Go Back  Bike Forums > Bike Forums > Classic & Vintage
Reload this Page >

Drive Train Skipping Under Load

Classic & Vintage This forum is to discuss the many aspects of classic and vintage bicycles, including musclebikes, lightweights, middleweights, hi-wheelers, bone-shakers, safety bikes and much more.

Drive Train Skipping Under Load

Old 10-18-19, 01:41 PM
Thread Starter
Join Date: Oct 2019
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Drive Train Skipping Under Load

I am at a loss here and any help would be much appreciated! I am trying to work on a ~2002 9 speed Ultegra 6500. I have replaced all cables, cable housing, and barrel adjusters. I have replaced the entire drive train (chain, chain rings, cassette, jockey wheels, and bottom bracket), re-aligned rear derailleur hanger, reset limit screws, and seem to have cable tension where it should be. On the surface every thing seems to work smooth if. I ease into things everything is really smooth the system can take any load. However if I start pushing the torque the chain starts to skip on the cassette. Is there anything else I should take a look at?


( !?!)
SuperK is offline  
Old 10-18-19, 02:42 PM
Senior Member
Join Date: Dec 2005
Posts: 12,325
Mentioned: 267 Post(s)
Tagged: 0 Thread(s)
Quoted: 1209 Post(s)
Liked 102 Times in 75 Posts
I'm sure you thought of it, but I'll ask anyway: You're using a 9-speed chain?
nlerner is offline  
Old 10-18-19, 03:34 PM
Me duelen las nalgas
canklecat's Avatar
Join Date: Aug 2015
Location: Texas
Posts: 9,864

Bikes: Centurion Ironman, Trek 5900, Univega Via Carisma, Globe Carmel

Mentioned: 176 Post(s)
Tagged: 0 Thread(s)
Quoted: 3055 Post(s)
Liked 410 Times in 290 Posts
Yup, be sure your chain and cassette are compatible. Often skipping is blamed on "worn" cogs and/or chains, but often it's just a mismatch.

Usually it's safest to go with Shimano chains for Shimano cassettes, but it's often tempting to go with the lower priced and perfectly fine KMC and SRAM. But check the specs to be sure they're compatible. I use KMC on all my bikes now, but since they revamped their catalog and model designations it's tricky figuring out which chains are compatible with which freewheels/cassettes.

An example is trying to use anything other than a Shimano or compatible "narrow" chain on Shimano MegaRange freewheels. Non-narrow chains will climb over the smaller cogs under torque, even with brand new freewheel and chain -- been there, cussed that, followed a tip from an Amazon reviewer, problem solved.
canklecat is offline  
Old 10-18-19, 04:35 PM
PM me your cotters
francophile's Avatar
Join Date: Jun 2015
Location: ATL
Posts: 2,491
Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 580 Post(s)
Liked 104 Times in 81 Posts
Above info is a strong culprit. But I'm just dropping this info "in case" someone else comes across this later with same symptom or if one of the above doesn't fix it. I assume the freewheel here is new, so one probably doesn't apply.

Two other common causes of skipping under load are bad freewheel (either internals or worn cogs allowing slippage) and incorrect chain length. Bad freewheel is easy enough to diagnose, just swap on compatible known-good wheels. Most often I've corrected this for friends, it's because of incorrect chain length, often too short.

Granted, there are some other specific cases. Like there's a certain Mavic rear derailleur which requires you change the routing of the cable for indexed vs. friction operation
francophile is offline  
Old 10-18-19, 09:57 PM
Senior Member
Join Date: Feb 2014
Location: Midwest
Posts: 1,870

Bikes: See the signature....

Mentioned: 64 Post(s)
Tagged: 0 Thread(s)
Quoted: 426 Post(s)
Likes: 0
Liked 28 Times in 17 Posts
Check for proper chain wrap at the cassette. A B adjustment screw thats cranked in too far and is pulling the derailleur too far rearward can adversely affect the chain/cassette engagement.
My bikes: '81 Trek 957, '83 Trek 720, '85 Trek 500, '85 Trek 770, '81 Merckx, , '85 Centurion Cinelli, '85 Raleigh Portage, '92 RB-2, '09 Bianchi
nesteel is offline  
Old 10-18-19, 11:27 PM
Ride, Wrench, Swap, Race
dddd's Avatar
Join Date: Jan 2010
Location: Northern California
Posts: 6,776

Bikes: Cheltenham-Pederson racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.

Mentioned: 90 Post(s)
Tagged: 0 Thread(s)
Quoted: 634 Post(s)
Likes: 0
Liked 68 Times in 61 Posts
One more possibility is that one of the rear derailer's tensioning springs has broken, or similarly that the chain is too long, or that the tensioning capacity of the rear derailer has been exceeded.
There needs to be a certain amount of tension in the chain in other words.

Note also that the upper "B"-pivot bushing is anchored at just one end inside of the knuckle, and that the attachment is known to fail under impact loading, leaving the pivot with an enormous amount of wobble/play.

Make sure also that the pulley bolts are secured tightly and that both pulleys turn freely.

A tight link in the chain is yet another common cause of chain skipping.
And check that the special connecting pin is not protruding excessively where it might contact an adjacent larger cog.

Lastly, be sure that the cassette is being effectively compressed by the lockring such that no cogs are loose against each other. Turn the wheel backwards and note whether the cogs are all parallel to each other, sometimes a spacer issue prevents the cogs from stacking up parallel. Also check that the last cog has it's splines indexed correctly on the freehub splines.

Last edited by dddd; 10-18-19 at 11:38 PM.
dddd is offline  
Old 10-19-19, 01:12 AM
Road Fan
Senior Member
Road Fan's Avatar
Join Date: Apr 2005
Location: Ann Arbor, MI
Posts: 14,431

Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 888 Post(s)
Liked 44 Times in 40 Posts
Could be dirty shift cable guides under the BB. If you apply high torque to the crank you increase BB flex. As it moves back and forth it can transfer motion to the cable, possibly pulling the derailleur out of position.
Road Fan is offline  
Old 10-19-19, 06:44 AM
Senior Member
jcb3's Avatar
Join Date: Sep 2014
Location: Irvine, CA
Posts: 604

Bikes: 1983 Trek 700, 1972 Peugeot PX10, 1989 Nishiki Cascade, 2014 Focus Izalco

Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 139 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
I had a early 1980s Trek 700 (25.5" frame) with the very long stays and it was very susceptible to ghost shifting under load (standing on the pedals on a steep hill, with my Clydesdale sized body)

I attributed it to rear stay flex causing the shift cable to tighten and loosen.
jcb3 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.