Volvo: 78 Volvo OD not working, volvo 245, oil level

Question
Hi,

I have a 78 Volvo 245. Only has 235k miles. Runs great but the overdrive
won't work anymore. It was popping in and out occasionally but now it just
doesn't go into OD. The light goes on but no shift.

Is this wiring or a fuse? Can I fix this or should I take it in?

Also, my stick knob is breaking apart around the OD switch, is this
replaceable?

Thanks!
Sam

Answer
Sam,
The switch and knob are in fact replaceable. You have to test and see if there is power to the overdrive solenoid. If there is and the solenoid clicks with the switch on, is the oil level in the trans ok? If yes then the O.D. unit maybe worn and need rebuilding.