Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Rear derailleur shifts on big bump

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Rear derailleur shifts on big bump

Old 10-09-19, 03:17 PM
  #1  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Rear derailleur shifts on big bump

This is with bar end shifters. If I drop off a curb, the shock can cause the RD to shift to a smaller cog and pulls the shifter accordingly. This isn't unexpected since the bar end shifters don't lock the cable in place solidly.

Is there a solution to this (other than tightening the friction on the shifter)? The RD is a 9 speed Deore - would an (old, 9 speed) XT RD solve this? If there was some damping at the derailleur, that would probably reduce this occurrence.

I don't see a solution to this but I thought I'd ask here.
tyrion is offline  
Old 10-09-19, 03:27 PM
  #2  
Jon T
Senior Member
 
Join Date: Jun 2017
Location: West Orange County, CA
Posts: 1,070

Bikes: '84 Peugeot PH10LE

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 381 Post(s)
Likes: 0
Liked 36 Times in 26 Posts
You answered your own question.
Jon
Jon T is offline  
Old 10-09-19, 04:51 PM
  #3  
02Giant 
Home School Valedictorian
 
02Giant's Avatar
 
Join Date: Jan 2011
Location: Iowa
Posts: 2,789

Bikes: 13 Orbea Orca 02 Giant Cypress 88 Mongoose ATB 79 frame-built to 80 spec. Schwinn Traveller

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked 63 Times in 43 Posts
Efficiency.
__________________
Excuse me if I, have some place in my mind,
Where I go time to time

I ain't broke and I ain't hungry but I'm close enough to care

Tom 2020
02Giant is offline  
Old 10-09-19, 06:20 PM
  #4  
hokiefyd
Senior Member
 
Join Date: Feb 2017
Location: Northern Shenandoah Valley
Posts: 2,477

Bikes: 2018 Redline Zander, 2018 Giant Roam 2, 1997 Trek 750, 1981 Peugeot PBN10, 1970 Peugeot UO-18

Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 852 Post(s)
Liked 106 Times in 85 Posts
Originally Posted by tyrion View Post
This is with bar end shifters. If I drop off a curb, the shock can cause the RD to shift to a smaller cog and pulls the shifter accordingly. This isn't unexpected since the bar end shifters don't lock the cable in place solidly.

Is there a solution to this (other than tightening the friction on the shifter)? The RD is a 9 speed Deore - would an (old, 9 speed) XT RD solve this? If there was some damping at the derailleur, that would probably reduce this occurrence.

I don't see a solution to this but I thought I'd ask here.
Is the derailleur (9-speed Deore) a newer Shadow type? Those typically have stronger springs and maybe more apt to pull a friction shifter back than a traditional derailleur, at least given the same friction adjustment on the shifter. You could try a derailleur with a lighter spring...or increase the friction adjustment on the derailleur.
hokiefyd is offline  
Likes For hokiefyd:
Old 10-10-19, 03:01 AM
  #5  
jimc101
Senior Member
 
Join Date: Oct 2007
Location: West Yorkshire, United Kingdom
Posts: 5,496
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 311 Post(s)
Liked 5 Times in 5 Posts
Have you identified what the cause of the issue is, as throwing parts at it with out knowing the cause is a waste of time/money.

Not getting the idea that the cable isn't held in place by the bar end shifters (I am doing a lot of riding with this 6480 shifters, and they are rock solid), in friction or index mode, both of these are held tight (unless there is play in the shifter, route cause?)

Is there a cable routing issue? is it fully in all the stops?

No mention of the frame/dropout, is this straight, if it's a replaceable type, is it screwed in properly?
jimc101 is online now  
Old 10-10-19, 11:43 AM
  #6  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by jimc101 View Post
Have you identified what the cause of the issue is, as throwing parts at it with out knowing the cause is a waste of time/money.
I know what the cause is: the jarring from the bump, together with the spring in the RD, shifts the RD into a smaller cog. The shock+spring overpowers the friction and click-stops in the shifter.

