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MG MGB Technical - gearbox oil

how often do you/should you change the gearbox oil and what oil do you use for this. is there a special gear oil or do you use straight 20/40 engine oil?

thanks
mal

Book recomends 20W50 Castrol.

Safety Fast
Dwight
dwight McCullough

The same as for your engine i.e. whatever grade is correct for your climatic conditions. 20W/50 is becoming less available these days, being replaced by 15W/50 from some sources, 15W/40 from others. 15W/40 is noticeably thinner and can leak where the /50 grades don't, they can also give lower hot oil pressures. Replace at 24,000 miles, according to the book, and clean the OD filters at the same time. OD and gearbox share the same oil, you can't get it all out, so fill according to the level marks not the original volume quoted, which is 5 1/3rd Imperial pints (3.35 litres). Drive the car, use OD, then recheck the level and top up if required.
Paul Hunt

Yes, 20W/50 in the UK but not above API SG grade, as SH, SJ and SL can contain friction modifiers which may affect the operation of synchro cones and O/D friction bands. This is well known in motorcycle wet plate clutches. Good quality SE or SF will be fine and were the grades around during production. Rich.
Rich

Absolutely correct i.e if you can find 20/50 at £2.99 for 5 litres then that's the one to go for.
Iain MacKintosh

If you shop around you can still get Duckhams 20/50 Classic, our local auto shop sells it at £7.99 a gallon.
Ron
R. Algie

On my ´64 MGB I have always used 20W/50, but on my ´61 midget I use synthetic Castrol RS 10W/60, and it works beautifully! I had expected synchro problems, but there has not ben any.

The weak point (well, one of them...) in these early gearboxes is of course the layshaft bearings, and I believe the 10W/60 gives them better protection. I will try it in the MGB too this summer. I do not have overdrive on my car - guess the synthetic oil will be more questionable on an OD gearbox.

Tore
Tore

I had full synthetic in my o/d gearbox for several years . Castrol technical department advised it would be OK , and so it proved . I have 20/50 in it now just because it seemed a waste when topping up . I'm not sure that gearbox oil is lifed , although changing it when you do the filters seems reasonable .
When one of the bellows split on my steering rack last year the oil was changed for the first time since leaving Abingdon in Dec 1966, oils in these applications do not have to cope with combustion by-products which eventually stop engine oils working.
S Best

As I understand it, the reason for engine oil in the trans is to protect the brass synchro parts from the corrosive effects of sulpher in gl 5 extreme pressure gear oils.

In my late overdrive I used a pint of 80-90 wt gl 4 (no sulpher) and the rest dexron III auto trans oil.
Tranny shifted perfect, ran quiet and overdrive clicked back and forth like brand new. I figure oil made for gears is better for a trans than engine oil.

A gear box doesn't need detergents, or high heat capabilities. It does need resistance to shearing and hi film strength, something that cheap, no detergent engine oils are not famed for.

I haven't read any reports of transmissions failing from lube problems, except putting 90 wt in an overdrive.

My guess is that the tranny's are quite lube tolerant.

Barry
Barry Parkinson

Barry - the V8 (basically the same box) took a thicker oil - nice g'change - pity the casing wasn't stronger

Roger

Oh..and the o'drive is limited to 4th gear.
RMW

Hi Folks:

If you have a "D" type and "LH" overdrive, it is recommended that you use 30W(non-detergent) oil, otherwise knows as compressor oil. The reason is that the detergents when pressurized to approx 400 psi will foam. The foam, and resulting air bubbles will cause the cone clutch to chatter, thus accelerating wear. Gear oil has sulfer for lubrication and will damage the brass/bronze components.

Good luck: Rich Boris 67B
Rich Boris

Recommended by whom? Abingdon always recommended the same grade of oil as used in the engine e.g. 20W/50 for the roadster and gear oil for the V8.
Paul Hunt

Hi:

Recommendation is based on past hydraulic experience with aerospace hydraulic systems, and technical interface with Quantum Mechanics; in which I consider the east coast expert regarding overhaul, rebuilding and servicing of LBC overdrive systems.

Rich Boris, 67 B
Rich Boris

Could be an issue I suppose though I've noticed no problems using 20W/50 SG in mine. A lower detergent oil, SE, was in use in 67 and an even lesser grade would have been around when the O/D was first fitted.

Minis had a problem with foaming oil I seem to recall and Duckhams made their name curing it.

You can get 20W/50 SE from Wilkos for £2.74 4.5L with a picture of an MGB on it :-)

Rich
Rich

This thread was discussed between 18/04/2005 and 22/04/2005

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