Is there supposed to be a washer under the rear wheel axle nut, or just the nut and cotter pin? thanks
There should be a washer. Part T-2506
No, there was not a washer under the nut from the factory - just the nut and a cotter pin. Part # 2506 is the fibre washer that goes in between the axle ends inside the differential.
No washer originally, but it is okay to add one if it helps align your cotter pin to castle nut hole.
If you have to use a washer behind the nut to align the cotter pin holes, I would be concerned that the hub or axle taper is worn excessively causing the axle nut to go on too far.
Steve, I think what Adam is suggesting is using it as a shim to cause the nut to stop in a different location where the pin can go in without having to tighten excessively or loosen the nut a bit. As you pointed out, if the nut goes on too far then Sammy's got troubles