Pinion adjustment

Hello,
Would someone be able to tell me the correct procedure for installing pinion bearings on a salisbury rear diff fitted to a series 3 109. I have had one go at this and ended up with a lot of play in the shaft after tightening the locknut down.
What is the story with the collapsible spacer?
Apparently this can't be re-used! I installed a new one initially.
Many thanks.

setting the pinion correctly is difficult for an amateur to do. its a skilled job to get it just right. some experienced mechanics cannot/wont do it.
its not impossible but it does take some time.
you will need a workshop manual at least.