adjustable final drive ratio

[SlideWRX]

A 4wd transfer case is effectively a two-speed final drive, although it is used to produce crawling speeds for off-roading. I think the current Jeep Wrangler starts with a 2.7ish? reduction in ratios. Gear the axles so the 'Low' range is normal driving speeds, and the high range would be a set of overdrive gears. It is a locked transfer case, so no differential in it, so it could run just the rear axles if desired. Although I think one isn't supposed to switch high to low at more than 5 mph...

[some_other_dave]

There were also external overdrives that were fitted to older Brit-cars like MGs and Triumphs. I believe those gave you a choice of two gear ratios between the output of the transmission and the input of the differential. So you effectively had twice as many gears--generally eight of them.

-soD

[niky]

Some modern six speeds use two final drive ratios, with the upper two gears mated to a higher final drive on a separate shaft. I suppose it allows you to run longer gears without compromising packaging or utilizing gears that are too small (and fragile).

[t vago]

Originally Posted by some_other_dave

There were also external overdrives that were fitted to older Brit-cars like MGs and Triumphs. I believe those gave you a choice of two gear ratios between the output of the transmission and the input of the differential. So you effectively had twice as many gears--generally eight of them.

-soD

Are you thinking of the Laycock overdrive? I remember those overdrives being fitted to Volvos. Chrysler retrofitted them onto the 46RE, I think. Gear Vendors bought the tooling and designs for these overdrives, and provides them now as an aftermarket add-on kit. I've got one of them sitting in my garage, but I'm not sure whether it would be a good idea to install it onto my truck.

There was another member who actually installed one of them onto his truck. Damned if I can't remember his name, right now.

[ex-x-fire]

Yeah, I did.
But there was a guy who put one one his diesel. The GV od is very strong.

[tortoise]

The Columbia 2 speed rear axle was a popular aftermarket accessory for pre-war Fords.

[user removed]

A truly adjustable final drive ratio, would mean you could change the ratios through a broad range. This would allow you to match best BSFC with load when conditions allowed that much power to accomplish the work required.

What is really needed is high efficiency capacitive storage so that when best BSFC power levels exceed the load requirement, best BSFC power production could be maintained with surplus power stored for future application.

When sustained loads are low and it is not possible to use best BSFC the the capacitive storage is replenished. When that same capacitive storage has reached it's maximum level then the drive can use storage and the fuel consuming power plant can be shut off for a short period of time.

Pulse and glide allows this most efficient use of best BSFC but requires speed variations since the vehicles mass is used for storage. When storage is separate from the vehicles mass then speeds need not vary as they do when incorporating P&G.

regards
Mech