...To my gearbox halfshaft leak
First off, the engine/gearbox driveline angle makes a difference. As you know I am about 5° nose down. Not only does this mess up the oil levels in the gearbox, it also upsets the measurement of engine oil by the dipstick - I've been habitually overfilling the engine with oil (dipstick at the back) and its been leaking in all sorts of unwanted places
Not filling the engine oil above halfway between max and min has helped, but that still leaves the gearbox problem. The main symptoms have been poor gear selection, especially of the lower gears and reverse, probably because the selector rods are not getting enough lubrication, and a persistent weep of oil from the offside halfshaft. Just the offside.
I believe I have now found the reason for this - I've been rummaging through the spare parts recovered from 'er ladyships gearbox and in one of the boxes was a complete offside halfshaft and bearing carrier assembly which Alex had sourced to replace the broken casting on my old 'box. I could tell it was the offside carrier because it has a cut-out for the speedometer pinion. On the halfshaft I can clearly see the speedo gear teeth and
the oil thrower ring, which is essentially just a fine helical thread around the outside of a pressed on bush.
And today's startling revelation is... the oil thrower has a right-hand thread
...Which means that with the shaft rotating clockwise in normal forward motion, the thrower is actually winding oil out
of the halfshaft, not pushing it back in.
I can only conclude that Alfa used the same thread on both halfshafts, so the nearside halfshaft winds the oil back in, while the offside winds it out.
And the reason why it is leaking at all is because of the driveline angle.