roth rothar

I upgraded my 2010 Trek 520 touring Bike to use Brifters instead of bar end shifters and separate brake levers. The Micro new 9 speed shifters work very nicely. The integrated brake lever had limited cable pull so I added Travel Agent™ brake cable pulley adapter to increase the cable pull. The brakes and shifters worked very well.

The second part of the upgrade was a new 36 spoke wheel with a Dynamo hub to replace the existing front wheel. The new wheel with dynamo works fine until I apply the brakes firmly which causes violent shuddering which can be seen at the fork.

I order to troubleshoot the problem I swapped the new Dynamo Wheel with the Original Trek front wheel and the brakes work beautifully with no adjustments.

I would like to use the Dynamo hub wheel, could the problem be inadequate spoke tension? Any other ideas?

JaccoW

For the spoke tension to be an issue the wheel would have to feel floppy in your hand, I suspect the rim is narrower than the original wheel and the brakes need to be readjusted for the new wheel. Have you measured the rim width yet?

roth rothar

Both rims measure 23.9 mm. I have also tried to adjust the brakes with the Dynamo wheel and can't stop the shuddering. The original wheel never has a problem with adjustment.

Bill Kapaun

I'd suspect the angle of the brake track between rims is different enough that the pads aren't hitting it "square", compared to the old rim.
I'd also suspect it'll get better as soon as the pads "wear in" to match.

Andrew R Stewart 

Well one could swap the rims to the other hubs and try test fitting again...

I have had a low spoke tension front wheel cause shudder when braking before. Low enough tension to allow the rim to shift WRT the hub but not so low tension that it flapped about otherwise. What does the spoke pluck tone say? Andy

Crankycrank

Along with the other suggestions try sanding down the surface of the brake pads until you have virgin material. Could be some embedded aluminum from the old rim causes problems with the new rim.

zacster

Are you sure you're not feeling the notchiness of the dynamo hub. Take the wheel off and spin the axle and you'll see it doesn't spin smoothly. It is inherent to the design. When the light is on it is even harder.

roth rothar

The Dynamo magnetic notchiness is present all the time and is only noticeable when spinning the wheel by hand. My problem is the violent juddering only occurs when the brakes are applied firmly.
I have tried to resolve this by sanding the rim, changing brake pads, allowing the pads to bed in for several hundred miles. none of these has helped. The only improvement I have is putting the original non dynamo wheel back on the bike. I suspect it has something to do with the spoke tension or play in the dynamo hub.

Road Fan

It's recommended that brake shoes be toed in when installed, to reduce the likelihood for chatter and squeal. I like to put a dime behind the back end of a brake shoe, and hold the brake lever or clamp it with a toe strap to hold the shoe in the desired position as you cinch the brake shoe clamp bolt. It may take a few tries, and you might need an assistant to give an extra hand. A Third Hand-like tool is also good for holding the brake caliper closed, but you will also need to hold the shoe in place as you tighten its clamp bolt. I don't know exactly how the physics work here, but it's worth a try.

Once the calipers and their shoes are positioned properly, I would next look at the cables as you squeeze the levers. Compression, squishiness, and excess play have to be eliminated. You should dress the ends of the housings (with a file) to be flat and perpendicular to the cable axis at every end of every segment of housing, and use ferrules that fit the housing snugly. The caliper pivots should be clean and adjusted for free motion without play. Any vibration should be conducted directly into the frame based on good conduction into the brake center bolts.

Moe Zhoost

You don't mention any specifics, e.g. make/model of rim and hub. I'm not sure that it makes any difference, but I'm curious. Most dyno hubs use cartridge bearings so play in the hub should not be a factor. You also did not mention whether the wheel was built by you or by a competent mechanic or if you just ordered it as a complete wheel. If the latter, you should do two quick checks. First, spin the wheel to gauge how true it is. If you have a bit of lateral wobble, that could initiate the resonance that you describe a violent. If the wheel seems true, then compare the spoke tension with your good wheel. You can do this by feel: grab two pairs of adjacent spokes and squeeze. A significant difference between the wheels would likely be the issue. You can also gauge tension by plucking the spokes. If the good wheel says "ping" and the new wheel says "plunk" it needs tensioning. Tightening each spoke by a quarter turn should not affect truing much and may solve your problem.

The other thing that may be happening is that the rim joint is not smooth so that the brake pad catches causing a pulsation. Probably not the violent shuddering you describe though. Have you tried braking gently at low speed to see if the shuddering occurs when the joint passes?

roth rothar

The Dynamo wheel is an Intelligent Design Cycles Stout model wheel, with Sanyo NH-H27 hub dynamo see website:
IDC Stout - Intelligent Design Cycles - Dynamo Wheels and Wheelsets | Intelligentdesigncycles

zacster

Having read the copy on that wheel I'd say they are doing their wheelbuilding right, as any competent wheel builder would. Tension, stress relief, accounting for the differences between front, drive side and non-drive side etc... I vaguely recall looking at them myself when I was putting a dynamo wheel on my bike, but ended up building my own. 5 years later I've never had to true them so I must've done it right.

The one thing I did note, and I knew this would be the case, is that these wheels are heavy. Dynamo wheels generally are. Maybe it is the rotational weight that is causing the brakes to amplify the normal stuttering of the hubs, and maybe you need stiffer brakes. The spec on the 520 shows Avid SD-5 V-brakes. I don't know anything about these but fwiw I have XT M770 V-brakes on my dynamo equipped bike. Make sure what you have is properly tightened to the studs on the frame.

andrewclaus

Perhaps you've built a perfectly tuned system for a certain harmonic frequency. Contributors could be the magnetic pulse in the hub, the shorter spokes with different tension, different rim material and geometry, a slight play in the headset, the phase of the moon, and the way you part your hair. The things you can change are spoke tension and headset adjustment.

Does it change with more or less electrical load on the hub?

mixed_ride_4422

You try swapping the rims ?

Moe Zhoost

Thanks. It sounds like these folks know what they're doing and so we can assume that spoke tension is probably not the culprit. I'll fall back to either the rim joint is uneven or pads are not well aligned. Also, it may be that the rim braking surfaces have some contamination. I'd recommend cleaning the brake surface with acetone and then follow up with wet/dry sandpaper (~240 grit).

Jeff Wills

Another variable: what kind of brake shoes are on the brakes?

I've had brakes grab very suddenly when I've laced new rims on a couple bikes. This has happened most often with Kool-Stop Salmon pads, once to the extent that the bike was unrideable. When I switched to Kool-Stop dual compound pads the grabbing went away. After a few hundred miles on the new rims I installed the Salmon pads again and the grabbing was gone.

IMO: brand new rims with machined surfaces have microscopic surface roughness that grab brake pads with a vengeance. Once that roughness is worn down the brakes will be more manageable.