Bike to Work

Hello,

I recently replaced my chain and rear cassette. I had also replaced the derailleur hanger as the previous one had gotten bent. After adjustments, there is no chain skipping on the rear cassette when the chain is on the large front ring, but it skips when it is on the small front ring. I made further adjustments on the barrel adjuster and B-screw. The skipping was reduced some but is still there. Is the small front chain ring the cause of the problem? Thanks for any advice.

2old

FME, there are instances in which a derailleur won't work throughout the range with a chainring/cassette combination (my experience may not be the same as others here). However it can be made to operate perfectly at either end of the gear ratios. If this isn't possible for your system, there is something wrong with a component or adjustment, and IMO it's the latter (probably the "B" screw).

Iride01 

Anything that may have changed the chain line up sometime in the past history of the bike? A slightly worn chain may have been flexible enough side to side and worked well enough. But with new chain and cassette it no longer does?

That'd pretty much be a crankset change or a BB of the wrong spindle length being put in.

Does it seem to be the smaller sprockets or larger sprockets on the cassette that it has the issue with when in the small front?

Perhaps you sized the chain too long. Did you match the length to the previous chain?

Even though you put a new RD hanger on, did you check to make sure it's aligned properly with the wheel?

But b-screw is the one of the first things to check as 2old said. It should be adjusted to let the jockey wheel be as close as possible without interference to any of the sprockets.

Welcome to BF.

bboy314

Could be a very worn chainring. Pictures of the teeth could help determine this.

FBinNY 

Nothing about a chainring would cause skipping on the cassette.

You mentioned replacing the hanger, but didn't say whether you made sure the new one was squared up. If you didn't align the new hanger, that's the likely cause of your issues.

When the RD isn't aligned, the cage's rotation moves the upper pulley in and out, messing up the trim.

Bike to Work

Thanks for all of the feedback. I am going to try out your recommendations and see how it goes.

Bill Kapaun

When on the small ring, does it skip on all the cogs or not.
IF it only skips on the smallest cog or 2, don't use that combination. It's cross chaining which could be part/most of the problem.

FBinNY 

Sorry, but no.

Cross chaining, or any chainring issue could cause skipping in the rear. The chain is fed onto cassette by the jockey wheel and anything forward of the RD wouldn't change that. (assuming that the RD is properly set up)

Bill Kapaun

However, it's a direct path from the top of the cog to the top of the chain ring aka the main pathway of the force being transmitted from front to back.
Let's hear from the OP.
EDIT- IF my assertion is true, it would tend to point to OTHER misalignment issues. Just that if skipping on the smallest cogs only, it's just pushed the misalignment to the point that NOTICEABLE problems happen. There may already be chain rub etc. issues that the OP doesn't realize that would be a red flag to us in addition to a simple visual inspection. It's not difficult to stand behind the bike and visually line up the path of the chain through the RDER to ascertain it lines up properly with the cog above it.

FBinNY 

A technical non-sequitor. You haven't explained how mis alignment where the chain is spooling off would cause skipping.

For a theory to hold water, you have to close gaps by connecting the dots.

FWIW the OP's issue is textbook for a misaligned RD, so that's the place to start.

grumpus

Skipping may occur if your chain is too long and the rear derailleur is unable to take up the slack, but it works fine when the large front ring takes it up. Or your rear derailleur is bent and/or its hanger is not correctly aligned - which ring you're on determines the amount of slack and thereby the rotation of the cage, the angle at which the jockey wheel is inclined to the cassette and it's distance from the cassette.
Fiddling with adjusters may reduce the symptoms but you need to address the root of the problem.

FBinNY 

IMPORTANT reminder to the OP.

You mentioned replacing the hanger because it was bent. Hopefully, you still have it, or can recover it from the trash, because odds are its perfectly OK and should be kept as a spare.

Hangers, rarely are true (squared up) and get tweaked when installed new. Likewise, your hanger can be reused the same way unless it's severely bent, or cracked. So save it, and possibly save some dough next time.

Kai Winters

New parts may not be perfect...when replacing a rear der hanger always check the new hanger's alignment...i've installed many that were not aligned correctly and required some tweaking.
Start from the beginning...check new rear der hanger alignment...make sure the new chain is the correct length...unless you are using a cassette with a different tooth count you should not have to adjust the B limit screw unless it was not adjusted correctly before hand but it doesn't hurt check and adjust again as necessary, at worst it eliminates a possible source of trouble...check and adjust H and L screws on the rear der...check der adjustment/cable tension, adjust as necessary...
As an afterthought was there a spacer between the old cassette and hub that perhaps was not used when installing the new cassette??? just a thought...I've done it in the shop and spent several minutes wondering why it wasn't shifting correctly...looked at the old cassette and there was a spacer stuck to it...popped off new cassette...put spacer where it belonged and voila shifted as it should...just a 'duh' moment but it happens...I always make sure to check for a spacer so I don't waste time doing a 'duh' again.
Good luck and keep us informed...

and yes apparently i love using '...' far too much...

soyabean

The OP made a mistake in swapping the hanger, and worse in assuming a new hanger is straight without verifying with something like the Park Tool DAG-3.

Your LBS should have this tool if the OP doesn't want to buy it for a DIY.

Bike to Work

I did save it. I am going to work on the straightening of the hanger.

Kai Winters

over/under on what is used to 'straighten' the hanger and how it works out
i'm thinking hydraulic press and now it won't work because it is squished and won't fit in the frame

oldbobcat

We can imagine all sorts of possible and impossible scenarios, but the only way to know for sure is to put the bike on a repair stand and watch the chain very closely as it's put through its shifts and just about to jump off the offending cog. That said, since I can't see the bike, here's my suggestion for a possible scenario that hasn't been suggested yet. While in the big ring the cage hangs vertically or somewhat forward of the axle, but from the small ring it hangs rearward to vertical. If there's a slight twist in the hanger, that will change the angle of the chain as it tries to mesh with the cassette cog. When aligning a derailleur hanger, check for longitudinal as well as vertical alignment.

grumpus

I suggested that here. My explanation could perhaps have been clearer, but "rotation of cage" and "angle of jockey wheel".

FBinNY 

If we're were going to play that game, I'd win.

You're post was #11, I said the same back in posts, 5, 8, & 10.

But it's a stupid, pointless game.

People don't always, or even often, read entire thread before posting. It's all OK, but the focus should be in helping the OP, and adding useful info to that end. Dupes happen, but that's fine because they lend credence to the earlier ones.

grumpus

Hydraulic press could surely squish it, but put it in a vise and tap it with a small hammer, tweak it with pliers or a crescent wrench; nothing drastic.

Kai Winters

or use a hanger alignment tool and be done with it and it is properly aligned in both axis

Duragrouch

I'd inspect the small chainring first for tooth wear. The OP may think it's skipping cogs when it may be skipping on the ring, might be hard to tell the difference. New chain and new cogs should match well, but I've gotten skipping with new chain on old cogs, so maybe this time it's new chain on old ring. If small ring checks out, look at the other stuff.

grumpus

Obviously use an alignment tool once its fitted, but if it's noticeably bent off the bike it's a good idea to flatten it first. Then when you come to use it, it will be close to correct.

Kontact

Why are most of your posts attacking new people for working on their bikes?

grumpus

A mechanic who isn't too busy to care?