sapporoguy

Bike: 2005 Co-Motion Speedster
Rear hub: DT Swiss Hugi, disc brake--tandem version of 540--18-tooth star ratchet
Drivetrain: 50/39/24T X Shimano 12-36 cassette, Shimano XTR RD with Wolf Tooth
We rode well over 10,000 miles on this drivetrain with no problem, including a 3,800-mile SF-Virginia cross-country tour this summer with 180,000 feet of elevation gain/loss.
Then! 100 miles shy of Virginia after 2 hours of riding, suddenly the top of chain began slapping the chainstay.
Back home, I cleaned the hub, put in new star ratchets (the old ones were pretty worn) with DT Swiss special grease.
No more chain slap. For about 200 miles.
Then the chain slap came back.
Took the freehub apart, cleaned, regreased, put in all new bearings.
Chain still slaps.
Tried a different RD.
Chain still slaps.
Put on a Rolf Prima wheel with Rolf hub and same cassette.
No chain slap.
So it's clearly the DT Swiss hub. What might I be doing wrong?

79pmooney

How easily does the culprit hub's cassette spin when the wheel is off the bike? (Both right after service and when the slap returns.) If the cassette is not spinning freely, that means every time you coast, it is being spun forward and in effect, pushing the top portion of the chain. Result - chain goes slack or at least, closer to slack. I"m not a freehub whiz but without knowing anything about your hub I would suggest lighter grease or oil and making sure that the bearings are not being compressed as you assemble the freehub after service or with the QR when insert the wheel. (Check again to make sure the cassette spins freely in ready-to-ride mode.)

LV2TNDM

The cartridge bearings inside the freehub body would be my next thought. They sit on either end of the freehub body and allow it to freewheel when you aren't pedaling. That's the only other place where friction exists, or is supposed to. Also, be sure there isn't any issue with any dust seal between the hub shell and the body. If that were damaged or deformed, it would rub the hub shell during freewheeling and causing friction. Bearings don't last forever, and you've put a TON of miles on that rear hub! (Good job!) So I assume the bearings have finally reached their end.

That said, try contacting DT/Swiss directly and inquire about your issue. Should be easy to remedy, but will require appropriate replacement bearings and the appropriate bearing puller.

base2 

My vote, first off is an error in reassembly. The metal/rubber dust seal the freehub side end cap mated to is installed upside down. Metal side towards the bearing, rubber side towards the end cap. The rubber side has a slight recess for the end cap to nest into. Being around backwards, this could be where your extra friction is coming from.

But, what else it could be is the metal seal between the freehub body and the hub could be clogged with something. The shape of it makes it ideal for catching grime & keeping it from entering the ratchet rings. This is what it is supposed to do. A simple toothpick can dig the grime out & restore the "just right" gap between the freehub body & the hub shell.

I, myself did both on a Hugi 240 today until I got it right. I'm not sure where else friction could come from.

Andrew R Stewart 

No, this is not how the system works. The freehub body bearings are riding on the axle, which is stationary. So when coasting the bearings are not spinning and when pedaling the FH bearings are spinning. It's the ratchet (and/or a seal) that transmits the relative movement between the FH body and the hub shell and allows for coasting. Andy

sapporoguy

Thanks, everyone, for the thoughtful ideas, which I pondered.
Then, reading this from Andrew, and picturing the assembly the way it's supposed to look in my mind--and matching it up with how mine now looks--it suddenly dawned on me what the problem is.
Duh! It was staring at me.
I'll tell y'all if you promise not to make fun of me.

Iride01 

I promise... <grin>

Andrew R Stewart 

I might shake my head, but I won't laugh. Andy

EddyR

I looked up your bike and it is very nice and a big investment. Why not just replace the hub. Less than $100 seems justified on such a nice bike.
Ed

sapporoguy

Where are you seeing a DT Swiss 40-hole tandem rear hub for under $100?
Same Hugi hub as mine is $465 here, for example. (https://tandemseast.com/hubs-cassettes/)

LV2TNDM

Andy, thanks for the correction. So yes, it's most likely the interface between the freehub body and hub shell, usually separated by a dust seal. Or perhaps the cylindrical spacer on the axle that sits under the ratchets is missing?

$100 replacement hub? Not a DT/Swiss, as the OP pointed out.
And if there WERE a $100 DT/Swiss tandem hub (there isn't), replacing it isn't just a hundred bucks. It would be a rear wheel rebuild, which may entail new spokes (depending on the replacement, and if the wheel builder would even CONSIDER re-using the unlaced spokes - some will, most won't. Either way, it's a PIA as all pulling and "pushing" spokes must be identified and segregated and put back into their correct respective locations on the hub flanges), and possibly a new rim. Either way, "replacing a rear hub" is an extensive "fix" and not cheap. It may be easier to just buy an entire replacement wheel.

