Engine/Transmission (1994 - 1998) TC Lock-up Question

[jtadysak]

I have a 95... . exactly what determines when the torque convertor locks up. . is it rpm. . speed... throtle position. . ???. . also what determines unlock. . will it lock up in third and shift to od. . when accelerating. . will it lock up when accelerating hard in od. . I guess what I'm asking is how it achieves the signal to lock up or exactly what causes it to lock up... . and the big question... HOW DO I KNOW WHEN IT LOCKS UP. . Do I feel it or see it on the tach... I can certinaly feel the transmission shift through 4th... whats the tell tale sign that lock up has occured..... Thanks for the info. .

 

[Joe G.]

The most obvious indication that the TCC locked up is a drop in RPM. With a stock trans you should feel the shift at the same time. Maybe not because it is pretty sloppy.



The main thing that controls lockup is the computer. Based on throttle position (if the accursed TPS is working) and whatever else it looks at it will place a ground on the wire to the lockup solenoid. The solenoid will activate. If hydraulic conditions are correct (have some pressure) the TCC will lockup.



If the computer decides conditions are have become not right for lockup (looks at all the things it does for lockup) it will remove the ground to the soldnoid which will unlock the TCC.



Now if the accursed TCC is a little ratty or other wise misbehaving you can get into a cycle where the TCC will lock. (most likely to happen with cruise control) Then because the throttle position will change (gear ratio is different, etc) the TPS will decide to signal the computer a different story so it will unlock the TCC. Conditions change again so it will lockup. This business can tear up your trans. Ask me how I know that.



With a 47RH transmission like you and I have the mechanical governor pressure is involved as an indication of speed.