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DT Swiss Ratchet Chipping

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DT Swiss Ratchet Chipping

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Old 02-01-19, 09:04 PM
  #1  
mikebian 
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DT Swiss Ratchet Chipping



The other side had no chips.
Weíre 3/4 through a loaded tour around the Big Island in Hawaii. My DT Swiss 540 hub was misbehaving today so I pulled it apart to see what was going on. One side of the star ratchet was really chipped. 12 of the 18 pawls had chips and all those pieces were floating around inside the hub. We climbed 1800í in less than 4 miles today! We weigh about 290 combined plus 35 for the bike and 45 in our panniers. Iím glad it didnít blow apart. Anyway I cleaned it all up and re greased it and hope it will last the rest of the trip.

On on to my question. DT Swiss offers 18, 36 and 54 tooth ratchets. Which one should I get? I donít really care about the sound or the engagement angle. Which is strongest? I donít really want this to happen again.

Thanks
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Old 02-02-19, 11:49 AM
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Mike, glad it wasn't a show stopper. I read of a ratchet spring breaking and the subsequent fruitless search for one, so I bring a ratchet set along just in case. I bet a email to DT Swiss would be helpful. Enjoy the warm,its cool here in PA. Paul F
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Old 02-02-19, 02:44 PM
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In all the years, since the DT 540 introduction used on tandems, I have not seen a ratchet look like this. It makes me think the metal on the one side is extra brittle for whatever reason so I don't believe it to be a strength or design issue. Does there appear to be any corrosion involved? The common form of failure is from lack of maintenance, the grease hardening up and being contaminated lessening full engagement. And once they slip, that is usually the end of the story, or at least any forward movement. I did hear of one that cleaned up and would engage again but generally the teeth are rounded off from that first slip and the star ratchet assembly is toast. We rode our Co-Motion quad https://www.precisiontandems.com/qua...nd_of_ride.jpg with this hub on many week long state crossing tours and tandem rallies while always having a spare ratchet kit on board, which includes both pieces and springs. We never needed the kit but would service the ratchet yearly. It is a good strong design evident by the load and stress on the hub seen from the link. It is good to have their special lightweight grease, too. I only know of one ratchet assembly that fits the DT 540, the factory original design that is kept in inventory here, so am unable to confirm whether other models are compatible. I recommend replacing it with the stock ratchet design as you will likely never see another one chip out again.
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Old 02-02-19, 05:53 PM
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I discovered 4 chipped teeth on a star ratchet from a DT540 4 or 5 years after we bought our 2005 Trek T2000. It still worked fine, I didnít find the damage until I took the hub apart for routine maintenance. The other ratchet was fine. After researching it, I concluded that I should stick with the 18 ratchet version for replacement. Iíve never had another problem with broken pawls. I have two wheels built on DT540s. The only other issue Iíve ever had was excess drag freewheeling in the big ring and small cog. After talking with a DT engineer, I switched to a less viscous lube: https://www.lubriplate.com/PDFs/PDS/3_9-Low-Temp.aspx

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Old 02-03-19, 01:18 AM
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Weíve ridden about 6000 miles since the hub was last serviced and the grease was clean and plentiful when I opened it up. It was last serviced by DT Swiss as I had a warranty issue with it. Weíre generally mashers when it comes to pedaling style so I wonder if that has anything to do with it. Also, Hawaii is really hilly! That 3/4 mile 14% grade to a crappy air b&b we stayed at night before last probably didnít help things either.

We did a nice climb at the start of today and then it was mostly down and rollers. At the start of the rollers I felt the hub sticking again when we coasted. At the end of the day I opened it up again and three more teeth were chipped. Called several bike shops on the island and no one has the part. Three more days of riding to go and no more big hills so I hope it stays together. Weíre trying to be really gentle on the hub.

Guess Iím going to buy two sets now. One to replace and one to carry as a spare. Hate carrying so many spare parts. Gates belt, chain section, quick links, cables, brake pads, screws, a cleat, a tire, tubes plus tools. Geez. Feels like more than 5 lbs of our load is just that stuff.

By the way, I have one of these to remove the cassette: https://www.bikeradar.com/gear/categ...oke-key-42692/

It works great!
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Old 02-03-19, 06:27 AM
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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.
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Old 02-03-19, 10:36 AM
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Originally Posted by Alcanbrad View Post
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 weíre under a power stroke where the chain can skip when jumping gears.
Yeah, Iím probably fairly guilty of that, especially on this trip. Iíve never used my granny gear as much as this. Stats so far are 345 miles with 24,000 feet of climbing. Probably get to 400 if the hub holds up.

