MGB SPEEDO CALIBRATION
Q I’m planning to change the gearbox on my MGB from non-overdrive to an overdrive one. Do I have to have to change the speedometer?
A A simple question with multiple detail answers all revolving on the age of the car, the gearbox and overdrive types fitted to different model years. As you do not mention the car’s age it complicates the answer. In very basic terms, yes, a change is needed as the speedo calibration is different between the OD and non-OD cars. Some of the complication arises as there are effectively three different specs. of gearbox: chrome bumper three-synchro; chrome bumper four-synchro and rubber bumper four-synchro.
To add to the complications there are two distinctly different speedo
