Are soon to replace our MK2 4.55 rear axle with a 3.77 Power-Loc. I have been searching for the proper oil to use.

Searches reveal that a 80W90 GL-5 "mineral oil" should be used. Mineral I presume means real dino oil and not synthetic.

Others say the oil must be designated for use in an LSD unit.

Others also say regular can be used but needs an additive.

So I am confused and the shop manual does not say anything about special oil for the Power-Loc that I found.

So what is a proper modern oil to use? I am looking at

Castrol Axle Limited Slip Gear Oil 80W90

Thanks
jjsandsms

 

As with engine oil, opinions will vary.

I use off-the-shelf, any name brand, 80/90 gear lube with an additive.

For a long time GM's 1052358 additive was considered one of the best but it has been reformulated over the years. I'm not sure how it compares to other offerings these days. In recent years I've used whatever LSD additive the local parts store has on the shelf and have never had any problems.

Some gear lubes are pre-formulated for LSDs and will say so right on the containers.

Let's hear what others have to say

Cheers
DD

 

In my Daimler, which has the same Thornton Powr-Lok, I use any modern fluid of the appropriate grade from a respectable oil company that has LSD on the label. The one from Castrol comes in DIY size bottles. For road use, it's better for the LSD to either lock smoothly or not work at all.

 

As an oil man I use Castrol Syntrax Ltd Slip SAE 75W-140 in my S Type. Runs dead quite & cool. Differential had 90,000 miles on it. Fully rebuilt with meticulous attention to pinion bearing preload & CW & pinion mesh. Original crownwheel, pinion & spider gears.

 

Decided to go this route after an extensive test program with Nissan 4X4's with LSD's & diff lock in the deserts of the UAE/Dubai.

 

BTW ~ the Powr-Lok LSD selected for Mk2, S Types, 420s etc. used friction material that did not call for friction modifiers i.e. Limited Slip Oil. However I believe, as Peter alludes to above, that friction modifiers (i.e. LSD oils) provide worthwhile benefits.

 

Thanks to all, will keep forum posted as we put the 3.77 together and swap out the 4.55.

BTW anyone interested in a 4HA 4.55 open diff complete axle assembly less brakes after I remove it. 80K+ miles on it.

jjsandsms

 

Glyn, Why as heavy as 140? What was the reason to go away from the usual 80W-90?

 

After desert testing it works so well & slightly thicker oil film without overheating. Nothing wrong with 80W - 90.

Remember this is a 75W - 140. Synthetic.

140 is not much heavier than a 90.



Note an official SAE 60 has been added to Engine Oils ~ This majority to accommodate a particularly hot running Porsche engine. There are now officially SAE 0W's available for flow reasons. ~ keeping up with official changes is a challenge.

Note Esso (now ExxonMobil) recommends 90 or 140 on the Jaguar plate for this differential.

 

So you really only need the 140 for hot climates? That's not applicable to me.

I've used 0W-30 engine oil for a long time, it does make a difference in the winter if I can't plug the car in.

 

Yes ~ not applicable to you JB with your temperature range. 0W-30 engine oil makes a lot of sense in your winters.

 

You should think of the 75/140 as a little less viscous when cold and a little more viscous when hot. The lower viscosity at low temperatures is a desirable quality in a cold climate. And even in cold weather, the diff can suffer from heat from the inboard brakes especially if you do a lot of mountain work.

 

Indeed Peter. Another sensible perspective.

 

Yeah as other members noted, don't think you have to get too fancy here. Anything that meets the specs will do. That's what I did on my XKR.

 

It's not a fussy unit & as a Tribologist I stick to my comments. The specs are outdated in the modern world of lubrication.