EdwardT

My chain keeps skipping gears.

I have an 11 year old HT mtb bike. Originally 3x9. Now it's 1x9. The cassette is 11-42. Love this setup.

Since last Fall, I've had my derailleur adjusted three times. The first 2 with a shop mechanic. The last with a guy working from home. Each time, it shifts great for a while... and then slowly starts slipping. It's a constant progression. The chain, ring and cassette are all in good shape. The shop mechanic said the derailleur is okay.

Not sure what the problem is. Input appreciated.

Oh yeah. Not interested in a new bike. At least not until there's decent selection out there.

Bill Kapaun

Friction shifter?
What exactly do you mean by skipping?
Gear slowly changing to the next higher gear....repeat.
OR
Jumping over a gear such as 1 to 3?

An 11 year old RDER may not be designed for a 42T cog?
Which shifter & RDER? Brand & model.

Unca_Sam

First you say your chain keeps skipping gears. You say "it" starts slipping. Then you say that the chain, ring, and cassette are all in good shape...

A skipping chain is usually a symptom that one of those things is no longer in good shape. Pictures of the parts can help. Did you replace the chain recently? Have you never replaced the chain? Do you lube and keep the drivetrain clean, or run it to sludge?

Another issue, if you've having poor shifts, is that your D hanger could be tweaked. Finally, if the cables are new, perhaps they've moved out of tension.

cxwrench

11 year old derailleur w/ a 42? I'd start there, no way that's within the max cog capacity of the derailleur.

cyccommute 

As will most everything derailer, it is probably a cable issue. Others have asked what you mean by “slipping” as will I. Do you mean it starts to ghost shift with the chain shifting to a higher gear (i.e. move to a smaller sized cog) without your input? Or does it try to downshift (i.e. move to a larger sized cog) without your input?

If it is trying to shift to a higher gear, that is due to losing tension in the cable. This could be due to the cable stretching as it gets pulled on through shifting. Cables often take a little while to bed in so that they get just a little longer. This is usually an issue that lessens over time. To check this, shift in to the highest (smallest gear) on the rear derailer and see if the cable is taut. It doesn’t need to be guitar string tight but the cable also shouldn’t be able to be pulled away from the frame easily.

If your cable is older, you might be slipping at the anchor nut. Coated cables can slip if the anchor bolt isn’t tightened enough. Don’t tighten the anchor bolt enough that it crushes and cuts the cable but it should be enough to keep it from slipping.

If the derailer is trying to downshift, the cable may be too tight and/or the cable may be hanging up on something inside the outer cable. First shift into the lowest gear like below

Library - 3391 by Stuart Black, on Flickr

Then upshift without pedaling. This will relax the tension on the cable

Library - 3392 by Stuart Black, on Flickr

with the cable looking like this.

Library - 3393 by Stuart Black, on Flickr

Now you can pull the cable housing out if the frame stops.

Library - 3394 by Stuart Black, on Flickr

Library - 3395 by Stuart Black, on Flickr

This will allow you to slide the housing up and down the shifter cable which allows you to inspect the covered bits for any corrosion, debris, or damage. Watch for breaks in the wider that may be hanging up on the cable. While apart, take a bit of grease between your thumb and forefinger and run it up and down the inner cable.

Library - 3396 by Stuart Black, on Flickr

You might also want to pull off the ferrules and inspect the ends. Some cable housing can be damaged like this one. Notice the little wire sticking out? That stray wire is from the housing and can jam the cable.

IMG_1361 by Stuart Black, on Flickr

This is what it looks like without the ferrule.

IMG_1362 by Stuart Black, on Flickr

ridelikeaturtle

^^^ was gonna suggest new housing, ferrules, and cable; but the housing and ferrules are very important. If these are squishy and old and frayed and all over the place, so will be your shifting.