Baffling rear derailleur malfunction
#1
Senior Member
Thread Starter
Baffling rear derailleur malfunction
I am pretty good about working on bikes, but rear derailleurs are a bit of a mystery to me. I successfully changed out, sourced, and adjusted one once when its chain tension spring broke, but that is really the limit of my experience.
So I've been riding my wife's older 21 speed mountain bike every day to work while I tackle various problems with mine. It was gradually getting harder to shift into the biggest gear of seven on her rear freewheel until yesterday. All of the sudden, I was stuck in that big gear. The shifter moved freely through all the clicks, but the bike did not shift. I assumed the cable had broken, and rode it home to fix it - No biggie as I still had low/middle/high on the front shifter. Drivetrain is Shimano.
When I go to replace the broken cable, I discover that the cable is fully intact and the shifter is shifting again. However, now I can't get back onto the big ring in back unless the front shifter is on the smallest gear, even if I physically try to push the derailleur over.
Thoughts? Do you think I have a weak (stretched/failing) cable? Or do I have a weak derailleur spring or something? Or just more adjustment?
So I've been riding my wife's older 21 speed mountain bike every day to work while I tackle various problems with mine. It was gradually getting harder to shift into the biggest gear of seven on her rear freewheel until yesterday. All of the sudden, I was stuck in that big gear. The shifter moved freely through all the clicks, but the bike did not shift. I assumed the cable had broken, and rode it home to fix it - No biggie as I still had low/middle/high on the front shifter. Drivetrain is Shimano.
When I go to replace the broken cable, I discover that the cable is fully intact and the shifter is shifting again. However, now I can't get back onto the big ring in back unless the front shifter is on the smallest gear, even if I physically try to push the derailleur over.
Thoughts? Do you think I have a weak (stretched/failing) cable? Or do I have a weak derailleur spring or something? Or just more adjustment?
#2
Senior Member
When were the cables last replaced?
#3
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 39,640
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Liked 3,480 Times
in
1,911 Posts
Let me confirm.
You couldn't get I to the big/big combination without crazy force. Then once you did, it was stuck there.
So, a question ----- did you replace the chain or freewheel lately? Maybe simply swapped the wheel from another bike?
I ask because the problem is most associated with a chain that's slightly too short. If it's not always been this way, then something changed.
You couldn't get I to the big/big combination without crazy force. Then once you did, it was stuck there.
So, a question ----- did you replace the chain or freewheel lately? Maybe simply swapped the wheel from another bike?
I ask because the problem is most associated with a chain that's slightly too short. If it's not always been this way, then something changed.
Likes For FBinNY:
#4
Senior Member
Thread Starter
#5
Senior Member
Thread Starter
Let me confirm.
You couldn't get I to the big/big combination without crazy force. Then once you did, it was stuck there.
So, a question ----- did you replace the chain or freewheel lately? Maybe simply swapped the wheel from another bike?
I ask because the problem is most associated with a chain that's slightly too short. If it's not always been this way, then something changed.
You couldn't get I to the big/big combination without crazy force. Then once you did, it was stuck there.
So, a question ----- did you replace the chain or freewheel lately? Maybe simply swapped the wheel from another bike?
I ask because the problem is most associated with a chain that's slightly too short. If it's not always been this way, then something changed.
Nothing whatsoever has been changed on the bike in years - it's my wife's and she barely touches it.
#6
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,341
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Liked 4,188 Times
in
2,471 Posts
By "biggest gear" do mean the tooth count or the pedaling effort? As they are opposites this clarity is very fundamental. I'll assume you mean physical diameters (tooth counts) of the rear cogs.
Cables can stretch (actually casing compression), rust, get gritty/grimy, develop kinks in either the cable or the casings, and slip at their attachment clamp. If the cables are routed outside of the frame it is fairly easy to follow the path and move the cable in each section of casing to test their conditions. Kinks act as a spring inline with the cable and make shifting into the lowest (as in effort, which is the bigger diameter rear cogs) gear less responsive. As choddo alluded to, replacing the cables and casings (and doing with the right parts and skills) can solve a lot of shifting issues without knowing more. I also wonder if the temps were freezing as water in the casing can freeze locking up cable movements yet freed up later when that water melted.
