Is a slight drivetrain clunk normal?



QwittenTyme

New Member
Mar 21, 2012
11
0
0
While pedaling new shoes on rollers I noticed a slight feeling in my feet as I pedaled- a light clunk that occurs in a different crank position every revolution. Put the bike on a stand, and if I grab the rear wheel and turn the crank, I can feel in my hands the chain striking the cogs, but I also feel the clunk about once every 1/3 rotation. Is this normal, and I just never noticed it before?

It'a s Shimano Ultegra/600 groupo from the early 90's with maybe 2000km's on it. 8-speed STI shifting on an HG cogset, dual crank.

I notice that the clunk feeling seems to happen when the chain settles onto the cog beside where the ramps meet the teeth.

Took the bike 2 LBS. One turned the pedals like I did and said it's normal chain running. The other tightened up the usual suspects- crank bolts, chain ring bolts, pedals to the cranks, but no change, and told me not to worry about it.

Well, I am. I never noticed this in many hours of roller riding, and I hate wearing out parts from mis-adjustment.

I did some work to locate the source of the clunky feeling:

- compared small/large chain ring (for wear- the large cog has very little wear)
- measure the derailer/cog alignment to rule out bent derailer hanger
- ran the derailer through its indexing range by loosening/tighting the adjuster
- replaced with fresh cogset
- replaced with new 7.1mm wide chain
- replaced the freehub (it was slightly loose and wouldn't take the 11-tooth cog without some filing)
- wrapped another new chain, bypassing the derailer
- drank a beer, smoked a bowl, turned the cranks reeeallly slloooowly, sooooo sloooowly....woah, man...

Anyway none of these steps has changed the light clunky feeling. But the drivetrain looks great.

I have 3 other Shimano-equipped bikes, but I don't feel the light clunk on them like I do on this one. They have a lot more wear on them than this one.

Any thoughts?
 

davereo

Well-Known Member
Jun 17, 2010
1,639
126
48
Originally Posted by QwittenTyme .


- drank a beer, smoked a bowl, turned the cranks reeeallly slloooowly, sooooo sloooowly....woah, man...


Any thoughts?
Naw, maybe I'll get around to it later.
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Good question, the clunk is in all gears, even the outboard cogs, and on both chain wheels.

I tried a second new chain, no change.

Tomorrow I'm taking it into a local pro shop, see what they say. I'm suspecting an alignment issue now, or something really pooched with the derailer.
 

oldbobcat

Well-Known Member
Aug 31, 2003
3,233
194
48
70
Originally Posted by QwittenTyme .

I tried a second new chain, no change.
All I can think of is faulty chain installation resulting in a stiff link. Are you using a Shimano chain pin, the original rivet, or a connecting link a la SRAM Powerlink?
 

AlanG

Active Member
Dec 26, 2010
333
36
0
Did you try turning the crank with the chain off of the chain ring? Maybe you have a bottom bracket problem. See if there is any play in this by pushing and pulling on the cranks in different directions. Then try turning each part individually to see if each runs smoothly... the rear wheel, each pulley in the derailleur, the pedals.

Do you see any movement in the rear derailleur when you pedal? Maybe one of your derailleur pulleys is bent, broken, or its hole has worn out causing it to shift, or it hangs up in some way.

"I notice that the clunk feeling seems to happen when the chain settles onto the cog beside where the ramps meet the teeth." Could the side of the chain be catching on sections between the two chain rings and rubbing somehow?
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Originally Posted by oldbobcat .

All I can think of is faulty chain installation resulting in a stiff link. Are you using a Shimano chain pin, the original rivet, or a connecting link a la SRAM Powerlink?
That's originally what I thought too. But it does it all along the chain, whether I use a connecting link or pin.




Originally Posted by AlanG .

Did you try turning the crank with the chain off of the chain ring? Maybe you have a bottom bracket problem. See if there is any play in this by pushing and pulling on the cranks in different directions. Then try turning each part individually to see if each runs smoothly... the rear wheel, each pulley in the derailleur, the pedals.

Do you see any movement in the rear derailleur when you pedal? Maybe one of your derailleur pulleys is bent, broken, or its hole has worn out causing it to shift, or it hangs up in some way.

