02-09-2020, 11:23 AM
Brett,
You may find this website useful:- www.magnetic-speedometer-repair.com - .Don't be put off by "magnetic" he covers governor types as well. ( I am assuming that yours is the governor type). If your drive train is as John Cornforth suggests then I would be reasonably certain that your speedo drive on the gearbox gives 1040 turns per mile. The website gives specific instructions plus a formula to check this. However you also need to know the TPM of the speedometer itself which is presumably higher. Some speedos have the TPM marked on the face but the Smith's governor type seem to use letters . I have a Smiths governor type marked TN which turned out to be 3360 TPM. As my gearbox is as yours, Speedy Cables ( same sort of work as Richfield Speedograph ) supplied me with a conversion gearbox to bring the 1040 up to 3360. Interestingly they insisted that the converter should not be more than 10ins away from the gearbox drive so the cable is in two sections ( I needed a new cable anyway). Something to do with potential cable breakage?
In the not too distant past there was a thread - 'Early speedometer and 4 speed gearbox' on this very subject.
Neil.
You may find this website useful:- www.magnetic-speedometer-repair.com - .Don't be put off by "magnetic" he covers governor types as well. ( I am assuming that yours is the governor type). If your drive train is as John Cornforth suggests then I would be reasonably certain that your speedo drive on the gearbox gives 1040 turns per mile. The website gives specific instructions plus a formula to check this. However you also need to know the TPM of the speedometer itself which is presumably higher. Some speedos have the TPM marked on the face but the Smith's governor type seem to use letters . I have a Smiths governor type marked TN which turned out to be 3360 TPM. As my gearbox is as yours, Speedy Cables ( same sort of work as Richfield Speedograph ) supplied me with a conversion gearbox to bring the 1040 up to 3360. Interestingly they insisted that the converter should not be more than 10ins away from the gearbox drive so the cable is in two sections ( I needed a new cable anyway). Something to do with potential cable breakage?
In the not too distant past there was a thread - 'Early speedometer and 4 speed gearbox' on this very subject.
Neil.