Trivia question -

Jon March

Member
I spent yesterday assembling the axle/swingarm/pinchbolt assemblies.

Question: Why are the threaded ends of the rear axles..
.....and just the innermost washers,
FLAT on one (1) side?

...causing the swing arm to turn the axle nice and smoothly in the middle of the washers...UNTIL the flat spot on the axle hits the flat spot on the (rather loose-fitting) innermost washer..
.....at which time there is a small "thump" as the axle is forced to contact the washer, and then forces the innermost washer (which does not move at all under minor "swing").... to suddenly turn with the shaft as the swing arm travels further (rubbing the flatsided washer between the brass end-bushing and the 2 Belvedere spring washers.)

A person might say, "well, you must be moving the swing arm too much when youre testing it"
Nope - it only takes about 1.5" of upward or downward movement of the swing arm for the flat spot on the axle to hit the flat spot and force the inner washer to move. The springs swing a good bit more than that up & down. Even tho all greased, this causes a metal to metal "thump" that can be felt and heard in the assembly.

Thoughts?
After calling a few places, including GI - all shrugged.

I have a theory - but want to know your thoughts first....





Screen shot 2017-07-22 at 6.35.30 PM.png
 

Ken Chambers

Platinum Subscriber
The flat on the inner thread of the solid axle keeps the washer stack-up rotating together with the axle. It's possible there's enough friction of the thrust washer against the inner brass bushing that the axle rotates slightly within the flat before the washers move. Make sure that surface is lubed properly and the cupped washers have enough preload.

The two cupped washers are the preload against the pinched bolt when the swing arm is installed. With the preload set properly those washers should be tight against the inner shoulder of the solid axle. The maintenance manual says snug plus 1/3 additional turn on the large adjusting nuts. Lock those nuts very tight together after the preload is adjusted.

And a note about the pinch bolt. The pinch bolt should never, ever be hammered or driven in or out. Preload must be released on the cupped washers either by loosening the nuts on the solid axle or by using a special tool on the outside of the swing arm. The grease fitting is removed and a clamp tool is fitted over the swing axle while a bolt in the grease fitting pulls on the axle to release force on the pinch bolt. The pinch bolt can then lifted out by hand, or no more than a light tapping.
 

Jon March

Member
Thanks Ken - I definitely did a stress-free install of a brand new, correct pinch bolt and nut.

and washers are all lubed and properly oriented and tightened -
now, Re the single flat sided washer:
The hole in that washer was clearly enginerred to not be not a tight fit on the shaft. Meticulous as they were, the engineers would probably not allow that kind of play in a suspension mechanism accidentally. This design seems to allow for routine/hiway/small axle movement -without- contacting the flat spots.

But in cases of longer swingarm travel, the axle flatspot does indeed finally come into contact with the washer flat:
thereby forcing the washer to move either clockwise or counterclockwise on the brass bushing.

There seems to be deliberate loose-fit - and i have a theory as to why it might have been designed this way- allowing the thrust washer to only turn occasionally - any guess as to what im thinking,..?!
 
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