stephr1

I have another thread going regarding some chain skipping issues (https://www.bikeforums.net/showthread...edux-again-%29) but I wanted to pull this question out as separate.

In adjusting the rear derailleur, in particular the high and low limits, I read (on e-How, I think) that these limit screws should be used to align the top pulley, chain and appropriate (1st or last) gear. Is this true?

I always thought the cable adjuster(s) were used to align the derailleur for best shifting and the limit screws were set just beyond their respective gear positions to prevent the chain from slipping off the cassette.

A little clarity is greatly appreciated.

Thanks and cheers...Steph

fietsbob

Stroke limit screws can be adjusted in isolation of ever hooking up cable and chain.

because all they do is stop the guide pulley to be directly under the 2 outermost cogs.

Drew Eckhardt 

The low limit screw may affect alignment in the smallest cog although its primary purpose is preventing a down shift off the smallest cog into the dropout.

You may be unable to get the shifter into the lowest gear if you turn the big cog screw enough to affect alignment.

You set them as far in as possible while still retaining acceptable shifts into those cogs without any tension on the cable applied by the shifter.

Right.

Al1943

A rear derailleur's "Low Limit" screw limits the derailleur's outer position for the largest (inner most) cog.

https://www.parktool.com/blog/repair-...nts-derailleur

ursle

Your assumption has been correct, the cable tension fine tunes the placement of the chain and the set screws stop the chain from going off either end. 9 and 10 speed, 5-8 speed the cable is adjusted with the shifter lever and the set screws keep the chain from going off the gears.

stephr1

@fietsbob

Thanks for clarifying. So, the limit screws ARE used to set 1st and last cog alignment. Not sure why I thought it otherwise.

Cheers....Steph

dsbrantjr

Follow the Park Tool procedure above step by step without skipping any. Using the shift wire to move the derailleur, set the limit screws just so that the shifts are crisp and reliable and no looser. Make your adjustments gradually, perhaps 1/8 turn or less as you get close.

Jeff Wills

No, they aren't there to set alignment. They are there to prevent the derailleur from shifting the chain off the cassette. The shifter's indexing controls the alignment of the chain on the cogs, and you adjust the alignment with the cable's barrel adjuster.

As DS said, follow the Park Tool procedure: https://www.parktool.com/blog/repair-...nts-derailleur . Do all the steps, in order. If it doesn't turn out to your satisfaction, start over from the beginning.

stephr1

OK. I went thru the Park rear derailleur adjustment process a few times and seemed to get it set. Shifting is crisp (that seems to have not been a problem) and the chain seems to ride correctly on all gears (I typically only use 3-7). However, the chain skip in 7th gear (very occasional on flat ground, definitely noticeable going over a bridge or reasonable incline) still just won't go away. I also rechecked the cage and it seems to be very much aligned and unbent.

I noticed something during the adjustment process. Adjusting the "B" screw doesn't do much at the low tension end of things and the guide pulley doesn't move until the screw is ~1/2 in. I can't get the guide pulley to rub (or even get very close enough to) the low/1st gear to be a concern.

I tried an experiment for my ride this morning. I put back in the old/original guide pulley to see if the slop in that pulley might provide enough play and get rid of the skip (The old pulley with the old chain and old cassette worked fine with no skipping ever). No luck. In fact, going up a hill and trying to downshift caused the chain to come off the 7th gear and jam up. Kinda scary. I had done the adjustment using a new guide pulley so I guess I shouldn't be surprised that the slop in the old one caused the problem it did. Interestingly, the shifting was still fairly crisp (had noticed some shifting "complaints" when going from 5-6 gear before putting in the new parts).

So, here are my thoughts (any feedback is welcome!!). The problem must be in 1 of 2 areas. Given the age of the derailleur (13 yrs/18K+ miles) it seems possible the springs have lost enough "spring" that it's not keeping the chain tight on the 7th gear (11T). The reason I didn't see it before might be because the old chain and old cassette had grown to work well with each other. The other is that the cassette I installed just has a poorly mfg'd 7th gear, plain and simple. The cassette may be so low end (not even sure any more if it's a Shimano that even the not too stressful riding I do (occasional bridges, some dirt) is still too much for the cassette to handle.

Anyone have any experience with a derailleur wearing out like this? Is this a common failure mode? I know, nothing lasts forever

Thanks and cheers....Steph

oldskoolwrench

Steph,

FYI... the upper derailleur pulley is designed to have a slight amount of side to side play; the lower pulley is designed with no float.
The upper pulley on an older Shimano rear derailleur should have the word 'Centeron' stamped on it except if it's a Deore XT, XTR,
600 Ultegra or Dura Ace.

