How can I disable the overdrive function?
 

I posted this in another forum before I noticed this one addressing trannys. I just bought a 1990 F250 4x4 5.8L with 240,000 orginal miles with an auto tranny rebuild 15,000 miles ago.

A friend is towing a 6500lb boat/trailer to Alaska for me this summer. I'd like to disable the overdrive so that it never accidently gets pushed/bumped. Is there a fuse or some other way of disabling the dash button or overdrive some other way?

How about the factory tranny cooler. Its about 6" x 11" in front of the AC condensor. Is that big enough for this load or should I put a bigger cooler on?

Thanks,

Lance

Are you trying to prevent it from shifting to overdrive, or prevent the driver from turning the overdrive off? Your post has me a bit confused as to what you're trying to do.

I want to make sure with 6500lbs behind that it never gets in overdrive. I toasted my 700R4 in my GMC towing a rather lightweigth trailer in OD and the tranny shop said its a definate "no" regardless of weight/road conditions.



Lance

If it drives in OD without shifting in and out, I don't see what would cause the heat to fry the transmission. If the transmission can lock the torque converter in overdrive, it should be fine. I don't know of any way to lock out OD the way you want to. Just be real pressing with your friend that you don't want the thing to be in overdrive (ever) while he's towing, and trust that he remembers to disable OD.

I tow an 8,000# trailer pretty regular with my 94 F250 E4OD. I would guess maybe 3-4K miles per year since 1998. I tow in Overdrive all the time. If it hunts gears I shift down.

So far so good. More important to tranny life, other than hunting gears, is good routine maintenance and fluid checks. I did damage a tranny because I towed a lighter trailer without checking the old(50Kmiles) fluid. Too many miles on the ATF and not enough volume. I think the manual recommends 12K changes for towing.

Good Luck,

Jim Henderson

thats interesting I towed a 3700 pound 20Foot Bassboat for over a 175,000 miles in a astro van i had. never ever had a problem with the trany 700r4, did a service every year and had a "lockout" defeet switch installed , I also installed a larger cooler as not having the tq converter in lock does raise the temp, I will in fact be getting a 700r4 for my 66 ford . 352FE as soon as I can afford it,(got to get one built to take the TQ) they are great towing tranys if taken care of, that 3.05 first gear is great for getting going. I would imaging the Aod would be the same if serviced regulary.