Hot Rod has been praising this overunderdrive thing since it came out. I think I'm a little fuzzy on the details of what it does.

It seems to me that it'd be real hard to fully use it's potential. Imagine, for example, a 4 speed manual with one of these units.

1)Start out in first,
2)turn the unit on to split first and second,
3)turn the unit off while simultaneously shifting into second,
4)turn on the unit again after second,
5)turn off the unit at the same time as shifting into third,
and so on...

Does anybody have one of these? How do they work? Do they have some sort of computer you can set to go on at a certain rpm and turn off at another?

 

I don't see a benefit for splitting gears on a street car, but would in a towing or truck application.

Underdrive would be useful for a 4WD crawler.

Benefit for a hotrod/street car would be...

TH400/350 tranny (or other 1:1 final drive tranny) where you'd run 3.73's/4.11/4.33, etc, and still have OD when the racing is done.

They've been out for many, many years. US Gear also makes the same thing.