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MG MGB Technical - Rear Axle Maintenance

I'm getting our 1974 MGB/GT ready for an extended drive in September, and my records show I changed the the hypoid gear oil on the rear axle some 10 years ago. At the time I used Castrol S.A.E. 90 EP, and while I have no real problems with the axle now I have concern that with the limited use on this car (say 3k/yr) should I change the gear oil to perhaps avoid acid damage on the bearing races, etc in the future?

I'd also like to know what adjustments some of the other drivers on this BBS are making for years rather than miles? Have any of you switched to a newer synthetic's for this particular application?

Regards,

Larry C. '74 B/GT & '69 midget
Larry C '69 Midget

I, too, have a 74 BGT. I use the synthetic stuff and have for years in all my cars. No trouble, but can't say it helps either.
I have 70 BGT with v6 and auto trans and raced with the MG axle and the synthetic with now problems.

Steve
Steve

That's the beauty of the hypoid gear and modern lubricants, they're basically maintenance free except to check for leaks and fluid level. If it's full then other than making sure the breather is un-obstruced there's nothing else to do.
Bill Young

Make sure it is *differential* oil, and not *gear* oil. There is a difference and it matters. I can imagine acid damage in an engine, but not really in a gearbox or axle. The loss of shear resistance in axle and gear oil with a lot of use is probably more of an issue than the passage of time with little use. In engines both are important, which is why manufacturers quote mileage as well as time. They are working on the assumption that if you do low mileage over a year then it is likely to be made up of very short distances per trip, where the engine doesn't get fully hot, and you get contaminants including acid and moisture building up. In a car that does little mileage, but when it *does* go out does 40 miles or more, you can forget the time limits. For an MGB it should be 6k or 6 months. I changed mine at 3k intervals on the V8 even when I was doing 150 miles per weekday, but currently change both cars annually when they are doing about 3k per year.
Paul Hunt

Paul,

Engine oil on our M.G.'s are changed annually for the Midget, and twice a year for the B/GT because it sees the most use. Both have been on Castrol 20/50 from new.

Castrol now sell a product called Hypoy-C (blend) that they call 'gear oil', but list for differentials. Easy to become confused with all this. I most likely leave the old Castrol 90-EP in place, and top up if needed.

Regards,

Larry C.
Larry C.

I changed my diff oil last year, it had been in there since 96. I was surprised by how dirty it was, as noted above you would expect it to have an infinite life in this application. Having said that I have no reason to believe it was not stil doing the job but I think I will change every 5 years now. The little plastic hat was still over the breather so the dirt did not get in there.
Stan Best

Stan,

You talked me into it, changed the differential oil this morning, and it was very dark in colour. Vent was replaced many years ago, and still in good shape. Not a big deal to change, I was already under the car for a general check, adjust brakes and lube chassis.

I would agree, perhaps a five year interval for this item may be in order for me as well.

Regards,

Larry C. '74 B/GT
Larry C '69 Midget

This thread was discussed between 21/08/2008 and 23/08/2008

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