A 6L90 tranny on the bench

I had to repair a 6L90 tranny at work the other day. This is one of GM's new six speed automatic transmissions. These units seem to be well engineered and thought out. They have a 6L80 and 6L90 truck longitudinal tranny which this is the 90 series version. They also have a 6T40/45 and 6L70/75 transverse version for cars which is pretty compact and tough





The pan off exposing the valve body/solenoid/TCM assembly


The valve body assembly taken off exposing seals



Remove bell housing/pump bolts


The pump can be pulled off exposing sealing rings


Parts to be put in

This tranny needed the three sealing rings on the back of the pump/bell housing cover to be replaced. This is done by first removing the valve body with solenoid TCM assembly attached as this unit has seals which push on the internal parts. Removing the bell housing without taking this off will break stuff! The pump bolts can then be removed and the assembly pulled off.

I replaced these rings for a slip in reverse and re-installed the pump assembly and then installed the valve body with new seals.

The transmission control module is in the sump on these attached to a plastic block that houses all the solenoid valves. This eliminates wiring, and allows the whole solenoid assembly to be bench tested as a unit. The range switch in this tranny is also inside the case mounted on the valve body. This isn't so bad as it keeps them out of the water/rust/air/snow/ice of the outside world. At least in the tranny they know just to expect 200 degree temperatures and tranny fluid, nothing else. The unit is very easy to remove due to some of these changes