the leaf springs on my AUII XR ute have been through a bit of a hard life, i took it to pedders to get the cheap'o suspension check and as expected the guy said, "its all ok except for the leaf springs have collapsed".

he mentioned something about the diff tracking due to the collapsing of the springs, can someone better explain this to me and also if it causes any other problems... i need to get the cash off my father for repairs (and by repairs i mean replacing them with lowered leaf springs), but first i want to know what im really talking about for when he asks if i REALLY need it done.

cheers...

The diff tracking probably means that the rear axle is no longer lined up properly with the rest of the body due to the collapsed spring/s.

If you replace the rear leaf springs with lowered ones, the fronts will need to be done too, or it will look a bit silly

The lack of tension in the rear springs would also probably make it drive strangely as well

If your springs have collapsed it will throw out your wheel alignment too. I just had this problem in an L300 4x4, I used he original leaf with the eyelets and replaced the rest of the leaves with a set from an XD wagon. That added 2 leaves and I also added helper springs and air shocks, a bit of over-kill, but I do carry a lot over the rear axle (same as a ute I suppose). It took me 2 days, but I don't think I'll need to even look at it again.

A small amount of rear end tracking (dog tracking) is normal on leaf-sprung vehicles. If it's significant, one spring has probably sagged more than the other, or one collapsed more in the front half of the spring and the other in the rear half. That would upset the handling, making it uneven, and I wouldn't personally take the risk.