Axle Fail leads to Brake drum bearing replacement Issue

i think it has little to do with torque figure spindles are tightened to or thread form just a design floor on the cush hubs

The cush drive rear hub puts more leverage on the axle thread where it joins the half spindle ( as the sprocket is no longer fixed to the main hub ) any sign of bearing wear will increase the load on the axle thread

if you are using the stock axle set up check your bearings and cush rubber fit and replace if in doubt they will run for many years without issue if maintained well

AS for Mr leadbeaters comment on thread form shear strength he forgot to mention that the cycle thread spindles that never break THE SPROCKET WAS ALSO BOLTED TO THE HUB and early hubs never suffered this issue
all the drive went through the three sprocket bolts to the hub and not to the axle joint when bearing became worn with use

it is not uncommon to see the cush hub with a loose bearing fit on the drive side as a result of the added leverage so make sure your bearings are also a good fit in the hub shell

Fitting a 1 piece axle as madass is a good idea as it removes the unsupported joint in the spindle where they are prone to fracture

CanukNortonNut said:

I have never experienced a broken rear axle. I weigh 170 lbs without riding gear/helmet. I use no torque wrench... only a 12" long ring spanner. I put my left foot on the rear brake pedal straddled over the bike while I torque(tighten) up the spindle. I keep an eye that the chain adjuster on the right hand side gap to stay close with the nut contact point. I apply maybe 50-60 # or when my brain say click. My eyes aren't bleeding from wrenching to torque and its with one arm. I don't try to kill it. So far the spindle has never come loose or broke.
Cheers,
Thomas
CNN

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I do exactly the same, though my spanner is a bit longer than 12". I snapped the axle doing that many years ago, so I've dialed my brain click down a notch and have not had a problem since. But I'm very aware of it whenever I adjust the chain.

So would anyone like to give the correct torque figure for the cush drive axle?

toppy said:

So would anyone like to give the correct torque figure for the cush drive axle?

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MKIII manual says 80lb/ft.
IMHO that's seems like a lot. I torque to 55. Dummie side first.

NASA fastening handbook lists normal torque range for a 9/16-18 bolt in 120,000 psi steel, with dry threads, steel on steel, no plating, at 73 ft-lbs to 109 ft-lbs (50% to 75% of yield strength), so 80 ft-lbs seems quite reasonable. Still, a one piece axle is a stronger design, and I'm among those who prefer it. I have a stock two piece axle on the MK3 I recently finished, but plan to replace it soon with a one piece. I'm influenced a lot by the fact that I had two of the two piece axles break a few decades ago. Not a fun experience.

Ken

Update;

Installed one-piece axle from Madass; very pleased. A very good fix.

BC

Fast Eddie said:

What causes it guys? Stress / flex? Over tightening? Raw untamed Commando horsepower :wink:

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IMO, the answer is flexing. The flex is concentrated at the last thread that emerges from the female hub. Threads inside the hub are captive and cannot flex.

The spindle moves up and down microscopically and over time the metal crystallizes exactly as GrandPaul notes above. The process is exactly like flexing the lid of a metal sardine can .... back and forth until it breaks off.

Slick

Edit: I should have said the proper term for the failure is metal fatigue, rather than crystallization, but as that is the appearance, I let GrandPaul's description stand.

Madass's one piece axle eliminates the flex concentration in the thread root. Any load flexing that may occur in the spindle is spread over the entire spindle with no point of concentration.

So if the std steel torque value is 80, what does that imply for the madass SS one-piece axle?
I've been using the CNN Thomas method to torque the dummy axle, and then walk around to do up the right side in the normal manner.
If the threads are placed to the right side to permit easy withdrawal of the wheel, do we still need to stand on the brake while tightening? My arms aren't that long.