I have an electronic overdrive. It works great...most the time.

When I first get in and start driving I have no problems with it, shifts in and out like a champ. When I go on long trips, the longer I drive, the funnier it acts. First, it starts taking a while to shift, I push the button and it waits sometimes as long as 45 seconds or more to shift. If I keep driving, eventually it almost stops working. I have to engage, wait and see, disengage then engage again. When I stop and the car cools down the cycle starts over and next time I get in it works great again. This is fine if I am going somewhere less than a two hour drive away. It consistently works flawlessly for that long, but over two hours and it starts acting up and by the third hour of driving I am really hesitant to shift out because I don't know if it will shift back in.

Any ideas? Should I change the relay? I would think if it was the relay it would always be intermittent. What are the conditions necessary for the overdrive to engage? Is the only requirement you be in 4th gear or is there other things it takes into account?

M46 or automatic?
Most of these problems are electronic. Regardless of the transmission does the O/D light go on and off when the O/D switches on or off?
If it's a M46 check the condition of the wiring from the gearstick to the solenoid. The solenoid terminals get covered with oil - clean these and tighten the wire connectors. If you have a 1984, it will have a Blue relay. The 4th gear lock-out switch can go bad. Solenoids seldom go bad, but can get sludged up. Fresh ATF and cleaning the solenoid can help. A transmission cleaner like seafoam can also clean a sludged transmission. Honestly, it sounds like sludge to me.

actually, like 240on280 posted, it does sound like a sludge build up. but you can also check, only if its an auto, make sure that you have enough tranny fluid in there. i had a K5 blazer once that on long trips wouldn't shift until i manually shifted the column shifter, later found out that i had been driving 5 hours while slowly losing tranny fluid from a bent tranny pan. there was no pressure in the tranny to shift. after replacing the pan and new fluid, shifted like a champ. just my two cents worth. :grin:

WARNING: Use ONLY correct oil type in tranny! AW7xx==Dexron2 only, according to my diagnostic CD's (circa 2003.)

True - but if it's a M46 he will need Type F.

Well we have an 84 240 as well, a DL, but yeah. Is yours a stick shift? My dad noticed that the wires for overdrive were too short and shifting would loosen up the wires. We removed it from the stick shift and kept it outside the shifter. Right now, since my car is now running Im running some longer wires from the shifter to the console and moving the button to the console (drilled a hole in one of the removable lids/shields) so they don't lose a good connection.

Perhaps it's this... or perhaps not at all.

I dunno though, I never drove the car when the button was in the stick so I dunno what kind of effects having a bad connection would be. I would doubt that this would be your problem but it may be worth looking in to? Just trying to help =/

It is a M46, the OD light in the cluster does go on and off with the switch every time, I have checked the wiring from the button to the solenoid and all seems okay, where is the forth gear lock out switch located.

I took a trip this last week, left my home which has a fairly temperate climate and went to see some family up in the high desert. I came back today and had an interesting discovery. When I left this morning it was 90+ degrees F and the OD would not work at all, the closer I got to my home the cooler it got and the last hour or so it worked perfectly.

As I thought about this I realized most every trip I take that takes a couple hours takes me to a much warmer climate, so it doesn't really seem like driving time makes a difference, it is more temperature, the hotter it is, the less my OD wants to work.

Do you still think it is sludge? Would that cause it to stop when it is hot?

Does it select initially while tranny is cold? If not selecting at higher temps suggests old/wrong fluid thinning out with heat. Check tranny fluid pressure at cooler line:(AW7xx) 10psi at idle +1lb/sqin for every 100rpm increase. Old/wrong/insufficient fluid/bad filter/sludge-check it all out.

The 4th gear lock-out switch is located close to the top of the transmission as is the reverse light switch. These look very similar - the 4th gear lock out switch has one terminal, the reverse has 2. What you're describing doesn't sound electrical.
I does sound like the OD is overheating. I would change the ATF and clean the OD filters first and see if that solves the problem.

It could very well be symptomatic of a poor electrical connection as an unsound electrical connection will actually get worse the hotter it gets (there are a number of reasons for this) and appear to get better when it cools down.