and red, hasn't been burnt at all, and I've got no real slip/shifting oddities. (Just the crap that's inherent to these Jeeps!!)

I'll third the not changing fluid if it's been long neglected.
A friend of mine bought a used '89 VW Cabriolet with unknown miles (the odo's 10k tumbler wouldn't roll over) and had me take care of the maintenance. It had some oil burning and pinging problems (I thought it was the stupid mechanical fuel injection, but in hindsight, it may have been simple carbon build up), so I was sure the engine would be the first thing to go. Nope... The transmission worked fine, but I decided to change the transmission fluid anyway since it was looking pretty brown. I drained the fluid, dropped the pan and installed a new filter. It was fine for about 5k miles, but then it started shifting hard and would cycle in and out of neutral when stopped in gear. Another 10k or so later, the transmission gave up the ghost.
I think it's a matter of the detergents found in ATF. When the fluid has been in the transmission for a long time, the detergents either break down or become saturated. Any additional gunk floats around in the fluid until it settles or becomes jammed in a nook, fills in the gap around a slightly leaky seal, or whatever. When you replace the fluid, you introduce a bunch of fresh detergent, which then cleans out all the settled gunk, opening up those plugged old leaks. That's my theory anyway.

Amazing. One more thing to dislike about automatics. Maintenance can make them fail. :-(

Take it to a GOOD automatic transmission place and see what they say and not a chain shop but a private run place with a lot of business. I friend with a Honda Civic finally had his rebuilt for almost $5000 and it never ran so good as it does after they rebuilt it. There was a lot wrong with it right from the factory that they didn't tell him about when he baught it used from a Honda Dealer.

using trans flush machines for a long time I've learned a few things. fords don't like the cleaner agent thats used but conditioner is ok with the flush. most cars can handle the cleaner/conditioner. some cars with black fluid get flushed out and the problems go away. the old fluid gets build up of gunk and can get sticky instead of slick. Ive seen crown vics/camaros/e350vans chatter (like rumble strips on the side of the road) while the trans activates the torque converter from that nasty old fluid, after the flush it engages smoothly.