Triumph TR3B (TCF) TR4-4A-5-250 Interchanging Components - 4 Synchro
The internal components of the 4 synchro gearbox changed hardly at all during TR3B, TR4, TR4A, TR5 and TR250 production. The problems of which replacement parts to fit really arise if you find you have a TR6 gearbox in your car - in which case the internal components changed several times during production. Changes that are crucial are those that mean whole running assemblies must be changed rather than individual components. Above is a table showing the gearboxes by serial number and the changes to internal components. The four basic sets of gears are interchangeable sets, the mainshaft will of course govern their use ultimately if overdrive is used. The most significant and frequent changes were to the helix or tooth angel of the gears - 3 in the life of the TR6! The spigot size on the mainshaft changed from imperial to metric which required matching constant pinion gears.