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Re: Transmissions

Subject: Re: Transmissions
From: "A. B. Bonds" <>
Date: 27 Jul 1995 10:25:24 -0500
In <>, Graham McCann wrote:

>80W/90 gear oil is in fact thinner (less viscous) than 20W/50 engine oils.
>Don't be fooled by the numbers, gear oils follow a different index.  If you
>don't believe me I will send you the Castrol bulletins on the subject.  Also
>the MGB GT V8, with the same gearbox, was specified to use 80W/90 gear oil
>in the gearbox by the factory (and that in 1973)>

OK, guys, a gentlemanly challenge from Oz.  Fact:  All standard
(factory) reference manuals state unambiguously that the recommended
lube for an MG tranny (TD, TF, A, B) is 30 weight motor oil.  Fact:  At one
point (perhaps in 1973) the factory issued a bulletin saying it was OK
to use 90 weight.  This was rescinded less than six months later with
no explanation.  Experience:  I have driven two cars in which the DPO
had put 90 weight (smell the sulfur) gear lube in the trannies.
Shifting was sluggish at best and the synchros worked poorly, if at
all.  Experience:  I ended up rebuilding both trannies, in which a
good deal of bearing damage (especially on the layshaft) was found.
Cause?  Effect?  I don't know.  Both the locals in our club and
discussants on the net have debated the general issue at length with
the general conclusion that 90 weight in a tranny is baaaaad, and that
either 30 weight or multigrade (e.g. Castrol) works well.

Further the deponent saith not.

Tell you what, Graham, you run 90 weight in your tranny for a year and
tell us what happens.  That should resolve the dispute.

        Regards,        A. B. "Not in my tranny!"  Bonds

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