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Discussion Starter · #1 ·
Trying to diagnose an issue where I can feel and hear grinding or popping as I'm pedaling under load. It happens several times per revolution and feels like chain links not engaging 100%.

I can spin the pedals on a stand and no grinding, shifting is perfect. I can replicate the symptoms by holding the rear brake while moving the pedal on the stand. I also replicated the noise/feeling by laying the bike upside down and pedaling while holding the rear wheel.

I also pulled off my pedals and pushed on the crank arm, no change.

I recently replaced the wheelset on this bike running NX eagle. At first I thought it must be a defective freehub, swapped back to my old wheelset, grinding persisted.

I swapped out the chainring with a new spare I had lying around, no change.

So I've eliminated freehub, pedal bearings and chainring. 4 things left that could be causing the issue unless I'm missing something.

Chain
Cassette
Rd pulleys
Bottom bracket

I would think the chain is the most likely issue (I've removed, cleaned and relubed it with no difference) but the eagle drivetrain has done less than 100kms, I highly doubt the NX chain is that poorly built.

BB (XTR) has probably done closer to 800kms and apart from the frame is the oldest component on the bike. Could a worn BB cause a grinding, popping feeling/noise several times per revolution?
 

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You can get grinding if the chainring/cassette and chain are of different wear rates. Ex: cassette brand new, chainring 2 years old, chain 2 years old. The chainring and chain will pair fine, but new cassette may have issue As it is at a different wear rates.


Before anything I would check your b-tension on your derailleur. Often a grinding feeling can come from your b-tension allowing your rear derailleur to come too close to your rear cassette. I recently had this same issue on a change to a new cassette.

Good luck!

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If you get someone else to hold the brake and look closely at the drive-train you should be able to see or feel where it happening. There are a few things it could be.
 

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Discussion Starter · #4 ·
The chain and cassette were installed at the same time. The chain ring was about 3 rides old at the time. I tried a new chain ring and an older one and both had the same popping.

I checked the b tension using that SRAM tool and it was good. I can't see the rd touching anything.

I did actually get someone to hold the brake, I couldn't visually see anything obvious going wrong. I can feel the popping through the crank arms.

I also checked the rd hanger alignment and that is still good, checked the qr skewer is set and properly fastened.
 

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Sounds like it could be a problem with the freehub or cassette installation then. Is the freehub body installed properly in the hub?

Also, b tension and chain length. How did you determine the length of the new chain?

You just replaced one nx cassette and chain for another?

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Discussion Starter · #6 ·
No I've had this NX drivetrain for 10 rides or so. Was running xt 11s before that. I installed the cassette onto a different set of wheels and the popping persisted, so it's not the freehub.

B tension I used the SRAM tool to set and chain length I used large/large + 4.
 

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Does it do it in all gears? If the chainline is very bad the chain can catch on the ring next to it on the cassette. I doubt that's your issue, just trying to eliminate stuff.
 

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Discussion Starter · #8 ·
Yeah tested on multiple gears, most prominent in the middle to lower (smaller) gears where you can really torque the drivetrain up. Harder to detect in the larger sprockets but it's still there.
 

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Discussion Starter · #10 ·
Tried that, I can only feel the popping under load, more importantly under torque. High cadence spinning doesn't reveal the symptoms.

Without the chain, I wouldn't say it's super smooth, a little grimy like dirt caught in there but no 'popping'
 

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Cassette rubbing on frame? Chain routed through the derailleur tabs correctly?

Other than that, and what was previously brought up, it sounds like it can't be happening.

Is the chain actually slipping? Or is it ghost shifting?

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Discussion Starter · #13 ·
Cassette isn't rubbing on the frame from what I can tell or Ghost shifting.

I agree sounds like everything has been checked which is why I'm looking at that BB and wondering if it's that.

I'll try capture a video, but you can feel it more than hear it.
 

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Discussion Starter · #14 ·
OK so ....

Bought a new xtr bb and fitted it ... problem remained. Dammit $30 wasted.

Swapped the GX chain off my other bike ... problem remained.

Cleaned the sh!t out of the drivetrain again. I used my old rock 'n' roll Gold I had lying around instead of my usual go to ... problem solved????? What in the actual?

Makes no sense to me, I ran the drivetrain clean but unlubed on the stand and I could still hear the popping. As soon as I applied the rock 'n' roll lube the drivetrain was perfect again. I had been using Muc-Off Hydro Dynamics which I thought was a much superior lube ... this drivetrain said NO!
 

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I'm thinking the edge of the chain was catching on something and the lube is now letting it slide. Something like that.

Years ago a guy brought his bike to be because the shifting was bad. I looked it over and couldn't find anything obviously wrong. Set-up all looked fine. Chain didn't look bone dry but I lubed it anyway. Shifted smooth as butter!
 

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Discussion Starter · #16 ·
I'm just surprised that changing the type of lube made such a difference. I'm not a fan of the rnr gold because you need to use so much of it, so I'll need to start looking into a new lube.
 

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Discussion Starter · #18 ·
Yeah I tried getting a video but outside of normal drivetrain noise it wasn't coming through on the video. Glad it's sorted, I have noticed the rnr gold doesn't turn into a paste like the mic off was doing.
 
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