Outer Limits 4x4 Board

Ok guys been driving round all day and no problem at all then back off in 3rd gear and get a bad knocking noise from the box also noticed it knocks alittle when under power aswell

Does not do it in any other gear only third

Its a 85 hilux with a G52 box

Any ideas on what it could be

PS-gonna change the oil tomorrow and see if that helps cause i dont remember changing it since about 60k ago

Yep you have blown third gear which means you will have to replace the cluster as well

Ok well i just hope its get me around tomorrow to pick up new box then out too mates workshop so i can put it in