P38A No Reverse In High range but works in low

Hi all

ive bought a £300 P38a Diesel manual, reverse works in low range but not in high, its had the electronic shifter removed and I have to do it by hand from under the vehicle, has anyone had this problem before? im quite happy to rip the transfer box off and take it apart if necessary

Peter

it wont be in the transfer box unless its not selecting, does it reverse in high if you increase the revs