[TR] tr6 reversing woes

[Frank Fisher]

my last post on this had my friend experiencing a difficult time reversing his TR6. its like the handbrake is on.
our of gear it rolls forward and backward very easily. but once you try and reverse using the motor in the normal fashion it struggles.
the car has laycock overdrive. we did not think it was working.
in talking to my friend last night we found when driving the car at +/-60 mph his revs are +/-2200.
sounds like the overdrive is stuck in the on position.
i have so little experience with overdrives.
so what could be the cause of stuck on and what are the remedies?
thanks
Frank