See Figure 1
The transmission type, serial number and part number are stamped on a metal plate which is riveted to the underside of the case on manual transmissions or the left side on automatic transmissions.
Manual transmissions installed in 1970-89 Volvos are the M40/M41, M45/M46, M400/M410 and the M47 models. Except for the 5-speed M47 introduced in 1987, all are fully synchronized 4-speed transmissions with all forward gears in constant mesh. The M41, M46 and M410 units are equipped with Laycock-deNormanville overdrive units, and except for the overdrive engaging switch and push plate, are identical to their M40, M45 and M400 counterparts.
The M40 transmission is installed as standard equipment on 140 series and the 1975 240 series models. The M41 overdrive unit is optional on the 140 series and the 1975 240 series, and standard equipment on most 1800E and all 1800ES models. The M400 transmission is standard equipment on 164 models. The M410 overdrive unit is optional on 164 models, and was installed on some early 1970 1800E models. The M45 transmission is standard on 1976 and later 240 series models and the 1980 and later DL. The M46 overdrive unit is optional on 1976-80 240 models and the 1980 and later DL and standard on 260 series models and the 1980 and later GL, GLE, Diesel, GT Coupe and 760 GLE.
In 1982 the M46 became the standard the M46 became the standard unit for all models with manual transmission and in 1987 the 240, 740 and 760 Turbo received the 5-speed M47. The M47 continues through 1989 in the 240 series and the 740 Turbo. The 1989 740 GL uses the M46 transmission.