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Gearbox Oil Again

Started by 2023, November 01, 2022, 04:11:23 PM

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I feel like I know you after watching so many of your videos (which are a god-send!).  I'm reaching out with a potential minor question, that has major implications. I recently acquired a 1978 rubber bumper MGB that has sat for over 7 years. After working through a lot of different things, I now have it running smoothly. I am building up to a road test, but know that the gearbox oil is low. I've been looking all over online and went through my whole Owner's Workshop Manual & Driver's Handbook, but can't find any reference to the grade of oil to use in the gearbox. The only reference I can find is in the lubrication section of the Driver's Handbook,

"Use the same oil selected for the engine" which I had selected a conventional Castrol 20w50. Having worked mostly on vintage motorcycles, I have limited car maintenance knowledge (hence my dependence on your videos!).

All my more knowledgeable friends (although not with MGB's) say that can't be right. They say that gear oil is much thicker than 20w50. 
I'm sorry for such a trivial inquiry... and I know you're never supposed to ask the "what kind of oil" question, but I didn't want to just trust my gut & use the Castrol to only find out I'm wrong on the road.
    Be well,


The factory required oil for the gearbox is 20W/50.  John Esposito of Quantum Mechanics, who rebuilds a great number of gearboxes, suggests straight 30 non-detergent.  There is no need to use high zinc oil in this application.  Drain out the old oil and refill the engine, gearbox, differential to ensure fresh and correct oil.  Differential takes GL4 or GL5 80/90 gear oil. 
    Glad the videos have helped.  Hope this helps, too.
    John H Twist
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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