"I notice that the clunk feeling seems to happen when the chain settles onto the cog beside where the ramps meet the teeth." Could the side of the chain be catching on sections between the two chain rings and rubbing somehow?
I did try the crank turning, several different ways, so that they were loaded like pedaling. I can't feel anything but silky there.

It could be something worn on the derailer, the cage does move a bit forwards and backwards.

You're probably right about the chain catching. I think the chainline is off very slightly, not enough to cause an outright skip, but enough to notice. I can see that the chain is centered as it wraps around the rear, but veers towards the centerline as it comes off the cogs.

I'll ask the shop to check the hangar alignment very carefully because the whole groupo has so few kilometers on it I doubt it's a wear problem.

Thanks to you both, I'll post back what the pro shop finds.
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
So the pro shop head mechanic listened to my story, put the bike on the stand and found the issue right away. Bent derailer hanger. Slight, but enough to cause the chain to drag on one side of the cog. I don't have the bike back yet, but will in a few days. I'll post back with the results then.

Thanks again for all the support!
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Well same here, bent hanger was my last suspect. This bike's been pampered all its life, so I'm really not sure how the hanger was bent.
 

oldbobcat

Well-Known Member
Aug 31, 2003
3,233
194
48
70
Funny thing is, two weeks ago I was working on the same problem with a brand new Speed Concept running Apex. The chain kept popping off the tension pulley of the rear derailleur. Sure enough, the hanger was off just a little, and that made all the difference.
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
The bike 's back, hanger straightened. But the bend event also bent the derailer. So there you have it, a graden variety bent derailer/hanger.

It feels about 50% better, but there's still a distinct clunk about 1x per cassette revolution.

Next step is a new derailer, and I'm thinking of putting on a wide range model, like an XT SG, instead of NOS or new Ultegra. I'm still getting used to the hills around here, so having another couple of teeth would be helpful. Plus, it's a 30T max cog now, and I have to be careful not to shift into a large/large combination.

I can run a 10-speed" top normal Shimano derailer on this 8-Speed cassette and STI shifters, right?

I mean, the cable pull ratio hasn't changed, and the limits are the same distance apart, correct? Shimano's marketing team have made it tricky to discover the truth of the matter, even though a couple of places have hinted it can be done, wink wink. I even took a caliper to the new derailers and they actually have more room for the pulleys' side-to side movement. Not much, maybe 1 mm or so.

Cheers to all-
 

AlanG

Active Member
Dec 26, 2010
333
36
0
My understanding is that all of the Shimano rear derailleurs, other than old Dura Ace, have a 1:1.7 actuation ratio. (Called 2:1) So it seems that it would be ok. The other factor is the width of the 8 speed chain in a 10 speed derailleur, so that might be a limitation that could eliminate the long cage road derailleurs. I'd expect that an 8 speed MTB derailleur would be fine, but don't take my word on it. Maybe someone can confirm this.

Here are some links about this:

http://en.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/Gear-changing_Dimensions

http://www.ctc.org.uk/desktopdefault.aspx?tabid=3946
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Very helpful links, Alan. Thanks! Still it's odd how hard it is to find an authoritative source that just confirms that you can interchange 10 speed derailers with 8-speed drivetrain.

I did measure the width of the cages to see about chain width, and as noted above, the 10-speed cages are a little wider. Actually they're tapered, or ramped towards the pulleys, where the old 8-speed derailer cage sides are parallel. On the new ones, the cage slopes slightly towards the pulley centerline. They start wider, and as far as I could measure, end up at the same width as my 8-speed RD-6401 derailer from '94. I suppose the taper gives a more flexible chainline.

