09-09-2020, 08:48 PM
(This post was last modified: 10-09-2020, 12:09 AM by Bob Culver.)
Choice of gearbox oil was determined largely by consideration of noise and leaks. A thin oil assists synchro but may slow crash changes. Until recent times an engine oil, including multigrades, was the common recommendation for very many cars. Unless perhaps of the classic type, such oils contain anti wear additives not present in the early 30s. The "crossover" temp where 20W50 is thinner than 30 is way below everyday temps. Moderns with enormous power have gearboxes sized much as the Seven so Seven lube is not critical.