[terry.sc]

It supports the belt side of the diff gear. With all the others the torque load is in line with the ball diff, on the Mid while all the torque from the gear drive goes through the ball diff, without the spacer supporting the pulley the belt will pull on the pulley side and try and twist the gear on the shaft. The spacer supports the pulley on the inside like a bearing so the gear stays centred. As the only time

A better solution would be to use a bearing, or a small bearing in a larger ring that's a good fit into the pulley. As there isn't a bearing in the centre of the diff it would also help support the diff itself.