MG Car Repair: Low maximum speed/rpm on 1968 MGB, transmission gearbox, clutch work

Question
I had restoration on my originally purchased MGB a number of years ago and am wondering if some unscrupulous mechanic replaced the transmission/gearbox. It didn't run as smoothly when it was returned and we stored it for many years afterward. Recently it was restored and has been running smoothly (clutch work, 2 barrel carb replaced by a single, gas tank replaced, etc). My problem now is I'm having trouble with attaining a higher speed than 45-50 mph without going into the yellow rpm band on the tachometer. I'm wondering if that early restorer replaced my transmission with one with a lower gear ratio. How can I tell? Should I be able to run the car at 55 - 60 mph without revving it up into the danger zone?

Answer
Hello:
Yes. You should be able to run it at 60 without being in the yellow or red zone of the tach. I would doubt that the transmission was swapped out- though I suppose anything is possible. I don't know of any easy way to tell from the outside looking at it. There is no way you should be in the yellow band of the tach at 45 mph cruising speed, though depending on how you shift moving up through the gears, it is possible you could get there as you accelerate, i.e. late shifting. If you live in a major metro area, try to see if there is a shop which specializes in British cars and take it there for a look see. If you live in the weeds, then I would just find by word of mouth and by good reference, a competent local mechanic who can look things over. It is possible the clutch could be slipping or the trans is binding up (check the oil level!). You should have 4 gears and reverse. Make sure you're using all the gears, i.e. don't cruise along in 3rd gear.  It is possible you could have an overdrive transmission, though you didn't mention that, and they were somewhat rare anyway.

Sorry I haven't been much help, but I hope you find your problem,