Mmmmm that was my thoughts. Can’t be locking brakes on as its all too basic. I would assume it locks something in the transfer box and yes perhaps that’s the **** metal noise it’s making after driven half a mile. Noise gets louder and louder (no metal in the two oil changes it’s had in 750 miles). I’ve replaced everything now as in everything on the 1978 RRC running gear, checked both diffs a light back lash but all good and drive shafts all round. yes it’s jacked up 2” but it now has wide angle props front and back, the only thing left to fit is the cranked rear trailing arms, but I can’t see that changing anything. A job this weekend and of course I will try the diff lock again.
yes you’re right on the old LT95 the diff lock is done by air on a pull button and a light comes on to let you know its engaged.
My guess it the vacuum diff lock, locks front and rear drive together, all of the brakes are separate standard calipers leading to servo, non abs.