Overdrives & Dual Range additions

[eDJ_]

I was talking to a guy the other day as I was looking at a Leonard Trailer he had.   He was remodeling the interior of a Wendy's in my area and he was as curious about my rig as I was about his trailer.

He noticed the plaque on the door that said Overdrive and asked about towing his trailer.  I explained that the 4th gear was the OD and could be switched on and off from the dashboard.   He told me he was curious about that as he had looked at some E 250 & E 350's like mine and had seen some with and some without it. 

So I told him that if he found one that didn't have it that there are after market providers of bolt on Overdrives and Dual Range features.  Thus you may have a low ratio for the hills or mountains and then switch to a high range for long flat land cruising.

I only know of "US Dual Range" and "Gear Vendors" and understand both of them are reputable.

The question is,  has anyone else here had experience with these devices.  Installing them, or driving a rig with one installed.  They aren't cheap but in a newer rig over the long haul they may pay for themselves and then yield savings.  

Your thoughts.

Ford Automatic transmission with bolt on Gear Vendors over drive (at left end)

Muncie 4 speed standard transmission with "Gear Vendors" Overdrive installed at right

Gear Ratio Chart

 

[highdesertranger]

US Dual Range is long gone as is Doug Nash OD. Gear Vendors and Advance Adaptors are still around. are you asking if installing a OD on a newer vehicle is worth it? most say no. newer vehicles already have an overdrive so now you would have double overdrive. double overdrive doesn't really work, you are out of your power band and fuel economy usually suffers. you could however split your gears turning a 4 speed into a 8 speed. highdesertranger

 

[29chico]

If you want to save fuel by lowering your cruising rpm's put slightly taller low rolling resistance tires on your rig,  same or higher load range, and drive slower.  You could just skip the taller tires and just drive slower.  Loaded rigs are not great candidates for overdrives anyway. 

In the old school trannys top gear is 1 to 1, not actually a gear at all, just straight thru.  Overdrives are step up drives, the output shaft turns faster than the input shaft.  Any step up or down gear has a certain loss of efficiency, a straight thru shaft has none.

So hoping to get better mileage and save money on a loaded rig that has a fair amount of frontal area by installing an OD is a bit of a fool's mission.

Even if you install an aftermarket OD yourself you will not break even on the cost of the unit for a long time. 

If one is swapping motors from a gasser to a diesel, like HDR is doing, installing an overdrive can be a good idea.  A diesel turns lower rpm's than a gas engine so an overdrive may get a diesel into it's rpm sweet spot at the desired cruising speed for optimal fuel economy.  The greater efficiency of the diesel engine will be greater than the loss inherent in the OD gears, but only if the diesel is operated at, or very near to, it's optimum rpm.

 

[eDJ_]

Thanks,  I'm not real sure that understand whether these bolt on units are overdrives or dual range. 

My E 350 has the factory "Overdrive" which is a dash controlled 4th gear if I understand it right.  It's behind the
original 351 V8. 

I'm left to agree that if you are out on the flat lands that taller rear wheels/larger tires may be the way to go.

I'm thinking of this for those who have the simple Van's where they aren't hauling huge amounts of "stuff" that they don't really need and rarely use.

Lastly,  Speedometer accuracy with larger rear tires ?    Just drive a few mph slower if you do that ?

 

[29chico]

Thanks,  I'm not real sure that understand whether these bolt on units are overdrives or dual range. 

My E 350 has the factory "Overdrive" which is a dash controlled 4th gear if I understand it right.  It's behind the
original 351 V8. 

I'm left to agree that if you are out on the flat lands that taller rear wheels/larger tires may be the way to go.

I'm thinking of this for those who have the simple Van's where they aren't hauling huge amounts of "stuff" that they don't really need and rarely use.

Lastly,  Speedometer accuracy with larger rear tires ?    Just drive a few mph slower if you do that ?

Since all of the vehicles that I have driven over the years report that you are going a little or a lot faster than you actually are, putting slightly larger tires on makes the speedo more accurate.  I suppose that there are a few all stock cars that report less mph than actual but I have yet to see one.

My '85 F250 diesel reports that you are going 65mph when the actual  speed is 58mph.  That is a 12% error. It has done this since it was new when my father bought it.  Stock tire size.  My '14 WR250r dual sport motorcycle was even worse before I bought a device to re-calibrate the speedo.