Ashford :
First, it's not such a large difference in viscosity. Gear oil is measured
differently than motor oil, with the result that 90 weight gear oil is
roughly the same viscosity as 40 weight motor oil. Motor oil viscosity is
measured at 100C, gear oil at either 0C or 20C (I forget which). The
numbers are also arbitrary, and don't follow any systematic scale.
Second, the motor oil recommendation came from Laycock deNormanville, the
makers of the OD. AFAIK, they never changed their recommendation, even
going so far as to specifically forbid 'hypoid' gear oils in their service
literature. (The TR2/3 factory service manual contains the same warning,
but gives a different explanation.)
Triumph initially followed Laycock's advice, the original TR2/3 information
was to use motor oil in the gearbox. Sometime around 1960 or 1962, they
changed their recommendation to gear oil, in an attempt to solve some early
gearbox failures they were seeing. Supposedly, there was a service bulletin
outlining the change, which coincided with some changes to the OD itself
that supposedly allowed the use of gear oil. (No, I don't have a copy of the
bulletin, although I have hopes of being allowed to sniff one someday <g>)
Dunno about "most people these days" ... I use 20W50 racing oil in my A-type
box. Works good, as long as I replace what's used to "mark it's spot" <g>
Randall
59 TR3A daily driver - with an early, "iron ring" OD
R. Ashford Little II wrote :
>
> Much confusion in my head about this. Apparently the original
> A-type manual
> recommends using 30wt engine oil whereas most people these days
> seem to use
> the more typical 80-90 wt gear oil. This seems like a large difference in
> viscosity so I was hoping that some of you can add your opinion to further
> confuse me.
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