Quietly Performing Award Winning Restoration Work on British Motorcars Since 1992

It is a mystery to many British car enthusiasts driving their Laycock equipped overdrive cars, how to properly engage and disengage the overdrive function with the least trauma to the car. A rule of thumb that I subscribe to, is to treat the overdrive function as an additional gear when upshifting. That means when accelerating up to freeway speeds and you are in fourth gear direct drive, depress the clutch prior to engaging overdrive for cruise, treating it as an additional normal gear, much like the gearchange from third to fourth. That eliminates the “kick in the butt” feeling experienced when engaging 450 PSI of operating pressure without clutch engagement and your foot on the throttle. You need to lower your engine revs by 400-500 RPM’s for smooth engagement. A depressed clutch and minimal to no throttle will accomplish this. Conversely, when downshifting from fourth gear overdrive to fourth gear direct, it is necessary to increase your engine revs approximately 400-500 RPM’s to match engine revs with road speed. The Austin Healey cars accomplished this through the kick-down switch located on the bulkhead that made it necessary to “blip” the throttle for electric disengagement of the overdrive to occur, thereby increasing engine revs to match road speed. Triumph and Jaguar overdrive equipped cars do not have this function, but disengagement of overdrive with the electric switch, coupled with a manual throttle blip with your foot and a depressed clutch, will increase the engine rev’s sufficiently to allow a smooth transition to direct drive to match road speed.  This habit of overdrive engagement/disengagement will extend the life of your OD clutch linings, as well as allowing the use of your overdrive to cause the least amount of stress to your British (or other Laycock equipped) car. Smooth is good. If you are using your British car in a competitive environment in full anger, forget I said anything. Thrash it until it breaks.

This entry was posted on Friday, May 28th, 2010 at 1:13 am and is filed under Articles, Ramblings, and Rants. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.