Derailleur pivot springs can lose their tension after a while, but it depends on the overall condition of the DR... does it have a lot of
side to side slop when you wiggle it?

BTW what model is the DR?

stephr1

@

Thanks for the suggestions.

I understand the guide pulley. The old one had lots of play in it (side-to-side and up/down/front/back). Been using that one for a long time and no problems (That's why I reinstalled it to see if it might clear things up). The new one I got (Shimano CenterOn) seemed to have much tighter movement...only maybe 1/8" side-to-side.

BTW - What do the newer guide pulleys say on them....or has Shimano used different technology in the later DRs so there is no longer a guide pulley?

As near as I can tell, the DR has very, very slight side-to-side play. Doesn't seem enough to cause a problem. Especially considering it's been that way for some time, I suspect.

It's Shimano's lower end Alivio, but I do not know the model number. It came on a Specialized Hardrock FS some years ago.

When you talk about "pivot" springs, are you referring to the springs that pull the DR cage to the outside gear? I was thinking more about the springs that a) seem to tie the DR to the hanger part and, b) put tension on the cage with the pulleys.

What's so frustrating is that when I did a chain/cassette replacement a few years ago, I did only minor adjustment to the DR and shift cable and everything was great. This is why I'm thinking either the DR spring(s) have worn out, or the cassette I bought just isn't up to the task. First time I've ever had this kind of problem with the bike drive train.

Again, appreciate the help....

Steph

oldskoolwrench

Steph,

From the ones I have seen, newer Shimano pulleys for their low and mid range derailleurs don't have any markings on them.
The upper pulley still floats whereas the bottom pulley has none. The Centeron pulley is an integral part of what makes the
indexing work on a Shimano drive train.

Sounds like the DR is 'tight' wear wise, and you are correct; the springs you mention are the ones I was talking about.
If you have 18K accumulated miles on that derailleur you very well may have worn out the parallelogram springs but
without any abnormal play it's hard to say. You have replaced the chain/ cassette, and have the indexing adjustment
and the limits taken care of. Does it skip under load in any other gear combination?

Reading through all of your posts it sounds to me as if it's one of two things;

1) You have a link in the chain that is binding ever so slightly that when you're in the 11t cog it bends enough to stick
the link. In High Gear (Lg F/ Sm R) SLOWLY, and I mean SLOWLY... pedal the bike backwards and see if the chain binds
anytime it's feeding through the DR's. If there's a link that exhibits this tendency, no matter how slight, fix it.

2) If your upper pulley doesn't interfere with the 28t cog in Low Gear with the B tension screw at 1/2 way screwed in,
unscrew the B tension screw just to the point where it unloads the spring tension in the little plate. Then shift to the 11t
cog and test ride the bike.

Failing that, replace the Rear DR. Like I said... the Alivio MC30 was a good DR but with 18K miles on it even a Dura Ace will get
finicky and mushy.

stephr1

@oldskoolwrench

Again, I appreciate your help.

As for kinks in the chain, when this problem began, even tho I couldn't see any obvious stiff links, I returned that chain to the LBS (Performance Bike) and got a new one, just in case I missed anything. I went thru this chain as you suggested and, again, there was nothing that indicated the chain was the source of the problem...stiff link-wise. I watched it go around the 7th gear cog and the 2 pulleys. All links appeared to be fluid in movement.

I readjusted the limits again, just to be sure. In 7th gear it looked as if the chain came too close to 6th gear so I adjusted the Hi limit (? Can never keep the 2 straight....the one that limits on the outside gear) to allow the RD to go a little farther.

I also turned the B adjust screw out as far as I thought possible without having a risk of losing it (Guide pulley is closer to, but still no threat of, rubbing in low gear cog).

Oh, and I reinstalled the new guide pulley before doing any of this.

I'll do a ride tomorrow morning to see if anything has changed (as in improved).

The problem is only in Middle chainring/7th gear. I wouldn't use it in small chainring/7th gear...too much cross stress on the chain. And I rarely go fast enough to use the large chainring.

That's about it. I'm thinking it could be the RD, but this problem didn't show up until I put on the new chain/cassette/guide pulley. I would have expected to see something like this occurring before the new parts...maybe not. The only other time I had chain skip was when I falsely believed I could replace the chain and not the worn cassette. Then it skipped in 5th (some), 6th (more) and 7th (most). Put on a new cassette, problem gone...and this was with the old, sloppy guide pulley.

