Does anyone know exactly what the grease nipple on the rear wheel lubricates and how often is it recommended to lubricate.
Nothing that I can find in any manuals

I'm a little confused.  I never saw a grease nipple on a motorcycle wheel.  Perhaps a pic is in order. Maybe it's a modification to pack the bearing cavity with waterproof grease in the case of beach racing ect?

Only time I ever saw a grease nipple near a wheel was on the Speedo drive on old British bikes.

Lubes the "free floating" rear brake backing plate bushing some models have. (250/360/400 twin shock models mostly) 

There is a danger of getting grease into the brakes so I've never used the fitting.  Easy enough to lube during rear wheel removal.  

Guess it fits into the threaded hole by the spindle boss?  Well I never.  Everyday is a school day!



 

You certainly never stop learning when it comes to Yamaha parts lists!

Pretty much every year RD from 1973-1975 had a different rear brake plate. And, if we're talking about grease nipples, on the 1976 onwards RD400 there was a grease nipple threaded into the crankcase cover above the gear change shaft, but on the RD250 (on which the cover was otherwise identical) there wasn't! Great one for the parts list anoraks, that!

Back in the "60's YG1T Landscouts had them on the brake cam shaft hole.
So you can imagine Mr Farmer & his big grease gun.
Was a nightmare but a good idea if ya didn't get carried away.
www.cmsnl.com/yamaha-yg1t-trailmaster-80.../partslist/D-03.html #23
XT550 had them too on the sprocket carrier. #33
www.cmsnl.com/yamaha-xt500-1976-dual-pur.../partslist/E-05.html

Exactly Mark!