The MGB propshaft length is determined by the combination of rear axle type and gearbox fitted. There are three distinct propshaft lengths in production and ordering the wrong one is a common mistake, the difference between some variants is only just over an inch, but fitment of an incorrect length shaft will cause vibration or prevent correct assembly. The four variants are: 30” for banjo axle cars with a 3-synchro non-overdrive gearbox; 31 1/8” for banjo axle cars with a 3-synchro overdrive gearbox, and also for all tube axle cars with either a 3-synchro non-overdrive or any 4-synchro gearbox; and 32” for tube axle cars with a 3-synchro overdrive gearbox. Confirm both your axle type and gearbox specification before ordering.
The universal joints at each end of the propshaft are available in two types. The sealed non-greasable type is the current standard replacement. A greaseable version with nipple was fitted originally to early cars and remains available as an alternative, requiring the grease nipple to be ordered separately. The propshaft-to-flange bolts also differ between gearbox types. 3-synchro cars use eight bolts split equally between the gearbox and axle ends. 4-synchro cars use a different bolt at the gearbox end, with the quantity reduced to four at that end.
Using the wrong bolt risks inadequate clamping of the flange and should be checked when replacing universal joints or refitting the propshaft.