I'm sorry for the likely redundancy of this question, but I've scoured the archives and still came up short...

89 740 Turbo Wagon, no 4th/OD. I replaced the auto tranny's OD relay to initally cure this problem. This worked for several months, until yesterday, when 4th disappeaed. After pulling out and replacing the relay, 4th gear returned. But the next time I took the Wagon out, it was gone again. The relay's working fine--arrow light goes on and off; I can hear it clicking also. I've tried checking the wiring from the relay tray behind the ashtray, which looks okay.

I've read alot about the OD solenoid on the tranny. I crawled under the car earlier today, but couldn't find it. Where is it, exactly? I want to check the wiring--think this is a likely culprit?

Thanks in advance,
Brian

One possibility.......

The wire going to the solenoid may have worn or frayed insulation, allowing the conductor to short against ground. This can happen intermittently, such as when you hit a pothole. The excess current from a short to ground often causes a foil trace inside the relay to burn. Then, even when the OR relay "kicks in," the current doesn't get to the solenoid.

If this is the problem, then you must repair the frayed wire.

And these relays are super-simple to resolder and repair.

$0, 15 minutes, no risk, clean 'n easy work.

The first pix below (240 OD relay) shows the burned foil. The second pix shows the same relay fully resoldered and the burned foil repaired.

This relay was repaired about 6 years ago and still works fine.

Easy to find, driver side of tranny, about halfway back, circular cylinder about 2" high with single wire going to it. With key on (not necessary to start engine) and helper pushing the button you will hear and feel the solonoid clicking. You also check for 12V at the solonoid when light is off.
If solonoid clicks on and off but still no 4th gear try a flush, worked for me and also cured a rough 1st to 2nd shift.
--
David Hunter

Thanks! I'll give a try...

-Brian

OD soleniods are notorious for failing. I replaced mine on a 91 245 and it worked for 1 week. After much fault tracing and headaches the impossible was true....the damn thing literally blew up-(blew the cover off and fried itself). I returned it, reinstalled and have been trouble free for some time now. Electronic parts are not infallable even when new. If it's a new unit and it's defective, return it and demand a new one.
--
1991 245 130k-(Volvo number 4)