Austarion

I removed a one-way valve that was on the vacuum advance hose and now the car boosts nicely... Went for a semi-casual drive out of town for 5km, didn't punish the diff or anything, just a gradual acceleration... only trouble is when I came back into town I noticed a loud whirring noise when decelerating and a slight vibration from the rear/passenger side... It's quite loud and too loud to drive the car at all... Any idea what might have happened?

Diff have oil in it? Has a half shaft cv stiffened up or failed? They'd be the first couple of things I'd check

Sorry for my ignorance, does the diff oil need to be emptied before being topped up? And is there a special type of oil for the diff? Haven't worked on a diff before

Depends on how long the oil has been in there and what condition it's in. If you haven't changed it before then it would be a good idea to now. But that doesn't solve the problem of it making noise.....if it's low/no oil then it may have already been damaged.

As for the type of oil it depends if the diff is open or limited slip. LSD uses a different type of oil. That said, LSD oil will not hurt a normal open diff.

Easiest thing to do is jack up the rear of the car and rotate wheels by hand and see if you can pinpoint where the noise is coming from. You may have a seized brake caliper which is holding a pad on, worn brake pads, a piece of wire or stone stuck between a disc and pad....any number of things.

Thanks for that... Well I raised both sides independently, and whenever rotating the wheels as if the car were travelling in a forward direction, there's a clunk clunk clunk clunk sound, with a bit of resistance that pushes through each clunk, like I can feel the cogs inside the diff... When rotated the opposite direction, there's no noise or resistance. Assuming this means it's not LSD? If I understand correctly

Lift both wheels in the air. Turn one of them. If the other turns the opposite direction you have an open diff. Same way,you have lsd. The fact you can feel it clunking does not sound right.

ah right, will need to check again. Anyhow, I think I'll book the car in to get the diff done... Perhaps I should buy a good diff so the mechanic can swap it over if needed, no doubt they'll charge a fortune if I don't

Check the diff area if there is a lot of oil about. CV Boots as well...any tears? (Being a JA, there's only a small chance it has a LSD).
If not, my guess is that your Tailshaft has ceased up and your torque tube needs to be greased up if not the bearing replaced inside.

New uni-joints on the tailshaft and a good grease inside the torque tube should get you out of trouble. Hopefully! :)
Standard maintenance things I've noticed these cars.

Turns out I haven't any stands to raise the rear end and I live on a hill, so not too keen to balance the car on jacks obviously... Wondering if you reckon it'd cost less than $300 to fix this issue if done by a mechanic? Presuming it's something damaged. Just asking coz that's the extent of my available budget this fortnight

I really think you have a either chipped the star gears or chipped crown wheel & pinion. It's a pain but drain the oil... any metal in it? if yes then remove the back cover plate & have a look inside. :beer

I can sell you a good second hand open diff for $150 shipped if you need one.

PM'd

It's possible nut not likely, but a crownwheel bolt or two may have come loose and are now possibly catching on the housing. Might only do it in one direction, it happens.