I am going to service the fluid and filter in my 98 LeSabre transaxle and I need to know what fluid is safe or recommended to use. I see these Dextron III/Mercon fluids; are they OK to use? Also saw a mention of a Dextron IV fluid. This car has around 197K miles on the trans. How many miles on average can be put on these trans before a rebuild is in order; I have done two or three transaxle rebuilds and several rear-drives trans so rebuilding is something I would do if need be.

By the way, what is the capacity of the trans when changing the fluid?

About 6 qts or so with a pan drop. Use Dex6,

Well, at 197K, if it hasn't been rebuilt yet, you are on borrowed time......

They recommend VI over III.....

If just dropping the pan and replacing the filter, add 6 quarts, then shift through the gears, and top off accordingly....it'* usually between 6.5 to 7.0 quarts.....

You actually have the tools to rebuild one? Is the vehicle worth doing this to? Complete rebuild is quite a job......with that mileage, a complete rebuild is in order......I'm talking hard parts and electronics and wiring.....I wouldn't even dream of doing a rebuild on one of these....

I have never rebuilt one of these GM trans. No, I would only do a rebuild of the cluthes/plates, replace all the seals in the servos; gaskets, etc. The idea is that the clutches will wear away over time and need to be replaced. If I was going to do everything then I would just buy a rebuild trans and do a swap. Maybe rebuild kits have gotten too expensive these days for one to do a rebuild. The last trans job was a rebuild of a Ford Taurus transaxle where it started slipping. The kit was not very expensive at that time and dissemble was not that difficult. Dad showed me how to do auto trans. For the Taurus, I removed the clutch packs and replaced all the servo seals, o-rings on anything, etc. That is what I meant by a rebuild. I did replace the torque converter on the Taurus because the clutch material had accumulated from sitting in one area and was throwing the torque converter off balance.

Thanks for the info, Dex VI it is then.

OK, been doing some reading on DexVI. I read that I should do a flush but I am unsure about this; not sure I have the means to do a flush. How much of the old fluid remains in the trans when doing a pan drop?

Total system capacity is about 13 quarts, after overhaul.
Aprox 50 % of old fluid remains if you are adding 6.5 quarts after a pan drop with new filter.
I would recommend using the Delco service kit, consisting of gasket & filter of course along with the Dex 6 as well.
Some shops/dealers have recirculating machines that are able to do the flush completely, but I would just try the pan drop, see if there is any particulate matter in the pan.
Is the transmission shifting fine? Any hard shifts or stored codes present?

There are no negative side effects in our application of mixing Dex III and Dex VI, you'll just not have all of the full benefits of Dex VI because it will be diluted some.

You can also easily pump out 4 quarts through the dipstick tube which can also help you with the rate of exchanging fluid before the pan drop. Not to mention it can help control some of the mess when you do drop the pan.

And if the transmission is not showing any issues, I usually recommend just leaving it alone (aside from maintenance of course). If it ain't broke, don't fix it. I have a 4T60E with 190k miles on it (I assume) and it shifts better than my unit with 73k miles.

If you are thinking of changing clutches, seals, etc., then it'* also imperative to replace the valve body, the solenoids, and wiring harness....gets expensive....