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Discussion Starter · #1 ·
When I ride in low gear the chain skips gears. This is not a significant problem when I am riding on level trails, but when I ride uphill, especially when I have to put my back into it (stand up) its awful. The gears/chain skips so much now when I ride up hill, my feet are knocked off the pedals and am getting gashes in my legs from the pedals. So I just dont ride in the lowest gears anymore on the trail.

This problem has happened before and the bike shop will just say it needs adjustment and adjust the gears, but it will just happen again. I looked over the Cassette and did not see any broken tips.

How would I go about fixing this issue. Again I want to do it myself because I do not feel the bike shop will diagnose or fix it completely.

Thanks
 

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Singletrack Slayer
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Need more info!!

How old is the drivetrain? Measure your chain, it could be worn out. Maybe your hanger is bent? Sounds like it could be a worn out drivetrain. If you provide us with more information, I am sure we could lend a hand.
 

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Have you changed the chain recently?

It can expose wear in your cassette. Very common.

In any case nothing on cassette needs to be "broken" but as things wear slipping can happen. Wear on the smaller cogs tends to be greater than the other gears as fewer teeth take on the whole load from the chain. Further, these loads can be greater, such as when you stand and hammer with greater and a more uneven stress. The load-bearing edges of the teeth which contact the rollers wear lose their sharpness and grip. This changes the distance between teeth and in order to accommodate this the chain must stretch. At this point the engagement is no longer optimal. With fewer teeth to handle stress and less wrap of the chain than on the larger gears due to the angle of the chain as it encounters the cog, the whole chain lifts forward on all the teeth and you slip.

New chain and new cassette are recommended.
 

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Discussion Starter · #4 ·
This is my Bike (about 1.5 years old)
http://www.performancebike.com/bikes/Product_10052_10551_1027903_-1_36007_20000_36502

I looked over the cassette closely again and saw that one of the nodes (or is it cogs?) was bent. Being cheap I tried to bend it back in place. That did not work. So I bought a new cassette this morning. This one
http://www.performancebike.com/bikes/Product_10052_10551_1032002_-1_400021_400002_400186

I bought the proper tools and put it on myself. Drove to my favorite trail and went riding. It did not fix the problem. So I speculate that that specific cog got bent due to whatever is causing the skipping. The chain is relatively new. It has about 50 miles of trail riding on it and that is being generous.

On the big cassette on the real tire which have 9 gears. I had the keep the chain on the middle gear for most of the ~12 mile ride which can be very unpleasant. Any smaller gears (which give more propulsion per revolution) all works well. On the largest gear all works well also. Its when the chain is on the 2nd, 3rd, and 4th largest gears that the chain skips to such a point that I cannot ride uphills with those gears. And those are the ones that I need to use to ride uphill as the largest gear does not give enough propulsion.

You will have to be more specific as to what a drivetrain is.

Thanks
 

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The 990 cassette is solid, I own 2 of them, I would always put a new cassette and chain on at the same time. I run only sram chains because I have never broken one and the masterlink is nice. Use a chain checker to see how streched your old chain is. It could also be a tweaked derailleur hanger. Sounds like that might be the problem. PS, if you still have a problem w/ a new chain then you know it is the derailleur alignment.
 

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Discussion Starter · #6 ·
There was originally an shimano chain on it. When I put the sram chain on to replace the shimano one that broke, I just put both chains side by side and made the new sram chain the same length of the shimano.

Could a loose chain be causing this problem? If I take a link out of the current chain, would that possibly solve this issue?
 

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A couple of other ideas...

I had a similar problem with a 1-year-old bike. It turned out to be the front chain rings. Both the granny and 32 tooth rigs were shot. See if the slipping occurs one (or two) particular ring.

As others noted, the problem could also be a bent hanger. When you look from the back of the bike, does the teeth on the cassette/chain/rear derailleur form a perfectly straight line? Also take a look from above. Does the jockey wheel align perfectly with the chain/cassette?

If either one is offer, it could be the cause of the problem.

Everythingyouneedtoknowaboutchainstretch...

http://www.sheldonbrown.com/chains.html
 

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Discussion Starter · #8 ·
I only ride on weekends so I am taking this slow. Also, though I am comfortable with fixing chains, flat tires, etc., that rear derailleur looks very complicated and intimidating. So I find myself leaning to other things that may be the cause of the problem. Yes, I think the derailleur is slightly bent...I have had my share of literally flipping the bile over me spills.

Looking on some of the sites listed, I came across this as being accurately describing my problem.
http://sheldonbrown.com/autoshift.html

If simply greasing the cable guide fixes this......
 

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I thought I would tag onto this post. My last ride I experienced "chain suck" and slipping. I have a nice gauge on my chainstay. Last night I did a hard nose inspection (being new I really wasn't sure what to look for). However, I found a bent tooth on the middle chainring. I also found a bent tooth on one of the cogs. It happens to bend inward so if the chain is on the cog above it, as the rotation happens the bent tooth will ever so slightly lift the chain above as it passes by. It seems that the chain is not stretched. I was wondering if I could bend the teeth back or should I just go ahead and replace the cassette, chainrings and chain?


I have a 99' Specialized Stumpjumper Comp. Any suggestions as to replacement parts woudl be great. Also, should I order online or just take to LBS? I don't have all the tools and have never really wrenched the bike myself yet. This may be a good time to learn a thing or two.
 

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From your description and the elimiantion of other possibilities, I suspect that it's either an RD trim issue, or more likely a "B" screw adjustment. Put your bike into one of the problem combinations, and get off and look closely ar the RD and cassette.

There should be a free section of chain of about 1" between the upper pulley and the cog. Often bikes are set up with the RD set too high, and the upper pulley is too close to the cog, causing engagement problems and skipping. Try adjusting the "B" screw to pull the RD down, and see if that helps.

The other possibility is a bent or twisted hanger or RD. On the smaller cogs there's enough distance for the chain to flex and mask the problem, but as the RD to cog distance gets short (on larger cogs) it becomes extremely sensetive to any mis-allignment, and skips.

Lastly, what do you use as a chain lube? (I have to ask, since that's what I do). A properly lubed chain is more supple, and engages the cogs much more smoothly, than a dry chain or one silted with grit between the plates.
 
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