Join Date: Jan 2011
Location: Tacoma Washington
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Your TC recieves RPM from the flexplate of the engine. It uses and oil splash design to multiply the torque and that turns the center splines to turn the input shaft of the trany which is at a lower rpm. When it is in "lock up" it is just that Locked together so the TC is just a 1:1 coupler between the engine & trany.
When the TC is multiplying torque it is also building heat. I found for towing over the mountain passes in western washington, if the truck won't pull in OD locked up I hit the OD off button but then flip the switch (I installed) to re-lock the TC in 3rd gear. It gives me a few more miles per hour and keeps the trans temps cooler.
These engines don't have much compression braking. that being said, the TC lock up swithc also keeps the engine from "free wheeling" (like it goes into neutral) when coasting down a hill. If you have any plans to install an exhaust brake the TC has to be locked up for the exhaust brake to work.
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1997 ext cab 2500, 2WD, SLT, 5 gauges, #10 fuel plate, afc tuned, head studs, 60# valve springs, 5in exhaust. DDP 75HP injectors. timing 18*, 4k GSK, HE351VGT, 13spd road ranger trany, Home made twin ram style intake, sump drain with FASS fuel system