QuestionHi barry, In the process of restoring a 1951 mgtd, wish to alter the diff ratio, have obtained a diff from a mgb, which is 3.909, i.e.11/43 . was told it was a 4.1. Question is, would the ratio be to low for my TD, and could you recomend a specialist to do the nessesary crown wheel/pinion change over. I can take the back axel plus the diff, to the specialist. Many thanks John Fay.
AnswerHi John
To be honest, a 1250cc TD would have great difficulty pulling an MGB rear axle - 3.9 is a bit too low. On a main road, even a slight hill would require you to change down to third gear, and around town it would be very slow getting away from traffic lights. Imagine that your existing gearbox did not have first gear.
The TD has poor aerodynamics, so 80mph is the theoretical maximum speed unless you have a supercharger, and with a 3.9 diff you would never be able to reach 5,000 rpm in top gear.
Personally I would go for a 4.3, as fitted to the MGA 1600.
I cannot recommend a specialist to do the job, but I would be pleased to hear from anyone who has found such a specialist.
