Volvo was not the only company to use the Laycock overdrive units. In fact, quite apart from improved fuel economy and allowing the car to sustain high speeds with lower engine RPM, hitting that switch and feeling my car slip into overdrive is one of my favorite driving delights. Often thought to be troublesome and unreliable by its detractors, I have found the M46 to be durable and really quite satisfying when its basic hydraulic and electrical needs are met. When out of overdrive, the power comes by way of the transmission output shaft through the one way clutch internal to the annulus gear (output shaft) of the planetary gear set. In overdrive, the planetary gears are driven by the stopped sun gear on the transmission output shaft which drives the annulus gear faster than the output shaft of the transmission. It contains a sun wheel with a sliding cone clutch and a planetary gear set that run in an internally toothed annulus with a uni-directional clutch that drives the output allowing for 0.8:1 gear reduction when overdrive is engaged.

The invention of Edgar de Normanville, it was originally called the de Normanville epicyclic gearbox. It's such a French sounding name from such a distinctly British company.

There's something about the Laycock de Normanville mystique that I just love. The J-type overdrive is said to be stronger and able to withstand higher torque than the older D-type. The M46 is the younger sibling of the venerable M41 found in 1800 and in some 140 and Amazons and the more robust M410 found in the 1 E/ES. It is found in both 240 and 260 from 1975 through 1986. The overdrive unit on the M46 manual transmission is surely one of the most maligned and misunderstood parts in the Volvo 200 series.

Laycock j type overdrive manual