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Drivetrain "Snap"?(6 posts)

Drivetrain "Snap"?Mike Prince
May 1, 2002 5:52 PM
Hi everyone-

My drivetrain is making a "snapping" sound. I am positive it is not chain skip, it's a very different sensation. The feeling through the crank/pedal is a soft click while the actual noise is quite loud. There is no interruption in the pedal stroke like with chain skip. It is VERY random, but when it does happen it is usually after a period of coasting or soft pedaling. When I apply force through the drivetrain to accelerate, in the first or second revolution I hear/feel it. Feels almost like the soft pedaling builds up some tension somewhere that gets released under power. I know it sounds crazy, but that's what it seems like.

I've checked most of the likely culprits (cassette, chain, bb, crank & chainring bolts, pedals, derailleur adjustment, etc.) and everything checks out OK. One thing I haven't checked because I'm lazy is the freehub (works fine but could it be a pawl problem??). Figured I'd check with the board to see if my fellow wrenches have any ideas.

FWIW, the drivetrain is Dura Ace derailluers/shifters/crankset/freehub, 53/39 and 12/25 (<1000 miles Ultegra), SRAM PC-89 chain (as old as cassette and no stretch according to my Park chain stretch gauge) and an XTR bb (don't ask, it's a long story). Everything is torqued down and the drivetrain is well maintained. Freehub was overhauled in January with Phil Wood grease and the cones are properly adjusted (I double checked tonight). BB still spins like new after 3000 miles.

Everything works great but the noise is bothersome. Help!

Mike
re: Drivetrain &quot;Snap&quot;?gtx
May 1, 2002 8:12 PM
"Freehub was overhauled in January with Phil Wood grease" My understanding, and this has been debated before, is that those freehubs are not really meant to be injected with heavy grease--generally it is best to just leave them alone, though some people recommend heavy oil (like Phil's Tenacious). Anyway, my guess is that your freehub is toast.
I think I said it wrong...Mike Prince
May 2, 2002 3:17 AM
Grease in freehub mechanism has not been touched at all, still has factory lubricant in there. The hub bearings were overhauled in January. Sorry, I got caught up in terminology.

MP
I think I said it wrong...gtx
May 2, 2002 6:24 AM
still sounds like your freehub--that's what it's like when they start to go. Try another wheel and see if it still happens.
I'll make a stab at this one. . . something to check anyway.Mike P
May 2, 2002 5:15 AM
My bike started making a noise like what you describe a while back. I couldn't figure out what it was.

Try this next time your out riding, coast with the pedals at 3 & 9, then stand up and bounce a little (just enough to weight the BB pretty good), sit back down, rotate the crank 180 degrees (pedals are at 9 & 3 now), stand up and bounce again. It you hear the noise when you do the bounce I would suspect the BB needs to be re-taped.

I have had this happen several times on two different bikes. Having the BB re-taped with teflon tape would fix the problem for another couple thousand miles but it would always happen again. So, last time I noticed it, instead of having it re-taped, I removed the BB, thoroughly cleaned the BB and BB shell, and coated the threads liberally with a thick grease. If you do the grease idea, after you install the BB be sure to remove all the excess before installing the cranks or you could end up attracting a lot of dirt to the BB shell. I haven't had the problem since, and it's been about 6000 miles now.

Mike
re: Drivetrain &quot;Snap&quot;?curlybike
May 2, 2002 5:44 AM
Can you borrow a good rear wheel to try? It may be a pawl engagement problem.