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MG MGB Technical - Diff Oil MGB

I was told several years ago to use Castrol Hypoy C 80W90 in the MGB rear end (on my MGA), but no one (NAPA, Car Quest, AutoZone, Pep Boys, O'Reillys) stocks that now. Has it been replaced by something better? I can still mail order it from Amazon.
Thanks for any advice.
Tyler
C.T. Irwin

It's crazy really why they have to keep changing the name of their oils, specially the gearbox oils some are Transaxle others Transmax----It takes a bit of keeping up with sometimes
Anyway--copied this off the Australia-Castrol website
for MGB rear axle----
--

Differential
Service Refill Capacity: 0.7, 1.3 Litres.
CASTROL ------AXLE EPX 80W-90
Extreme pressure, multi-purpose gear oil designed for the protection of heavily loaded steel gears. It is recommended for use in differentials, gear boxes and steering gears of passenger cars, light trucks, farm tractors and earthmoving equipment
William Revit

Been using Red Line 75/90 high performance synthetic. Seems to work very well.
Bruce Cunha

These days GL5 and GL4 classifications are used, which is easier to deal with than myriad manufacturers designations. For cars such as ours it's typically GL5 in the axle and GL4 in the gearbox (in the V8 as far as the MGB goes). In the UK Castrol supply axle oil in a container saying 'Differential' and GL5 and showing a picture of an axle, and gear oil in one saying 'manual' and GL4 and showing a picture of a gear lever.

Modern FWD cars which may or may not have the diff in the gear oil may well use either. Whether using gear oil in the diff is particularly harmful on an MGB is a moot point, but for me the Castrol labelling is good enough, and it's easier to go by the .


paulh4

Personally I won't use GL5 in either gearbox or axle. The additives in GL5 formulas are not "kind" to copper alloys, which are used in both boxes and axles.
Allan Reeling

A combined 160k in my roadster and V8, even ignoring what went before, hasn't caused me any problems ... yet! That's a bit of a myth that applies more to gearbox synchro components ... but then I think we have been here before ...
paulh4

Interesting that Castrol names their oil Differential in the UK and Axle here
It appears to be the same oil, same pic. on the bottle only axle instead of diff
and yes it's GL5

Give the Castrol Australia oil selector a try on the Castrol Australia web site, It's realeasy to get around and lists all the older cars where the UK site doesn't

Here's their description---

CASTROL AXLE EPX 80W-90

Multipurpose axle oil which may be used in differentials, final drives and other applications

Application

Approved by ZF for use in a range of axle

Features & Benefits

Wide range of European OEM approvals
High load carrying capability ensures gears operating under high loads are protected prolonging component life
High film strength ensures protection against wear and shock loads
Good thermal/oxidation stability protects against the formation of harmful deposits and oil thickening thus prolonging of both lubricant and components

Specifications

API GL-5
William Revit

If you have the time, I found this. It's an interesting read; http://www.widman.biz/uploads/Transaxle_oil.pdf
Allan Reeling

Came across that some years ago. However it's for transaxles i.e. diff and gearbox in the same oil so not applicable to the MGB, and refers to the damage that can caused to synchromesh by GL5.
paulh4

I, but it does mention the process of "stripping" copper alloys.
Also
1. that temperature has an effect on this process. I should imagine ours diffs run reasonably cool.
2. Most GL5 formulations these days, are "buffered" to inhibit the effects of phosphorous on copper alloys.
3. It does make reference to diffs, but of course not the bronze containing diffs in our MG's.
4. GL4/5 formulations are actually just GL5.
5. There was once a GL6, used for high offset CWP's.
It would be interesting to examine, as was done with gearboxes, the copper content in drained diff oil. That would tell us a lot.
Allan Reeling


Thanks Allen interesting read---
As Paul mentioned it starts out as being an oil choice article for transaxles--but then not all transaxles are equal ,There are different combos of g/box final drive
Some all in the same oil and some seperated

What I got from that mostly was that the oil additive in the GL5 doesn't eat brass, copper etc any more--

"Somewhere around 25
years ago a deactivated or buffered sulfur was developed that would react with
the phosphorous to create the protective/sacrificial layer in the conditions created in the gear boxes
(temperature and pressure) without being corrosive to the brass, copper, etc
This additive system is
used in most gear oils today."

Where you mention above--

"I, but it does mention the process of "stripping" copper alloys."

aren't they refering to the stripping of the
oil's protective layer which is a process needed for synchro's to work properly

I read it as --
AP4---gearboxes
AP5---axles
and transaxle oil selection determined by the vehicle manufacturer

willy
William Revit

Willy, I read that section on "stripping" as the molecular bonding of the high pressure additive is so strong that on soft metals this sacrificial layer takes some of the copper alloy with it when it goes. Hence the point about the measurement of copper in drained gearbox oil. But I did read a couple of articles and might be mixing their information up a bit!!
My axle is due for some input so I may go GL5 when the work is done, on the strength of this article.
Allan Reeling

I guess GL5 is it. I appreciate the input from all over the globe.
thanks, Tyler
C.T. Irwin

This thread was discussed between 15/10/2017 and 23/10/2017

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