I could just increase friction on the shifter to address this, but I'd like to avoid that.
tyrion is offline  
Old 10-10-19, 11:47 AM
  #7  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by hokiefyd View Post
Is the derailleur (9-speed Deore) a newer Shadow type? Those typically have stronger springs and maybe more apt to pull a friction shifter back than a traditional derailleur, at least given the same friction adjustment on the shifter. You could try a derailleur with a lighter spring...or increase the friction adjustment on the derailleur.
I think it is a Shadow type, judging by looks. So maybe this design with the stronger spring is simply problematic with bar end shifters, in which case going to lower-end RD might be the solution.
tyrion is offline  
Old 10-10-19, 11:51 AM
  #8  
hokiefyd
Senior Member
 
Join Date: Feb 2017
Location: Northern Shenandoah Valley
Posts: 2,477

Bikes: 2018 Redline Zander, 2018 Giant Roam 2, 1997 Trek 750, 1981 Peugeot PBN10, 1970 Peugeot UO-18

Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 852 Post(s)
Liked 106 Times in 85 Posts
If you have a co-op nearby, or similar source of used bike parts, you could probably pick up a used 6/7/8/9 speed derailleur for $5-10 and try it on your bike. If your current one is a Shadow derailleur, you will likely have shift cable length issues, unfortunately. Traditional derailleurs have that extra 6" or so required to make that 180-degree loop that the Shadow design effectively avoids. But -- for relatively small money, you could try a used derailleur and longer cable just to test the hypothesis that the strong spring is overcoming the desired friction setting on the shifter.

If it does work, then you'll already be set up with the correct shift cable and housing length, and you could either stick with your used derailleur or buy a new higher end traditional derailleur like an RD-M591, considered by many to be about the best of the type, at least as far as mountain style derailleurs go. If it doesn't work, and you still get bump shifts, then you'd have to decide whether it's worth it to keep the parts you just installed or return back to your factory equipment...and then your only other move is probably adjusting the shifter.

You could also consider an indexing shifter. I presume from your post that you have friction barcons. Do they make indexing 9-sp barcons?
hokiefyd is offline  
Likes For hokiefyd:
Old 10-10-19, 12:34 PM
  #9  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by hokiefyd View Post
You could also consider an indexing shifter. I presume from your post that you have friction barcons. Do they make indexing 9-sp barcons?
They currently are indexed. The shock of the bump + the spring overpowers the click stops.
tyrion is offline  
Old 10-10-19, 09:22 PM
  #10  
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Posts: 21,537

Bikes: Some silver ones, a red one, an orange one and a few titanium ones

Mentioned: 98 Post(s)
Tagged: 1 Thread(s)
Quoted: 2663 Post(s)
Liked 175 Times in 131 Posts
Originally Posted by tyrion View Post
This is with bar end shifters. If I drop off a curb, the shock can cause the RD to shift to a smaller cog and pulls the shifter accordingly. This isn't unexpected since the bar end shifters don't lock the cable in place solidly.

Is there a solution to this (other than tightening the friction on the shifter)? The RD is a 9 speed Deore - would an (old, 9 speed) XT RD solve this? If there was some damping at the derailleur, that would probably reduce this occurrence.

I don't see a solution to this but I thought I'd ask here.
Id check to see if the cable housing is long enough, especially at the rear derailer. If it is too short, it could flex and pull the derailer. Ive had this problem with full suspension bikes where the cable runs under the bottom bracket. The housing was too short and pulled on the rear derailer causing ghost shifts after the frame flexed.
__________________
Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
cyccommute is offline  
Likes For cyccommute:
Old 10-10-19, 11:30 PM
  #11  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 12,045

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1890 Post(s)
Liked 111 Times in 85 Posts
Some earlier bar end shifters that had indexing also had a friction option. Controlled by usually rotating a bezel or ring on the outer end of the shift pod. It is possible to have this ring partially positioned so that the index detents don't fully engage. Generally there were aligning marks to insure complete positioning.

