Originally Posted by
Alcanbrad
I am not familiar with your specific hub, but metal chipping like that is usually caused by high force impact such that can occur by shifting under power. We have damaged a Spinergy hub and several cassettes over the years by doing this. We have had to change our shifting behavior for these scenarios by shifting in advance of when we might normally and limiting to multiple single shifts rather than multiple. Again, just for the scenarios where we’re under a power stroke where the chain can skip when jumping gears.
I was going to comment about torque loads not being very high during shifts compared to the loads exerted with both riders are climbing a steep in the lowest gear. And that I couldn't believe that would be the circumstance explaining their failure. However, you may be onto something here. Given the nature of the failure, I wonder if perhaps this issue might involve shifting under loads, which are causing the cassette to flex sideways (as the chain is pulling on the cassette kinda sideways while crossing over cogs). I'm wondering if this may cause the faces of the ratchets to go off-parallel and causing failure at the outer radius of the ratchets. Because short of this, these chips don't make a whole lot of sense. How is force causing that without causing complete catastrophic ratchet failure? A freehub body flexing relative to the hub shell may explain ratchets chipping on the outside circumference.
I'd suggest you check your axle for wear around where the freehub body meets the hub shell and where the sleeve fits against the cartridge bearing in the hub. This may reveal axle flex issues. Plus, check your dropouts and the interface between them and the axle. If the dropouts aren't spaced properly, or, more importantly, they aren't nice and parallel, this will be putting the axle under flexing loads before even taking the first pedal stroke. I assume you're using a QR axle, because if it's a through axle, then my suggestion should absolutely be moot. Also, are you using a beefy QR and not some weight-weenie excuse of a quick release? Also, was the bike loaded with a lot of weight over the rear wheel and is this the first time you experienced this? Because adding a bunch of weight over the rear wheel will add additional loading to the rear axle. Add steep climbs to that and you may simply have been flexing the rear hub enough to prevent proper ratchet engagement.
I'm familiar with the DT Hugi hubs in that I went through three of them under high offroad pedalling loads, until switching to Phil Wood. (I didn't choose King way back then because he was using aluminum ring drives.) I've subsequently split my first Phil in half between the flanges and damaged the second hub's four double-pawls and engagement ring, so my wife and I are pretty hard on rear hubs. So given my experiences with rear hub failures, I'm really curious to find out the cause of your issue. I'll add that I've had a Union Hugi on my road tandem for 30 years without one single issue. And I haven't even serviced the hub EVER! (I know, how could I be so negligent?!!!) Additionally, after researching and discussing the issue here and in other forums, I've decided that my next rear mountain tandem hub will probably be a King now that his ring drives are stainless steel. The spline drive is the ideal solution to prevent ratchet slipping in my opinion.
Anyway, keep us abreast of what DT/Swiss say about your issue. And yes, order at least two sets so you always have a fresh spare on hand.
Good luck!