We have been building Model T & A Overdrives for over 10 years. In first gear the overdrive is having to transmit several hundred percent of the torque the engine is producing because the gearbox is AFTER the engine and multiplying its torque BEFORE the overdrive. The overdrive is $1850.00 with a usable torque tube & drive shaft in exchange. They all come with a push pull switch that goes on the gear shift & a reverse lockout switch that goes on the transmission to prevent backing up with the overdrive engaged. Mickey Gustafson - Mick & Rich in Bakersfield, CA make an excellent unit for the Model A and the Model T.
The reduction ratio is signified by the serial number prefix of the Laycock unit. two year warranty rated at 30,000 pounds applications for Chevrolet, GMC. Overdrive provides a 22 reduction ratio to the engine speed for a given road speed when engaged. Laycock overdrive J Type oil seal NKC39, Triumph Stag, Spitfire, TR6, MGB. Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear.1 The term is ambiguous. He does or did Volvo units that are a bolt in for the Model A's. The only exception to the rule is for the overdrive unit originally fitted to TR2s up to TS5979, which operates in 4th gear only. It can sheer or break if it has some kind of bolt or pin. The drive shaft should be welded where the splined coupler goes into the back of the Laycock. The Summer 2005 issue of the Model A Times reviewed the Laycock overdrive. When overdrive is not engaged, the power comes by way of the transmission output shaft through the one way clutch internal to the ring gear (output) of the planetary gear set. In overdrive, the planetary gears are driven by the held sun gear on the transmission output shaft, which drives the ring gear faster than the output shaft of the transmission. It contains a sun gear with a sliding cone clutch and a planetary gear set that runs in an internally toothed ring gear with a one-way clutch that drives the output, allowing for 0.8:1 gear reduction when overdrive is engaged. The J-type overdrive is said to be stronger and able to withstand higher torque than the older D-type. Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption. Various different types were built but the unit out of the 244 series Volvo seems to be the one that suits the Model A application.
Went out of fashion when regular manual shifts came with a 5th speed overdrive gear as standard. The Volvo overdrive was made by Laycock de Normanville in England and was fitted to many different British cars as well.