Tandem Cycling - Oscillating sound in rear huv
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09-04-11, 03:44 AM
We bought a new Speedster this spring from Tandemladen in germany. After 300 km it developed an oscillating sound coming from what seems to be the rear hub. The hub is a DT Hügi tandem hub. The LBS says there is nothing wrong with the rear axel, the hub is running perfectly: in PBP we runned past all except fast recumbents on the downhills.
What can be the reason for the oscillating sound - is it something that doesn´t matter?
Carsten & Dorte, Denmarkl
09-04-11, 05:19 AM
Oscillating sound while you're coasting? Or, while you're pedaling?
As TG mentioned, coasting or when engaged.
I suspect it is when coasting. All of our DT hubs have experienced a "waaa, waaa, waaa" sound when coasting. While no immediate damage will result, like a fire alarm, it is an audible indicator to clean and lube the drive.
One way to make the noise stop is to always pedal...
09-04-11, 05:58 AM
The sound is there when coasting only - we do that a lot and enjoy it all way through... But the sound. Yes, the answer from PMK could be the it - it is the waa-waa-waa one we hear, but the sound started after only 300 km - could that be true?
09-04-11, 06:21 AM
... but the sound started after only 300 km - could that be true?
Not all that unusual. We've had the same "pulsing" sound on two sets of Phil Wood hubs over the years and we hear it on various other brands of hubs.
Yes... it usually takes a little while for it to become audible. My guess is, as the factory pawl lubricants begin to break down and thin the star ratchet / pawl noise simply becomes loud enough to hear. It you clean and lube the mechanism, it will get quiet again. We were able to use a pretty heavy lube on the Phil Wood pawls (Phil Wood waterproof grease + a drop or two of Tenacious Oil) given the very heavy springs and pawl design, and once serviced coasting was absolutely silent.
As for the true root cause, that's up for debate. I suspect the pressed-in ratchet rings or the machining of the Phil Wood hubs was a bit off... we're talking very, very small tolerances here ... and it was that slight misalignment between the axle and pawl engagement section of the hub that causes the noise. On our first Phil Wood hub, it was actually out of alignment enough that the pawls would sometimes skip under heavy load and the hub had to be replaced under warranty. Over time, the wear pattern on the engagement rings of our Phil Wood hubs has somewhat confirmed this to be the case.
Bottom Line: So long as the hub is still engaging correctly and doesn't slip, it should be fine. Routine cleaning and relubrication per DT's instructions is your best bet for keeping it a bit more quiet and for many years of trouble-free service.
09-04-11, 07:41 AM
FWIW, I mentioned this to others about how easy these are to clean, inspect and service, but this one simple mod makes easy totally true.
On the DT hub assemblies, they use a small thin cross section "O"ring to retain the right side axle end cap. Remove and save the "O"ring for a time when you may want to reinstall it. With the "O"ring removed, the axle end is able to be slid off with fingers, retention is via the QR and springs.
Hypothetically, you are riding / traveling and are miles from a bike shop or home. The freehub acts up, or possibly the chain has lodged into the spokes. Unseat the QR, remove the wheel downward from the dropouts. This alone will free the stuck chain. If you need inside the freehub, pull the QR and springs, the axle end will then be removed, grasping the cassette slip of the cassette / freehub body as an assembly.
The springs and drives can be cleaned easily with solvent or even brake cleaner. The hub and freehub body splines can be cleaned with a toothbrush if needed. For reassembly, DT calls out a cetain grade of molykote available from them. The amount applied is very thin film, most of these hubs find neutral from excess or old grease. Depending upon the event or conditions, I have used thick oils like Phil Wood or M1 gear oil. I don't endorse it any longer on account of how conservative many tandem teams are. It has worked fine for us, requires more frequent cleaning and replacement, but engages and holds fine.
All the best with it.
09-04-11, 11:27 AM
Since you only hear the noise while coasting and the suggestions made by others seem to have resolved your issue, this isn't likely to be relevant to you, but felt it may be helpful to others who find this thread when trying to resolve another similar symptom.
We have experienced an unpleasant grinding type sound coming from the rear hub on 3 of my tandem wheels that use the DT Swiss 540 TDM hub. However the noise only occurs while we are pedalling, typically getting worse during a ride and more often than not, while climbing at around a cadence of 60 rpm. We've been trying to work out what has been causing this noise for about 5 years and suspect it may have been related to the free wheel failing as mentioned in a recent post.
However, having pulled the entire hub apart, the only noticeable signs of wear are where the bearings in the cassette carrier rest on the axel, where the finish on the axel has been warn away. We lubed this for the first time yesterday to see whether it did indeed resolve the issue and while we didn't get quite as far as we would have liked due to another mechanical issue, it did seem to help.
However, this does seem to be a design flaw in these hubs as there doesn't seem to be any way to prevent it from happening. The tollarances are clearly very small and under the load from the drive chain, and possibly some kind of resonnance being set up when not pedalling smoothly as when climbing, any movement at all would seem to allow this to happen and the sound resonnates through the entire frame.