EddyR

Sorry i did not know that it would not come apart like many free hubs i have replaced. I looked up dt swift and found many of them online $58-98 . I did not know yours was different. I looked up that hub and found people having problems with them. Hard to plan a long trip not knowing if it will fail.
60 years ago i went on several long trips over 1000 miles on simple three speed and i had many parts fail but it was easy to fix. Back then tires were the weak point. I am now 81 so my long rides are ony a memory
Ed

sapporoguy

OK, y'all promised! Here's the answer.
First, in my defense, I'm getting slow-witted with the years, so there's that.
I have replaced the star ratchets once, cleaned and degreased them several times, and replaced all 4 bearings once. So I know what it's supposed to look like.
And when I took it apart last week, I DID have this gut feeling something was amiss. But I was busy and had to move on to something else. And then when I was reading your answers and mentally running through the components, it hit me.
Duh.

So, take a look, and tell me what's wrong and NO LAUGHING:

LV2TNDM

Looks like an axle failure! That's too short for the hub, unless it's a funky perspective. Plus, do I see the broken end of the axle inside the cartridge bearing? Sure looks like it.
(Obviously the ratchets & springs are missing.)
But the sleeve spacer is also missing.

If you broke your DT axle, then call me impressed! That take some serious effort right there. That's a cause of freehub drag that's worth bragging about! I've bent and broken a lot of axles in my time, but not any of the freehub variety (all freewheel hubs). But as I've mangled/destroyed six rear hubs on my mountain tandem, I feel pretty confident that even though I haven't broken an axle yet, I've caused some carnage. Splitting a Phil Wood tandem hub literally in half was our proudest moment!

And if you did, be sure to have your dropouts checked to be sure they're aligned.

sapporoguy

Bingo! See the two ends in photos attached. Broken clean through.
I can only think it first developed a hairline crack that was causing the axle to bind under our weight when we rode for 100s more miles. When I spun the cassette or wheel with no load, it spun fine and the chain was taut. Only when riding did it slap.
And, in retrospect, the chain slap started suddenly, like from one minute to the next--like from a sudden crack, not gradually like from normal wear. But the axle was definitely still in one piece when I took it apart a few months ago. So it must have broken clean through since then.
I emailed DT Swiss last night. They responded immediately, said it's probably fatigue failure after 15+ years and 10,000s of miles, many of them fully loaded, so not my fault! They're sending me a replacement free. Another reason to keep the hub!


One half of the axle, in place through the cassette.

The other half, broken end peeking through the hub.

base2 

Color me impressed. Bravo, to you sir!

sapporoguy

What embarrasses me: When I took it apart last week, I thought, wait, I didn't know this was a 2-piece axle, how did I not notice that before? Then I moved on mentally--until my "Duh" moment.

Andrew R Stewart 

Not even a head shake here! Good job at figuring this out. Andy

LV2TNDM

Nice! Again, that's an impressive failure. But I guess 10,000 miles on a tandem, many of which loaded will tend to impart a little fatigue, no? Looks like it failed right at a bearing location. Be sure to get those dropouts checked. Axle failures often bend dropouts.
Edit: They're sending a free replacement? Oh man, that's awesome! Drop some love for DT/Swiss in the future. I'm pretty sure I have the same hubset on my Co-Motion. Nice to know DT/Swiss is standing solidly behind their product.

sapporoguy

Yep, right at the bearing. See pic below of whole axle after taking it out just now. The bearing was just to the left of that flange where the break is.
That's 10,000+ just since we bought it used about 5 years ago, and it's a 2005 model, so who knows how many 10,000s of miles are on it!
And thanks for the advice on the dropouts. That's my first task as I wait for the axle to come.
Yes, DT Swiss gives great customer service. This is waaaay out of warranty, and yet no hesitation. I've emailed them about a bunch of stuff and they always respond almost immediately.
This hub says Hugi on one side and Co-Motion on the other, so very well may be the same as yours. Basically a 540.

Racing Dan

Yeah, most modern rear hubs have a weird design that share the or even amplifies the #1 shortcoming of the older freewheel type. That is the right hand bearing being located all the way in, near, or even behind, the right hand flange, greatly amplifying stresses on the axle. That is what caused it to eventually break, even if it looks extra heavy duty. With few exceptions, older Shimano hubs have the right hand bearing all the way to the right and would not suffer from this particular issue.

sapporoguy

Thanks much for the analysis! I've been running through various reasons it might have failed, and this makes total sense.

EddyR

A little searching shows a long history of problems like yours ,chain slap, and it ending up a broken axle. I found some going back over five years. Not really a very difficult repair if you have the tools. There are a lot of sites online showing how to do it.
EddyR

sapporoguy

Thanks much. Could you post some links? I'm not immediately finding anything about broken DT Swiss axles and repairs thereof, but the search function here befuddles me.

base2 

sapporoguy I've gotta hand it to you. You've got class.