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Old 05-12-08, 09:25 PM   #1
yeamac
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LBS put on new chain, cassette, RD cable--drivetrain now jumps under load

I took my bike in to the LBS for an overhaul and supplied them with a new chain/cassette (SRAM replacing like SRAM components) to put on, and they said no problem -- wouldn't charge me any extra to put on components as they take the whole bike apart anyway for an overhaul. (hey, I even saved them from having to clean those components, which they normally would do during an overhaul)

I got the bike back last Thursday and on my first ride Friday I stand to pedal and the chain goes "Ka-chunk!" and I thought that can't be good. Chain was still on, everything seemed fine, I was even in the same gear which is odd because it sounded like it shifted very quickly and very hard. I continued to ride seated, and I shifted through the gears and everything was smooth. Next intersection I stand to pedal and again under load my chain jumps on the rear cassette very quickly. I never saw it, but it seemed like the chain was going up to a larger cog on the cassette and then rapidly jumped back down. This only happened under pressure. It happened one other time when I hit a pretty good bump and was pedaling hard.

I took my bike back to the shop. They put it in a stand and took it through all the gears, which worked very smooth. I explained that it only happened under load (standing) and not during normal pedaling. The mechanic then took my bike for a ride in the parking lot and couldn't get it to happen (he weighs about 50 pounds less than me). I said I'd try and reproduce it and sure enough, was able to get it to jump on cue by standing and pedaling. He looked my bike over and told me I had a defective chain. I said no problem, I have a second chain at home I can put on. CRAP, bought the 991 chain from PBK months ago so wouldn't be able to return it.

I took my bike home, set the new second chain (951) to length, and then put it on. Right away I could get it to jump while standing and pedaling hard, so I took my bike back to the shop, as it obviously was not a chain issue. Then the mechanic tells me it must be a defective cassette. He put on a new Ultegra cassette from their shop and it didn't seem to happen (I took it for a spin too and it didn't happen). So fortunately they had not emptied the trash and they dug my old cassette out and put it back on. The mechanic installed that and rode it in the parking lot and said same result, no jumping. I didn't ride it this time but just took it and left, as I had other things to tend to. That was last Friday.

This morning (Mon) I had time for a short ride and the first time I stood to pedal I had the same jump. So I took my bike back in after my ride. I had read on this forum over the weekend from others with a similar problem the possibility of the cable tension not being set properly. One thing they DID do to my bike during the overhaul was to put a new rear derailer cable on. I suggested this to the person I spoke with (different guy) and he indicated that couldn't be the issue because the cable "wouldn't cause the chain to jump like that." I surely don't know as much as the bike mechanics, but don't understand why the cable couldn't be the issue. So far it is the only other variable in the equation that was changed. But he asked me what I wanted to do and I explained the problem again (which he already knew) and said I wanted my drivetrain to work properly, like it did before I brought it in for the overhaul.

So if anyone has any suggestions on what this might be, I'd like to hear it. I believe the new chain and new derailer have been ruled out since replacement parts exhibit the same behavior. Also, this shop has mixed up brake/shift cables on me on the past. If they put a brake cable in for the shifter, would that possibly cause this problem? I didn't think to check that until now, and my bike is back in the shop at the moment. But I can compare cables and can tell the greater thickness in a brake cable.

It seems to me the cable tension might be the issue. I was surprised the guy I spoke with today seemed to think that couldn't be the issue. He sure made me feel dumb for suggesting that could be the problem.

Edit: just want to add this is a 9–speed, and all components (chain and cassette) are all 9 spd as well.

Last edited by yeamac; 05-12-08 at 09:31 PM.
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Old 05-12-08, 09:47 PM   #2
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Have you tried turning the adjusters say 1/4 turn one way testing no change turn it back and 1/4 the other direction just to see first if it makes a difference under load and on a stand are quite different?. From their possible something is bent like the drop out.
Also take note if its in a particular gear that does this and or a particular chain ring combo.
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Old 05-12-08, 10:00 PM   #3
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ive heard of frame flex sometimes having that effect under certian circumstances. do you mind if i ask how much you weigh and what kind of bike your riding? frame material? the person at your LBS didnt happen to be a slack jawed pimplefaced teenager with really bloodshot eyes did he? were there empty pizza boxes all over the shop? was it really smokey when you walked in?
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Old 05-12-08, 10:00 PM   #4
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You mean they charged you and didnt do it right?

[QUOTE Have you tried turning the adjusters say 1/4 turn one way testing no change turn it back and 1/4 the other direction just to see first if it makes a difference under load and on a stand are quite different?. From their possible something is bent like the drop out.
Also take note if its in a particular gear that does this and or a particular chain ring combo.
][/quote]

Didn't the bike shop do this?You pay all that money and it goes "Ka-chunk!"

