we have a 1982 bedford mj 4x4. she will only reach 45 mph and we have been told that its possible to fit a 5 speed g/box to improve top end speed. its got the 330 non turbo engine. any advise or info would be much appreciated.

andy, April 2009

Presumably achieving higher than 45 mph results in the enginer revs going into the red arc?
If you are only getting 45 mph at full throttle and the engine rpm is staying in the green arc or slightly above it, then a 5 speed gearbox is not going to make any difference.
The gearbox just matches the speed of the roadwheels to the engine speed which is most efficient, giving greatest power at lowest specific fuel consumption and also matching engine torque to that required at the wheels. If you don't have sufficient engine power to overcome body drag (skin friction drag, form drag), frictional losses in the drivetrain etc then you won't get any increase in top speed - extra gear ratios may just help you to get to that top speed a bit sooner.

JD, April 2009