There are other reasons why shifting can be bad. Besides the usual stuff limit screws, chain/teeth conditions, hanger alignment. Most are either wear or incident caused. One often overlooked reason why shifting into the lowest rear gear (that big cog) is from guide pulley bushing slop becoming so great that the top of the pulley can rock away from the cog it's assumed to line up with when shifting. I still wonder about the BB play and shifting being of the same cause. Andy
Cables can stretch (actually casing compression), rust, get gritty/grimy, develop kinks in either the cable or the casings, and slip at their attachment clamp. If the cables are routed outside of the frame it is fairly easy to follow the path and move the cable in each section of casing to test their conditions. Kinks act as a spring inline with the cable and make shifting into the lowest (as in effort, which is the bigger diameter rear cogs) gear less responsive. As choddo alluded to, replacing the cables and casings (and doing with the right parts and skills) can solve a lot of shifting issues without knowing more. I also wonder if the temps were freezing as water in the casing can freeze locking up cable movements yet freed up later when that water melted.
There are other reasons why shifting can be bad. Besides the usual stuff limit screws, chain/teeth conditions, hanger alignment. Most are either wear or incident caused. One often overlooked reason why shifting into the lowest rear gear (that big cog) is from guide pulley bushing slop becoming so great that the top of the pulley can rock away from the cog it's assumed to line up with when shifting. I still wonder about the BB play and shifting being of the same cause. Andy
__________________
AndrewRStewart
AndrewRStewart
Likes For Andrew R Stewart:
#7
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,341
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Liked 4,188 Times
in
2,471 Posts
It seems that what has changed with the wife's bike is that it's being used and likely by a stronger and "higher milage" rider. Andy
__________________
AndrewRStewart
AndrewRStewart
#8
Senior Member
Thread Starter
I am about 99% sure that I can replace a cable competently - I have done that before several times on other bikes It seems like a no-brainer to start there, and I already have the parts.
#9
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 39,640
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Liked 3,480 Times
in
1,911 Posts
It's possible that the RD rides too close to the freewheel causing interference between the jockey wheel (upper pulley) and largest sprocket.
There should be visible daylight and about 1/2" minimum free chain between the RD and sprocket. When there's less the RD is trying to jam the chain against the sprocket rather than leading it on.
So, shift to the 2nd biggest sprocket then eyeball the situation, checking that the pulley is forward and below the sprocket and free to move across without touching.
Last edited by FBinNY; 12-10-23 at 05:05 PM.
Likes For FBinNY:
#10
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,341
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Liked 4,188 Times
in
2,471 Posts
Have you tried to shift the rear with only your hands pushing on the der, therefore removing the cable completely for the der's function? Do you have chain droop in the small/small cog/ring combo? Is the guide (the top one) pulley contact the underside of that low gear cog (that big one) and trapping the chain from lifting off the cog teeth (this would require the pulley to not be in contact)? Is there a lot of slop in the der parallelogram or the pivots? Andy
__________________
AndrewRStewart
AndrewRStewart
Likes For Andrew R Stewart:
#11
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 16,142
Bikes: Tarmac Disc Comp Di2 - 2020
Liked 5,404 Times
in
3,729 Posts
Some of the issues might be lack of use. And things just needed some movement to let them loosen up. However not being able to get back into the big cog on the rear, even when you push on it, might be that the low limit either was changed or never quite right in the first place and never presented itself till you used it.
Might be some other stuff going on too that is confusing the issue because there are really several issues. You might not need to change the cables yet. Maybe adjustment is all that is needed when you solve whatever is keeping you from being able to push the RD onto the big cog.
Why at first it wouldn't shift out of the big cog is curious. Because if the shifter was giving the cable slack to let it go to the smaller cogs, the spring tension should have moved it there. In fact, if the cable breaks, your RD will or should go all the way to the smallest rear cog.
With a 3x front, on the two smaller rings, the chain is at a better angle to get onto the big rear than when in the big front ring. So if the low limit is what kept the RD from going into the big rear cog when you were in the big front ring, it still might be that the angle of the chain on the smaller rings was letting it grab enough of the cog teeth to make the shift.
Might be some other stuff going on too that is confusing the issue because there are really several issues. You might not need to change the cables yet. Maybe adjustment is all that is needed when you solve whatever is keeping you from being able to push the RD onto the big cog.
Why at first it wouldn't shift out of the big cog is curious. Because if the shifter was giving the cable slack to let it go to the smaller cogs, the spring tension should have moved it there. In fact, if the cable breaks, your RD will or should go all the way to the smallest rear cog.
With a 3x front, on the two smaller rings, the chain is at a better angle to get onto the big rear than when in the big front ring. So if the low limit is what kept the RD from going into the big rear cog when you were in the big front ring, it still might be that the angle of the chain on the smaller rings was letting it grab enough of the cog teeth to make the shift.
