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.

[Gregory Guineapig]

Ruairidh Dunford wrote: "I use the engine dipstick for a three speed box  ...."

To the same mark as for the engine oil?

PS. Couldn't get the 'Quote' function to work, for some reason

[Steve Jones]

Yes. Same mark as engine. Just make sure the dip stick goes to the bottom of the gearbox. Just changed gearbox oil in one of my cars this afternoon.

Steve

[Gregory Guineapig]

Thanks

[Dave Mann]

Here's a picture of the 4 speed box and filling to the bottom of the filler plug threads is getting close to over flow into the clutch.     . It wasn't Austins who recommended filling to the bottom of the filler plug threads.

[Tony Griffiths]

Here's a picture of the 4 speed box and filling to the bottom of the filler plug threads is getting close to over flow into the clutch.. It wasn't Austins who recommended filling to the bottom of the filler plug threads.

Here's a picture of the 4 speed box and filling to the bottom of the filler plug threads is getting close to over flow into the clutch.. It wasn't Austins who recommended filling to the bottom of the filler plug threads.

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David states in regard to the 4-speed schromesh gearbox: "½ pint - at this level I needed the top on the box to prevent oil being thrown all over my bench". As a similar example, many machine tool gearboxes with spur gears need only the lowest gear to be half-submerged for the oil to be flung around the whole of the inside. Hence, from the above discussion, is the conclusion that, as a precautionary measure, a 4-speed synchro box might be best with 3/4 pint i.e. enough to lubricate the box yet not so much as to prevent clutch slip?