So over the weekend, I was towing my trailer and used the overdrive button to lock it out while going through a hilly area. I tried to enable overdrive again and had some issues getting it back (hit the button but the O/D off light would stay on). I finally got O/D back and told myself to not use the O/D lockout anymore. On the way home at random times the O/D off light would come on and the only way I could get O/D back was to turn the truck off and start it back up. I feel like this might be an electrical issue but would like a 2nd opinion. Trans shifts great (it should with only 60k miles on it).

 

You are not supposed to tow with the OD enabled. It's actually in the owners manual.

 

If the trans gets too hot, it will also disable O/D, but, doesn't turn the trans temp light on until it gets even hotter. You may be operating in that small window between disabling o/d, and turning on the lite. If you still have the check valve in the cooler line for the trans, time to get rid of it.

 

Good to know, and I'm sure the check valve is still in there. I'll look at removing it this weekend. Anything special I need to remove it?

 

The cool little disconnect tool for the fittings. Spend the money, and get the nice aluminum feller, it actually fits in the tight space down by the radiator you have to get into. I believe it's 3/8ths. (and will also work for the fuel line, if you ever need to disconnect that.)

 

I used the kit Harbor Freight sells, worked just fine for me. But I reinstalled my clean check valve, as the design of the cooler seems just as restrictive as the valve. Read about the negatives of the removing the valve before executing to make sure you want to perform preventative modifications.

 

Deleting the check valve gives you a delayed shift into gear the first drive of the day. That's it. No other downsides. The problem with the check valve is, it gets clogged up over time, and fluid stops flowing, trans gets hot, and you get weird behavior. Worst case, it stops flowing entirely, and you burn up the trans. Flushing the cooler lines really isn't a bad idea either. Just don't flush the trans.

 

Check valve keeps the converter full when you shut the truck down. Converter doesn't get fluid in park, so its spinning when you start the truck, but w/o the check valve its no longer full of fluid. Doesn't sound like the best situation to me from a lubrication point of view.

I think while the check valve may appear to be the first potential clog, the plate style cooler wouldn't be far behind. When I pulled the check valve out for inspection from my 2000 185k trans, it was clean as a whistle and the spring was fine. I pulled two out of jyards with high mileage as well, same clean situation. I think if you're having that kind of issue, you're trans has probably been poorly maintained or you've been abusing it by hauling/towing with OD engaged and the trans or converter lockup is on its way out anyway. YMMV. I chose to keep mine installed, and had a spare on the shelf in case the spring ever got tired.

If you really want to remove some risk, you'd need to go further than the check valve, install a tube and fin cooler; remove the small orifice plate and fin factory cooler.
https://transmissioncoolerguide.com/...-cooler-types/

 

Simply due to the way the torque converter is shaped, there is always fluid trapped in it, so, lubrication is not really an issue. I removed the valve very shortly after I got my 96, drove it for another seven years, and never had a problem with the trans.