Guess Iíll buy the 18 tooth. Advice off board from a mechanic friend says itís strongest. Seems to me though that more teeth might have less chance of chipping when I do shift poorly as the slip will be a shorter angle.
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Old 02-03-19, 01:32 PM
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Just a heads up regarding Dt Swiss hubs that we recently experienced. When traveling with our S&S coupled bike I put one wheel in each case. I leave the rear cassette on and it is upside down in the case with the cassette hanging down. I have done this numerous times. This past trip to Vietnam I opened the case and the cassette was laying separately in the case with the cassette body in the cassette. The ratchet rings and springs were loose in the case. The axle end caps on DT Swiss are only held on by o-rings. Apparently the bouncing on the plane allowed the weight of the cassette to pop the end cap off. No big deal to reassemble except one spring was missing!!!! Both my wife and I tore the case apart to no avail. We started a search in Saigon to find a spring without initial success. Fortunately when we returned to the hotel the spring was sitting with the other parts as the housekeeping staff must have found it cleaning the room and set it with the other parts laying on a towel. It must have popped out when the case was opened. Solved our problem but could have been a real problem if it had been lost during a TSA inspection etc. I now put a zip tie though the thru axle so it can't happen again during travel and will probably carry at least a set of springs and rings in the case for backup.
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Old 02-06-19, 01:51 AM
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So we managed to finish the trip without the hub failing. But see the pic for what it looks like now. Probably going to send the pic to DT Swiss to see what they say.

415 miles with over 26k feet of climbing. It was a great trip.






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Old 02-06-19, 06:41 AM
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We run DT hubs on both our road and mountain tandem, and previously sold mountain tandems.

18 teeth is strongest since the tooth depth is deeper.

Never have we had a star ratchet chip like that.

On both bikes, I removed the small O ring that retains the freehub. Two reasons for this.

First is that you need no tools to disassemble the freehub. Simply remove the wheel, remove the QR and everything slides off with the casstte still installed.

Second, on rare occasions off road, the chain has jumped between the largest cassette sprocket and the spokes. With the O ring removed, the assembled cassette / freehub easily slides over to free the stuck chain once the QR or thru axle is released.

I have a small tub of the official DT Molycote grease. While it does work, I find the grease has a short life. Typically I use Mobil 1 automotive gear oil, or in some cases I use a moly fortified Krytox.

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Old 02-06-19, 08:26 AM
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Somehow I find a design that would suffer mechanical issues like this disquieting and truth be told, really make me want to replace the hub with a more robust design. Racing is one thing. Touring is something totally different.
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Old 02-06-19, 12:18 PM
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As in my case, all the serious damage is to just one of the two ratchets, yet both ratchets see identical forces. Makes me think that the root cause is variability in manufacturing.
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Old 02-06-19, 04:16 PM
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Not that there would really be a difference, but the first time I opened it, I flipped the sides, which had no effect on where the damage continued. It really does seem like a defective part.

PMK: I was being dumb earlier in the week thinking I had to take the cassette off for some reason, which as you state, you donít. I can just pull the cassette off with a good tug, even with the O ring on the end cap.

I sent the pic to DT Swiss weíll see if they respond.
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Old 02-06-19, 04:19 PM
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Originally Posted by reburns View Post
As in my case, all the serious damage is to just one of the two ratchets, yet both ratchets see identical forces. Makes me think that the root cause is variability in manufacturing.
I would take the queue from DT. They may ask about the operating environment and come back and say that donít recommend their hub for those operating conditions in which case itís time to find a different wheel, or they may want you to return it for failure analysis which should get you a free replacement, or they may say ďthat happens sometimes, keep an eye on it and replace it when it doesĒ
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Old 02-06-19, 07:28 PM
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Surprised to see that happen to a DT540 hub. That is a huge amount of climbing you did though. Chapeau!!
would like hear what DT have to say.
We are currently touring on our CK hubset and so far so good. I have a DT540 40h hub that Iím going to build up to a Blunt 35 rim to be our heavy duty wheelset. Looks like I need to pack some spare ratchets just in case.
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Old 02-07-19, 06:08 AM
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Originally Posted by scycheng View Post
Somehow I find a design that would suffer mechanical issues like this disquieting and truth be told, really make me want to replace the hub with a more robust design. Racing is one thing. Touring is something totally different.
This is, if not the strongest drive setup it is certainly one of the strongest.
Considering tne abuse our DT hub experiences on the mountain tandem the strength is substantial.

