I went through this last year, while fitting a Laycock overdrive to my
non-overdrive S IV, and to a Bristol. It turns out that the gearbox
likes hypoid (gear) oil, while the overdrive likes ATF. If you have a
car in which the oil is separate for the gearbox and the overdrive, then
you use these two lubricants. If, on the other hand, you have a set-up
like that in the Alpine, where a common fluid services both gearbox and
overdrive, then a compromise must be reached. The manufacturers,
certainly in the fifties and the early sixties, decided that
non-detergent single weight engine oil was the best compromise, and made
that recommendation. I have stuck to that recommendation over the years,
and have never had on overdrive problem.
Laycock is no longer in business. Their repair and overhaul business was
taken over by a company called Overdrive Repair Services in Sheffield,
UK, which I think is owned by former employees. They have a web site
(ORS) and an e-mail address, neither of whose URLs I can lay my hands on
right now, but I have found them to be difficult to communicate with.
For what it's worth
John Slade
Manotick, ON
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