The overdrive is energized by the simple fact of oil being picked up from the pump in the bottom through the screen, pumped through the system, through the control valve, and into two pistons about 1″ in diameter that are behind a device called an actuating bar. When the pistons move forward, the actuating bar pulls two rods from the back and pulls the cone clutch in the opposite direction, activating the overdrive. So 99% of the time, if you can hear it energizing and it is slipping, it is something in the hydraulic system. So let us do a quick rundown on the things you can test, some of them not requiring you to have to remove the gearbox. One of the big problems we have with the Laycock overdrive is that people will fill the gearbox initially and not realize that it is somewhat difficult for the oil to work its way back in the overdrive unit. With that idea in mind, they do not realize thai once the gearbox has been filled and the thing has been run for a while, part of the oil has run back into the overdrive. That simply means that both units are now low on oil. What we generally do is put oil in the gearbox and jack the car up from the front, let it run back into the over drive for 10 minutes or so, then sit the car down with the plug out and a tray underneath and allow all the excess oil to drain back out of the gearbox. But first thing, check the oil level, as it is entirely possible you have an inadequate supply of oil. This can also be checked out from under the car. If low oil is indeed not the problem, then the next thing to do is to drain the overdrive from the large bronze plug in the rear and look at the condition of the filter inside. If it is completely covered with trash, it may be that the filter is prohibiting a satisfactory amount of oil from finding its way into the overdrive and consequently not allowing it to function properly. In the center of the cavity that the filter came from is a plug with a head of about 9/16″ or 5/8″. Removing that plug will give you access to the overdrive oil pump, at least to where you can see the plunger in the pump.

Laycock Overdrive Serial Numbers