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MG Midget and Sprite Technical - Gearbox oil

I know the original specification for gearbox oil was the same as engine oil but I was wondering if more modern transmission oils are being used now. I'm thinking Redline MTL which I have used in other cars.
Roger D

Oh, my gawd, you've done it now!!! :yikes:

I'm one of the very few silent minority which such oil beliefs that includes using gearbox oil in the gearbox instead of engine oil and BL (in USA possibly agreed it was backwards compatible).

Check with the oil manufacturer which they think is best.

Personally I go for 75w90 but if you want to go 75w80 or 80w90 I wouldn't hold it against you.


Now, please forgive me, and I'm not saying you can or should but, and the others know and despised me for it, but, er, I use a modern GL5 in my Ford Type 9 gearbox - I have sinned!
Nigel Atkins

A quick search found various discussions about people using modern gear oils including MTL, in place of engine oil in various cars.

This extract comes from a morris minor site.

"SAE30 non-detergent is what I use. It's definitely suitable and still available. In the Mini BMC utilized a common sump containing the workings of the gearbox so engine oil itself can't be that bad, though the contaminants picked up by running through the engine mean you really should change your oil every 3000 miles just to protect the gearbox. This wouldn't be a problem with our separate gearbox in the Morris. I've heard of people using 75w90 gear oil with no problems in the Morris Minor so I'd doubt you'd have any issues with Redline MT-90, as I seem to recall it doesn't have any friction modifiers added for limited slip differentials like their 75w90 that might negatively affect synchro engagement and wear.
--Alex Haugland
Eugene, Oregon
USA"
anamnesis

I should have put, especially after anam's post, I DON'T use Redline 75w90, I use Millers CRX 75w90 NT (GL5), a UK/British/England blender, just to keep it local and I believe they do good products (as many others do).

If you use that as a reference to search the Archive you'll find plenty of threads and posts, and debates, on this subject, any with that reference will have posts from me - but I'm not an engine oil denyer, go with what floats your boat and best fits your oil belief.
Nigel Atkins

Oh, I forgot the BL Technical Service Bulletin which may be from the USA (altho' BL weren't, as such) which is always greeted well.

If it is from USA then you'd probably be best with USA oil, but would that only be if the car is in the USA, what does the "MG vehicles" in this document actually mean, the delivery lorries, factory/office fleet? It's all beyond me.

See attached PDF.

(took me ages to get the typed font)
Nigel Atkins

20/50 engine oil in mine and has been for over 100,000 miles.
Jeremy MkIII

it seems to refer to the MGB and MGB GT (top right hand corner of bulletin).

Personally I would stick to engine oil or sae 30.
Bob Beaumont

Ah yes, the proverbial can of worms. I shall have to sift through all the available data and see what floats my boat or oils my 'box. Hmm, that sounds a bit rude.
Roger D

Cigar to Bob, I forgot to blank that out. 😃

Yes MGB and BGT, but says "MG vehicles" and, and, "is suitable for vehicles equipped with or without overdrive" that gets the old boys with Bs, in the overdrive!
Nigel Atkins

Roger,
could have been worse you could have put what lubricates your box, no you're right, oils sounds worse.

I sure you will but always practice safe lubrication.
Nigel Atkins

100000 miles from a single ribcase or smoothcase Jeremy? Well that's damned impressive no matter what oil you are using. 😁
anamnesis

In my newly rebuilt ribcase (which came with a tag saying 20/50 engine oil only) I have opted to use a special Mini 20/50 which supposedly has additives for the gearbox. I’ll report back in 20 years or 50k miles whichever is the soonest!
John Payne

I found a similar discussion on a lotus 7 bbs, about the pros and cons of using mtl in a type9 box.

Some say mtl is great, chris at bgh says no, he doesn't like it at all.

Just like two shovels leaning against a wall. You take your pick 🤣.
anamnesis

Anam, ribcase. Probably put a curse on it now :(
Jeremy MkIII

Well that's more than pretty goood then.

When someone reaches very old age and gets interviewed on tv, they get asked "what's your secret?".

