Originally Posted by Kyle.Gilmour
Right... keeps you from going into Reverse or Park unless you push that lever....
but I also have another button for the LockUp, not shown in the pics,
Russ explain that... I have to run to a meeting..... haha
The lever is for locking out reverse and park. The button on the handle and the button not seen in the picture (wasn't installed yet) is for locking the torque converter. These performance converters heat up the transmission (this is also why you want a transmission cooler). I honestly don't know the ins and outs, but I know if you don't have a lock up you'll have too much heat and horrible gas mileage. The lockup is for cruising in 4th gear. On a full auto transmission like mine the computer triggers the lockup (at 61mph in my case). In the 4L80 it can't be automatic. The black button on the side of the shifter triggers it. Obviously it could get tiring holding down that lockup button all the time on the freeway, so Owen installed a button next to the shifter for that purpose. You do have to push it again to unlock the converter though or the car will die when you come to a stop (at least I think that's what happens). Speedster could probably explain this better than me.