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Am I correct to assume that in my 1978 R80 that for the final drive and transmission that I need a gear oil with a SG designation on the bottle?
Thanks in advance
90 weight is hard to find but 80W90 GL5 rated is the acceptable substitute. Do not use 75 or 80W140 in the final drive. It is OK in the transmission though.
As recommended by Oak a long time back, I use a non-synthetic gear oil, typically Castrol or Valvolene GL5 80W-90 mixed (5% by volume) with Dow GearGuard M (which I've also seen under the name Molykote). GearGuard M was available from a local bearing distributor. The GearGuard M contains molybdenum. The molybdenum (or "moly" for short) coats metal parts and acts as a friction reducer.
I use it in all of my BMW bikes. On the Airhead bikes there is a noticeable increase in the shifting "smoothness". It is still necessary to be somewhat "deliberate" when shifting gears.
More info on Dow GearGuard M including the ability to search for local distributors can be found from the link below -
I have noticed on some other gear lube posts the advice to add molly to the gear lube. I buy a good bit of Scheaffer's synthetic oil for my diesel trucks and it has given me very good service with extended oil changes. I checked to see what they had for 80/90wt GL5 lube and they advertise the addition of moly to their lube. On the spec sheet they state that it meets or exceeds a multitude of specifications, one of which is GL5. Has anyone run this lube or have comments on it?