As for why these drive ratchets failed, at a guess improper heat treatment or when manfactured they induced grinding cracks.

I still have as now spares, a pair of ratchets that slipped from the old original grease turning into wax. This was our first DT type hub on a tandem. Even with the slip style abuse, none of the teeth chipped. They did however very slighly wear the leading edge of the engagement point.
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Old 02-12-19, 12:29 AM
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Originally Posted by PMK View Post
18 teeth is strongest since the tooth depth is deeper.
I'm totally willing to believe this and don't meant to be argumentative.
However, thinking it through: Each of those 18 teeth has a certain depth. For each tooth on an 18t, there are two teeth on a 36T--wouldn't each pair of teeth on a 36T ratchet together have at least as much depth, combined, as a single tooth on the 18T? So each tooth on a 36 needs to be only half the depth? And on a 52T, there are 4 teeth for every tooth on an 18T; wouldn't those 4 together be as strong as a single tooth on an 18T?
THere's probably some engineering or materials-science explanation so I'm just idly speculating here.
I ask because I just took apart my DT Swiss hub on the Speedster and was considering putting in more teeth.
Has anyone done tests of these various ratchets with tandems?
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Old 02-12-19, 07:03 AM
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Originally Posted by sapporoguy View Post
I'm totally willing to believe this and don't meant to be argumentative.
However, thinking it through: Each of those 18 teeth has a certain depth. For each tooth on an 18t, there are two teeth on a 36T--wouldn't each pair of teeth on a 36T ratchet together have at least as much depth, combined, as a single tooth on the 18T? So each tooth on a 36 needs to be only half the depth? And on a 52T, there are 4 teeth for every tooth on an 18T; wouldn't those 4 together be as strong as a single tooth on an 18T?
THere's probably some engineering or materials-science explanation so I'm just idly speculating here.
I ask because I just took apart my DT Swiss hub on the Speedster and was considering putting in more teeth.
Has anyone done tests of these various ratchets with tandems?
On the road, the tooth count on the drive rings is not that important regarding strength. Yes the OP destroyed them, but in the off road tandems, I am certain we induce greater driveline impacts and loads. I still suspect his failed from grinding flaws at manufacture or improper heat treatment,

The logic you present is adequate on paper. This link explains the system. Note that it focuses on engagement angle. The words do state that angle minimum limits are considerations in hub reliability.

https://www.dtswiss.com/en/technolog...em-technology/
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Old 02-12-19, 07:20 AM
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I had some email exchanges with DT Swiss support yesterday. They didn't really have much to say as to why this happened. I suggested shifting under load as a cause and they did not just say yeah, that's why. They suggested maybe a bent axle, but I checked and mine is not bent. I suggested a material defect, to which they replied: "Typically if there was a material defect of the ratchets, they would let go right away – this is a rarity." So, in conclusion, no idea why this really happened.

One thing though. Being home now and looking at the damaged ratchets, it really seems like other than the tiny chip pieces causing some skipping issues,
even with all of the teeth damaged, I think the hub would not have failed. Unless the actual ring cracks, there is still a lot of material to engage and make the hub work. It is a pretty cool design.

And they are sending me a new star ratchet.
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Old 02-12-19, 01:17 PM
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Good white paper on Star Ratchet Gear (STG) failure analysis:

https://drive.google.com/open?id=13g...hi9oFU4DfFJnYk

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Old 02-12-19, 02:31 PM
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Originally Posted by mikebian View Post
415 miles with over 26k feet of climbing. It was a great trip.






This is a really cool graphic. I need to look into this program.
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Old 02-12-19, 02:41 PM
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VeloViewer.com is a great add on to Strava. I still use the free version of Strava because there really isn't anything in the paid versions that I want enough to pay for. I almost feel guilty for that because I use it so much, but the free version has everything I want. However, I do pay for VeloViewer because it has some great stuff, especially since I am a numbers geek. You should definitely check it out. If Strava offered what VeloViewer does, I would gladly pay them.
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Old 02-13-19, 09:25 AM
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For touring on a tandem, IMHO, a set of 48 spoke Phil Wood or White Industries hubs are the way to go. Just my opinion.
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Old 02-15-19, 02:28 PM
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Originally Posted by Alcanbrad View Post
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!

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Old 02-15-19, 04:31 PM
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If the forces acting upon both ratchets are identical and only one is damaged, then the ratchets themselves are different. I can’t imagine an explanation other than manufacturing or supply chain variance.
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