2wheelfelicity

Hopefully someone can help. I have looked through what feels like every thread that has to deal with skipping chain to no avail.

I recently bought a new omnium cargo frame and pulled most of the drivetrain off my old 90's mtb I had built up the year prior. It was a 1x and used an older shimano deore sl thumb shifter that I used in friction mode shifting the same derailleur on a 7sp cassette.
When I transferred the drivetrain over I put on a used but still good condition cassette from another bike I upgraded. For the derailleur I had been using, the bolt that clamps onto the cable had stripped so I bought a used shimano alivio derailleur, a fair bit used, but friction shifting so I figured no problem.

The setup on the mtn bike frame was flawless. When I put the parts with the previous mentioned alterations on the cargo bike, the chain slips CONSTANTLY unless its in the hardest gear, I imagine because its not contending with the cable.
I have tried two new derailleur cables and 3 different derailleurs. The problem has persisted. I have made sure ALL the slack is out of the cable. I have no idea why this is happening all of a sudden. I have a rivendell shifter on standby for when the handlebar clamps come in but why would the original shifter not work all of a sudden? and will buy a new derailleur if thats what the problem ends up being, can I really have 3 bad derailleurs?

Any thoughts are much appreciated. Thanks!

cxwrench

If you have SL-M700 that have the flip up wire twist thing on top then all you should have to do is tighten it up. If you have the newer shifters that just have the name plate on top you'd have to give me an exact model # so I can look it up. Or better yet you can look it up yourself. Shimano tech site

Andrew R Stewart 

I question your assumption of the cable being an issue. From your description my first thought is the chain and cassette are not liking each other. So if you have a different cog set and/or chain perhaps try them.

But to directly address you're cable theory- take an old cable, can be either front or rear in length as you'll only be using a few inches of it. Remove the current cable. Thread the test cable through the rear der's cable casing stop (often this is also a barrel adjuster) so the cable head seats into the der's seat. Now secure the cable with the der's anchor bolt. By also manually moving/shifting the der to any one of the cogs and tightening the anchor bolt there and fine tuning the der's being well centered below the cog you can ride the bike in a cod with no chance for the shift lever or cable routing being involved. If the system still skips the problem isn't the cable routing or the shift lever.

I have seen frames that have a lot of flex cause the der to move about (and sort of try to shift) and in the extreme tug on a friction lever causing the lever to creep/slip a bit. The above test will eliminate this possibility.

There are many reasons why a system can be skipping. Miss matched chain/cog wear, slipping shift lever, tight/twisted/damaged chain links, bent/damaged teeth, broken axles or drop outs, slipping axle in drop out, cable friction (in casing or about guides), fraying cable and more. Then there's the ratchets in the cogset... Andy

Bigbus

Almost every time I have a chain skip/jump but not changing gears on me it always turns out being a stiff link. If everything else is indexed properly (I know-friction) and there isn't any cable slop or stickiness, it's always the chain, assuming nothing is worn out (cogs, etc) It only takes a minute to work each link and eliminate it as the culprit. Going through the cogs and chainring it's always flexing in the same direction, but it has to back over itself on that little derailleur guide. Good luck

2wheelfelicity

cxwrench Thanks for the link. Its an SL-M730. I looked it up and found the manuals but nothing that I could see that would solve the problem. It doesn't have that flip up wire you mentioned either. Thanks for the help though.

Andrew R Stewart I hadn't thought to isolate the derailleur like that. I will give it a try. It's a brand new 8sp chain on 8 sp cassette that's still in good shape so I don't know why they wouldn't be working well together, but if it doesn't appear to be the derailleur, then I will turn my attention there. Otherwise it has brand new dropouts and a thru-axle so hopefully that's not the issue. I realize it could have been bent in shipping or something, but doesn't appear that way. Crazy about the extreme fram flex. Thanks for all the tips, I'll start working through them tomorrow.

Bigbus Thanks for that tip as well. I'll run through it. Didn't think to have chain problems with it being new, but that's definitely not a guarantee aganist defects.

Andrew R Stewart 

This is the kind of problem that an experienced wrench can often figure out in short order if given the chance to have the bike in hand. After you get really frustrated you might see is some one else (at a LBS?) can take a look at it. Andy

79pmooney

Question: when you say the chain slips, is it wanting to shift into a smaller cog or is the chain not seating right on the teeth of the cog it is on? I read your post before any of the other answers and got the impression the derailleur slips continuously toward the smallest cog and that gear works just fine because the derailleur can go no farther. I started to reply based on that assumption and got sidetracked. So, just in case my gut was right, I'll post what I wrote.


This is an issue in the friction shifter. You don't say what type it is so I can only give you general answers. Most friction shifters consist of a lever on a shaft. Outside that lever is a bolt that tightens to increase the friction level. Inside the shifter are two plates. One moves with the shifter. The other is anchored to the shaft. The friction is between the plates. What you are seeing - almost certainly - is either inadequate friction between those plates or incorrect assembly of the shifter as a unit. (Typically there is one way the shifter assembles. All the parts have to be there and in exactly the right order.) If you've never taken the shifter apart, assembly should be fine. If you choose to take apart, document well the sequence!

So, this leaves two easy causes for inadequate friction - 1) that bolt not being tight enough. (Different derailleurs use different springs and have different cable tensions. If your new one has a beefier spring, you need to tighten that bolt. (Usually with a regular screwdriver but I have also seen hex head, allen head and Phillips head. Better shifters often have a "D" ring that allows hand tightening so a racer could tighten mid-race if needed).

Another possibility is that oil has gotten between the plates. And guess what? No friction. If that is the case, you will have to take the shifter apart, at least down to those plates, take them off and clean with detergent or solvent until they are completely oil free and dry. Reassemble with light grease on elsewhere but not the plates.

Yes, all the other stuff you looked at should be in good working order but your problem is too little friction, not too much. All that good work has probably just made it worse! (But the only place friction is "good" here, other than making a bad situation a touch better, is in that shifter mechanism; between those two plates.)


I may be totally out to lunch here and the posters above right but if I am right, only attacking the shifter itself woll fix your problem.

Geepig

You are sure that the lever is still set to friction, and hasn't been knocked onto SIS?

ClydeClydeson

THis is the problem. You generally cannot tell if a cassette is in good shape by looking at it. The only sure-fire method of determining if a cassette is too worn for a new chain is to try it with a new chain - if it skips under load then the cassette is worn. Your description of the problem sounds like the primary indicator that you are trying to use a worn cassette with a not-worn chain.
A new cassette will fix the problem, as would re-installing the old chain that used to run on that cassette (if possible).

The reason it doesn't skip in the smallest (hardest) cog is probably because that cog was used less than the others and is less worn.

As for the potential that the shift cable may be causing the problem - extremely unlikely. Even if the cable is completely fornicated, once you get the chain roughly aligned with a gear it should function properly. It might be hard to get it to accurately land on a gear every time, but your description of the problem doesn't sound like this is the cause.

2wheelfelicity

Thanks for all the advice everyone. It ended up being the cable, but my post was unknowingly deceptive as I thought I had pulled all the slack out after several times having wrapped the excess cable around my finger and pulling tight. Last night before a short ride and before delving into the other fixes I tried one last time. I put the barrel adjuster all the way in and used pliers to pull the cable. It pulled a tad more then I backed out the barrel adjuster until it started moving the derailleur. Without hope for success, it ended up working fine. The frame's "triangle" is actually a square and I think I underestimated how tight it needed to be with the longer than normal cable.
Thanks for all the input and sorry for my overconfidence in the assumption all the slack was out.