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ive heard of frame flex sometimes having that effect under certian circumstances. do you mind if i ask how much you weigh and what kind of bike your riding? frame material? the person at your LBS didnt happen to be a slack jawed pimplefaced teenager with really bloodshot eyes did he? were there empty pizza boxes all over the shop? was it really smokey when you walked in?
Hey I see a few of these guys working at the bike shop.
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Old 05-12-08, 10:20 PM   #5
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I wonder if you keep posting derisive comments about shop employees if that will make them post the answers you need?
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Old 05-12-08, 11:02 PM   #6
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I wonder if you keep posting derisive comments about shop employees if that will make them post the answers you need?
relaaaaaax dude..... unless i just happened to randomly describe you, i dont see how you can take that comment as a slam against all bike mechanics. if i did just describe you,, i apologise.. im sure your really good..
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Old 05-12-08, 11:31 PM   #7
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relaaaaaax dude..... unless i just happened to randomly describe you, i dont see how you can take that comment as a slam against all bike mechanics. if i did just describe you,, i apologise.. im sure your really good..
I just don't appreciate generalizations like that being bandied about, especially in a forum dedicated to bicycle mechanics. It denigrates my chosen trade and devalues my work.

Think about someone going to a forum dedicated to your trade and making similar disparaging comments. How would that make you feel?
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Old 05-13-08, 12:14 AM   #8
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What is your weight?
What is the bike make and model (and material)?
Have you ever dropped your bike on the side of the RD possibly tweeking the RD?
I have had a problem with a chain jumping under extreme load sprinting but, the frame was a bit noodley and did flex. Good luck and keep us posted when you find a solution.
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Old 05-13-08, 12:45 AM   #9
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I have seen some very expensive high end bikes that had the problem described. Believe it or not most of the time it was a chain that was too long. I always shift the chain crossed over on the large rear and front chain rings and adjust the chain length to just be barely long enough to shift. No one would ever put his chain on both large chain rings except by accident but the chain should be just long enough to avoid damaging the derailer if it is.
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Old 05-13-08, 01:00 AM   #10
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Sounds like the chainring/s is/are worn out. Sometimes the teeth on a ring will appear fairly symmetrical, but will allow skipping under load. The only solution is to replace it/them with a new one.
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Old 05-13-08, 06:24 AM   #11
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I weight just under 200 pounds. Ride a 2003 Bianchi Vigorelli (steel frame). My bike has about 5,000 miles on it. I know steel frames have some flex but I never had this problem until the bike shop did this overhaul. Plus I want to mention I got a new rear derailer hanger about 200 miles ago, and during that 200 miles the bike rode great.

The components are new and have no wear. Chain has no stuck links. Chainrings on my old cassette were somewhat worn, but probably still have a lot of life it in as I never had any chainring problems prior to this (had gone through 3 chains so I replaced them fairly regularly). New cassette came out of brand new sealed box and looks to be fine -- no worn edges, obviously.

The guy at the shop is an older (I'd guess around age 50) hispanic man. Seems to know his stuff and probably has been doing this a long time. So it is not like he is a teenager learning what to do.

As for the adjusters, I think he tried that the first time I brought it in and he put it in the stand. I'm not very confident about messing with that stuff myself, but think if they don't fix it this time I'll have to learn through a little trial and error.
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Old 05-13-08, 06:30 AM   #12
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Quote:
Originally Posted by Wordbiker View Post
I just don't appreciate generalizations like that being bandied about, especially in a forum dedicated to bicycle mechanics. It denigrates my chosen trade and devalues my work.

Think about someone going to a forum dedicated to your trade and making similar disparaging comments. How would that make you feel?

bro, i AM a bike mechanic.. i really dont think my joke denigrated the trade. just a little comic relief. do you ever watch Seinfeld?

im not going to muddy up this guys thread anymore beyond this.

cheers!
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Old 05-13-08, 08:05 AM   #13
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When it makes that "Ka-chunk!" noise does it actually slip or just a noise?
Does it do it on more than one chain ring up front?
Single out were it makes the noise, its a process of elimination at this point.
Could be worn chain ring if it only does it on one of them, chain to long or B screw adjustment Rear Derailleur OR?
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Old 05-13-08, 09:25 AM   #14
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Then the mechanic tells me it must be a defective cassette. He put on a new Ultegra cassette from their shop and it didn't seem to happen (I took it for a spin too and it didn't happen). So fortunately they had not emptied the trash and they dug my old cassette out and put it back on.

First let me say that you wrote a very thorough description of the problem, with follow up info as well. Good job.

The problem you're describing could be caused by a misaligned derailleur hanger, cable tension not adjusted properly, frame flex, etc., BUT, I've highlighted what I think is a key part of the story above.

The problem apparently went away with the new Ultegra cassette installed. I have no idea why you had the problem with the new cassette you provided to the LBS, but maybe it was indeed defective as the mechanic suggested (I've never had that happen, but who knows).

But when they dug the old cassette out of the trash and re-installed it, and the problem re-occured, that leads me to believe that there was enough wear on the old cassette that when paired with the new chain, it caused the chain to skip. That's a common issue (old and new parts not playing well together).