I don't know that it's an MC-30. The only markings on the RD are "Shimano" and what looks like a stylized "A" (Alivio?) in the background. I've looked at pix of other older Alivio-class RDs and there is some similarity, but not an exact match. So, I have no idea of the model.

Again, thanks for helping.

Cheers...Steph

Lord Chaos

Just a wild idea here... could the chain be a couple of links too long, so that there's not enough tension to keep it wrapped well around that 11-tooth cog?

stephr1

My initial response would be "Of course the chain has the right number of links. I checked it a couple of times!" (Measure twice. Cut once.)

However, the thought has crossed my mind that maybe I miscounted. Even tho I'm fairly certain I recounted the number of links 2 or 3 times, my own second guessing and your "poking" makes me think it might be time to do another recount. When I cut the new chain down to size, I both compared length (accounting for chain stretch) and link count. For my own peace of mind, I will check again.

Thanks for the nudge...

JonathanGennick 

Could there be a wear issue? I know you have replaced chain and cassette, but sometimes it's necessary to also replace the chain rings.

stephr1

@Lord Chaos

No. links in old chain = No. of links in new chain.....Sighhhhhh...I wish it were that easy.

@JonathanGennick

I went and checked the chain ring again (did it when I first began this journey The middle chain ring (one I spend pretty much all my time on) shows only a bit of wear and tear. The chain settles nicely into the teeth all the way around the ring.

Something else I tried was to put the gears into middle front/smallest rear (where the problem occurs), stood hard on the crank to see if I could get the chain to break loose. Felt like I might have been bending the crank (know that's not true), but the chain never came loose. This seems like a dynamic issue, one that only occurs while the bike is moving....and that's tough to check out with out some sort of rolling stand to test it on.

One of the other things I noticed some time back, but haven't given it much serious thought, was that there seems to be a small bit of play on the freehub near the base (at the hub side). The outside end is fairly tight (recently cleaned and regreased the outside bearings). I've thought that maybe this could be a source. The freehub is as old as the derailleur. I'm wondering if even the slight play in the freehub, combined with the crisper performance of the new guide pulley, is just enough to occasionally make the chain work to get onto, and stay on, the 7th cog. Having said that, tho, I put the old guide pulley back on and it didn't fix much of anything.

The whole thing still seems somewhat non-intuitive. None of the obvious things seem to be causing the problem, and it must be something pretty subtle.

The bike's rideable, except for the occasional skip on flat ground and definitely not in 7th gear going up.

I'll keep looking. If anyone has any other ideas, please feel free to pass them along. Thanks for all the help so far. I'll post back if/when I find the problem.

Cheers....Steph

JonathanGennick 

I'm sure I thought the same thing when it happened to me. In the case I'm remembering, it was the mismatch in wear that seemed to be the problem. I remember spending an entire evening playing around at replacing just two out of the possible three parts. (I had a bunch of spares to play with). Only when I replaced all three -- cassette, chain, rings -- did the skipping go away.

bradtx

Steph, When on the center chainring, which rear casette's gear does the chain line up with in a straight line? Can you tell if the chain is trying to shift onto 6th gear?

My initial impression is that the chainline is perhaps a little off spec and combined with a stiff chain it's maybe trying to shift off the top of the cog. All you may need to do is to exercise the chain side to side as one would after installing a Shimano replacement pin.

Brad

PS There's no problem when on the large chainring, is that right?

oldskoolwrench

steph,

Freehubs will have a slight amount of side to side play; if the freehub body was going bad there would be warning signs like grinding
and intermittent locking, until it seizes up for good.

If you stood on the pedals in the middle CR & the 11t cog and could not get it to skip or dance then the mesh between
chain/ cassette/ chain ring sounds like it's OK.

Without being able to personally see the bike close up, I'd surmise that your DT is okay, and that you may have a slight burr on one of
the chain ring teeth that catches the chain under certain load conditions and causes the skip; something that should hopefully correct
itself as the new chain breaks in to the cassette and chain rings. One of those 'bike gremlin' things...

I'd go ahead and put some miles on her, and see how she's doing after a couple hundred miles.

Hope this helped you out!

stephr1

Thanks much for the continued help, suggestions and support.

@JonathanGennick

Your point's well taken, but I had somewhat the opposite experience. When I replaced chain/cassette a few years ago, the chainring (middle one I use) looked fairly worn, much worse than the current middle chainring. I would have expected there to be skipping problems then. However, up until this recent parts replacement challenge the bike has never had any skip problems. While my logical sense of things tells me this is most likely not the problem (and I don't have a spare crankset/chainrings to test it), I'm sure it's something to which I may circle back around. Also, it really doesn't feel like a chainring skip.