100k? What's your boxes secret Jeremy? 😁
anamnesis

The original oil spec for the ribcase is 30 weight oil. The g/box won't get anywhere near as hot as the engine so it could be argued that a 20/50 will stay nearer 20 weight meaning a monograde 30 *might* be better. I don't know, just a thought. I think the reason for engine oil is to allow the synchro rings to work I.e. a thicker oil might reduce the friction that they need. That does suggest that there might also be more friction between gears and bearings but, in the absence of more definitive information, you have to assume the g/box was designed to work with engine grade oil. Well that's what I'm doing.
Bill Bretherton

Haha Anam, it was drained and stood upright for about 15 years while the restoration was 'ongoing'.
It can't be the only 100,000 miler?
Jeremy MkIII

Bill,
you might like this, an extract of an article "By Gavin Scott who is technical sales manager of Delta Oil Ltd." from July 2005 on The Volvo Owners' Club website. - https://www.volvoclub.org.uk/engine_oil_history.shtml

"Straight SAE 30 oil tested in such a fashion shows it is useable down to minus 10 degrees, thus this oil can be called an SAE 20w30. By adding viscosity modifiers to thicken the oil to an SAE 50 viscosity at high temperature then the oil becomes an SAE 20w50. A 50 weight oil, only good for operation at 0 centigrade, can be called an SAE 30w50. Two oils, both SAE 50, identical under the old definition, are thus now easily distinguishable. This became the world wide accepted commercial method of identifying engine oils. To the benefit of both the oil producers and the motorist, the pre-war standard SAE 30 was converted by means of an easy additive into the beloved 20w50."
Nigel Atkins

Oh no, Jeremy, you've let so many people down, so you're saying you changed the gearbox oil in that 100,000 miles, only once I hope!
Nigel Atkins

Nigel

Thanks, interesting article. 20/50 it is then. That's what I've put in (mineral).
Bill Bretherton

Sorry Nigel. I refilled it with the original oil when it was put back in the car - why has my nose just grown?
Jeremy MkIII

Jeremy, you must have money to burn, you could have saved that oil and just topped it up on completion of the resto.
Nigel Atkins

Bill,
you know 'mineral' oil despite being in the ground millions of years, goes 'off' quicker than 'synthetic' oil.

And that most 'synthetic' oils ain't really synthetic (only one if you want to be really pedantic) so you just want a suitable oil and not worry too much about the marketing description. The oil I use went from plastic to tin container and a more nostalgic presentation to compete in oil classic car market - and the price went up, to pay for the changes(?).
Nigel Atkins

Currently running mine on Penrite GB30 Gear box oil.

Which is their recommended oil for g/boxes that were originally specified with 20/50 engine oil.

Too early to tell as I’m nowhere near 100,000 yet (or even 10,000).

R.
richard b

I use Penrite GB30. Its been good so far and has included 3 European tours to Spain, Switzerland, SW France and a run to Scotland!!
Bob Beaumont

There are more local blenders that sell good products.

If the product is good I like to support stuff from UK/England but I'm certainly not against good products from elsewhere and of course many UK/British companies aren't really having been sold off years and decades back.
Nigel Atkins

Roger,
you could contact Motul and see what they can offer to compete with the Redline.
Nigel Atkins

Nigel

I've used mineral oil because I already used it for the engine and there's just enough left for the g/box. Nothing against synthetic - use it in the moderns.
Bill Bretherton

Bill,
nothing wrong with thriftiness.




But how do you know which is leaking the most if you use the same oil in engine and box? 😁
Nigel Atkins

Nigel

Check the engine dipstick? Although, you have a good point. Is that Penrite stuff a distinctive colour?
Bill Bretherton

Bill,
sorry, I've no idea, I buy local oil, though for no absolutely no good reason I think the Penrite might be brown.

Put the gear oil in the gearbox and you could sniff what gets to the ground.

Put the modern GL5 in and you could feel the "yellow metals" in it. 🤣

(or possibly there wouldn't be any, but who can you trust)
Nigel Atkins

This thread was discussed between 30/07/2021 and 01/08/2021

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