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Loud pop from drive train when under torque, what is it and how do I fix it

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Loud pop from drive train when under torque, what is it and how do I fix it

Old 02-27-12, 04:31 AM
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Chris_F
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Loud pop from drive train when under torque, what is it and how do I fix it

Good morning,

Every now and then when putting a lot of torque on the pedals I get a loud pop sound, a brief moment of zero resistance, and then the bike goes back to normal. This happens on both my bikes (a Shimano 9sp drivetrain Cannondale CAAD5 road bike and a SRAM 9sp drivetrain Cannondale Rush full suspension). I see/hear other bikes do it as well, some more than others. It seems to be a very common affliction.

What is this (there must be a name for it), what causes it and how do I minimize/eliminate it?
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Old 02-27-12, 07:14 AM
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not a locked up link in the chain? I've had that issue a few times. One link is cramped too tightly, under heavy pressure it hops n pops around the freewheel with a moment of no resistance (or very little).
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Old 02-27-12, 07:55 AM
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Could be the pawls in the freehub not properly engaging, then slipping and re-engaging. I only know this happens on my Shimano and Mavic freehubs. I've been able to minimize it by cleaning and oiling the internal parts regularly on the Mavic. Haven't done the freehub on the Dura Ace hub.
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Old 02-27-12, 12:41 PM
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Does it happen in all gears or just one? It could be worn teeth on the rear cassette.
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Old 02-27-12, 01:42 PM
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Originally Posted by JReade View Post
Does it happen in all gears or just one? It could be worn teeth on the rear cassette.
Since it only happens occasionally and you hear it with other bikes, I'm guessing it's a rear derailleur issue; the usual suspect is a stretched cable. .However it could nothing more than a rear derailleur slightly out of adjustment. Adjusting the barrel adjuster is usually a compromise where the chain is centered over some cogs and slightly off center on others, which is corrected by side to side play in the pulley wheel. However if the adjustment is a 1/4 turn off, sometimes the chain mis-shifts up or down, then returns to the proper cog. Campy's shifters have a little quirk that if you have any minor pressure on the shift lever under the brake lever, you derailleur will start to shift again, causing the chain to jump to a cog and than return when you release the pressure.
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Old 02-27-12, 07:01 PM
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Thanks all for the tips, you've given me some places to start. I had thought about the chain but hadn't thought about the free hub palls. I'll have to crack her open and re-grease. My deraileur seems to be pretty well tuned so I don't think that's the problem. How would I check wear on the cassette teeth? I regularly check chain stretch and replace at 0.75mm but don't know how to check the teeth themselves. They don't seem overly worn to my eye (comparing more used larger gear teeth to less used inner teeth).
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Old 02-27-12, 08:21 PM
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Grease is actually the wrong lube for freehub pawls. Use oil. Grease will cause them to stick and create the problem you're trying to solve.

I'm not sure what sort of winter you're having up there in NH, but if it is the freehub pawls, it can be cold related. The cold temps cause the lube in the freehub body to thicken and the pawls stick.

BL
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Old 02-27-12, 08:38 PM
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Does this happen after you shift, or JRA. As far as cassettes go, it doesn't take much to make a small cog slip. The chain wrap on small cogs is poor and they wear faster than the larger cogs. I tried a number of ways to figure this out buying used freewheels. Best way is to take a new chain and lay it over 1/2 of the cog and pull the chain tight. The chain pins should bottom out in the cogs. If it appears the chain needs to be stretched out more for the pins to bottom out then the cog is worn. Another way is to try and find an identical cassette (a good photo will do) and compare the tooth profiles of the smaller cogs. Unless you are familiar with all the profiles or have a something to compare it to (some start out looking shark finned) it is difficult tell if the profile has changed due to wear.

Best way may be to try and make the chain skip. Start off in your large chain ring and shift from cog to cog, putting a lot of torque on the pedals. If the cassette starts skipping with one or more cogs, you'll know where your problems lie. BTW, you drivetrain must be moving to make a cog skip, it won't work if your stationary.
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