Differential Gear Oil- GL-5 or GL-4 with additive?

[mtnjag]

1962 Eype, original limited slip diff, not rebuilt, good condition.

Can I use a GL-5 lube like Redline 75w90?
or
Should I use a GL-4 with an LSD additive?

[44DHR]

As there have been no other replies, this is my opinion on those two oils.

Both GL-4 and GL-5 are EP, (Extreme Pressure) oils. GL-5 has more EP additives than GL-4 and has a higher shock rating than GL-4. GL-4 gear oils are typically recommended for spur and helical gears such as found in manual transmissions and transaxles operating under moderate loads, whereas GL-5 gear oils are typically recommended for hypoid gears in automotive axles operating under high-speed, high-load conditions.
In this specific example of the Salisbury Powr-Lok differential, this has hypoid gears and a set of clutch plates which require a further additive of a friction modifier to assist the clutch engagement and disengagement to reduce potential “chatter” of the plates. Both your options would work in normal road use - as opposed to heavier race application - but I use the GL-5 option to give a higher level shock protection, plus by buying a proprietary high level brand specifically made for Limited Slip Differentials it will already have the correct level of friction modifiers already in it. In the UK, in my E Type differential I use Castrol “Axle Z Limited Slip 90”, which is GL-5 oil.
You also mention Redline 75w90, but the only Redline I use as a 75w90 is in my E Type manual gearbox, which is MT-90, but that is a GL-4 not a GL-5 specification. I do also use another Redline product on new rebuilt diffs to help new clutch plates “break in” and that is called “Redline Limited-Slip Differential Friction Modifier/Break-In Additive.



I trust this helps,
Cheers,
Dave

[rswaffie]

Hi
When Alan Slawson rebuilt my 1963 powerlok diff, he included the following info re oil:

Warning Note – Castrol ‘Axle Z90’ limited slip oil or quality equivalent oil to be used for the LSD unit.
Synthetic or semi-synthetic oils do not work in these units and MUST not be used

He supplied the Z90 oil for the diff as part of his service.

[mtnjag]

Any idea what the problem is with a Synthetic like Redline 75w90 GL-5?

[tim wood]

When Alan Slawson rebuilt my diff he was adamant the the castrol oil noted above must be used.
He knows more than me so I followed his advice.

Tim

[Paul bow]

Just to throw my hat in the ring.. I also had my diff rebuilt by Alan slawson and he too was adamant on the oil..
However Castrol changed the name, instead of Z90 it is now Castrol transmax limited slip 85/90..
Same oil different title..
I checked this out with Alan who confirmed that indeed this was the case, and only this oil was to be used..
This is recent, probably about 4 months ..
The MT90 is excellent in the g/box.
Hope that helps

[44DHR]

For Layne at Post #4.
No problem with Redline “75w90 GL-5”, where that is the specific name on the label, but there are two versions. One is Redline “75w90NS”, which on some on-line forums states that means “No Sulphur” and has no friction modifiers, so I would be wary of using that version as it would not be suitable for our application in the Powr-Lok differential. As it has no friction modifiers, it would be more suitable in racing applications or with weak locking clutch plates to “grab” quicker as the clutch plates separation and re-application are not so critical as on a road car in terms of performance and noise levels. The other product as a straight Redline “75w90” states clearly on the product label that it is suitable for Limited Slip Axles, so there would be no doubt with that version. (Sorry, if my reference to the Redline product with the name “MT-90” on the label being a 75w90 GL-4 caused any confusion as these are completely different products - one suitable for manual gearboxes and the other for differentials.

For Paul at Post #6
Yes, Castrol Axle Z Limited Slip 90 is now discontinued, but still available from some suppliers. It used to be called Hypoy LS 90 before that. It is not “same oil, different title” and as the oil specification classification is SAE 85w90, it differs from the “straight” 90 in the characteristics below. It certainly is an equivalent oil to use.





Cheers,
Dave
P.S. Final version. Apologies for all my editing on this post, but wanted to get my information as clearly as I could !

[Paul bow]

44DHR..
Could you help us in where the Z90 can still be bought
“ still available from some suppliers”
as I tried and failed, could not find a single bottle anywhere. That was when I called upon the guru Alan Slawson to find out if he could help being he took care of the rebuild.
I was advised by Alan that indeed this was the equivalent oil now being used, z90 discontinued .. in my layman’s terms “ same oil different name”, perhaps I was being a tad casual in my language. I will endeavour to be more precise in future posts ..
Should have said .. “Does the job perfectly..being Z90 unavailable”
Hope that clears that up guys

[44DHR]

Paul,
I’ve done a real quick “google” search tonight and found a potential supplier, but I can’t vouch for them or their stocks. It will be harder to find, but there are plenty of smaller suppliers who could still have it as I can’t believe all the UK stocks have been sold.

https://www.vintageandsportscarservices ... e-66-p.asp

In my quick search I found some specialist lubricant supply companies who show present availability of 12 x 1 litre packs or 20 litre drums. Also the bigger Classic and Motorsport companies could still have this specific oil as they would have bought it in the larger 20 litre trade sizes and may be prepared to supply you. There always the large internet auction site who could show some old stock being sold from time to time.
If no joy, go with Alan’s recommendation to the present Castrol oil as he is the diff guru !

Regards,
Dave

[rswaffie]

Try Opie oils, I’ve used them in the past.

https://www.opieoils.co.uk/p-77290-cast ... tid=112094

[mtnjag]

I use Redline MTL in my trans. Works very nicely.

I can't find the Castrol products in the US.
How about a mineral oil recommendation available in the US?

[mtnjag]

Talked to Castrol US (Transmax a European product only) and Valvoline US and they both say a GL4 is recommended for the pre-73 Jag differentials.
They say GL-5 is corrosive to Yellow metals-copper/brass/bronze and should not be used if those materials are present. Same reason not to use GL5 in our transmissions.

I have heard this before.

The Castrol Transmax is a GL5 rated product, but evidently recommended by a respected garage.

I have not been inside my 62 E diff.

Do the early diffs contain Yellow Metals?

[mtnjag]

Calling out to you differential guys.

Any yellow metal (thrust washer or ?) like Brass or Bronze in the early Eype diffs?

[mgcjag]

Hi Layne....you've been told that GL5 is corrosive to yellow metals....this isn't correct...some maybee but not all....Jaguar recommended ep90 for the diff..... Millers classic ep90 is GL5 and the spec says its suitable for Hypoid and yellow metals....so whatever you choose read the spec yourself.....some early Jag diffs had yellow metal thrust washers....I dont know if early Es did....if I had an early E I would assume it might have and use a suitable oil...Steve

[mtnjag]

Thanks Steve. I'll check around for safe to yellow and look for Millers EP90 GL5