I grew up driving a 2-ton grain truck. When you are hauling 30,000 lb of truck and wheat with a 304 cubic inch engine, split shifting with the two-speed rear end helped to get up to speed faster. You have many seconds between each shift, like 8 or so at full throttle.

The GearVendors overdrive IS the Laycock deNormanville overdrive that was used in British sports cars in the '50s and was used behind Volvo four speeds in the '70s, when they didn't want to have to buy a 5-speed. At the time, even with a 2-liter four cylinder pulling the 245 wagon, no one ever tried to do any split shifting. This is the same as what happened in the States in the '50s with the Borg-Warner overdrive found behind many 3-speed manuals. The shift pattern was 1,2,3,OD. For the Volvo it was 1,2,3,4,OD.

It takes about a second to shift into Overdrive and I think you have to get off the gas a little. On a 0-60 run in 6 seconds, where is the time to shift the overdrive box?

I think the GearVendors people would tell you they aren't advertising that at all. They are advertising the extra ratios that allow one to tailor the gear ratio to conditions. For example, going over a 10,000ft mountain pass in a pickup with a typical granny 4-speed can mean you spend several miles in 1.7:1 ratio Third because it won't pull Fourth at that attitude. So there you are with the engine singing along for mile after mile. Yet every time you stick it into Fourth the truck slows down to a crawl. It'd be nice to have a gear in between. That's what the GearVendors can do. Shift down into Third and regain your speed, then shift into OD. Third OD has an overall ratio of 1.36 which the engine can pull. Everything is so much more relaxed.

That's the other advantage of the OD besides flatland cruising.

Knowing the origins of the GearVendors OD it is amazing to me that they have increased its torque capacity by something like a factor of three.

BTW, the internal workings of the GV look very similar to innards of a TorqueFlite, a planetary gear system with a multidisc clutch. The pressure for the clutch is provided by a pump in the casing. Hint: If the pump inlet gets clogged the OD won't work, but you still will have direct drive.

R.