Triumph TR3B (TCF) TR4-4A-5-250 Mainshaft Gears - 4 Synchro
Early TR boxes used rings made of “Iron Bronze”, a sintered metal containing copper and iron predominately. This provided synchronising (of sorts) and long life. The brass compounds used these days offer improved synchronising, though nowhere near that of modern gearboxes. In reality the actual ring size and friction area are inadequate. The working life of the ring is indicated externally by the gap between the dog teeth on the ring and the gear, from the 0.045" (new) down to 0.025" (worn) range. It is not unknown for less than scrupulous rebuilders to skim off the back face to give the appearance of a new ring. The problem here is that this ignores the relationship between the areas shown, A and B, to give the internals of the box their correct clearance.