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Front chain jumping too far

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Front chain jumping too far

Old 09-24-22, 07:09 AM
  #1  
alias5000
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Front chain jumping too far

Hi everyone,
I have a weird issue. I have a bicycle with a 9 speed Shimano M442 deore crankset. The middle chainring got worn out, so I replaced it with a 9 speed Shimano chainring (M590), same 32T - the only I could get a hold of. Now quite often when I shift from the big to the middle chainring, the chain jumps too far and either goes onto the small chainring, or rides somewhere in between before settling.
I've played around with the front derailleur adjustment and can reduce that behaviour, but then I'm kind of at the extremes of adjustment ranges (chain touching the FD in more than the extreme gear combinations). Front derailleur positioning (its clamp) has been touched, but I think it's positioned correctly (parallel to chainring)

Any clues?

Thanks!
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Old 09-24-22, 07:18 AM
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If you still have the old ring, the place to start is by removing the replacement and laying both on a table.

Chainrings vary in the offset between mounting surface and tooth centerline. That's a critical dimension, and if not matched, can cause problems like yours.

Your be options are to find as better matched replacement, or somehow correct for the difference.

Last edited by FBinNY; 09-24-22 at 07:22 AM.
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Old 09-24-22, 07:27 AM
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FBinNY I don't know about these things, so a question: is the offset built into the ring on one side? That is, could the OP have created this problem by using the right ring but flipped inside for outside? 40 years of prefessionally repairing things has shown me that people can be remarkably creative in putting things back together wrong in spite of all of the clues (like ignoring which side the countersunk screw holes are on, for instance.)

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Old 09-24-22, 07:57 AM
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I've checked for inside/outside and it's the right way around.

Interesting about the offset! I had just assumed that 9 speed is 9 speed. But of course, different cranksets could be made differently..
I do not have the old chainring anymore. I suppose I could attempt to use small shims and see what the result is - and if it would interfere with the small chainring.

It looks difficult to come buy a matched original chainring for M442 now.
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Old 09-24-22, 09:59 AM
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Some rings are symmetrical, with the teeth centered, while others have teeth offset toward one side or the other.

Unfortunately, there's no standard. Manufacturers adjust the offest to work with their cranks to yield the exact separation they want.
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Old 09-24-22, 10:11 AM
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Is it fair to assume that the chainring tooth spacing between the three chainrings should be equal? (Likely yes!?)
Then I can just measure the difference and shim accordingly
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Old 09-24-22, 10:22 AM
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If you didn't replace the chain you might also try doing so. Or at least check if the chain has any measurable wear. If it does, then that also might contribute to it not meshing immediately as the shift occurs.
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Old 09-24-22, 10:22 AM
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Originally Posted by alias5000 View Post
Is it fair to assume that the chainring tooth spacing between the three chainrings should be equal? (Likely yes!?)
Then I can just measure the difference and shim accordingly
It's a decent starting place, but may not be that exactly. Your OP is a bit ambiguous in the details.

On one hand you say the chain overshifts going from large to middle. That implies that the teeth are a bit outboard (closer to large ring). OTOH, you say it hangs up in between. This is common when the gap is too large allowing the chain to ride ride the tops of the teeth while leaning on the face of the outer ring. If that's the case, then the teeth are too far inboard, (the opposite of the first situation).

So, the first step is to decide whether the chain is over or under shifting, vis a vis the middle ring. If it's consistent one way or the other, you know what's needed. However, if it's not consistent, you need to consider other possibilities.
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Old 09-24-22, 01:34 PM
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Chain is being replaced regularly and checked for wear.

Ah, let me clarify my statements then:
If the small ring is position 1 and the big ring is position 3, when shifting from large to middle ring the chain sometimes moves to a 1.7ish position where the sides of the chain ride on top of the teeth (no engagement), before the chain falls on 1 or 2. Is that less ambiguous?
It's as if the middle ring teeth are too close to the large ring
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Old 09-24-22, 03:56 PM
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If you don't have the old one to compare with and it looks like the ring is closer to one ring than the other, then possibly you put it with the wrong side out. You did put it on the opposite side of the spider from the outer didn't you? Or perhaps it is different and not compatible.

If you are willing to spend another 15 bucks + shipping, then this place claims they'll have some for the FC-M422 crank in stock about the end of the month.

https://www.universalcycles.com/shop...s.php?id=16039

Though in their details they don't even mention FC-M442 and they do say it's for a FC-M510

https://si.shimano.com/en/pdfs/ev/FC...10-L-1873A.pdf

Shimano shows that part number for the correct middle ring is Y1DS98010 in their EV's for both the FC-M442 and FC-M442-8

https://si.shimano.com/en/pdfs/ev/FC...-M442-2527.pdf
https://si.shimano.com/en/pdfs/ev/FC...42-8-2528B.pdf


But then Universal says that it's also compatible with the FC-M590, though the Shimano EV shows that as a different part number. So maybe call them and see if they know more about the compatibility.

Last edited by Iride01; 09-24-22 at 04:09 PM.
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Old 09-24-22, 07:48 PM
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Originally Posted by alias5000 View Post
.....
It's as if the middle ring teeth are too close to the large ring
This is easy to fix with some homemade paper shims.

Start with a sheet of paper and punch or cut 10mm holes into it. Then cut out the holes to make shims. FWIW- I've done this often enough that I made a punch from a steel chainring bolt ---- sharpened to the outer edge by holding against a conical grinding burr. Once you've made the shims, soak them in oil (any oil) so they cannot later absorb water and they'll outlast the crank,'

From the description, I suspect that you'll need something a bit thicker, ie. a postcard, cereal box, etc.
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Old 09-27-22, 10:43 PM
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Does the cable tension of the front shifter pull the cage tight against the high limit screw? This can result in a slingshot effect on the the downshift. When the cable tension is released, the chain gets knocked off with too much velocity. If so, loosen the limit screw a quarter turn. Also, check that the chiainring is in correct sync with the crank. There's a sync mark on the ring that goes behind the crank.
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