What oil for the V8 gearbox?

David Halliday enquired "what oil is everyone using in the gearbox of their Factory V8? The manual recommends EP90 in the MGBGTV8 as opposed to the 20w/50 engine oil in 4 cylinder cars and MGCs. My overdrive is being replaced because of an issue with the overdrive clutch. Speaking to Overdrive Spares in Rugby and Overdrive Repair Services in Sheffield, they both recommend using 20w/50 engine oil in an MGBGTV8 gearbox! The suggestion is that the use of EP90 could be what caused my overdrive to give trouble. The late Geoff Allen, the V8 expert, always used EP90 in V8 gearboxes.
I would be very interested to hear what others think. The suggestion from the overdrive specialists is that the EP90 can damage the clutch in the overdrive.
Of course whatever oil you use, you need to steer well away from anything with friction modifiers in it.

Peter Beadle responded saying "the BGTV8 overdrive had an uprated relief valve 37H8070 to cope with the EP90 oil (see AKM0039 parts book, page 108-C48.02 item 28).

Bob Owen added " I have always used EP80 or EP90 as recommended originally. As far as I can see nothing has changed to alter the original recommendation. The higher gear loads of the V8 are what presumably caused the change from standard 20/50 engine oil. Note that it should be gear oil not differential/axle oil as the additives are different". EP90 is for temperatures over -10C and EP80 for below -10C which are rarely experienced in the UK.

See a copy of AKM0039 parts book page 108-C48.02 item28 and a copy of the recommended lubricants table in the MGBGTV8 Driver's Handbook, AKD8423. More
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