Gearbox oil AGAIN

XJ
1

Sorry to be a pain and hark back to the old 4spd all-synchro overdrive oil question,

The background is that just about every vehicle to use the Laycock overdrive specifies 30w monograde non-detergent oil, or 20w50 engine oil, or a modern 75w80 GL4 gearbox oil(similar viscosity to 20w50 engine oil - different scales!)

This includes Triumph TR, MG, Jensen 541, big Healey, and Jags with the Moss box (pre 1965 or so)

Those in the know about the overdrive say heavier oils might cause excessive hydraulic pressures, break components, cause the o/d to fail to disengage; or that newer EP friction modifiers might “cause sludge”

Nevertheless, it is crystal clear that Jag specify a EP90 hypoid type heavy gear oil for 420, Mk10 4.2, XJ6 series 1 and 2. Obviously not a typo.

It does seem odd,tho. The new jag box doesn’t seem to have EP/hypoid gear trains and apparently is nothing out of the ordinary compared with the others listed above (TR,MG,541etc). WHY did they change their specification (hopefully not just to simplify inventory).

So - further questions- are modern “equivalents” to EP90 actually safe for components in the gearbox? Thank heavens the old lead-based friction modifiers are gone, but are replaced by GL5 sulfur based agents that are said to damage brass/bronze components

A pop quiz of experts has reaped a mixed bag of opinion. Overdrive rebuilding experts in the UK recommend 20w50 engine oil for our application, classic jag workshops with decades of experience offer advice ranging from 30w mono, via 75w90 GL4 to 80w90 or 85w90 GL5 EP oil.

surely there is a proper answer?

2

80/90w
Don’t over think it. They will all work. :smiley_cat:

1 Like
3

30 ND works great as did redline MT90. I’ve used both with success.

4

What the factory specs will work, and my only caveat to that is one should not use heavier oils in climates where it can consistently drop below 5C.

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I would use Castrol Transmax 75/90 GL4+ in my all synch KCN box with overdrive. GL5 is best avoided as it contains addictives that are likely to damage any yellow metal.

6


Ford full synthetic manual transmission fluid
XT M5 Q5

7

Some further information- I have had the privilege of an email opinion from Richard Michell - a classic car owning petroleum engineer who is the author of “Which Oil?”

I asked him this :-“ G’day again Dick

I wonder if i can ask another OverDrive question?

I’ve now got a Jag with an all-synchro 4spd and Laycock o/d. I was surprised to see that Jag specify EP90.

It’s not clear to me why they need EP protection- the tooth geometry looks pretty standard.

There is great dissent regarding modern oils. The mob who rebuild the most overdrives in the uk replied recommending 20w50 engine oil, The workshop (in melbourne) that rebuilt my gearbox (and are long standing jag specialists) recommend a “universal” 80w/90 oil (and suggested 3 brands they use - all GL5. They had no concerns about bronze components. He said he would avoid Penrite as it is suitable for limited slip diffs).

Another melbourne marque specialist says he uses a penrite 80w90, but “would avoid EP”. The Penrite product he specifies is a GL5 EP that is labelled “suitable for limited slip diffs”. A Brisbane specialist would use SAE30 (although his workshop manager suggested ATF!).

The forums have 1000 opinions- avoid GL5 (use GL4 75w90), “use what’s in the manual”, and a zillion brand specific recommendations

Castrol, Penrite and Peak oils all recommend 80w90 GL5 on their “selector” and reinforce this opinion when the tech helpline is called

I’m inclined to use GL4 75w90

It’s a minefield!”

And got this reply, which i feel is very useful:-

“Hi again,

I have a copy of the 1988 Ampol Lube guide and for a 1969 – 1987 XJ6 2.8 and 4.2 litre 4-speed manual it specifies a GL4 gear oil
.Multigrade gear oils were not available.

I also note that the description of the GL4 gear oil uses the phrase “a multipurpose extreme pressure gear oil”. So EP was not being related directly to GL rating but was more descriptive (or marketing blurb).

So for the box I do not thinks that there is any doubt – GL4 gear oil as you have surmised. Modern GL5’s may well be suitable but they will give no gains that I can see and may carry some risks, albeit small.

For the overdrive, in period the spec was probably monograde engine oil. Back then such oils had high zinc contents and met GL4. So the choice was easier (at least in theory).

On balance I would agree with your suggestion of SAE 75W/90 GL4.

Dick”

8

Russell,

the confusion that inspired your question has good reasons as Laycock-de Normanville OD gearboxes ask for different oil types. I found SAE 30 for MGB, EP 90 or 80/90 gearbox oil for Triumphs, Volvo uses ATF.

One - usually reliable technical source - expressly mentions this apparent contradiction and explains it with the assumption that the OD is less picky about the oil than the gearbox it is coupled to. Thus, the gearbox determines the quality of the oil and not the OD. For those who love to read German it is in Oldtimer Praxis 12/2016 “Getriebeöl”, p. 25.

Given that the OD was mated to the same 4sp box that was sold without OD and all Jaguar 4sp boxes required EP90 I’d go for anything as close to EP90 as possible. The SI ROM specifies Texaco EP90, Duckham Hypoid 90, BP Gear Oil 90 EP, Esso Gear Oil G.P. 90/140, Shell Spirex EP 90, Castrol Hypoy, Mobil Mobilube GX90.

That being said, I don’t think you’re wrong: as GL 4 is designed for highly stressed gearbox oils, notably hypoid gearbox oils and 75W90 covers single viscosity 90 in all likelihood you’ll get what you need.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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I think JLo is right, the overdrive is not too picky about the oil. I‘ve found recommendations from ATF and SAE30 to 20W50 and EP90.
The only real change for the OD is the friction until the clutches grab, and it’s a minor difference.
I would choose based on the gearbox, and use what the factory decided on, or if you want to experiment use what people say is better, Redline, etc.

I bought the gearbox oil recommended and it sits on a shelf waiting to be needed.

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The issue is that the oil that the factory recommended 50 years ago is not available. The notional “equivalents” are perhaps not equivalent - with some authorities anxious about the o/d and others anxious about bronze gearbox components. Most of these units do few km, so failures are rare (and likely to be blamed on fair wear and tear)

The advice from Richard Michell is likely to be the best informed- he has worked in the field over the period since the cars were new and is a classic enthusiast

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Yes, the other thread in Racing shows that it is certainly not that simple