Bicycle Mechanics - Gear questions

Hi all,

Recently my gears have been playing up.

Now before I go on a number of things I should confess to:
- my bike is very dirty!
- my chain is stretched and the gears worn a bit (I left it too long when checking chain wear and now I will need to replace the cassette and chain)!

So one day my gears started to skip horribly, so when I got home I adjusted the cable until they worked nicely. The next ride was fine, and the shifted worked perfectly. The following ride, however, things started to skip again. I got home, adjusted the cables and the same thing happened on the next two rides.

My questions are:
- what can be causing this? Surely the chain cannot be stretching in between rides, and the gears can't be wearing that quickly - so is it cable stretch?
- if I was to replace the cassette and chain, would I also need to replace the chainrings and the jockey wheels?

Thanks

Daven

Check to be sure the cables are clamped securely. If they are slipping in the pinch bolts the shifting will go out of time. Unless your chain is very badly "stretched" your chainrings should be ok as will the rear derailleur pulleys.

Adjusting your RD won't do anything for the skipping.

You need to change your cassette and chain anyway; do that, and if you are still having problems come back and get help. With all of the adjusting you are doing now, start over from from scratch after you've installed the cassette and chain.

Fix what you know is wrong (cassette and chain) before you go farther with troubleshooting. While you have things apart check the condition of your cables and housings and be sure that the housings are properly prepared and installed; ends cut cleanly and filed flat, and the proper ferrules installed. Pay particular attention to the lower loop of housing going into your derailleur; it tends to collect dirt and crud. Dirty or poorly-installed cables and housings are a frequent cause of shifting woes.

Check to be sure the cables are clamped securely. If they are slipping in the pinch bolts the shifting will go out of time. Unless your chain is very badly "stretched" your chainrings should be ok as will the rear derailleur pulleys.

Forgot to mention, this was one of the first things I checked. How badly stretched is "badly stretched"? I think mine, after a quick measurement with a digital caliper, is 3.216 inches instead of 3 inches, which to me is pretty badly worn! I have been very bad with maintenance this year :o


Adjusting your RD won't do anything for the skipping.

You need to change your cassette and chain anyway; do that, and if you are still having problems come back and get help. With all of the adjusting you are doing now, start over from from scratch after you've installed the cassette and chain.

Well to be honest, the skipping just seems to be the derailleur not moving enough to get the chain onto the next cog and the chain skipping between the two. When I adjust the cable then the shifting is perfect with no skipping.


Fix what you know is wrong (cassette and chain) before you go farther with troubleshooting. While you have things apart check the condition of your cables and housings and be sure that the housings are properly prepared and installed; ends cut cleanly and filed flat, and the proper ferrules installed. Pay particular attention to the lower loop of housing going into your derailleur; it tends to collect dirt and crud. Dirty or poorly-installed cables and housings are a frequent cause of shifting woes.

I will check out the cable, was thinking of replacing it anyway. The cable and chain haven't been changed since I bought the bike (about 10,000 miles and 3.5 years ago!) so I was going to get together a shopping list.

Thanks for the replies,

Daven

Forgot to mention, this was one of the first things I checked. How badly stretched is "badly stretched"? I think mine, after a quick measurement with a digital caliper, is 3.216 inches instead of 3 inches, which to me is pretty badly worn! I have been very bad with maintenance this year :o
(3.216/3.000)*100 = 7%!! That can't be accurate as the chain would have broken long since. If you are measuring using the inside of the rollers as indexing points, that will give a misleading reading. Use a good ruler and measure the center-to-center distance between two pins that are 24 pins apart (i.e. 12 full links). On a new chain that should be 12.00 inches. If it's 12-1/8" or more (1%) your chain is overdue and the cassette with it.

(3.216/3.000)*100 = 7%!! That can't be accurate as the chain would have broken long since. If you are measuring using the inside of the rollers as indexing points, that will give a misleading reading. Use a good ruler and measure the center-to-center distance between two pins that are 24 pins apart (i.e. 12 full links). On a new chain that should be 12.00 inches. If it's 12-1/8" or more (1%) your chain is overdue and the cassette with it.

ok I will try it again with a ruler! The batteries are on the way out in the caliper so it might (hopefully) be out!!

From the general direction of this , I'd say:new chain and cog set , for sure ..
freewheel or cassette, depending on what you have on the wheel.

If you buy cables, get decent-quality ones with compressionless lined housings and die-drawn stainless inner wires. There are a number of good ones available, no need to go with anything exotic. Here's a good guide to cable preparation and installation: http://sheldonbrown.com/cables.html Pay close attention to the sections "Cutting Housing and Preparing the Ends" and "Cable Lubrication" lubrication will probably NOT be required with modern cables.

Check your cable housings.

Whenever I've encountered a bike that needed frequent cable tension adjustments, the cause was a cable housing that was gradually shortening itself.

A worn chain on a dirty bike sounds to me like a candidate for some major component replacements.

"Now before I go on a number of things I should confess to:
- my bike is very dirty!"

I think some cleaning/lubing cables may be in order???

If it helps, here are some pictures of my chainrings and cogs - do they look worn, they don't look to bad to me (although the only pictures of worn cogs I've seen are off Sheldon's website). Either way they are disgustingly dirty, and I have a new cassette and chain in the post, so even if I don't need them now, I have them for when I do need them! :)

243248

243247

Thanks

Daven