Likes For Iride01:
#12
I would flush all the pivots and pulleys on the rd with a light lube, and lube the chain.
#13
I'm sorry if I missed this, but is the chain long enough?
#14
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 39,640
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Liked 3,480 Times
in
1,911 Posts
Yes, that was confirmed earlier. The problem is happening on the middle ring.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
#15
Do the cables go under the BB? Is the cable guide under the BB loose and swiveling?
#16
Senior Member
I had a situation where the cable was getting caught up for no visible reason, until I removed the cable and looked at the housing. The person who assembled the bike cut the housing with a crude instrument and it left a spur . The cable was getting caught on this spur and eventually wear out the cable.
#17
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,341
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Liked 4,188 Times
in
2,471 Posts
I had a situation where the cable was getting caught up for no visible reason, until I removed the cable and looked at the housing. The person who assembled the bike cut the housing with a crude instrument and it left a spur . The cable was getting caught on this spur and eventually wear out the cable.
__________________
AndrewRStewart
AndrewRStewart
#18
I am with Andy. Cables and cable housing is cheap. I would replace both the cable and the housing with new quality items to include die drawn cables. When you cut the ends of the housing make sure that the opening is patent without any burrs.
#19
Senior Member
Not heard “patent” in this context before. What does that mean?
Likes For KCT1986:
#21
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 39,640
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Liked 3,480 Times
in
1,911 Posts
There's a big clue here that pretty much rules out anything cable related. Assuming the OP is telling us the whole story accurately (which rarely happens) the problem only occurs with shifting into the largest rear sprocket. That implies something within the RD or between the RD and sprocket. (see post 9 for my suggestion).
Of course, it could be a kink or fray in the cable binding qt a particular spot, but that kind of thing is rare.
To the OP
Try shifting by pulling the gear wire away from the frame along the down tube. If it shifts fine, then it's cable related, most likely in the shifter itself. If it's still difficult and binds, then it's the RD and/or freewheel clearance.
Of course, it could be a kink or fray in the cable binding qt a particular spot, but that kind of thing is rare.
To the OP
Try shifting by pulling the gear wire away from the frame along the down tube. If it shifts fine, then it's cable related, most likely in the shifter itself. If it's still difficult and binds, then it's the RD and/or freewheel clearance.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
#22
Senior Member
My HVAC mentor says " be a tech or a part changer, you can't be both". Detach the cable from the dlr and follow the multi meter readings...
#23
Senior Member
Thread Starter
For various reasons, I still haven't started messing with that rear derailleur yet. If you number the gears 11, 12, 13, 14, 15, 16, 17, 21, 22, 23, 34, 25, 26, 27, 31, 32, 33, 34, 35, 36, 37, I am only missing 11 and 21 (maybe 31 but who cares) - not a great loss in the grand scheme of things. Everything else works perfectly.
Anyhow, this weekend it stormed and I rode the bike through some flooded streets on the way to work, so now regreasing the bearings is a bigger priority than the derailleur......
Anyhow, this weekend it stormed and I rode the bike through some flooded streets on the way to work, so now regreasing the bearings is a bigger priority than the derailleur......
#24
The pandemic is not over yet. It may never be. So this is kind of vague. Regardless, as you say you haven't messed with the rear derailleur yet, consider removing it, giving it a good cleaning with a quality degreaser and toothbrush, lubricate, and reassessing it's limit adjustments.
Last edited by Jicafold; 12-20-23 at 11:38 AM.
Likes For Jicafold:
#25
Quasi homeostatic system
Join Date: Nov 2022
Posts: 152
Bikes: '79 Trek 739, '81 Fuji America, '82 Team Fuji, '84 Woodrup Giro Touring, '85 Nishiki Bel Air, '97 Bob Jackson Super Tourist Custom, '98 Klein Stage Comp R
Liked 294 Times
in
97 Posts
This is a common issue I see during free bike repair clinics our local nonprofit holds. Especially OP's trigger shifter clicking and not pulling any cable to move the derailleur. Assuming the RD passes the range of motion test that Andy recommended, I would think it's old, gummed up lube in the shifter itself. Open up the shifter's cover (beware flying parts, losing tiny scres etc.) and flush the shifter's gears with PB blaster, solvent, boiling water or whatever you've got that will loosen up gunk while working the triggers up and down through the clicks repeatedly until the triggers engage pulley mechanism and it starts pulling cable again. Then relube and reattach the cover. Not foolproof but this technique has worked miracles on some very scabby old bikes.