Sierra Axle/Diff Lifetime?

[Highway-Star]

Hi People.

I've just finished doing a major service on my '92 WT SWB Sierra. It took me two days due to all the unexpected bits I ran into. Anyway my car is nearing the 300,000km milestone, and A few things are concerning me slightly.

When I drained my rear diff oil I expected to see the usual amount of metalic paste on the diff magnet (5-10mm), but I had about 20mm of paste on the magnet! (about 25000km since last change) The rear diff play (backlash) is small though evident. And I know when I did a rear oil seal about 25000km ago the rear axle splines were looking a fair bit thinner than they should be.
In comparison my front diff, gearbox and transfer all had the expected amount of metalic paste on the plugs.

I know these components wear, and will eventually die, but at what mileage have people found wear to be excessive, or components to start failing (I dont mean from failing from a one off shock loading etc)?
Its dailing driven on 31s, and I'm averaging about 500km a week, so it piles on the kilometres at a fair rate.
Should I be keeping a look out for a newer rear C&P and shafts?
For that matter does anybody sell replacement new 3.7 C&Ps ?
Would a 300,000km old rear end put up with the strain of 31's reduction gears, and then If I lock the diff too?

Sorry If I sound paranoid, but I like to look after my car, and worry when things are not exactly how I expect.

Cheers

[dank]

pull out the 3rd member and have a look at the R&P, you should be able to notice any wear on the teeth as the contact pattern will never use 100% of the teeth. You could probably pick up a good second hand 3rd with r&p to replace yours if its cheap enough, them seem to go for anything between 70 and 250 bucks depending on where you look. I know front cvs and axles usually go for about 150 a pair in victoria at the wreckers. I dont know about rears, shouldn't be much more.

You could probably get genuine suzuki but it will prob cost you an arm and a leg. Aftermarket R&p from states are about 215US a set plus shipping.

Maybe check spline depth on yours compared to a zook with fewer km to see the actual difference. it could be your bearings and if the backlash isn't too bad and there is no up/down side/side play in your pinion at the driveshaft flange I wouldn't stress too much

[Highway-Star]

Thanks Dank

If I hadn't of spent 2 days doing my service I may very well have pulled out the centre to check, time is my enemy :(. I wont have free time till early Nov now.

The splines I have compared to a couple of others I've seen (from memory though, not putting one next to the other). And I'm yet to see any that look as worn as mine, they are triangles, without any flat top left. One zook was my fathers which has about 240K on it, and another was some random NT ones a bloke had that I bought some other gear from.

The backlash does seem alright, and there is absolutly no sideways/up/down play at all. Rear wheel bearings were replaced about 40K ago, haven't touched centre bearings.

When I bought my car about 4 years and 40-45K ago it was a mixed bag of what had been rebuilt and what had not (eg: brand new engine, old radiator; new gearbox but transfer oil looked like mud) , and I'm still putting together the puzzle...