Rear Sprocket info needed

[SoCal250]

also remember.. the large axle nut is on the opposite side from 350 to 400. so it -may- have a 350 swing arm in it as well.

The swing arm, where ever it came from was lengthened 3" so I didnt want that. I found a nice one on Ebay.  . 

If you purchased a replacement swingarm did you get one for a 400 or a 350? As Mark pointed out, the axle slots are different between the two to accommodate the different wheel collar diameters. If you have a RD350 wheel, which it seems you do, you'll need an arm designed for the 350. (or you'll need to fab up some custom collars to make it work with a 400 arm).
RD350: wider L axle slot
RD400: wider R axle slot (and the arm is about 1" longer than the 350)

Post up some photos of what your working with.

[Joe6v6]

RD350: wider L axle slot
RD400: wider R axle slot (and the arm is about 1" longer than the 350)

Thanks for the info - The right slot is wider on the new swing arm, so it will be a 400 arm with a 350 wheel. I can fab what ever is needed to make it work but any information on what to do is appreciated. The new swing arm is 17-3/4" from the center of the pivot to the back of the axel slot.    .     

[manicmecanic]

I'm an old survivor of those years.
Owned every ac model from R5 to the last RD 400 except DS7 and your US model 400 Daytona.
Every RD with what you call coffin tank has had disc brakes in the rear end.I sold a few of these hubs to the USA quite some years ago because Yamaha never sold spoke wheel models in the USA.
When new Yamaha sold them in the old world with both wheels.Cast ones had a higher price but as they were the modern way many buyers chose them instead of spoke wheels

[stresa]

@manicmechanic
Richard,
not quite right. In Germany the 1976 RD400C came with cast wheels as standard. The spoke wheels were a higher priced option. On the other hand the RD250C came with spoke wheels as standard and cast wheels were a higher priced option. God knows why it was that way as it was.
From 1977 on all RD's had cast wheels as standard.
In the UK the 1976 RD250C model came with spoke wheels as standard but a drum rear brake instead of the disk.
The RD250 from 1976 on was never sold in the USA
Regards Uwe