Lots of posts suggest clutch slip comes from poor seal at front of gearbox or overfilling of gearbox. Could it come from overfilling of sump? I run 2/3 pint in my gearbox and I get occasional slip. I keep my engine oil level at the bottom of the stick in case this is the cause but if engine oil level is irrelevant I'd rather too it up a bit, especially as it will receive a vigorous workout this weekend at brooklands. Can anyone advise? Also hoping to avoid clutch slip on the test hill but I assume that if it's coming from the gearbox it should be worse going down rather than up hill!

Location: UK herts

Hi John,
Usually there is oil coming out of the bottom of the crankcase from a small vent hole under the flywheel housing, or the brass cover on the bottom of the (in my case three speed) gearbox. What colour is the oil?, if engine oil it's usually blackish, of if very clean it's coming from the gearbox. In theory the black engine oil seeping through the rear crank seal should only run down the back of the flywheel exiting through the vent hole and not get on the clutch linings - but it does, somehow. Or it did on my chummy causing smoke smell and slipping. If engine oil the choice is, engine out job, or the time honoured bodge of chucking into the clutch a handful of Fullers Earth, remember that one?
Peter.

Location: Truro(ish)