Bicycle Mechanics - Derailleur tuning--What am I missing?!
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I am working on a Dahon Jack city bike-- Drivetrain is SRAM 3.0 Comp 7 sp Grip Shifter, SRAM SX4 rear derailleur and a generic 7 sp cassette. It has a single speed chainring.
So far, I've trued the derailleur hanger, checked frame straightness, installed a new OEM SX4 derailleur and no MATTER WHAT I DO (!!!) I can't get the chain to stop skipping/chattering on the smallest cog. :mad: It works fine on the other 6 speeds, but the small cog is just miserable. (BTW, I've fiddled w/ the shifter barrel adjuster ad nauseum)
Did they not engineer the chain angles into this thing?
What other options am I missing??? I'm ready to throw the thing under a bus!!! :mad:
05-10-06, 03:41 PM
Skipping could be a stiff link. I experienced something similar on both my bikes (73 Schwinn LeTour and my new C'dale Cyclocross Disc). The Cyclocross was skipping on the small cog right out of the store. Took it to my LBS mechanic (he's the best!) and he immediately diagnosed it as a chain problem. There was one link that wasn't rotating freely. On larger cogs, it wasn't noticeable because the chain doesn't have to flex so drastically to get around those. On the small cog (an 11), it was causing a problem. I didn't observe exactly what the chain did as it went around the cog, but, I did observe the slight tendency to stay "kinked" coming off the cog.
I recently had my LBSM change out the OEM cranks on the C'dale with stuff from TA. I wanted their largest chain ring (63) and their extra long cranks. The additional size of the chain ring necessitated a new chain (LBSM took his longest chain and added links to it). The first 100 miles or so, nothing we did would get rid of that skip when using the 11 cog. LBSM suggested that I just live with it a while to see if the problem would disappear - it did.
BTW, the skipping only occurred when I applied pressure while on that smallest cog.
Today, it almost never skips.
Hope this helps.
OK--I never would have thought of that. I'll check it out when I'm back at work tomorrow.
Thanks a million. I'll post if that was the cause.
05-10-06, 07:45 PM
have you tried the limit screw? Or lubing the cables/housing? Are the gears/chain worn out?
Literally fiddled w/ the "H" limit screw for 1/2 hour. Never quieted it down.
It's a brand new bike. No wear on anything. Everything still has factory lube on it. Never worked right from day 1 of assembly.
The other 6 cogs shift perfectly--the trouble is all on the smallest cog. Cable tension doesn't come into the picture when it's on the smallest cog.
If it's not the chain, then I give up. Customer brought it in after buying it off of the web, so it's not my problem (I'd replace the bike if it were one of ours). Good components, nice bike--grouchy ***** to tune.
I stepped back and thought 'outside of the box'.
I pulled a wheel off of another 7 speed bike on the sales floor and mounted it up. Sure enough--no skipping. So for some reason, this brand new cassette skips on the bottom cog. Seems odd that a cassette would be defective like this.
Problem solved, although the customer won't be happy to have to wait for another cassette from Dahon bicycles.
05-11-06, 11:34 PM
you'd be much better off just taking one out of stock than waiting for the replacement from dahon. keep the customer happy, and when the replacement finally comes from dahon, put it into stock. i used to have to deal with them and they'd take months to fill a simple bike order, let alone warranty a seatpost or stem. although, maybe you'll have better luck with them than i did.
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