Chunk of square tubing that fits. A hole for a handle. or weld on a strap as a handle. ;
Isnāt it the same Salisbury thatās used in scads of American automobiles, including some Corvettes from back in the day? What oil do those cars call for?
Correct. Weight and LS additives should be the only important thing I would say. Brand is your choice.
I canāt seem to get my head around why would they use two different plugs in the diff. It seems to me that if the square hole was designed to accommodate the end of a Ā½ā extension or ratchet, then why not use the same plug for both holes. Iām gonna check to see if both holes are the same size. If they are, I have a few spare transmissions lying around that I can rob from.
To follow up I eyeballed a cursory look at one other 3.54 that was just sitting in the cage there is a square protruded plug sitting in the refill hole. My initial thought is there doesnāt seem to be any rhyme or reason for which plug went where. Probably whatever was available in the factory at the time?
I did remember to check the interchangeably of the two plugs and they are in fact the same size, with the other distinction being that the protruded square plug is the one with the magnet.
I thought it had to be a straight 90 weight ? 
I always thought they were the same holes (size and config.), too ā¦
Well, actually the factory lit. mentions that Castrol (canāt remember which weight, etc.) can be used for ātopping upā but not for refilling ā¦ I donāt understand that, unless maybe the Castrol stuff does NOT have the L.S. additive in it. ?
As I understand it, that LS additive once came from whales. I presume eventually a synthetic substitute was developed; I certainly hope weāre not still killing whales to prevent chatter in our LS diffs. Whatever, my impression is that when whale oil was the only suitable LS lubricant it was used sparingly. So, most bottles of gear oil did not contain the additive. Since the advent of the synthetic stuff, itās considerably more common to find gear oil that is suitable for LS diffs right out of the bottle.
I always wondered what the actual difference between the two axle lubricants is (and actually, I really donāt understand what a L.S. differential itself is - doesnāt that mean that whenever one wheel makes one revolution the other wheel on the same axle ālocksā into synch with it? I think in the U.S. we call that āpositive tractionā, or āposi-tractionā? ) So how is it disastrous if we use a non L.S. lubricant in the axle instead (supposedly)?
There are actually several different ideas in diffs that are intended to allow one wheel to propel the car when the other is spinning freely on black ice. My '66 Mustang had something I think was called āpositractionā which was a fixed clutch pack between the two axles, something like 200 ft-lb of torque required to turn one wheel when the other is restrained. The āLimited Slipā in our Jags, on the other hand, is a clutch pack that gets more and more compression on the discs when more torque is applied through the drive shaft. When coasting itās not too difficult to turn one wheel relative to the other, but when lots of power is applied the two wheels are more resistant to moving separately.
With any of these, though, I think the need for the additive package is for those clutches. With just regular gear oil, those clutches will start to chatter. I think it may damage the clutch pack, too.
80W-90 is a 90 weight oil.
LIke I said, Gear oil is Gear oil. There is nothing special about what gear oil you put in your differential, as long as it has Limited Slip additive. If you put in straight gear oil, the clutches in your differential would be destroyed and youād have no limited slip. It would be just like a dumb one-wheel-drive differential.
I changed mine to the Castrol oil I recommended about a year ago. Immediately, my limited slip worked miles better, and it has been up until now. Iāve never had a car with LS until now - it sure gives you quicker starts when both of those tires are pushing!
Both tires are pushing equally with an open diff. The difference with a LS diff is that one can push harder than the other if need be. With a live axle, it needs to be on every hole shot, as the torque of the drive shaft is trying to lift one tire off the road and is pushing down on the other. With an open diff one tire spins wildly, with a LS diff both tires spin and the car turns sideways violently. But the XJ-S has IRS, so the LS diff makes little difference on hole shots on clean pavement. Its primary benefits occur when one tire is on sand or black ice or whatnot.
Makes sense.
The main difference I felt - before changing out what I expect was original diff oil (and low by 1/2 quart), my hole shots on pavement felt more like an open diff with one tire spinning. After changing and filling all the way up, i get a bit of push to the right, but BOTH tires seemed to catch faster.
So i get less tire burn, and quicker traction.
AKA ālockedā differential !!! Cheap way. Weld the spider gears. Better. After marked blockā¦
Racers cope with them !!
Odd side issue. They are a bear to push!!!
Carl
Oh, man, Iāve seen a couple of those. One had the entire carrier welded into a solid block. I recall a racing TVR that, when backing out of a stall in the paddock, one rear tire would grip, then slip, then grip, jerking the whole car each time.
Are those like the Detroit lockers found in many GM and Chevy Pickups?
The only problem with welding those gears is it makes for difficult turning because the inside wheel is locked it will skid something terrible 
Well not to be problematic, Gregmatic (
) ā¦ but 80-90 should be ā80ā weight part of the time, ā90ā part of the time, and at other times something in between the two figures, depending on the temp. of the lube. āStraightā 90 is just that - 90 weight 24/7. That would be like saying ā10-40ā motor oil IS 40 weight oil (or 10 weight oil, FTM). At least that is my understanding of it ā¦ Iām thinking there must be a reason why Jag specifies specifically ā90ā weight.
On another note, assuming my differential is currently low on fluid like yours is, what did it sound like - was the noise - kind of a low-pitched mild āgrowlā - proportionate to road speed and noticeable usually only around the 30-40 MPH range? If not, I wonder what the real issue is ā¦ Iām thinking possibly u-joints needing a lube job and/or those rear hub bearings (all of which are accessed via the Zerk lube fittings). 
Sure is. And pushing a car so equipped by hand in a turn is the bearā¦
In dirt track, not so much, the inner wheel can slip a bitā¦
Straight away on black top also OKā¦
My son has a little low T hot rod. power from a very healthy 460 Ford. Fat rear cheater siks and a āspoolā . The "right " way to lock the reatr end.
It can lay down smoking hot strips of rubber easilyā¦
Carl
Actually, the noise isnāt really a growl but more like a loud low-pitched humming. 