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Trouble with front derailer after crankset replacement

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Trouble with front derailer after crankset replacement

Old 06-09-07, 02:54 PM
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Trouble with front derailer after crankset replacement

I have a 21 speed '98 Diamonback Sorrento SE MTB, which came stock w/ the Shimano Acera X family of front and rear derailers, crankset, and index shifters. It's getting long in the tooth now, but up to this point it's worked well for commuting and the occasional trails. I'm competent to perform basic maintenance and upgrades but I've run into a problem I've not been able to muddle through on my own.

Last week while riding to work I started to experience really bad chain slip on the middle chainring when climbing hills, concurrent with problems keeping the chain on the middle chainring (it was slipping both down to the smallest and up to the biggest). Upon visual inspection, the middle chainring (and the other two as well) was pretty worn and mangled, and since the crankset didn't have replaceable chainrings, I pulled off the whole crankset (it was a 42/34/24) and replaced it with the first reasonably priced crankset I could find at my local store, a Shimano FC-M440 44/32/22. I figured the slight difference in teeth count wouldn't hurt, and I thought I'd like the slightly lower middle chainring.

Anyway, I installed it without incident, and adjusted my front derailer to fit the new slightly bigger chainring. I went through the usual setting the low and high range adjustment screws, but even after that, I'm still having shifting problems. If I start on the smallest chainring (largest rear cog), I can't shift up to the middle chainring unless I turn the tension adjuster on my shifter counter-clockwise quite a bit. Then, I can't shift back down to the small chainrin without adjusting the tension the other way.

I've read that index shifting derailer systems are adjusted for a particular chainring configuration, and might not work as well when changing the chainring sizes. Is that true? Do I need to find a 42/34/24 crankset? Any other ideas what could be wrong? I appreciate any help...
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Old 06-09-07, 05:22 PM
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Todd Downs (Bicycle Maintenance and Repair--Rodale) suggests checking to see that the cables are moving freely. Any frays or dirt or kinks could cause erratic shifting. If your bike is long in the tooth, the cables could be showing some wear. Also check to be sure the derailleur cage is parallel to the chainrings. The nose of the derailleur should be bent inward slightly. Are the spacers on the middle chainring in their correct respective places? Is the middle chainring installed with the correct side out?
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Old 06-09-07, 07:17 PM
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I actually have the fifth edition of Downs book, which I love. It walked me through replacing the crankset, which went without a hitch.

I did read and attempt to follow the directions about derailer alignment, but I've not had to do that before so it's entirely possible I messed it up. I'll go over the alignment steps again.

In the mean time, I've replaced the chain, since the previous chain was pretty worn, and I figured since I've added some teeth my old chain probably wasn't long enough. Didn't help, but at least I have a new chain now.

That's a good suggestion about the cables. I picked up a replacement set of Aztec cables; once I track down a tool powerful enough to cut through their seemingly-indestructible outer housing, I'll install and adjust per the Downs book.

Thanks for the suggestions.
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Old 06-09-07, 08:12 PM
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I am hardly expert at the problem you have. But, no one else had responded to you. We both have the same edition of Downs. I looked at Zinn's book, but chose Downs. I was looking at p. 199. I remember another post on another forum with a problem similar to yours. In that case the derailleur cage was not quite parallel to the chainrings. I have read other posts where old cables in need of cleaning, lubrication, and perhaps replacement were the cause of the problem.

I actually have two road bikes. One is from the mid-1960's. The other is a new bike with triple chainring. When I first got it in November I had front derailleur problems on the first ride. I did not have Downs yet, so I spent some time on the Internet reading what I could about setting up a triple chainring front derailleur. Fortunately, I did not run into quite the problems you have, but I did not get it right the first time, either. I would be curious to know what finally solves your problem.
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Old 06-11-07, 12:06 PM
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Well I replaced the gear cable with a new Aztec cable and housing, and while at it checked the cable guides and the shift lever. All that seems fine, and I still have the problem. I went on a short ride today with my chain stuck on the middle chainring, and the chain slip problem is definitely gone now that I have the new crankset, but the front derailer is not doing its job.

As a test, I tried shifting by pulling on the cable instead of operating the shifter, and had the same problem, which pretty much rules out the shifters as the culprit. At this point I assume I just haven't figured out the front derailer adjustment trick yet, so I'll keep trying. Fortunately I can ride to work entirely on the middle chainring, so at least I'm not out of commission.

Thanks for your help; I'll post again when I finally get it working.
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Old 06-11-07, 10:44 PM
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Adam,

Thanks for the update. I am sorry the new cables did not solve the problem. I guess new cables cannot hurt.
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Old 06-18-07, 09:26 AM
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So I spent some time last weekend going through the front derailer adjustment steps yet again, this time w/ a repair stand so I don't need three hands to pedal and shift. Despite following the instructions to the letter, I still can't get the derailer to shift across all three chainrings.

I finally broke down and took it to A-1 Cycles here in Herndon (incidentally, if you're in NoVA and need bike work done, A-1 in Herndon is great, and Performance Bike in Reston is horrible). According to the wrench there, the bottom bracket used on my bike (remember, nearly 10 years old) is wider (120+mm) than the bottom bracket for which the crankset is designed (117 or something), and thus the chainrings are sitting too far from the frame for the derailer to reach. He's going to install a modern-sized BB and hopefully that'll do it.

I'll post again when I have some resolution.
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