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Random Skipping Under Pressure

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Random Skipping Under Pressure

Old 03-21-23, 11:48 AM
  #1  
bampilot06
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Random Skipping Under Pressure

Couple of months ago I built a trek 5200 with Ultegra 6500. The group set came off of my Ritchey Breakaway, which I bought used a couple of years ago. I think I put about 4,000 miles on the groupset but I have no idea how many miles are on it before I owned it. Never had any issues with it while it was on the ritchey, but I also never did much hard riding with that bike.

The 5200 has become my crit bike, and I also I use it for training, specifically intervals and sprint training.

I have noticed that recently it has started to skip when under a heavy load. I have narrowed it down to the number 8 cog but the wear seems fine. I replaced the chain, and it still does it, but I am not sure if it is still just the 8th cog or if the issue has moved to other cogs as well. Have not been able to ride it.

The other thing I have noticed, when I shift to a smaller cog, occasionally it will get easier to pedal 1 or 2 strokes before it engages. It is not consistent and I hear it shift, I canít figure our why it does this. When I put the groupset on, I installed all new cables. Iíve put about 500 miles on the bike since I built it, and it does not do either issue in a bike stand.

Thoughts? If itís the cassette I have no issue replacing it, just didnít want to do that if itís not the problem.
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Old 03-21-23, 11:52 AM
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when my 11t and 12t were skipping, the wear was pretty much impossible to see (even when removed and cleaned), yet replacing it completely them completely fixed the problem.
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Old 03-21-23, 11:56 AM
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Originally Posted by mschwett
when my 11t and 12t were skipping, the wear was pretty much impossible to see (even when removed and cleaned), yet replacing it completely them completely fixed the problem.

Awesome. I have like 4 spare 11 spd cassettes, 1 spare 12 spd, 1 spare 10 spd, No 9 spdÖÖÖ.
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Old 03-21-23, 11:59 AM
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^ Agree with mschwett, it can be impossible to determine a skipping cog just by sight.

Ran into this problem recently on a really nice looking vintage freewheel where one cog in the middle of the cluster slipped terribly under load. Just had to bite the bullet and replace it. Problem solved.
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Old 03-21-23, 12:04 PM
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Originally Posted by SurferRosa
^ Agree with mschwett, it can be impossible to determine a skipping cog just by sight.

Ran into this problem recently on a really nice looking vintage freewheel where one cog in the middle of the cluster slipped terribly under load. Just had to bite the bullet and replace it. Problem solved.

Thanks, could the other issue be caused by a worn cassette as well?
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Old 03-21-23, 12:23 PM
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Originally Posted by bampilot06
Thanks, could the other issue be caused by a worn cassette as well?
If that happens after coasting, it is usually the freehub pawls being slow to engage. It is not easy to lube them on a Shimano freehub body, other hubs can be easy.
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Old 03-21-23, 12:26 PM
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Originally Posted by Kontact
If that happens after coasting, it is usually the freehub pawls being slow to engage. It is not easy to lube them on a Shimano freehub body, other hubs can be easy.

I didnít pay attention enough in the past to see if itís after coasting. Iíll ride it tomorrow and see if thatís the case.
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Old 03-21-23, 01:24 PM
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If it's just one cog that's skipping, 99 percent of the time, it's not the pawls, it's the cog.
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Old 03-21-23, 02:11 PM
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"The other thing I have noticed, when I shift to a smaller cog, occasionally it will get easier to pedal 1 or 2 strokes before it engages. It is not consistent and I hear it shift, I canít figure our why it does this. When I put the groupset on, I installed all new cables. Iíve put about 500 miles on the bike since I built it, and it does not do either issue in a bike stand."

sounds like a Freehub Pawl engagement issue to me. they can be quite random.
there's a chance enough grunge has built up on your cassette to cause this, but that's usually only on an MTB...How old is your chain? check it for wear or have someone do so that is qualified. If the chain and cassette are ok, then it's definitely the Pawls in the Freehub not engaging consistently.

try this quick test.. lay the bike on it's left side.. shoot a "psst" (a few drops) of penetrating oil into the freehub's center... clockwise spin the wheel for a minute or so..... go ride the bike and see if the skipping still occurs...

Last edited by maddog34; 03-21-23 at 02:16 PM.
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Old 03-21-23, 06:00 PM
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Originally Posted by maddog34
"The other thing I have noticed, when I shift to a smaller cog, occasionally it will get easier to pedal 1 or 2 strokes before it engages. It is not consistent and I hear it shift, I canít figure our why it does this. When I put the groupset on, I installed all new cables. Iíve put about 500 miles on the bike since I built it, and it does not do either issue in a bike stand."

sounds like a Freehub Pawl engagement issue to me. they can be quite random.
there's a chance enough grunge has built up on your cassette to cause this, but that's usually only on an MTB...How old is your chain? check it for wear or have someone do so that is qualified. If the chain and cassette are ok, then it's definitely the Pawls in the Freehub not engaging consistently.

try this quick test.. lay the bike on it's left side.. shoot a "psst" (a few drops) of penetrating oil into the freehub's center... clockwise spin the wheel for a minute or so..... go ride the bike and see if the skipping still occurs...

Chain is brand new less than 100 miles, that was my first attempt at getting to to stop skipping.

Iíll try lubing the free hub tomorrow. Thanks.
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Old 03-22-23, 09:09 AM
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Originally Posted by SurferRosa
^ Agree with mschwett, it can be impossible to determine a skipping cog just by sight.
Yup. Essentially the definition of "worn cog" is "skips with new chain."
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Old 03-22-23, 06:09 PM
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Rode it today, did intervals, and it didnít skip once under load.

Then randomly during easy spinning it started skipping a lot on different cogs.

I pulled the wheels and the cassette off. I put the cassette on a different set of wheels and will give that a go tomorrow.

I also poured a generous amount of tri flow on the free hub body of the old wheels.
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