Gears slipping - please help

King of Spain

My Durace keeps slipping when I am on my lowest gear (39 x 27). I am off to the Alps on Wednesday so desperate to remedy it. When I tried loosening the cable with the black plastic screw I lost my next gear too !...and when I re-tightened it it made no difference. Now I am two gears short !

Please help or advise anyone ? I am a bit of a mechanical novice but am sure it must be quite easy really ?

Many thanks for any advice offered.

chriskempton

You need to screw the adjuster on the rear mech out (anti clockwise) until the chain sits in the biggest cog happily. If the rear mech still doesn't go far enough in toward your spokes then you also need to adjust the 'Low' screw on the rear mech (there are two next to each other the outside of the body). These two screws are limiters that stop the mech going so far in or out that the chain drops off either end of the cassette.

Have a look on Sheldon Brown's website, or download the manual from the Shimano website, or get someone from a bikeshop or another cyclist to show you how to do this. You need to learn this before you go to the Alps - gears do go out of adjustment every so often so you'll be spending your time wisely.

whyamihere

Slipping how? Was it dropping onto another gear, or was the chain skipping forward on the cassette without turning the wheel properly?

If the former, index your mech. If the latter, look at the shape of the teeth on the cassette. If the teeth are worn (the 'valley' between the teeth will be either longer than usual or the teeth will resemble a shark's fin with the back of the tooth worn away), then the cassette and chain will need replacing.

If the cassette isn't worn, the chain might have stretched. To quote Sheldon Brown:

Measuring Chain Wear

The standard way to measure chain wear is with a ruler or steel tape measure. This can be done without removing the chain from the bicycle. The normal technique is to measure a one-foot length, placing an inch mark of the ruler exactly in the middle of one rivet, then looking at the corresponding rivet 12 complete links away. On a new, unworn chain, this rivet will also line up exactly with an inch mark. With a worn chain, the rivet will be past the inch mark.

This gives a direct measurement of the wear to the chain, and an indirect measurement of the wear to the sprockets:

* If the rivet is less than 1/16" past the mark, all is well.

* If the rivet is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.

* If the rivet is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.

* If the rivet is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

King of Spain

Thanks to you both so much. It's actually a new rear cassette and chain (3 months old, about 1000 miles) so would hope it shouldn't be wear and tear.

Sounds like I just need to keep loosening the rear screw to remedy, not tighten it which was one of my attmpted solutions !

I'll refer to the websites you mention and keep my fingers crossed. Thanks for some invaluable advice both.
KoS

whyamihere

Actually, if it's failing to reach the lowest gears, then you need to increase the cable tension, not decrease it. The mech is pulled towards the high gears by the spring, and this is counteracted by the cable tension, which pulls it towards the lower gears. If your cable tension is too low, then instead of changing to a lower gear, your shifters will just take up the slack. An easy test is to shift into the smallest sprocket, and see how much spare cable there is to the mech. My guess is that there will be lots. If you eliminate the slack (best to use the cable fixing bolt if there's lots, your problem should go.

Doobz

check out this video on youtube.. Its really simple once you have watched it a few times..

http://www.youtube.com/watch?v=SkzvfCaIbyQ

hope this helps you out