Who Wants to Play "Name that Drivetrain Noise?"

[Litho]

Some context: put a new wheel on my Appaloosa a few days ago.  New wheel, all other parts of the drivetrain the same.  A few minutes  into the first ride around the block, I heard a ping from the rear of the drivetrain.  Stopped to see if the chain was off.  Nope.  Got on and didn't hear it again until later in the ride.  But only once more.  

Back at home, admiring the new wheels, spun the pedals backward and hopped on to ride down the driveway.  As soon as I pedaled, PING.  

So, drivetrain noise are notoriously irritating to root out.  This one is driving me nuts.  I've done the following: 

-Put another wheel on the bike to see if it still made the noise. It did not. 

-Put a new chain on. Still made the noise. 

-Tuned up my rear derailleur. Still made the noise. 

-Swapped cassette. Still made the noise. 

-Put the rear wheel on another bike. It made the same noise on the other bike. 

-Tightened every bolt / nut in the drivetrain to manufacturer's spec using a torque wrench. 

- Pulled apart rear hub and examined freehub pawls. No apparent damage. Cleaned and relubed freehub. Reinstalled. Still made the noise. 

-Inspected and reinstalled the axle. Still made the noise. 

 -Checked and adjusted spacer on cassette. Still made the noise. 

What variable have I not yet isolated and tested???  Where does the pinging gremlin live???

I'd love to hear some suggestions.  

Here's a video complete with the ping: 

https://youtu.be/4v4TO9NKpAE

[Patrick Moore]

New spokes automatically establishing tension equilibrium? All my new rear wheels "ping" occasionally for the first few miles.

If it's more than episodic or if it continues beyond the first ride or 2, then there is probably more to it.

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

[Justin]

Call me crazy but in the vid to my ears it actually sounds like chain slack, slapping taught, more of a slap than a ping. Engaagement looks good. I'm sure in person its different to hear. Sorry I don't have any suggestions. Just giving my observation.

best of luck

[Litho]

It's every time I'm on the bike, now.  It's occasional under normal riding, but typically happens if I slow down, coast, or backpedal.  I took a slow motion video of the chain when the pinging happens to see if it's sticking or suddenly releasing slack, but if it is, I don't see it.  

[Bill Lindsay]

Here are my questions:

1. Why did you put a new rear wheel on your Appaloosa?

2. What rear hub is on your new rear wheel?

3. In the youtube video you aim the camera at the cassette but don't show what you are doing at the input.  What are you doing at the input?  I think you are backpedalling a little and then deliberately jerking the pedals forward.  The chain isn't going slack and slamming tight on it's own.  You are doing that on purpose to illustrate the noise.  Correct?

4.  When you "pulled apart the rear hub and inspected the freehub pawls", how many pawls are there?  2?  3?  6?  To be clear, the pawls are the tiny pieces of metal that are springloaded and individually click into the splines of the drive ring or drive shell, depending on the way your rear hub is architected. 

5.  When you say you inspected the pawls, did you actually inspect the pawls, or did you mean you looked at the splines of the driveshell?

6.  Do your pawls have a single engagement end like most freehub and freewheel pawls, or are they toothed with two or three teeth on their business end?  

I have a theory, and I'm pretty sure it's correct, but I don't want to post a long and correct description for the wrong rear hub, because it will confuse people who are not mechanics.  I don't mind confusing people with long correct descriptions when they are relevant to the problem at hand.  

Bill Lindsay

El Cerrito, CA

[Litho]

Howdy Bill, 

1.  I upgraded to a new wheel set that included beefier rims and a dyno up front. This is an upgrade from the Silver / Alex that came stock on the Appaloosas.  I'm also in conversation with the builder, but we are on other sides of the country so I'm trying to crowd source some ideas! 

2.  Bitex BX103r

3.  The input is me turning the crank by hand, backpedaling a little at a time and then pushing it forward to simulate pedaling load.  I'm not pushing particularly hard in the video.  I'm doing it to illustrate the noise.  

4.  6 pawls.  I removed the lock ring, the pawls, and the tiny, tiny return springs under the pawls from the freehub body.  I didn't touch the bearing cartridges.  Pawls are in the freehub on this one, ratchets in the hub body.  

