Howdy Folks! This idea ha been floatin' around in that grey matter between my ears for awhile now, so I figured it was about time to put it out there.

Here's the story: My Dad owned a residential excavating company for my whole life, and back when I was a kid and his operation was still small, he had 3 old single axle dump trucks. He still has a '55 F600? well, a '55 single axle dump truck, that I spent many hours in on the passenger side of the bench seat in the late'60s and early '70s. Anyway, It has a 2 speed rear axle.

Now, owning a 2001 f250 CC 4x4 with 3.73 gearing, I can see the need for 2 things: 3.54:1 rear end ratio for most highway driving, and 4.10:1, 4.30:1, or 4.56:1 ratio for towing and 4x4 use.

My idea is to take the original design of the 2 speed part of the rear differential on this old truck, and make a prototype that is scaled down to the size of a f250 or f350 rear diff, like is currently found underneath a modern ('99-up superduty) truck.

The reason for this is that 3.73:1 is CLEARLY a compromise ratio, especially for a v10 powered truck. I'm thinking that I would like 3.54:1 for hiway, and 4.30 for towing, or whenever the need to lock 'em in comes up.

So, the question is: Is there any interest out there for such a setup? or does one already exist that is small enough to fit under a 3//4 ton or 1 ton truck? If I knew that I could sell a few, I would go ahead and do the research necessary to produce a quantity of them. With the diversity of off the shelf parts currently available, I can see this being accomplished with relatively few unique parts needing to be made, and those unique parts never needing service. Please feel free to comment on the idea, or point me in the right direction if someone is already doing this. Thanks.

 

I would say the interest here would be for you to develop and test it, use it, sell it to others, and then people here would buy one used years from now for under $100.

For smaller vehicles, something like the Gearvendors unit behind a 5 speed with 4.10 or 4.xx gears in the axle would make more sense.

 

I like the idea a lot. I've been looking for a rear end like this for a while. Of course, level of interest is a function of price vs. performance, but I would love to see this develop. I have some old Fords and parts laying around, and run a shop in NE Ohio. Please PM me if I can be useful.

 

Have you all made any progress on this? I would be interested- muahahahahaha...... (sinister laugh).

 

This would be cool to see in a super duty but I worry about people with 4x4. You would need to find a way to lock out what ever gear doesn't match the front end while going into 4x4. I would also keep the 3.73 as going to a lower gear in a gas truck would be kind of counter productive in that it would want to downshift to much. Adding a 4.56 or 4.88 would be great when towing

 

All you would have to do if lockout the unit for 4wd purposes; either by vac/el or el/el switches.

 

6 or 7 or 8 or 9 speed transmissions with double ODs are the answer. The two speed axle is not the answer.

 

Doesn't Gear Vendors already make an aftermarket unit like this one proposed?

Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.

 

This seems the least labor intensive and the greatest engineered for use with the manufacturers specifications, but I do not think it will pay for me.

According to my mileage figures, I would have to drive 69 years or 48,412 miles (700miles annually) to cover the cost of purchasing the unit at the lowest price of $2,900.

If I drove 15k miles a year I could cover the cost of the investment in a little over 3 years.

[EDIT: Here is how I came up with my figures--------------------------------------------------------------------------------------------------------------------------------------------------


Best case scenario for me:

Current highest mpg 18.8 X 30% increase = 5.64 mpg increase = 24.44total mpg.

$2900 Gear Vendor/ $3.75 (assumed) per gallon fuel = 773.3 gallons.

773.3 gallons X current highest mpg of 18.8 = 14,538 drivable miles.

14,538 drivable miles X 30% increase = 4,361.4 increased miles for my investment at 14,538 miles annually.

14,538 miles driven miles per year / 4,361= 3.33. At 14.5k miles it would take me 3.33 years or 48,412mile to just cover my investment, minus labor and additional costs.

Currently, I drive my truck 700 miles a year (average for the last 3years).

48,412 miles / 700 current miles driven = 69 years just to cover my investmentof $2,900 for the lowest units purchase price.-----------------------------END EDIT]

 

Quick change axles that use change gears (swap them out manually) are already available, could simply design a bolt-on housing with slider gears.

Another option would be to use a planetary gear set mounted on the nose of the axle, between drive shaft and pinion. then use a clutch or sliding collar to engage or disengage the gearing. Just drive center gear to lower the ratio for hauling, drive the planet carrier for straight through, or the ring for higher gears.
This would be the easiest and cheapest option I think, could come up with most materials from the junkyard since they are used in almost every single automatic transmission made, and they would be a bolt-on addition, not a complete rear end or center section.
From a manufacturing standpoint, it would be cheaper, you would have one main unit, and different mounting kits to fit the pinion flanges of the truck, leaving the installer to shorten their drive shaft.
I think could sell it for $500 or less and still make a few dollars. I'd buy one at that cost.
HowStuffWorks "The Planetary Gearset" shows basic operation.

 

Wow---that's an impressive bit of cogitating there my friend--waaay more than I'd ever do on such a thing!

While on the surface your concept is sound since you drive but 700 miles annually tooling up for production of your idea would extend your figures quite a bit. I'm thinking near 400K miles and 25-30 years.

Mind you that's quite facetious and meant in humor but something off the shelf and proven reliable as is would still seem to be the most viable alternative.

 

Agreed. Think of a ZF-6 (ZF-7?) with two OD gears, less gap between 5th and 6th, and lower overall cruising RPM at highway speeds.

 

My family is a huge ford family, my father and I both drive ford f250's mine is a 1985 his is a 1975, has there been any progress on the rear ending an we both are looking to purchase a 2speed

 

I don't think it was a serious project.
The closest thing for street vehicles would be over or under drive units that mount between the transmission and axle. If you have 4wd, you NEED to ensure that it does not engage when in 4. otherwise instant dead axle or broken drive shaft.
cheapest way would be to install a 4wd transfer case if 2wd for 2 speeds, or mount a divorced t-case behind the stock t-case in a 4wd for a double under drive. The original t-case is only used as a pass-through, drive shafts mounted to new t-case, many sites will show how to build a 'doubled' t-case if you have time and money to build one, Use highway gears in axles for mileage. Most production t-cases are in the 2:1 - 2.5:1 range.
If you are creative, you can also drive a transfer case in reverse for a very high overdrive.

I understand the 'X transmission gives this ratio' argument, but you know what?, if I can change the axle ratio with the pull of a lever, I just doubled the range of any transmission you can name.

 

The transfer case that comes with these trucks has a ratio of 2.7:1.

If you have a 3.54 gear and put it in low range you now effectively have a 9.56:1 gear. That's useless for towing.

If you change the axle to a 4.30:1 for towing and install a transfer case backwards you'll have a 1.59:1 ratio. That would be totally undriveable.

So this nonsense about using a transfer case as an under/overdrive is just that, nonsense.