Brad and Alan,

As for the chainline...unless the specs of the parts I've put on were out of spec, I have tried to ensure that the chainline remains as it always has. It is something to consider. Thanks.

The possibility of the burr is interesting. I have ridden over 100 miles at this point and the skip has not seemed to changed at all...no better, no worse (unless I try to compensate by over/underadjusting. Then it actually gets worse).

However, if not a burr, then maybe something with an actual tooth.

OK. More homework for me

Thanks again...and cheers...Steph

stephr1

OK, I'm back with new info....but not sure if it's going to help me

On my ride this morning, it really seems as if the problem is "stress" related. Even tho while not moving (static) I can stand on the cranks and not break the chain free, when moving, a slight incline seems to stress the system enough to cause a skip. And going over a bridge definitely makes it very problematic to pedal (but only in middle chain ring and top/7th gear).

I found was that the chain line at the middle chain ring is ~49 mm. At the rear, it's ~45 mm (maybe closer to 44.5 mm). At first, it was an "Aha!" reaction...that maybe I switched/forgot washers when I redid the hub bearings. Then I realized that this actually put the top/7th gear (trouble spot) closer to the chain line (I expect the engineers figured riders would spend most of their time in the upper gears...which isn't too far afield for me). As such, it should have been less of an issue. And while 5 mm isn't a lot (visually), it looks like the tire/rim are fairly well centered in the frame.

The other thing was that the adjustments seemed off when I checked them, yet again. Not sure why (maybe too tired when I did the adjustments previously? More likely unable to do a good job of eyeballing the limit adjustments). So I went back and readjusted the RD limits, etc.

I'll do a ride tomorrow morning and know pretty quickly if I messed up the adjustments before, or really screwed them up this time.

Cheers....Steph

JonathanGennick 

I don't really trust the static test. The chain won't skip in just any position, else you could just stand on a bike and spin the cranks. It's when the rings and cogs rotate, and everything lines up in a way that magnifies the mismatch in wear, that's when you get a skip.

stephr1

Nope. Wasn't saying that the static test was going to tell me where the problem is. It was only another data point for me to consider. It gave me the sense that the problem was prob'ly not caused by the freehub and that the gears/chain were prob'ly OK, just there was that "something else" that I just wasn't seeing.

Having said that...the previous comments about chainline and gear burrs got me to thinking on this morning's ride. I mentioned somewhere along the way (maybe in my other thread) that I noticed a "wobble" in the cassette. I had discovered it when I spun the rear wheel at a reasonable speed opposite direction of the freehub lock (cassette not moving). At the time I originally noticed it (not long after I changed cassette/chain) I pulled the rear hub apart again to see if I lost a ball bearing along the way. Everything was fine. So, I really didn't think of it much during this "process". However, I'm now thinking the wobble may be that "subtle" issue I refer to above.

Yesterday I took the cassette off and manually turned the freehub trying to figure where the wobble was coming from. The freehub appeared to turn fairly straight. There was a little bit of play, but nowhere near enough to justify the wobble). In fact, when I spun the cassette while on the freehub, I didn't see any wobble at all. So, it was something from the dynamic motion of the wheel. And it wasn't a too loose mounting of the hub. Checked that a number of times. The wobbling just wasn't making any sense to me.

As I mentioned, on the ride something struck me. Sometime after I changed the parts, I decided to do some truing of the rear wheel (The rim had an interesting "warp" in it). I was able to flatten most of it out (A bit more work to do, but straight enough for my needs at the moment). I haven't checked it yet, but I suspect in the truing I did, that I may well have adjusted the hub off-center. This would definitely explain the wobble, given the physics of this whole assembly.

On the larger gears, there is much more margin of error. When you get down to the smaller gear (i.e. 11T), the chain connects with only 5 or 6 teeth (~1/2) and missing 1 tooth connection during rotation can have a profound impact...as in skipping. While I still don't think the wobble is a lot, on the 11T gear, it may be more significant than I know (especially with the tighter shifting from the new guide pulley).

I won't be able to check it out till tomorrow, but will report back. In the meantime, any insight, observations or corrections about my assumptions is always appreciated.

Cheers...Steph

Al1943

I just now woke up that you are talking about slip on an 11t cog (even though the 11 has been mentioned several times).
Is the cassette lockring the special one made to run with an 11? If not then that is the problem.