My truck: 1995 F-150 with 302 (5.0), 4R70W & 3.73 l/s

In a couple of recent threads, inmates opine that switching the O/D to Off is a good idea unless you'll be spending extended time on the expressway (@ 70+ mph). So, I tried to get into the habit of doing this while running errands over the most recent weekend. I failed on more than one occasion. I was reminded of such when I felt the tranny shift, into OD, @ ~45 mph.

So, I was wondering if there's a modification that defaults the O/D to Off instead of On. I did a Google search and found a thread over at Serious Explorations (LINK). I was just wondering if there was an F Series specific thread so I might be able to implement this mod on my truck. I'm guessing that the Explorer's wiring harness isn't necessarily the same as an F Series. I'm smart enough to do the mod but not smart enough to figure it out. If there's no thread, I'll revert to the tried-n-true Post It note on the dash.......

TIA, Dave.

 

There isn't anything to be gained with locking out OD at city speeds unless you spend a lot of time right at that speed where the trans would be constantly in and out of OD.

 

On my truck, that seems to be @ 45 mph. So, there are times when I'm right on the cusp of shifting yet it doesn't (like, if traffic conditions prevent it). However, once it shifts into OD, it never seems to downshift/up-shift ("hunt").

So, you're saying that because my tranny doesn't shift in/out of OD there's no reason to turn OD off?

 

Well there may be 1 reason to do it, better gas milage, as mentioned in some other threads lugging an EFI motor has the opposite effect from what you might think in terms of fuel consumption.

 

That's the general consensus of most of the manufacturers as well. They typically state in their owners manuals that the button is there to use when you're in conditions that the transmission is hunting back and forth more than a few times in a row and you feel the conditions are going to remain the same. When no button is present, pulling it out of OD and into D is the same idea.
Otherwise they're cool with you shifting into the normal drive mode, which is OD on the shifter and just driving it. They feel the transmission control mechanism is smart enough to handle things "most of the time" for most people.
But it's up to you to decide whether conditions warrant making your own shifting decisions. Which is why we still have shifters with three or four positions anyway.

Under heavy loads, such as towing, they may recommend disabling the overdrive because it's well known that this will often cause the transmission shifts to hunt all over the place hoping to find a happy place. Hence the name "tow mode" on some trucks. Same for just the right grade on a hill, or just the right speed on a slight hill, or when under a little additional load.
Like most things with a truck, it's a balance that has to be struck.
Up to the owner ultimately to decide what needs doing, but most of the time the transmission can handle normal driving situations without pulling it out of OD. Maybe yours or the others you were citing would benefit from the default being Tow Mode vs OD mode, but I've never heard of a hack to do that.
But I've never read the whole book either! And there's probably someone out there these days that can re-tune an PCM to do whatever you want I would think.

Paul

 

Oh, and I don't know if the circumstances are still the same (though I bet they are to a certain extent at least) but the main reason for not wanting a transmission to shift a lot more often than normal is heat.
Aside from being very annoying to most drivers, each shift back and forth is clutches slipping, fluid flowing to different places, and other types of voodoo magic going on inside the box. Much of which builds additional heat as well as putting additional wear on friction materials.

So longevity, reliability and sanity are all good reasons for the different modes.

Paul

 

That is correct.

 

I guess this is what I was thinking about and referring to. I might as well try it for a few weeks to see if it has any effect on MPG in my truck. If not, I'll not worry about it.

Mark & Paul: Thanks for the thoughts.

 

I learned this the hard way back in the fall. I was towing a trailer which is about 1200 lbs it had some stuff on it but less than 6-700 pounds. I forgot about taking turning off overdrive. Luckily I stopped about 7 miles into my trip when I noticed I was dripping transmission fluid. I checked it and I guess it got hot and boiled some out. I had to add 2 quarts. I waited until it cooled off and drove the rest of the trip (about 40 miles) with the OD off. It did fine. That was several months ago and I haven't had any problems since.

 

Lucky you!
Well, not luck entirely of course. You were observant enough to note the issue, experienced enough to wait for things to cool down and add enough fluid before continuing. And smart enough to take it out of OD there on out.
Good calls all the way around I'd say. Well, after that first little forgetful bit that is!

Paul