reverse gear problem

[PigFmr]

hi
wondered if you guys could help me out please,
3b series 1973 109 landy factory standard 38000 true kms on the clock,
right the problem is revrse gear,wont go into gear even if you hold it in as the gear lever touches the dash but neally engages if you not what i mean but not enough to move the landy,
is there a selector that you can adjust?? is a common problem??
and the kms are correct so 38000kms the box should be ok??
1st 2nd 3rd well others gears are fine.

any help would great , as i aint got a clue about landrovers,

forward thanks
vince