Laycock deNormanville Overdrive in Bentley

After spending a very busy 12 hours to remove the transmission on the 1935 Rolls Royce, I was not looking forward to removing the transmission in this 4-1/2 liter Bentley. The owner of the car was telling me that the car had a trick overdrive set up but I wasn’t really listening so when I finally crawled under the car and say what he was talking about, my motivation improved.

This car has a 4 speed transmission that isn’t geared high enough and the engine runs out of steam at 60 mph and about 50 mph the engine is spinning too fast to feel comfortable. To remedy this, a different ratio ring and pinion could be made for the rear axle but then you would have a very tall first gear which would be hard on the clutch. A shop in the UK installed this great little overdrive unit behind the transmission to lower the engine speed when cruising around.

The car is here at our shop for us to remove the non-synchronised transmission and install a transmission that has been modified with dog teeth type gear engagement to make shifting a little bit easier. This is a racing style of transmission that allows super quick gear changing without the crunching associated with a typical “crash box”. The way the transmission is set up, there is only a tiny amount of travel to go from one gear to the next even though the shifter is about 3 feet long! The owner of the car has some great connections in the UK and seems to know all the guys for this clever type of work on pre-war cars. I am not sure if the new transmission is made from all new parts and new castings or if it is a nice original unit but the workmanship inside is stellar. Once I do a few modifications and make an adaptor the car will be on the road so I can test out how much the overdrive knocks down the engine speed. I am guessing the engine RPM will drop by 15%.

Original Bentley transmission with Overdrive unit

New parts inside Bentley transmisison