The rubber donut is how the output shaft of the transmission, mates to the drive shaft that goes into the final drive for you non-Uralisti. It's part number 2 in the diagram below, you can see why its called the donut right?
I would be replacing the assembly labeled as 13 in the picture above. This would give Fiona a drive shaft with coarse splines vice the old fine ones which are reputed to strip out easily.
Parts 4-6 came assembled. Part 7 gets mounted onto part 1, forward (closer to the gearbox) of the splines. Part number 8, which helps keep part 1 in place when mounted onto part 8, was positioned in the middle position.
On the final drive side, I had to replace the final drive bearing nut (came with new seal) since the updated drive shaft is of a different size. Assembly #16 below:
Disassembly was pretty straightforward, thanks to this video put out by Gobium of SovietSteeds, aka Van Le. LINK. You have to remember the final drive bearing nut is reverse threaded in order to remove it.
The old shaft assembly used the castle nut/cotter pin method to secure
the wedge bolt, which secures the shaft to the final drive gear.
The end of the old wedge bolt was flush with the assembly.
A view of the fine splined shaft's connection to the yoke
that goes into the donut.
View of the new drive shaft's coarse splines, tougher hopefully
than the fine splines.
Fiona's FD came with three shims as shown above.
I reused these with the new drive shaft.
I made a note to make sure I put the side of the new wedge bolt
with the tapered cut facing the FD.
Once you've got the new u-joint and bearing nut in place and tightened, you insert the wedge bolt with tapered side facing the FD gear and tap it into place You insert it so that the threaded end finishes opposite the raised end shown in the above picture.
The new u-joint assembly mated onto the final drive and secured by the new
bearing nut, note how I made sure the end of the wedge bolt is flush or damn near.
The new drive shaft assembly uses a Nyloc nut to hold the
wedge bolt in place.
I'll be cleaning up the old drive shaft assembly and parts and keep it as a "get me home" spare. Now all I need is the repaired gearbox (its awaiting delivery of better rear bearing for input shaft) and I'll be ready to put Fiona back together and on the road once again.