I read in a post a few days ago not to use overdrive until you get up to highway speeds. I have been driving with over drive on all the time. When I start my truck it automatically puts the overdrive on, I have to turn it off if I want it off. I think the manual says turn it off when pulling loads up hills or something to that effect, dont have it in front of me at the moment.

I was just wondering how this (driving with it off until highway speeds) benefits the life of the tranny? I have been doin it and its a bit more responsive and using more fuel...lol.

 

The OD is a relatively weak link in the transmission due to its design and what it is asked to do when under load. I have always run OD off until I know I am going to be doing 55 or greater for an extended period. With the OD off the trans will still lock up the TQ in 3rd so, with my 3.55 gearing, I stay around 2K rpm until I let the OD kick in. If you lug the OD that is when it really gets chewed up the worst. The TQ lockup plate has a much better ability to handle the torque of the CTD than the relatively small OD gears and at 1700 rpm the trans has enough hydraulic pressure to keep the TQ locked up solid. If you are in OD at 45 mph and hit the pedal or even a grade the trans will hunt down to unlock and then will try to re-engage the OD at a relatively low rpm - it seems to me that all of the lock/unlock/in OD/out of OD shifting is gonna cause alot more wear than leaving it OD off.

I gross over 20K pounds with my one of my trailers sometimes and will use OD when I can get it up to 65 mph on the open road (3.55 gearing). Around town I just keep it OD off most of the time. Added benefit is the acceleration is much better.

My trans is a stock rebuild with a crappy stock TQ and I have 100K miles yanking stuff around on the rebuild. So far my habit is keeping the trans happy. YMMV.

 

Good write-up Red.
Main damaging effect I see driving around town with OD on is not so much when it kicks on but how slow you can drive before it kicks off.
It's almost the equivalent to driving a manual 25 mph in 5th gear.

 

Thanks for the response. Well I guess I'll keep driving with it off until highway speeds. My fuel mileage has dropped from 21 to 16 since I have done that. I wonder if its cheaper to use more fuel or let the damage occur with the overdrive? 6, 1/2 dozen, or the other.

 

Pleas allow my laziness to shine for a moment!
My vote is it may or may not be 'Cheaper' but it's DEFINITELY EASIER to add fuel to your truck than it is to pull an auto trans!

I do agree with the others that have replied. It can't really be a good thing to keep an automatic tranny shifting (up, down, sideways) anymore than it has to. You're only putting unneccesary wear and tear (and heat) on it. I do pretty much what redramnc does, Keep the O/D OFF until extended periods of 55-ish.

 

My OD stays off until I hit 50mph or so. I've wired in a switch inverter so it locks out OD automatically whenever I start the truck. Works super slick. The instructions are here OD Inverter