I'm a pretty good back yard mech but don't understand the TC lock-unlock cycle. Last time I worked on an auto transmission was back in 72 .. yieks, I'm out of touch. Anyway I see a lot of troubleshooting refers to the TC locking up or not. Mine is the E40D and as I'm trolling down the road through the gears how do know if/when the TC is Locked or not?

Jim

 

My truck shifts thru 3rd then the TC locks then OD shifts. It will stay locked usually (depends on PCM calibration) until you hit the brake or drop below 40-45 MPH. The TC won't lock on most trucks until the tranny has warmed up.

 

At the very front of the torque converter there is a lock clutch. It is hydraulically applied. When it locks, the output shaft of the torque converter is locked to the engine.

Just like clutches on a stick, it has springs in line to cushion the pulsation in the engine torque.

The computer locks the torque converter when the transmission is in drive or overdrive and the throttle is depressed. It is briefly released when shifting. Above 2/3 throttle the torque converter is commanded to lock in 1st or 2nd above 2200 RPM to keep from overheating the transmission on steep grades.

For a little more mechanical detail:

There are three shafts going into the torque converter.

The outermost is attached to the shell of the toque converter so it spins with the engine. It has to flats that engage with the pump to spin the pump in the transmission.

The second shaft is the stator support shaft. It is fixed to the pump support and can't move. Inside the torque converter there is a freewheeling clutch between the stator support shaft and the stator that lets the stator freewheel at low slips but holds it back from rolling backwards when the torque converter is multiplying torque.

The innermost shaft is the transmission input shaft. It connects the turbine of the torque converter to the overdrive planetary inside the transmission.

The input shaft is drilled its whole length and has a split Teflon seal on both ends. When placed into the torque converter, the hole down the shaft is used to send hydraulic fluid into the lock clutch when the computer tells the transmission to lock.

Oil is sent into the torque converter between the pumps shaft and stator support to cool it and oil comes back out between the stator support and input shaft to go to the transmission cooler.

 

Nice post joe, reps sent!