T-20 Chatter After Fluid Change

[Eldon]

I have managed to connect some of the dots in a problem I have had with my Max II with the T-20 transmission.I change the transmission fluid twice annually and as recommended I use GM's limited slip additive. R.I. calls for 4 oz.,ours comes in a 114 ml bottle but the conversion is precisely 4 fluid ounces.For some time ,probably a month or more the transmission will chatter on a turn or when backing up if laterals are not fully back,it does this more after it has been running for an hour or so than when cold.In time this problem will lessen then virtually disappear,then come the next fluid change this problem repeats.Does anyone have any suggestions regarding the limited slip additive,is GM's any good? It seems like a big enough bottle for the amount of fluid it takes.Also when changing I dump in the additive first then the fluid.Should I be pre mixing before dumping in?This particular maintenance procedure seems to create more trouble than it avoids. I use "F" auto transmission fluid and with machine level fill to the level hole in transmission.Any suggestions would be appreciated.

[Mike]

Sounds like you are adding too much fluid. You only need 1 quart of fluid total. You don't have to fill the transmission all the way to the hole.

If you don't use the additive, use one quart of Type F. If you do use the 4 oz. of additive then leave 4 oz. of fluid out so that you have only one quart.

How many quarts have you been having to add to get it to the hole?

[Eldon]

I will have to look it up in the manual but I am following the recommended amount of additive and fluid.It is a bit less than a quart I believe.

[Eldon]

Yes Mike it is a bit less than one quart.The manual states under "Transmission Fluid" Item #7 "Pour in transmission fluid until it reaches the bottom of the level/drain hole" That is verbatim what I do with total fluid of right around a quart. The manual calls for 28 oz./0.841 liters Type "F" ATF and 4 oz./0.120 liter of GM part no. 1052358. The additive container is 0.114 liter which converts precisely to 4 oz. . When you ask how many quarts to the hole you must be referring to the vented fill hole instead of the drain hole.
The mystery remains why the problem follows a change that over time gets better and there are definitely no leaks.The additive would be a friction modifier that probably lengthens the service life of the fluid.I appreciate your response Mike.