some people say you can and some dont

i have a 1986 chevy with a 700r4

can i and what will happen if i do

As long as its not shifting back and forth from 3rd to OD its fine.

yes you can but how much you are towing should enter into this as well, if you are at gcvw I would say run it in third to be on the safe side, if you are towing light I would go od.

Most trucks with higher gears (taller) than 4.56 put a lot of strain on the engine and transmission if you do any towing in OD. Also as stated before trailer weight and terrain factor in also. I would not do it if you don't have a large aftermarket cooler and a temp guage. The overdrives are very expensive to repair!

Jason :)

I do on the flats and mild hills, but then again, I'm flat towing a 4K $Runner with maybe 1500 lbs in the bed of the tow rig. The tow rig is a 1997 3500 Chevy Silverado Crew Cab dually with the 454. Plenty of leftover towing capacity :D:D:D.

I towed 5,000 lbs from Texas to Cali. I have a 89 Chevy truck. I left it in overdrive, but in 3rd on the big hills. No problems.

I wouldn't do it towing something heavy... Your tranny will build up LOTS of heat in OD. If you still insist on trying it, get a good tranny temp gauge and closely monitor your temp. If it starts going up, drop it out of OD and slow down.