Nissan Repair: 1997 UD Truck 1400 series.., torque converter, nissan truck

Question
Hello Von.... I have a UD Nissan Truck that I just purchased down in Florida. I am not sure about the way these trucks operate with the auto transmission that it has, but it is a 1-2-D and it has an overdrive button on the shifter handle. When I drive off with it, it goes through the gears great 1-2-D, but it seems after I reach 40 miles an hour or above, that it needs to shift maybe one more time. With the overdrive button activated and the indicator light on the dash off because of being activated, it makes no difference it seems, but if we switch the overdrive button to the off position and the indicator light comes on showing it in the off position, then the truck will take a nose dive as if someone shifted it into second gear from drive at 50 miles an hour.

We drove the truck from Florida at 70 miles an hour with the overdrive button in the on position, but it seemed as if it still needed to shift at least one more time to us, I mean at some point, but then again maybe not.. It just seemed to be either not working with the overdrive or the torque converter, or whatever as we drove it back to South Carolina. The motor ran great and the truck did well, but I don't know about these trucks at all. Just learning a bit just encase.  

Answer
Beagle9,

The overdrive button resets each time the vehicle is started.  It defaults to being on.  Make sure to leave it on since it will cook the transmission leaving it off.  So, leave the button a lone and you should be fine.  Overdrive it 4th gear and the torque converter locks when it is in 4th.  If off the torque converter is not locked and the transmission will overheat.  If you have not thought about an auxiliary cooler you should do so if you are going to keep the truck.  Just run it inline with the discharge line from the radiator.  A Hayden 404 is my choice I install on all of my vehicles.