5.  I took high res photos of the pawl assembly under a studio light and inspected the high res photos.  My vision is pretty good, but not that good!  I looked at the splines in the driveshell with a bright light and ran a toothpick over each one to see if I could feel any deformations, nicks, etc.  

6.  Each of the six pawls is cut into two teeth on the business end.  The locking goes in between the pawl teeth.  Let me see if I can upload a photo.  

I'd love to hear your theory!  I'm well beyond the scope of my knowledge!

[Litho]

[Bill Lindsay]

OK, you answers are all as I expected.  I don't like the idea of six pawls.  It's what we call an overdetermined system.  The idea with six pawls is that each carry 1/6th of the load, but in order for that to happen, the machining has to be absolutely positively perfect.  The hardness of pawls themselves is extremely hard.  The hardness of the splined drive shell is extremely hard.  All six have to hit their groove perfectly.  Imagine building a wooden table with six legs out of hard oak in your garage.  It would be really hard to build that table with such precision that all six legs carry 1/6th of the weight of the table.  It would be hard to even get all 6 legs to reach the ground.  

I suspect the requirement for absolute perfection is not attainable every single time with hubs with that design.  You might get lucky and have all six perfect, and you may be unlucky.  To convince yourself that you are just a little unlucky, turn the freehub body backwards as slowly as you can.  If it was manufactured perfectly, you will hear one CLICK, but it's really all six clicks happening simultaneously.  See if you move slowly enough to separate the clicks.  I suspect you'll find it easy to identify that there is one early, or one late.  

To prove this is the cause, the test I recommend is to do exactly what you'd do with your six-legged table: change it to a three-legged table.  A three-legged table self-levels because it can.  Remove three of the six pawls and ride your bike.   I bet a dollar the PING is gone.  

If that works as I expect, then you have something to discuss with your builder.  I personally think that six pawl design is dumb and three pawls is ample.  I think "upgrading" from 6 to 3 is an improvement.  I'd just use the wheel with three pawls and have a three spare pawls on hand.  You may decide it's a manufacturing defect and demand a new wheel under some kind of warranty.  I won't instruct you how to resolve the issue. 

best of luck

Bill Lindsay

El Cerrito, CA 

On Monday, September 21, 2020 at 8:34:15 PM UTC-7 Litho wrote:

[Litho]

Thank you, Bill.  You got me to open the freehub again and remove all of the pawls and springs.  I tried to put it back with 3 pawls, but the retaining ring wouldn't hold just three of them in place very well.  They were flopping all over the place and had so much play that the return springs did nothing.  Which got me to thinking about the strength of the return springs under the pawls.  The "spring" of the pawls was really weak when I pushed down on them, even with all six in.   They barely popped back up.  To the point that the hub made almost no ratcheting noise when coasting.  Very quiet except for the occasional pinging.   I actually remarked to my wife how strangely quiet the hub was, much quieter than the XT hubs on my Atlantis and far quieter than any other hubs I've had.  I figured it was a design feature.  

Long story short, I pulled on the springs a bit to elongate them just slightly and then put the hub back together.  It's buzzing nicely now, the click of the pawls ratcheting is not perfectly simultaneous but much closer (you were spot on about that!), AND I can't make it ping anymore.  The pawls have more force pushing them against the ratchet in the hub now.  I don't know why the springs wouldn't have been like that out of the box.  

I'll have to test it some more tomorrow to see if that really took care of it, but it seems to have made it better for the moment. 

Thanks again for the detailed analysis.  Very helpful!       

[Tom Wyland]

This thread is the craziest bit of bulletin board wrenching I've ever seen.  Well done!

[Bill Lindsay]

Good work.  It sounds like you'll get it sorted.  I'm glad I could point you to the right area

Bill Lindsay

El Cerrito, CA

[Litho]

Took it out for 30 minutes and it sounds normal now, with no pinging / catching noise.  I think I'll consider the case closed!

[spencer robinson]

Wow!  That was really nice of you and Bill to take the time to pass all that on. I am adding that to my bike knowledge section of my brain!

I know a guy that had one of those Bitex hubs and it was making a noise that bothered him, he wound up replacing the hub with a White Industries...I gotta ask him if he still has the old hub, maybe I can get it fixed up.