I have a R31 rear end and one side you can move the hub in and out about 1 - 2 mm, whilst the other side is fine.

I was thinking that the oil seal may be worn and thus when you tighten up the 4 bolts to hold the axle in it is not applying enough pressure to the bearing?

Or the bearing retainer has not been pushed onto the axle far enough.

Or the bearing itself is stuffed?

So maybe a new wheel bearing kit would solve the problem and eliminate all 3 ???

Or is this amount of movement acceptable for the R31 diff? Dont know if these are the original bearings, the good side has hammer arks on the bearing retainer so I assume that side has been changed at some stage.

Cheers

dunno if replacing the bearing will fix your issue, but it cant hurt to do so.
Wheel bearings are not an expensive or hard to replace item. Just do if you think they are suspect, and then recheck.

I doubt if it is the wheel bearing, at least not originally.

My guess is the location of the bearing collar. Not pushed on the axle far enough. There are shims there, but won't fill out 2 mm.

Take the axle out and measure it. You can fit a pipe over the axle and puound the retainer on a little more. But don't get it too tight!

have the same problem with excesive movement of the axle, replaced the wheel bearings 3 times to try and fix it, when they first go in and the bearing and collar and still in one piece it has no movement as you would guess. but when the bearing and collar are split apart and then its put together it had atleast 2mm of movement
with the original r31 brakes on the diff you dont notice it as the caliper can slide with the disc and axle

i sure as hell noticed it with the r32 twin piston calipers on there though as when the axle and disc moves it pushes the caliper pistons back in and gives you a #OOPS# brake pedal

my analysis of it was the thats just a #OOPS# design, wow who would have guessed, the reason its a #OOPS# design is that they have uses a tapered bearing with no forseeable way or applying any pressure to it to actually hold it in where its supposed to be. tapered bearings are generallu used in pairs so that ones pushes or pulls on the other and they hold each other in place
single tapered bearings are used in lots of commersial vehilces as wheel bearings, but if you look at how they are done compered to how the BW diffs use them you can see the problem
in commersial stuff the bearing points the other way into a housing that then bolts onto the end of the diff, bearing preload is applied by an adjustable nut in the axle that also holes the bearing on place. then the axle is bottomed out into the diff centre to hole it outwards whilst the housing on the end of the alxe is pulling it inwards. then this is all shim adjusted also to get the right preload
or atleast thats how it see it as working when i look at it

the BW diff however relys on the axle seal pushing against the outer edge of the bearing to hold it in, but if you grab the bearing by itself and hold just the outside of it (not the shell but the bit the rollers stick out of) you will see that the axle can move around a bit when your holding onto the bearing....so thats why it has movement

thats all how i see it anyway and if there is anyone that can say no actually its just coz of such and such thats its got it. i'd like to hear from you as my current solution is to find a flat roller bearing like what the datsun diffs use thats the same size as the BW wheel bearing and use it instead

Having never seen a BW wheel bearing set up its a little hard to understand from the description given the exact bearing set up used, however a single row tapered bearing can only support a thrust load in one direction as opposed to a double row tapered, a pair of single row tapered bearings installed opposing each other or ball which can be thrust loaded bi-directionally. This means that for a single row tapered bearing to be used singlely (without a second single row bearing installed in opposite direction) in a wheel bearing application there must be a mechanism to support thrust load in an opposite direction to which the single row tapered bearing can supqort, ie. a thrust block which slides over the diff pinion pin in the center of the diff which the machined end of the axle butts up against and prevents inward thrust movement of axle. Out ward thrust force is supported by outer race of single row tapered bearing which is held by bearing retainer/brake backing plate, that bolts onto end of axle housing. End float and preload are adjusted by shimming in general. Hope this helps..

exactly, as i said in comersial vehicles the axle bottoms out in the thrust block in the centre. in BW diffs diffs the bearing tapers in the opposite direction so that the bearing is supporting the thrust inwards as opposed to the comersial ones that support load outwards with the thrust block supporting load inwards

so in the BW diff there is nothing supporting the load outwards, apart from the centre of teh bearing not being able to be pulled out of the case any more...which is where the movement comes from

Well - ????

Guess will have to run it and see how it goes. As pigdog said there is the ability within the R31 caliper for some movement. Just thought that the rotor would rub on the pads or the pads would end up being pushed back resulting in reduce braking performance on that wheel.