Chain/cassette issue on 7spd

ahajdar said:

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[font=Arial]I own an older model of DiamondBackRacing (7spd) mtb which has the following equipment on it: XT bottom bracket, STX-RC rear derailleur, 7spd cassete (not sure which model is). I installed a chain (Shimano HG-53) and I'm having a following problem: my rear cassette in gears 6 and 7 have a tendency on occassion to force the chain on lower gear (in other words: the chain seems slightly unstable when putting heavy pressure while riding in gears 6 and 7). I thought that I should replace the rear cassette but don't know which model to choose. Would you please suggest me the right model of the cassette for my bike (even the on-line place where I can buy it), or perhaps you think there is a different problem with this skipping issue?[/font]
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[font=Arial]Thanks,[/font]
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[font=Arial]Amir[/font]

"A new chain on a worn sprocket. Most of the driving is happening on the left side, where the chain first engages the sprocket. Due to the mismatch in pitch, the rollers in the part of the chain that is about to leave the sprocket is doing very little to push their teeth forward, instead, they are being forced upward by the slope of the teeth.
Since the teeth/rollers on our left are doing most of the work the load is concentrated on them.

In addition, as the roller follows its tooth around the sprocket it rolls up the "ramp," while under load. This promotes wear to the insides of the rollers and to the "bushings" they roll on. With a properly meshed chain, the roller only turns a tiny bit as it rolls onto and off of the chain.

Due to the pitch mismatch, the chain will not reliably mesh with the sprocket under load, and will tend to jump forward, skipping over the teeth."

The above is extracted from Sheldon Brown's web site at URL:

<A new chain on a worn sprocket. Most of the driving is happening on the left side, where the chain first engages the sprocket. Due to the mismatch in pitch, the rollers in the part of the chain that is about to leave the sprocket is doing very little to push their teeth forward, instead, they are being forced upward by the slope of the teeth.
Since the teeth/rollers on our left are doing most of the work the load is concentrated on them.

In addition, as the roller follows its tooth around the sprocket it rolls up the "ramp," while under load. This promotes wear to the insides of the rollers and to the "bushings" they roll on. With a properly meshed chain, the roller only turns a tiny bit as it rolls onto and off of the chain.

Due to the pitch mismatch, the chain will not reliably mesh with the sprocket under load, and will tend to jump forward, skipping over the teeth."

The above is extracted from Sheldon Brown's web site at URL:

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

You need a new Shimano HG 7 speed cassette. Sheldon has those too:

<http://sheldonbrown.com/harris/k7.html#10>

Dave,

Thanks for your help. It looks like I was stuck in the middle of various standards Shimano has placed on us customers. I bought a new chain and 7 speed cassette but I have had a chance to replace the old ones. Hopefully, I'll do it this weekend and solve my problem.

Thanks again!

Amir