I have a 2008 XC90 with the 3.2L six. I have a question concerning the 6 speed AWTF-80 SC transmissions. It deals with the torque converter lockup. Does the torque converter lock up in 3rd and 4th gears as well as the higher gears?
Does the torque converter lockup disengage when the brakes are applied?
The reason I'm asking is that I'm trying to isolate a vibration problem during light acceleration and I would like to rule in or out a problem with the torque converter.
I would appreciate any info.

 

Received this reply on another forum, from a fellow called Deeks:

Yes the convertor will go into lock-up at speeds as low as 30km/hr. in 3rd gear and should release on braking. I have had to replace a couple of the MY 07-08 6 speeds due to what was most likely a pressure bleed or valve body problem causing a shudder when the client would start to lightly accelerate in 3rd gear in lock-up at about 30km/hr. This is similar to the 'convertor chuggle' problem that plagued GM transmissions for many years usually caused by a torn o-ring on the input shaft feeding the lock-up clutch in the convertor. If you accelerate hard you would not feel the problem. No amount of trans flushing would make the problem go away and we even tried the fluid for the second generation 6 speed which has improved friction modifiers in it.

There is no TCM software upgrade that addresses this issue in the TF-80SC. Also we only saw this issue with the XC-90 and not in the P3 models with the SI6/TF-80SC most likely due to the large difference in GVW. We had a local trans shop repair one for us as the vehicle was out of warranty and it worked out good and the cost was considerably less than replacing the trans.
We still service that vehicle 4 years after the fact and all is still fine.