Another overdrive that was popular on Brit and European vehicles was the Laycock unit. It can be found on Jaguar, Triumph, Austin-Healey, Volvo, and a few others. It's the basic unit that's used by Gear Vendors for their add-on OD systems. That one has a built-in hydraulic pump to provide the OD functions, and a solenoid to turn the hydraulic pressure on and off. With a little creative machining and the addition of a crossmember to mount it on, a Laycock OD can be installed as a divorced unit similar to a transfer case, or a Brownie on a big rig.
Jerry
