[TR] OD lubrication

[Randall]

> Is there anything intrinsically wrong in using an 80W/90 gear oil as
> recommended by the factory?

See, for example, service bulletin VANGUARD/4/E dated October 1954 which
notes a change in factory policy to NOT approve use of "Hypoid" oil in
overdrive gearboxes.  

Also Standard-Triumph publication part number 502274, Service Instruction
Manual for the Laycock-de-Normanville Overdrive Unit with Electrical
Control, which warns:
" Under no circumstances should extreme pressure gear oils be used, ..."

> What are the
> benefits (proven or otherwise) of using a lighter weight oil?

The 20W50 motor oil we've been discussing is actually somewhat more viscous
than 90 weight gear oil at operating temperatures.  The reason for the
apparent disparity is that the "grades" for gear oil and motor oil are based
on different temperatures and viscosities.  Believe it or not, this was done
to make things less confusing <G>

So it's not a matter of the oil being thinner at normal operating
temperature.  However, the 20W50 is thinner when starting out in cold
weather, and IMO that is a Good Thing.

> Am I
> reading here that users prefer the violent to the more gentle?

A matter of opinion.  On the TR3, I do prefer the hard shifting A-type OD.
Seems totally appropriate to the concept of a 50s "sports car" where the
emphasis should be on performance and responsiveness.

And many racer types like to upgrade their later A-types (with the softer
shifts) with the earlier components to get the hard shift.

> If so, then
> the 'thumper' on engaging
> is putting a strain on the engine as it somehow has to suddenly lose some
> 500-750rpm

Actually, if you engage the OD at full throttle (as God and Laycock
intended), the reduction in engine rpm is not all that sudden.  Instead, the
car speeds up for at least part of the difference.

And if you are looking for a gentle engagement suitable for cruising the
boulevard, there is always the clutch pedal.

> Maybe I've been plain lucky because all my overdrives have been of the
> 'slur' type

Which has me wondering if they have also been J-type overdrives.  Very
different, as the J-type does not have a pressure accumulator and so cannot
produce the instant shifts of the A-type.

Randall