What's wrong with my wheel? Thumping feel when braking (Possibly resolved)

[StressStrain]

Originally Posted by osbk67

Is the thump happening once per wheel rotation?

If so I’d ride it as slowly as I could to try to identify _where _ the rim is thumping.

Or walk push bike under front braking to do so.

Identifying the where should greatly assist the what.

I suspect it’s an imperfect rim joint.

^ very good advice here. Find where the thump is in the wheel's rotation.

[bshell]

You mention your truing stand. Curious why this wasn't the first step?

[makoti]

Originally Posted by bshell

You mention your truing stand. Curious why this wasn't the first step?

You're assuming something similar wasn't. Sighted, between fingers, nothing obvious. I put it in an actual stand and it was the same.

[bshell]

Just asked a logical question.

[benb]

Have you cleaned the brake tracks + pads? (Yes I know another obvious one)

I have had something similar when one or the other got contaminated.. the pads were slipping/grabbing and the chatter feels like thumping.

Whatever it was I gave up and replaced the pads. It's rare but in some sense it's no different than contaminating some kinds of disc brake pads, it's just easier to move on with a replacement.

[makoti]

Originally Posted by benb

Have you cleaned the brake tracks + pads? (Yes I know another obvious one)

I have had something similar when one or the other got contaminated.. the pads were slipping/grabbing and the chatter feels like thumping.

Whatever it was I gave up and replaced the pads. It's rare but in some sense it's no different than contaminating some kinds of disc brake pads, it's just easier to move on with a replacement.

Was a thought that it was pads. Maybe toeing was off. That's why I put it in another bike and tried it. It was much worse on the 2nd bike whenever I applied the brakes, to the point it was unrideable. So that should rule out pads.
I thinking hub, but it also feels smooth.

[marciero]

I'd be surprised if it wasnt some type of the above rim imperfections. I've had similar that either did not show up in the truing stand; eg rim joint, or were only faintly visible-dent from bottoming the rim. If it is the latter and you have a wide brake track you might get it to disappear by slight re positioning the pads.

[Mark McM]

Originally Posted by marciero

I'd be surprised if it wasnt some type of the above rim imperfections. I've had similar that either did not show up in the truing stand; eg rim joint, or were only faintly visible-dent from bottoming the rim. If it is the latter and you have a wide brake track you might get it to disappear by slight re positioning the pads.

I'm of the same thought. Even though rubber brake pads are somewhat compliant, it doesn't take much variation in rim width/flatness to cause brake pulsing.

There's also a small possibility that there some variation in the contact surface, such when a portion of a ceramic rim coating is worn through in one spot, changing the coefficient of friction in just one area. But again, this is more likely on the moving part (the rim) rather the stationary part (the pads).

[benb]

Originally Posted by makoti

Was a thought that it was pads. Maybe toeing was off. That's why I put it in another bike and tried it. It was much worse on the 2nd bike whenever I applied the brakes, to the point it was unrideable. So that should rule out pads.
I thinking hub, but it also feels smooth.

Yah I was confused, I couldn't tell if your previous mention meant that you tried the pads on another bike or the wheel in another bike.

Can't you check for a bulge in the brake track with the truing stand? I have never had a truing stand, but I do have digital calipers and would probably check with those. But a good truing stand would do a much better job.

[makoti]

Originally Posted by benb

Yah I was confused, I couldn't tell if your previous mention meant that you tried the pads on another bike or the wheel in another bike.

Can't you check for a bulge in the brake track with the truing stand? I have never had a truing stand, but I do have digital calipers and would probably check with those. But a good truing stand would do a much better job.

The brake track seems smooth and even, though worn for years of service. I cleaned it up, and they were dirty with some sealant residue but it didn't seem to change what I am feeling when I apply the brakes. I guess next stop is the bike shop with it.

[makoti]

So I took it to the shop. He looked it over. Cleaned the rim real nice, adjusted the hub, said the tire was old enough to be starting to dry rot, and he thought there might be too much sealant in it, but nothing seemed to point to a reason for the thumping. I took it home, and the thumping continued. I decided to drain a little of the sealant out, just in case that was a weird reason for it.

As I did and was cracking the bead to drain it, I felt something firm in the tire. INSIDE the tire. If it was alive, I'd have thought it had a tumor. Well, it kind of did.

You couldn't tell to ride it. It gave enough that the wheel ran smoothly, No hop every rotation. 67g of old sealant. I pulled another wheel, about the same age as this one, and only got 22g of old sealant out of that one. My guess is the tire had been on for maybe 2 years. Front, so didn't wear as quickly as it would have on the back. Never flatted, so never needed to pull it before this.

[Mark McM]

Originally Posted by makoti

As I did and was cracking the bead to drain it, I felt something firm in the tire. INSIDE the tire. If it was alive, I'd have thought it had a tumor. Well, it kind of did.

You couldn't tell to ride it. It gave enough that the wheel ran smoothly, No hop every rotation. 67g of old sealant. I pulled another wheel, about the same age as this one, and only got 22g of old sealant out of that one. My guess is the tire had been on for maybe 2 years. Front, so didn't wear as quickly as it would have on the back. Never flatted, so never needed to pull it before this.

But that doesn't explain why you only felt the thumping while braking. Unless somehow the excess dried sealant cause the tire to bulge out a bit, causing it to rub against the brake (pad or arm).

[makoti]

Originally Posted by Mark McM

But that doesn't explain why you only felt the thumping while braking. Unless somehow the excess dried sealant cause the tire to bulge out a bit, causing it to rub against the brake (pad or arm).

I'm guessing that the weight in one spot caused the forces of braking (don't ask me what they technically are) to be thrown all off kilter, and possibly it did bulge a little under the braking forces. Not sure. I did say "possibly", since I haven't remounted the tire and it going to be raining for the next 3 days, so it'll be a bit before I can verify.
It quite possibly could turn out to be an incidental finding

[Peter P.]

"It is not a toomah!"

Yet another reason to use tubes.

[thwart]

Originally Posted by peter p.

"it is not a toomah!"

yet another reason to use tubes.

+1000.