Thread: D3 auto hunting gears randomly

Likely the TC lock up failing.

Originally Posted by Ilike2disco

Is this transmission judder the lock up feature of the torque converter locking and unlocking in response to changing loads?

I’ll have to read more I think to educate myself better on this.

The judder is from wear in the torque converter lock up clutch plates and it not being able to lock up under constant load. Basically the lock up mechanism is a steel diaphragm spring hydraulically activated. This pushes on a set of clutch plates to lock the input and output shafts mechanically. Wear in these plates and the fluid ports due to contaminated fluid means it can't reach the right pressure to move the plate spring. Most of obvious when under constant load (e.g. towing) and engine rpm varies or "flutters". Regular fluid changes and using sport or command shift to keep the engine rpm above lock up speed (1250rpm on the 2.7 and 3.0l diesel) will look after your tc lock up plate. An additive like Dr. Tranny is a friction modifier and just a band-aid. These tc are rebuildable, should cost around 500 bucks, the rest of the cost is getting the transmission out of the vehicle. A new genuine tc is around 2500-3000.

One from left field: how long since you've cleaned/replaced the MAF sensor and pre-/post CAT oxygen sensors?
Their outputs coupled with the throttle position sensor output can affect the auto transmission change points. I discovered this years ago in RRP38...the 4sp auto on the P38 would drop back to second gear on the slightest incline rather than choosing third...even though I reset transmission numerous times with the "BlackBox/Laptop" it was to no avail and was driving me nuts.... I discovered that a few sprays of the MAF with CRC cleaner made an enormous difference ... it improved even further after I'd replaced the MAF and O2 sensors on the P38 and reset the adaptive values....
I'm not saying this is your issue... just another consideration...

Originally Posted by Hoges

One from left field: how long since you've cleaned/replaced the MAF sensor and pre-/post CAT oxygen sensors?
Their outputs coupled with the throttle position sensor output can affect the auto transmission change points. I discovered this years ago in RRP38...the 4sp auto on the P38 would drop back to second gear on the slightest incline rather than choosing third...even though I reset transmission numerous times with the "BlackBox/Laptop" it was to no avail and was driving me nuts.... I discovered that a few sprays of the MAF with CRC cleaner made an enormous difference ... it improved even further after I'd replaced the MAF and O2 sensors on the P38 and reset the adaptive values....
I'm not saying this is your issue... just another consideration...

Good logic, however this one is Nothing like the P38 transmission.

As Eric detailed. The TC clutch is playing up.