Broken Rear Hub

I was riding yesterday and my hub just snaped. All of my sproket bolts were good and snug. I run a o-ring chain, but had plenty of slack. I was riding down a straightaway when it broke, luckly, because it locked the rear wheel up and broke my sproket in half. I understand It must have been cracked before that, but just wondering if anyone else has had the same problem with there hub. I contacted Yamaha, and they said that they have had no problems with this in the past. I makes me wonder why they put the same hub on a 125 as they do on a 426.

If the sprocket is broken in half then I would at least partially suspect the sprocket. If it was already cracked or somehow weakened then I could see how that could easily put stress on the hub that it wasn't designed for and cause it to break.

If I remember correctly most broken hubs here have been from overly tight chains. Maybe someone else will have more conclusive info for you.


A poor casting on a hub can be seen by closely examining the break lines. If the lines are shiny and clean, your hub was good.

Any dull spots in the break indicate a bubble in the casting, hence a weak area.

Oh...and sometimes a hub will break on a landing, but not come apart until you're on the straight.

Perhaps you should tell us how you measure chain slack and align the rear wheel.


I bought a 74 yz250 brand new, Bake then it was the creame of the crop, Used it for Short Track and 1/2 mile

Befor ei converted it the rear hub shatter, (Magnizium) the bike was one month old Yamaho told me Tuff Egnog when I asked if they would replace. I even worked at a Yami Shop and the owner who raced TZ750;s for em could not sway.....

Thats a drag

Thanks Dave for your input. I looked my hub over and it has 2 spot that show signs of what you called a bubble. I use 3 finger to check my chain. I run it alittle lose because I run a O-ring chain. I have been racing for 10 years, so I am not new to motorcycles. I have just never seen a wheel come apart like this. And why do they use the same wheel on a yz125 as they do on a yz426? I do not understand the thought process behind this.


There are a few riders on this forum that have had hubs come apart due to bad castings.

There is always a tolerance in every manufacturing process that allow a given failure. Not your fault, but you may have a case if you could reach the right people inside Yamaha. Call 800-962-7926 if you wish to chat with them. Be diplomatic.

And don't get me started on the old school process of using one's anatomy for taking measurements in critical areas. These bikes are worthy of better and more accurate instrumentation.

Best of luck!


Thanks for you help Dave.

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