[Healeys] Overdrive problem

[Neil Blackshire]

Hi Listers,

I just got back from 2000 mile round trip in my 1960 3000, after about 1000
miles sometimes the overdrive would not stay engaged up hill, as journey
continued it gradually got worse until it would disengage straight away. I
was reading about possible causes and solutions and in the workshop manual
it says not to use extreme pressure oil,  I have been adding 75w80 extreme
pressure oil to the gearbox since I have owned the car, 3 years (several
litres) and before leaving on the journey I used 80w90 by mistake. I know
that there are different views on which oil to use, but I thought to try
draining oil and replacing with 20w50 engine oil but manual says removing
filter drain plug  leaves about < pint in the overdrive. Could this small
amount of oil still be a problem? Or am I just wasting my time anyway as the
problem is more likely to be the clutches or an oil pressure problem.

Any comments please.