It is in the power circuit to the solenoid where many problems occur. Now that you've got a headache reading about the drive principle, let me tell you that it's not necessary for you to understand it totally, at least not for the majority of problems. I thought you'd have given up by now, you are obviously a dedicated enthusiast. It is therefore important that no oil additives are used.ĬONGRATULATIONS!! on your perseverance. Note The brake ring has a friction material that effectively operates in oil.

While in this mode, thrust on the planet gear carrier causes a 'one-way' clutch to lock inside the annulus and drive is transmitted directly through the unit 1:1. With the Overdrive turned off the brake ring is pushed back from the casing by return springs and an inner surface makes contact with the annulus, causing them to turn at the same speed. The annulus, driven by the smaller step of the planet gears, is made to turn faster than the planet carrier. The planet gears are now forced to turn on their individual axis around the stationary sun wheel. Upon contact with the case of the unit, the brake ring holds the sun wheel firm. These operate a brake ring connected to the sun wheel. When we select Overdrive, current is transmitted to a solenoid valve causing oil pressure to be directed onto pistons. The larger side of the planet gear is in contact with the sun and the smaller with the annulus. The planet gears are stepped, and run on a carrier splined to the gearbox output shaft. Overdrive gears consist of a central sun wheel that meshes with three planet gears, which in turn, mesh with teeth on the inside of an annulus gear. It gives a higher ratio drive than fourth gear and is engaged by using an external electrical system to redirect hydraulic pressure within. The Overdrive is a self-contained gear unit, fitted between the gearbox and propeller shaft. It was therefore never explained that the majority of problems occur in the engaging process, and that there is often a simple solution.

The Technical College taught me in a Workshop Manual fashion, without the advantage of many years post-production knowledge. I have tried to simplify everything giving you an initial introduction to the Laycock Overdrive explaining the principle of how it works and covering the most common problems you may experience, not requiring the removal of the unit to effect a repair. WARNING! If your idea of an Overdrive is that it's a switch that doesn't do anything, or if you suffer from a nervous disposition.DO NOT READ THIS!!!! The original article can be seen in Enjoying MG magazine published by MGOC UK November 1993 issue

Laycock overdrive rear seal squeak