How much movement on rear diff bushes???

Hi all,now and again when reversing on a tight lock i get a bang/knock from rear diff area and after a post on here was told to check rear diff bushes with a screwdriver levering them to check for worn/movement.I checked them by hand (grabbed diff and was twisting/moving)and i could get some movement?My question is how much movement should there be?should i get much by hand?i will try again with a lever bar,cheers for any help

also check for cracked chassis and subframe attachment bolts. see FAQ section.

you will always get movement, but it should be with resistance from the bush, when the diff just lifts all floppy then bushes are naff, do a tippex test as well.