Normally speaking, if a car slips while it is in direct, it generally means that the spring pressure, for one reason or another, is gone (by the way, this is an extremely unusual situation), because the mechanical advantage always favors the direct drive, and consequently, the higher pressure and operating the higher pressure and operating conditions are needed for overdrive, or at least to energize overdrive. It tolerates very little internal leakage consequently, it requires very close control on the oil level in the gearbox. Unlike a regular automatic transmission, which works on relatively large volumes of low-pressure oil in the order of 50 or 60 psi, the Laycock unit operates on a very small volume of extremely high pressure oil at 400-500 psi. The overdrive shift is always controlled by hydraulic pressure. That is, the spring pressure you see when you put the gearbox and overdrive units together, created by eight springs. Direct drive is always controlled by spring pressure.
The Laycock A-type overdrive is a two-speed hydraulically controlled planetary transmission.
