Question -- lockup and drive gear clutches 700R4

[dennislbrooks]

I have a 700R4 with a lockup converter that has an electric connection.

When the trans reaches the OD you can feel the lockup shortly after.

1) When OD is reached does the trans open a pressure valve to supply the converter lockup clutches?

2) And is full pressure put on the drive gear clutches regardless of TV position?

thanks

[AussieinNC]

Originally Posted by dennislbrooks

I have a 700R4 with a lockup converter that has an electric connection.

When the trans reaches the OD you can feel the lockup shortly after.

1) When OD is reached does the trans open a pressure valve to supply the converter lockup clutches?

2) And is full pressure put on the drive gear clutches regardless of TV position?

thanks

1/ Torque converter clutch lock-up is controlled by a solenoid in the case of the transmission. Pressure to activate the TCC is supplied by the front pump (as are all auto tranny functions). However, the pressure is only supplied to the TCC when the tranny is in 2nd, 3rd, or 4th gears. The solenoid actually closes off the return for the TCC pressure passage, such that when the solenoid is activated, the return is shut off and pressure is applied to the clutch disk. When the solenoid is deactivated, the TCC fluid flow just returns to the pan.

12 volt positive power is always applied to the solenoid when the brake pedal is not depressed (applying the brake opens a switch and removes the power from the solenoid circuit). The circuit is completed by the ECM to energize the solenoid by grounding the electrical return. Some vehicles are programmed so that the ECM will not lock up the TCC unless the transmission is in 4th gear, sensed by a pressure switch in the 4th gear pressure passage in the valve body.

2/ No....the TV cable adjustment is CRITCAL to the survival of a 700R4...

[dennislbrooks]

AussieinNC, the reason I ask is that I was in a vehicle that the TV came out of adjustment when the throttle was stuck wide open prior. It was not known the TV came out of adjustment. No ECM vehicle either.

Going up long hills in OD on return trip-- lockup switch off (toggle) -- you could smell oil/trans fluid getting hot. If the lockup switch was energized (and lockup occurred) the smell went away. It seemed like the lockup "on" really seemed to lock all clutches with sufficient pressure - otherwise they were slipping. This was done more than once to confirm what was causing the smell/condition. Also shifts were lazy not firm.

I must be wrong. Been wrong before. May need more beer.

The trans fluid was dumped and did not appear or smell burned and the TV was adjusted. The vehicle shifts and appears to run fine and now has no smell when OD is in with no lockup.

[AussieinNC]

Only thing I can think of is the TV cable stayed "out" and kept the tv valve pushed into the valve body...the smell of burned oil may well have been due to some leakage...

When the TC lockup solenoid is energized the valve open and dumps oil pressure from the front side of the lockup clutch....system pressure then pushes the lockup clutch against the convertor body for lockup.

Has this trans had an aftermarket shift kits added to the valve body?

There are some constant pressure modifications possible the the TV circuit...

In any case, you are very lucky...I have seen 700R4's die totally fater less than 5 miles of driving with a disconnected TV cable.

[dennislbrooks]

The trans is a Monster 450 HP rating with a shift kit. Lockup torque converter is 1500 RPM behind a 350+ HP bbc. It drives best with lockup on when it wants. With normal driving, OD comes in at 47 mph. Lockup very soon after. Kicks off with brake and acceleration downshift or auto downshift out of OD. It only hunts for a gear at about 37/38 mph - 35 mph zone. OD can be turned off with a switch. Trans acts like it should under heavy or light acceleration. Just off idle shift from 1 to 2 is very very noticeable.

55 mph is about 1400 rpm in lockup.

thanks - just trying to understand.