Correct amount of oil for seven gearbox

[Chris KC]

I've only ever used 4 speed boxes in my cars. I fill to the base of the filler plug hole, never had an oily clutch (not oily enough to cause clutch slip, anyhow).

[Colin Morgan]

Just my experience, but when I put my Ruby back on the road twenty years ago I soon suffered clutch slip (usually in top when it is transmitting the most torque, of course).  On taking the box out, found that the Borg & Beck clutch plate was black and shiny (glassy) with oil.  Changed it for a good used one.  Within a few thousand miles had clutch slip again.  Burned the oil off using friction by propping the car against a kerb.  But the slipping returned after a while.  Then I heard about dropping the oil level in the box so syringed about half an inch out - not had clutch slip since.  

Colin

[Bob Culver]

As all this is being raised over again, over the decades my RP was always maintained to the book and filled to bottom of threads. Used in a city with very steep decents it always gave trouble with oil on the clutch until a modern seal fitted. (The best single improvement ever!)
Curiously the 1957 Austin Motor Company publication Austin Cars 97H843C pitched mainly at the late Ruby advises 1.5 pints...
On most gearboxes there is no load on the mainshft gears when these move relative to the shaft, but the Seven is different. This may have prompted a high recommended level. Racing, with alternating loads, may not be as onerous as never ending uphill grinds in standard cars. Those many using non original plain 1st/3rd shaft bush report no problems despite running low oil. Based on experience with other makes these components are first to show trouble if oil circulation dubious.