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MG MGB Technical - Gearbox oil

I am thinking of changing from Halfords classic oil to Castrol GTX; is this suitable for the gearbox and overdrive on 1975 MGB?
R E Merrall

It is one of the recommended oils for engine & gearbox in the owners & workshop manuals.
Chris at Octarine Services

Do you mean GTX or XL (Castrol 20w50 XL)?

The important thing is to do timely and thorough oil changes.

Workshop manual has gearbox oil / o/d changes at whichever is sooner of 24k-miles or 24 months.

Get the existing oil as warm as possible and let it drain for as long as possible (and perhaps a pouring flush with the fresh oil as the existing oilcomes to the end of its drain) to get as much existing oil and muck out and as much fresh clean oil back in.

Follow the Driver's Handbook on cleaning the o/d filters.




Nigel Atkins

I would consider a wider range of alternative oils than most posters on here but to keep the traditionalist (rather than purest) happy the following was pointed out to me as being especially suitable for engine oil in a gearbox. -

"Designed for when the engine and gearbox share the same oil such as original Mini, and gearbox applications specifying an engine oil."

Millers Classic Mini Oil 20w50 Engine Oil - https://www.millersoils-shop.co.uk/classic-mini-oil-20w50-engine-oil
Nigel Atkins

Much the same as all the other brands of oil then!
Chris at Octarine Services

Yes and no and depends on what you're comparing it with.

As I put a hyperlink so I didn't bother highlighting a claim, but here's the list they put up (including those that don't apply).

USER BENEFITS
. Improved engine and gearbox protection versus a normal 20w50 engine oil
. Longer life for gears, plain bearings and needle/roller bearings
. Improved gear change quality
. Longer idler gear life in transverse Mini engines

and

PERFORMANCE PROFILE
API SF, GL4 - SF! GL4! - yes, I do realise. ;)

It was just one oil to mention, one that was mentioned to me.

I did wondered if R E might be going for the adventure of a modern Castrol GTX, I knew Duckhams 20w50 was back (updated) but don't know about Castrol GTX mineral.
Nigel Atkins

Anything that is good enough for the engine is plenty good enough for the gearbox. There is no point in having anything other than the same oil in engine and gearbox for the 4-cylinder MGB, unlike the V8 where gear oil is specified for the gearbox. Engine oil and filter changes are more important than gearbox oil changes, and there is about a pint of 'old' oil left in the OD and gearbox after conventional draining.
paulh4

Well you've covered a couple of the points why it may be a good idea to have good oil in the gearbox. -

To allow for gearbox oil changes being of such less importance that they're irregular, ignored or forgotten so the engine oil in there could have much of its life bashed out of it with use and age.

If one pint of oil out of a capacity of say five pints is left that means at change 20% is already used oil with only 80% refreshed so better oil and regular changes are required to sustain higher effectiveness of the oil.

I agree with you that a good oil is a good oil, and just about all are, timely and thorough oil (and filter) changes are the important bit.

On the other hand these engines, gearboxes and cars will run despite lots of abuse and neglect so why worry about any particular or type of oil or bothering with changes especially as many do so few miles and are only bimbled along - horses for courses, each to their own.

Nigel Atkins

Nigel 'bimbled' love it!!

Quote:

The word bimble, meaning 'to move at a leisurely pace', is sometimes said to have originated amongst British soldiers serving in the Falklands, and much of our early evidence supports this.

Colin
Colin Parkinson

Now that's interesting as I thought it was from earlier times as I first heard it from a chap that likes vehicles from the 30s and 40s.
Nigel Atkins

Lower down on what was possibly the same page:

"I joined the Royal Marines in 1972 and served 12 years. This word was common place in our vocabulary. Like most service sayings some are unique to a service and as far as I'm aware we were the only service that used it and I've worked with them all. As we were known for our serious 'yomps' hiking long distances carrying heavy loads, the alternative was known as a bimble; a simple 'amble' but with a little more discipline."
paulh4

By coincidence I heard the word used on the telly last night in Good Omens, IIRC from Bill Paterson's character.
Nigel Atkins

Any 20W50 is good enough for the gearbox, its only there to keep things cool. We have involute gears and rolling element bearings so no sliding there. Bulk rinks and synchro cones don't want much lubrication do they ?. selector forks ? I would probably not have changed my gearbox oil if I hadn't just done a major overhaul.
Paul Hollingworth

A bit more than that, I'd have thought, especially with OD.
paulh4

I'm impressed Paul was in the Royal Marines. I was an Ordinance Artificer in the Royal Navy and whilst doing training at HMS Fisgard in 1960/61 did the marines assault course; it damned nearly killed me! The worst was the ' death slide' when all they gave us was a piece of knotted rope dipped in a bucket of water. On the way down you could see the rope smoking!! Talk about scary.
R E Merrall

Why bother with 20w50 or even oil if it's a matter of just cooling and a bit of lubrication.

I'm sure there are lots of classics, old cars and old bangers/runabouts with fluid in their gearboxes and axles that are years and decades old and much mileage and they continue to function, I've seen or know of a few. And they have engine oil and filters that have missed quite a few service intervals so you don't need to worry too much about the engines either.

Brakes, steering, (tyres), suspension, lights and windows are the important items - engines, (carbs), and gearboxes (and axles) aren't, more niceties, vanity items perhaps. :)
Nigel Atkins

It's a quote, R E :o)
paulh4

Engines are different - lots of sliding contact in there.
Paul Hollingworth

Yeah, but, no but, engines are proven to carry on without faffing about of changing the oil and filter that often. So why also worry about a good oil. Some know all the oils are all the same with just corporate marketing offering brands and different prices just to squeeze more money out of the poor consumer.

If you've got an old engine and vehicle why bother, even if you're doing high mileage, let alone the miniscule bimbling most classics get. It makes the repetitive oil changing just that repetitive, an unnecessary routine, a learnt, trained or compulsive habit.








I don't follow the above but do think sometimes it is relevant.
Nigel Atkins

Nigel - I think you are taking the p*ss.
I would never advocate not changing engine oil and filter at regular intervals. I do mine every couple of years and that means about 4000 miles these days. I would always recommend a recognised brand of 20W50 oil with an API rating not above J, so it contains ZDDP
Paul Hollingworth

Paul,
I didn't say you were advocating such, and yes I was being provocative but it is a point of view, not one I follow or endorse, indeed I'm known as a disciple of the Driver's Handbook.

You're being a bit restrictive with your recommendations you can go passed a J and still get enough (whatever that is) ZDDPs in the can and/or other protectants.

You may prefer to be conservative I prefer to be a bit more adventurous and modern, neither of us need be wrong and both could be correct at the same time. Room for all.

IF R E Merrall wanted to stay with the more purist type of oils then he may not have wanted the current GTX but in case he wanted to widen the choice to more modern types or alternatives I threw an idea in (repeated from a suggestion by someone else).

A mate of mine doesn't even use 20w50 - but let's not go there. :)

Nigel Atkins

This thread was discussed between 27/01/2020 and 31/01/2020

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