As mentioned above, the end loading on these hubs is only applied by the end caps and cannot be increased by loading the skewer according to my pilot. So there's no way to to tighten every thing up, and not even sure it would help anyway based on our synopsis.
If anyone has had a similar issue and got any solution I'd be very grateful.
Climbing at 60 revs sounds like enough load to flex the axle. Additionally, it is a decent load on the bearings.
Have you ever removed the bearing seals and checked or better still replaced the lubricant in the bearing itself?
As for failing a DT ratchet set, god bless you if you have that kind of power output. The design is one of the most robust when engaged.
We do not baby our stuff in any way. The 540 tandem rear hub is a sister to the tandem TD hub. Our hardtail off-road Fandango has a couple or possibly few thousand miles of often abused off-road miles on a 540. Our road TD hubs never see this kind of abuse. None make a peep of noise, but I do maintain them with a 5 minute lube change to the drives. Bottom line on the design...we beat the poop out of the hubs off road, if flawed, we have yet to see it. In my opinion I don't see a design flaw.
As for the tightening concept of the hub, it does require close tolerance of parts. If you feel you must make a shimmed adjustment, the shims you require would be available from a motocross suspension tuner shop. If you provide the OD x ID x thickness (by 0.1mm) they could help you with this. If required, easiest shim location is the spacer between the freehub and hub itself.
Hope you someday get it resolved.
As far as the ratchets is concerned, it had done around 3,000 miles of hard riding and so was pretty well warn and had a good innings - much as htough I'd like to think it was just down to our power!
Thanks for the thoughts though re the noise. We haven't tried taking the bearings apart yet and lubing them so could do this to see if it helps.
We had thought that this could be being caused by the axel bending slightly under heavy load but dismissed this as a potential cause because once the noise starts during a ride, it never goes away. So while it does seem to be worse while climbing, it does continue when we get back on the flat alhough at a high frequency as you'd expect with the wheel spinning faster and increased cadence.
The thing that I perhaps find more confusing is why others haven't experienced the same issue? This has happened now on 3 different wheels that use the DT Swiss TDM hubs and on 2 different tandems. We haven't had any similar issue with any of the other tandem wheels I use (yet) which include Hope and Shimano HF08. We do around 7,000 miles a year which while a reasonable mileage, isn't massive and am sure others will do similar mileages and even more. The only other thing I can think of is that the terraine around here is very varied, with areas of flat, long steady climbs, long steap climbs, and shorter very steap climbs, all of which we ride most of the time. Although we can't ride the very steap and of the beaten track climbs in winter or when it's wet because we don't have enough traction and the rear wheel just spins. But maybe there is just something about the riding we do, combined with the mileage and way we are pedalling that is causing this issue to occur.
Anyway, thanks again and if anyone has any other ideas on how we could prevent the issue, short of replacing the hubs which have been otherwise reliable, let us know.
Ian, since I believe the OP has had his question hopefully answered, we'll deviate towards your hubs again. Do you have a digital camera that can take good photos closeup? Can you post photos of the trashed drive rings? Can you post photos of the disassembled hub?
When the hub is disassembled, have you or you technician placed a finger into each bearing and slowly rotated the bearing to inspect for any roughness or dry feel.
Your other topic mentions seldom coasting, so unless the drive rings had become stuck from lack of maintenance then resulting in slippage, I still can not see anyone ever wearing out a set of drive rings.
Assuming the grinding noise is in the hub, and it may be. The number of parts is few, and if assembled correctly has 8 moving parts. A pair of drive rings, a pair of springs, and 4 bearings (two in the hub and two in the freehub).
The springs should be installed with the wide ends towards the hub and freehub, ie opposite the drive ring they engage. Even if installed incorrectly, these lay in place without any rotational movement.
The drive rings, while rotating and locked to the hub or freehub, have no relative movement except for sliding while ratcheting.
Suffice to say, these parts should make no grinding while engaged and pedaling. During coasting or freewheel mode, the drive rings slide back approximately 2mm, and constantly bump the opposing drive ring until reengaged. Once reengaged, they are locked together and turn as an assembly.
This leaves the bearings, improper axle step dimensions, or the spacers to cause concerns. The axle and spacers are held stationary while the wheel rotates. Any contact of the freehub body or drive rings to the spacer could make noise. To verify this clearance, test fit the drive ring spacer into the drive rings, there should be respectable clearance. To test the freehub spacer clearance, slide a tool such as a phillips screwdriver into the space between the freehub bearings. Try and displace the spacers to the side. The amount it moves is the clearance. IIRC, both spacers are approximately 2mm clearance.
Last items left are the bearings. Without proper lube they can howl. The bearings as supplied are often decent, but probably will not last forever without some maintenance.
Post some photos if possible. Three trashed DT hubs seems a bit extreme, but then again anything is possible.
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