O/D on or off when driving down the highway

I can't remember when or IF I have ever turned it OFF

I get in truck, start it place it in 'D' and go

If hooked up to 5th wheel I place it in 'D' and turn Tow/Haul ON

I turn Tow/Haul on sometimes when not towing


But turning O/D off......never.

I leave mine on but of course in TH mode(Aisin 6 speed) unless climbing a decent sized grade or descending a grade. No temp increases at all, at any speed (even 80 MPH in Utah!) :-)
Basically, it it hunts in and out of 5th and 6th, I turn it off, otherwise always on.

JIMNLIN wrote:
When my trannies TC clutch runs a lot unlocked or the tranny shifts up and down a lot I take it out of OD. Works with the car or my trucks.

This and other similar advice. If the transmission doesn't keep kicking out of OD and dropping back in, frequently, leave OD on. That's what we do with our E450. It has a four-speed called 4R100.

Newer Fords have a five- or six-speed with TOW/HAUL like the GM Allisons do. With those, just drive it in TH.

That's 'cause the TH transmission still uses Overdrive when it can. It just modifies its behavior under the assumption it's carrying a heavy load. This is a good assumption where an RV is involved.

RVER wrote:
Thanks, did I do damage to drive with it off? I will leave on now that I know. NEW rig to me so getting used to it and did not know it had the on and off switch for O/D. LOTS to learn.

As others have said, you did no harm at all. I don't think there's any vehicle around that would overspeed the engine in drive (rather than overdrive) at reasonable highway speeds; locking it out is benign from the point of view of breaking things. If the transmission is hunting between overdrive and drive, it is better for its longevity to shift out of overdrive rather than have it keep changing gears, besides making for nicer driving.

Even things that at one time could damage the transmission or overrev the engine (like downshifting to low gear at too high a speed) are basically much impossible with modern computer controlled transmissions. If you move the lever to downshift and you're going to fast to do so, it will not actually downshift as requested until you slow down sufficiently. Even things like shifting into park or reverse while moving, on many transmissions at least, won't cause trouble because it won't do them until you're practically stopped. I wouldn't suggest testing these things out intentionally, of course, but it's nice to know that you're pretty well protected from any ill-advised or unintentional moves.

Thanks, did I do damage to drive with it off?

No. The vehicle could be driven for it's entire life with OD off.

Thanks, did I do damage to drive with it off? I will leave on now that I know. NEW rig to me so getting used to it and did not know it had the on and off switch for O/D. LOTS to learn.

JIMNLIN wrote:
When my trannies TC clutch runs a lot unlocked or the tranny shifts up and down a lot I take it out of OD. Works with the car or my trucks.

This is the same thing I do. When it starts shifting back and forth I turn OD off, Ford recommends turning it off when towing, but on flat land I leave mine on, better gas mileage.

With "normal" driving, leave it ON.
It will switch itself OFF when it needs too (downshift).

If that happens too often for your comfort....or you know you will be pulling a big load or fighting a lot of wind or mountains, turn it OFF.

When my trannies TC clutch runs a lot unlocked or the tranny shifts up and down a lot I take it out of OD. Works with the car or my trucks.