Are the torque converters in our DII's electronically operated for partial/complete lockup of 4th gear or mechanical? Just wondering as I continue to have issues with 4th gear prematurely (@ 35 mph ) shifting into what would be used for highway speeds. This started happening when I changed the ATF to Mobil 1 Synthetic ATF. With a possible lower friction coefficient, it could be the culprit.

I have since changed back to a regular Dex 3, changed filter etc. and still experiencing the same thing. Lubeguard Black is up next to alter the additive package a bit to give it some friction modifiers to help get this thing figured out.

 

Any codes at all? Did you change the fluid this last time, if so, how burned was it?

 

No codes that I know of, no lights etc. Yes, I did the change to M1 and the ATF that came out looked like new. The M1 has been in there for about 15k miles and also came out looking like new. Would it be worth disconnecting the battery in hopes the TCM/trans would relearn it's shift points. I just feel it's mechanical if indeed the torque converter is locking up too quickly, if it's electronically controlled then I might be screwed.

Here are some interesting answers I got at Bob Is The Oil Guy forum:

"That really does sound like the transmission is expecting to have a friction-modified fluid and the TCC is just grabbing instead of smoothly engaging or going into a partial-lock mode. Modern (post 1990) transmissions do very complicated things with the TC clutch, locking it partway in some gears, and the slowly locking it as speed builds in final drive so it almost acts like a continuously-variable tranny. To do that most of them use friction-modified fluid to keep the TC clutch from grabbing or chattering. (like Mopar ATF+ 4, but there are many others)."

"if the M1 has a different friction coefficient, AND the LR is using a partial engagement, what's happening is that the partial lockup is now becoming a complete, or more complete lockup.

I experienced same in another vehicle. your AT wants a more friction-modified fluid. you can correct this by adding SMALL, CAREFUL amounts of LubeGuard Black. just a little at a time."

 

From the RAVE shop manual:

The automatic gearbox is a four speed unit with electronic control of gear selection, shift quality and torque converter lock-up

and

Software in the EAT ECU monitors hard wired inputs and exchanges information with the ECM on a Controller Area Network (CAN) bus to determine gear shift and torque converter lock-up requirements. Resultant control signals are then output to the gearbox solenoid valves.

 

GREAT information! Thank you... Do you have an educated guess to what is happening?

 

I would do another drain and fill with regular trans fluid to get the rest of the Mobil 1 out.

 

Agreed - it is certainly the least expensive alternative.

 

I also agree, with one addition, throw an bottle of Lucas tranny additive in the tranny to help clean up your valving and solenoid action.
DO NOT disconnect the battery unless you just want your different ECU's to loose their memories, leave them alone. Now if all else fails, then you might consider having a shop clear and reset your tranny's adaptive menory and then do a half hour of stoop and go city driving to let it re-educate it self.

 

Will do guys, thank you for your thoughts. Will report back.