Jeff,

I'm assuming you're talking about the AW 71 (automatic transmission)

If the tranny is slipping into reverse, it sounds like the shift linkage is messed up. There is a linkage from underneath the shift lever to a spot near the front of the tranny drain pan. A haynes manuel ($12) should tell you how to adjust the linkage.

I'm not sure exactly sure what you mean when you say "slipped into overdrive." The OD should activate at about 40 mph if it is engaged. (button on the side of the shifter)

There are a few things that can happen to the OD set up.

1. The relay behind the center console ashtray could be bad. The relay can be resoldered. Remove the plastic cover and resolder the circuit board.

2. The wire from the shifter down to the OD solenoid could be shorting due to insulation corrosion. Splice in a new wire and use plastic tubing to protect it.

3. The solenoid itself could be bad electronically. The solenoid sits hear the back of the tranny on the dirver's side of the car. Follow the wiring from under the shifter if you're uncertain. The solenoid bolts on with 2 bolts. ($220 to replace - free to modify)

4. Low fluid. Make sure the fluid is topped off, especially if you're leaking out of the rear seal. Low fluid can prevent the OD from engaging.

The tranny calls for Dexron III or whatever. If you have Type F, drain it out, but I don't think that would be causing your problem. More likely the linkage for the reverse problem and relay, solenoid, or wiring for the OD.

Can you clarify the problem. Also, who told you to replace the OD? Volvo, tranny shop?