If I can find a good road derailer that's take a 32-tooth cog, and still tension an 11/38 combo, then great. But I suspect there are few of them, and no advantage over the "mountain" derailers. Not that I would ever ride 11/38 on purpose, but there's no guarantee someone wouldn't shift my over-limit road derailer into oblivion.
 

alienator

Well-Known Member
Jun 10, 2004
12,596
310
0
QwittenTyme said:
Very helpful links, Alan. Thanks! Still it's odd how hard it is to find an authoritative source that just confirms that you can interchange 10 speed derailers with 8-speed drivetrain.
I did measure the width of the cages to see about chain width, and as noted above, the 10-speed cages are a little wider. Actually they're tapered, or ramped towards the pulleys, where the old 8-speed derailer cage sides are parallel. On the new ones, the cage slopes slightly towards the pulley centerline. They start wider, and as far as I could measure, end up at the same width as my 8-speed RD-6401 derailer from '94. I suppose the taper gives a more flexible chainline.
If I can find a good road derailer that's take a 32-tooth cog, and still tension an 11/38 combo, then great. But I suspect there are few of them, and no advantage over the "mountain" derailers. Not that I would ever ride 11/38 on purpose, but there's no guarantee someone wouldn't shift my over-limit road derailer into oblivion.
What is you current gearing front and back? Have you considered just switching to a triple crankset and front derailleur?
 

AlanG

Active Member
Dec 26, 2010
333
36
0
Originally Posted by QwittenTyme .

If I can find a good road derailer that's take a 32-tooth cog, and still tension an 11/38 combo, then great. But I suspect there are few of them, and no advantage over the "mountain" derailers. Not that I would ever ride 11/38 on purpose, but there's no guarantee someone wouldn't shift my over-limit road derailer into oblivion.
Yeah I don't know if there is an advantage using a road DR over a mountain derailleur. I have a bike that uses a triple CR and a long cage Ultegra derailleur. It works on a 25 cassette and 30 CR on my setup and should be able to handle more capacity but I don't need lower gearing than that on it.
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Right now it's 11-30, 39/52, soon to be 38/52, and maybe 11/32 since I found a good local source for new, wide-range 8-speed cassettes.

The triple conversion turns into money pretty quickly and I haven't had an experience that made it important. I've hardly ridden the 11-30 cassette though, so I'll have to see how it works with my legs. Anyway if I get a mountain derailer, I'm set whether I go triple or not.

As for mountain vs road derailers I've never noticed road versions being more snappy or whatever advantages the short cages are supposed to offer. I'm not racing. So if the system shifts a little more slowly I won't lose any sleep or pride over it. I just like things that last, run smoothly, and require less work to keep running.
 

AlanG

Active Member
Dec 26, 2010
333
36
0
Originally Posted by QwittenTyme .

Very helpful links, Alan. Thanks! Still it's odd how hard it is to find an authoritative source that just confirms that you can interchange 10 speed derailers with 8-speed drivetrain.
Yes, but one of those articles says, " Standard Shimano
As already noted above, all current Shimano mechs have the same shift ratio, so you're free to operate mountain-bike mechs with road shifters, use an ostensibly 9-speed mech in a 7-speed system or whatever. And because Shimano 9-speed mountain-bike mechs can cope with sprockets from 11 to 34 teeth, they're something one most often wishes to combine with something else. Also note that Shimano 9-speed mechs will accept 8-speed chain, that 8-speed chain is the same thing as 7-speed chain and that it also runs fine on 5 and 6-speed sprockets."

So it looks like you are good to go with the 9 speed MTB rear derailleur so why not just get that unless you expect to switch the entire system to 10 speed someday? Some are pretty inexpensive too. I think this article is from before 10 speed MTB systems came out but maybe they can work too.
 

QwittenTyme

New Member
Mar 21, 2012
11
0
0
Going with 9-speed appears to be a safe option also, you're right. Sheldon's table only goes up to 9-speed for derailer compatibility, and only mentions that 10-speed Dyna-sys derailers aren't compatible with previous systems because they use a different pull ratio. Just not a lot of info out there in an easy-to find place. It's like people stopped writing about it once 10-speed came out. The Shimano compatibility sheet is useless, because it only refers to current product.

The big catch with Shimano's 10-speed mountain derailers right now is that many are Dyna-Sys, and some are low-normal. Then of the candidate derailers, the XT models don't have barrel adjusters- so I'd have to figure out a solution for an in-line, indexed adjuster. So the only slam dunk is a Deore. Not quite the level of gear I was hoping to match with Ultegra, but it does go 6T larger than the 28T Ultegra.

I'm going to have a close look at the XT to see if I can add an adjuster by cutting threads into the cable stop channel.