Could the problem be that the transmission was built to not go into overdrive? Maybe the assumption was that overdrive clutches would be too weak for turning such large tires with so much torque?

So wouldn't that mean he only has a 3 speed transmission? Lol

Overdrive is 4th gear in these transmissions right?

Yes it should be 1st, 2nd , third, lockup, and Od. What he describes would be like a late 70' s-80's vintage 518 with 3 speeds and lockup. What year is the truck? 2001?

Od should still occur...however there are electrical mods to disable the selenoid from actuating OD. You can add a relay and change the wiring so when the engine is started OD is off. Then you use the OD switch to turn OD ON.

I think grounding the OD selenoid would work but I would think that would throw a code.

Dan, do you run 3:55 or 4:10 gears? Maybe thats why the builder disabled OD, but I would think the tranny would run hotter. When OD engages the tranny is in a mechanical lockup and the TC and planetary are in a free spin mode. At least thats how I'm reading it. The fluid is not under load so it cools down. Using TC lockup only would be a load even on the thickest TC clutch facing.


Dave, cut and paste is an amazing thing. :)

That's what I'm thinking is that there actually is no overdrive in the transmission. I mean it goes into 4th gear. Cuz it'd be awkward to run 110 mph in 3rd gear. But yes trouble I have checked codes and there is nothing that has came up about overdrive or the tranny in general. I'm at a complete loss.

I'm not entirely sure what gears are in it actually, Al.

4th gear is overdrive.

Now I feel like a complete f***ing retard...

Haha don't it happens to the best of us. Next time you drive it going down the road, push the button on your shift lever, that turns O/D on and off. If it jumps up the rpm's, that means its working and kicking it up into 3rd gear. Push it again and it'll shift back into 4th (O/D). That'll verify that its still working. There's also a little orange light that comes up on the dash that says "O/D off" when you push that button.

I knew that lol but I have noticed a difference now. Idk I'm a jackass.

Well at least we know your transmission is ok now! Lol