I recommend going back to the shop, explaining to them that the new Ultegra cassette seemed to fix the problem, and have them re-install it (and charge you for the cassette, of course). Take the bike for another test ride, making SURE the problem is fixed, and make SURE the shop understands you're going to do this. At that point, do what you can to get your money back (if possible) on the apparently defective cassette you supplied originally, and chalk it up to a freak thing.

Bottom line, if the new Ultegra cassette fixes the problem, install it and ride on-

Last edited by well biked; 05-13-08 at 09:30 AM.
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Old 05-13-08, 09:39 AM   #15
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From your very good description it sounds like the shift cable needs an adjustment. Or possibly the derailleur hanger is bent.

Al
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Old 05-13-08, 09:46 AM   #16
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I agree - I'd go with the simple answer first. Ockham's Razor. Sounds like a little derailleur misadjustment or cable stretch, which is a common symptom with a new cable. Might just need a little re-tune.
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Old 05-13-08, 10:03 AM   #17
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I think I had a similair issue the OP describes.... I tried numerous adjustments without much success, in the end turned out the derailleur hanger had developed a small crack which was probably allowing some flex to occur under load. I don't have the issue anymore. I might post a pic of it once I'm home tonight.... but the crack was barely visible, in fact the store employee at first asked "whats wrong with this one?" when I brought the old one to match a new one.

Also, maybe the cassette wasn't installed properly? Either mis-aligned slightly or not tightned fully?
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Old 05-13-08, 02:25 PM   #18
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When it makes that "Ka-chunk!" noise does it actually slip or just a noise?
Does it do it on more than one chain ring up front?
It is actually slipping. The first time it happened it was completely unexpected and I about fell over! My first thought, while it was occurring, was that my chain broke. When I was able to be seated I noticed my chain still on and that I could pedal normally. This was only on the middle chainring on my triple, which is a 42. I never tried it on the 52. Frankly, I'm a little afraid to have this happen at greater speed. If I loose control I'll be dealing with road rash and broken bike parts.

As for the ultegra cassette seemingly fixing the problem, I just rode it in the parking lot at the shop and stood up 3x to pedal and it didn't happen. I think if I took it for a test again I could probably make it happen. It took me a couple of times to get the original SRAM cassette to also cause the chain to jump, too. It doesn't happen every time I stand to pedal. And the Ultegra cassette I tested was a 12-23, and I'd rather have the 12-26 of the PG970 SRAM cassette.

Thanks for all the replies. So once I get the bike back if it is still not fixed I should look for a crack in the rear derailer hanger. They just put that on about 200 miles ago, literally only 5 rides ago. I probably will also give the tension on the cable a quarter turn or so. I have no experience of messing with cable tension so am hopefully the bike shop can get that figured out for me.

I'll post back when I get the bike back. May be tomorrow, hopefully Thursday at the latest.
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Old 05-13-08, 04:47 PM   #19
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OP, read the Sheldon Brown page on RD adjustment.
It'll tell you everything you need to know about setting the barrel adjuster. I read it a couple times and it told me all I needed to set both my road bike and my MTB.

PS, I had my MTB jumping as well, and it was outlined beautifully on Sheldon's page. Had it fixed in about 15 minutes.
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Old 05-13-08, 05:47 PM   #20
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Either the chain or cassette is used or defective.

The chain, of course, can be ruled out with the replacement you have had installed since. That said, I would say that one of that the shop:

#1: Did not replace the cassette
OR
#2: Replaced only certain cogs in your original cassette (out of the question on SRAM Red, of course)
OR
#3: Was sent and installed a defective cassette.

In my experience, the one and only cause of genuine chain skip is a worn chain on a new freewheel/cassette, or a new chain on a worn freewheel/cassette. Seeing that chain is a non-issue at this point, I would focus attention on having the entire cassette replaced once again under suspicion of defectiveness.

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Old 05-19-08, 09:29 AM   #21
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Just wanted to follow up ...

I got my bike back Thurs with the new SRAM cassette put back on. Went for a test ride -- the chain still jumped on me when I stood and pedaled hard. I had a 60 mile ride planned with a friend for the next morning, so I thought I would just ride my bike and take it easy.

At the start of the 60 mile ride the chain jumped on me 3 times. Then after about 5 miles it never happened again. I even stood up and hammered away at the end of that ride and again on a ride today and the chain has not jumped on the rear cassette.

So it seems my problem was solved by a little cable stretch. Too bad the LBS couldn't have suggested that might be the problem -- to just give it a little time and it might clear up since they put a new RD cable on (I brought the new RD cable to their attention the 2nd time I took my bike back as a possibility of the problem, but they dismissed my suggestion as to them everything was adjusted correctly so it couldn't be the cable.) Live and learn. I'm going to do them a favor and tell them the issue has been fixed with a little cable stretch.
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