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I ask as I have never had to replace a diff due to noise or oil leak, spy a diff in that corner of my shed, another in another corner as I cart in yet another and start to group them together. WTF am I doin' hoarding all these normal diffs I ask self ?

Remind self of another monkey on my back - a 3.9 ratio diff to suit my spare box, sitting out where I gave up on it - four or five years ago my pin punch (stamped SUBARU so can pick it out from its brothers) got jammed in the axle - never to come out - until today .

Three hose clamps and my EA81 lifter puller slide hammer, Lanotec, a few shifters - got the pin punch out, then a struggle to get the half length pin out.Looks like previous worker used a broken roll pin for emergency, the break was angld and kept off centreing my pin punches.

Rear diff axles are weird, needing 5mm ? to drive pin halway, then a mm less - 4mm to pop the pin right out of the DOJ hole. Must be intentional engineering to keep the pin instead of lose it.

Currently draining the black sludgey oil out, will need a new gasket and breather - anyone tried to a new breather plug for these diffs ? Option is to fit some brass adaptor and run a breather hose up high somewhere

Only ones I've seen fail, as they go back to Datsun 1600 rally car days, were non correctly serviced one's. Fixed by adding 3 banana's.
Look after them and they last forever???
Serviced, they are very reliable.
The main time they are replaced is with different ratio gearbox changes, so they are still wanted.
MY 3.9 boxes and diffs are getting rarer.
3.7 diff's I have a pile of them.

New breather??, just pop one out of another similar diff.
Brass adapter and fed to a higher point, with a "U" bend, is the safest.
Remember that for your next deep creek crossing Jonno.

Yep old rear diffs seem to outlive the rest of the cars, unless punished by some dim witted moron. A good reason to keep even openwheelers, just sold a 3.9er to another forum member - you never know!

I've seen those shitty plastic breathers melt, esp on LSD pushed hard. Fix is really easy.

I agree with the above. Water in the oil is a great way to make them whine.

I've only ever swapped out my rear diff for a welded unit or a ratio change. Still got the other diffs too.

Cheers

Bennie

The diffs are good, cant saw the same about the stub axles, 3 different types/strengths I am aware of, broken a few of those, but the guts of the diff was fine.

I busted a front CV joint so in desperation pulled the front shaft out and ran in 4wd as effectively rwd, after a week the diff was making whiney noises so I dropped the oil and it was silver.

I've seen a few crap out but this is due to lack of servicing. I too only hang on to them for different ratios when changing out gearboxes.

Speaking of rear diffs, what oil are people running and happy with? Poking around and people seem to be having good results with Castrol VMX 80 in the gearbox, so chuck this in the diff as well?

anything will be better than what comes out !! 4 litres of VMX 80 at SCA is under 45 bucks. 3.3 litres for a 4WD L box, dunno if the remaining is just enough for a diff ??

Only need 800mL for the diff. I chuck in a little extra though.

I've used Penrite 80w-90 Mineral LSD oil, now I use something that's basically the same but they've apparently dropped the LSD specific type of oil or something... I use it in both my gearbox and rear diff, even though I don't have a clutch plated LSD.

Cheers

Bennie

Need to check what type of diff you have (i.e. Open, VLSD, PLSD, etc..) to know what oil will be ideal. I use Motul oils for rear diffs, Motylgear 75/90 for open and FF-LSD for Plated and Viscous LSD diffs.

Paul, left youself open to more questions like - any old motor oil in plain diffs 20W50, 60, 70 ?

Who are you asking?