Perhaps more info like the brand and version of the shifters might help us help you. It's easy for us to assume and be wrong. Shimano had a known failure issue with some of their earlier 9 speed bar end levers where the outer housing would fail and not contain the internals. The symptom was a vague lever movement into the next detent and a lot of "overshift/free play" between detents. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 10-11-19, 02:57 AM
  #12  
Lemond1985
Sophomore Member
 
Lemond1985's Avatar
 
Join Date: Jan 2019
Posts: 1,916
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1117 Post(s)
Liked 429 Times in 288 Posts
I have a chain that's too long on one of my bikes, which causes auto-shifts into a smaller cog when I hit sharp bumps while pedalling. Gotta get around to shortening it a couple of links.
Lemond1985 is offline  
Likes For Lemond1985:
Old 10-11-19, 07:25 AM
  #13  
55murray
Senior Member
 
55murray's Avatar
 
Join Date: Apr 2017
Location: Lafayette, Indiana
Posts: 338

Bikes: 1955 20" Murray modified cruiser, 2015 Trek FX3, 1980 Miyata 610, several other vintage coaster brake machines

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 163 Post(s)
Liked 22 Times in 15 Posts
You could work on your curb dropping technique to try to reduce the impact on the rear wheel...
55murray is offline  
Old 10-11-19, 09:23 AM
  #14  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by Lemond1985 View Post
I have a chain that's too long on one of my bikes, which causes auto-shifts into a smaller cog when I hit sharp bumps while pedalling. Gotta get around to shortening it a couple of links.
Interesting. My chain is on the long side, could lose a couple links.

edit: as I think about it, this might be the problem. Too-long chain puts the RD arm in a horizontal position, a sharp bump swings the arm down, then it thwacks back up and knocks the RD into a smaller cog.

Last edited by tyrion; 10-11-19 at 10:51 AM.
tyrion is offline  
Old 10-11-19, 09:26 AM
  #15  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by 55murray View Post
You could work on your curb dropping technique to try to reduce the impact on the rear wheel...
Shifting up when dropping off a curb isn't that big of a deal - it's kind of my test case. It's when I'm off road and going up hill and getting that ghost shift into a harder gear that's really irritating.
tyrion is offline  
Old 10-11-19, 10:47 AM
  #16  
tyrion
Senior Member
Thread Starter
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 2,390

Bikes: Breezer Radar

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1264 Post(s)
Liked 136 Times in 87 Posts
Originally Posted by Andrew R Stewart View Post
Perhaps more info like the brand and version of the shifters might help us help you.
It's an indexed Microshift. Doesn't have friction mode (you can adjust friction but can't disable click-stops). Feels fine, nice and tight and clicky.
tyrion is offline  
Old 10-11-19, 06:46 PM
  #17  
Boxkite
Senior Member
 
Join Date: Jan 2007
Location: Kentucky
Posts: 180

Bikes: old and new

Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked 62 Times in 39 Posts
Check to make sure the RD parallelogram hinges/ hinge pins aren't worn out. Remove the cable and check for play. Loose (worn at the axle) jockey wheels might be a problem, too.
Boxkite is offline  
Old 10-11-19, 07:05 PM
  #18  
Lemond1985
Sophomore Member
 
Lemond1985's Avatar
 
Join Date: Jan 2019
Posts: 1,916
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1117 Post(s)
Liked 429 Times in 288 Posts
This is the bike. You can see from the angle of the RD that there's too much chain. It ought to ideally be at very close to that angle when I'm in my smallest cog, but I'm a fan of big-big combinations on the local hilly roads, so it works well in combos like 50x28, which I use a lot.



A mechanic at a bike shop I knew, said that's how he adjusted chain length, was put it in the smallest cog and the biggest sprocket, and the RD should be right at the middle of its range of travel, IIRC.
Lemond1985 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.