I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not really sure what to adjust ... cable tension or rear derailleur alignment, or both?? Any help would be appreciated ... maybe a recommended procedure to identify the problem and eliminate this issue?
I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not really sure what to adjust ... cable tension or rear derailleur alignment, or both?? Any help would be appreciated ... maybe a recommended procedure to identify the problem and eliminate this issue?
Thanks!
Try diacletic grease (found at auto stores) and put some where the rear derailleur cable goes under the crank, through the plastic guide that is there. Diacletic grease won't hurt plastic. Dis this on my wifes mountain bike, it was doing the same thing.
Try diacletic grease (found at auto stores) and put some where the rear derailleur cable goes under the crank, through the plastic guide that is there. Diacletic grease won't hurt plastic. Dis this on my wifes mountain bike, it was doing the same thing.
Good possibility this is it.
Worn chains and sprockets can cause the chain to jump over a cog tooth under hard pressure, but it normally will stay on the same cog, not shift to a different cog.
If it's shifting on its own, that means something is pulling on the shift cable. Frame flex combined with excess cable friction can sometimes cause that.
If it's shifting on its own, that means something is pulling on the shift cable. Frame flex combined with excess cable friction can sometimes cause that.
- Frank Krygowski
Called "ghost shifting" I'm sure Sheldon Brown's web site says something about this phenomenon
If it's shifting on its own, that means something is pulling on the shift cable. Frame flex combined with excess cable friction can sometimes cause that.
- Frank Krygowski
Called "ghost shifting" I'm sure Sheldon Brown's web site says something about this phenomenon
"The usual cause of the problem, believe it or not, is the cable guide that the derailer cable uses to get around the bottom bracket. As you pedal the bike, the frame flexes from side to side. This causes the gear cable to get tighter and looser with every other pedal stroke."
the concept - that a steel truss, mounted on flexible wheels/axles, with the next reality interface - rubber tires - contacting a less than adhesive surface FLEXES!! is not believable
"Ron" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Quoted message said:
I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not really sure what to adjust ... cable tension or rear derailleur alignment, or both?? Any help would be appreciated ... maybe a recommended procedure to identify the problem and eliminate this issue?
Thanks!
Try diacletic grease (found at auto stores) and put some where the rear derailleur cable goes under the crank, through the plastic guide that is there. Diacletic grease won't hurt plastic. Dis this on my wifes mountain bike, it was doing the same thing.
If they look at you funny try asking for dielectric grease instead.
"The usual cause of the problem, believe it or not, is the cable guide that the derailer cable uses to get around the bottom bracket. As you pedal the bike, the frame flexes from side to side. This causes the gear cable to get tighter and looser with every other pedal stroke."
the concept - that a steel truss, mounted on flexible wheels/axles, with the next reality interface - rubber tires - contacting a less than adhesive surface FLEXES!! is not believable
Well, for six bucks for the grease it was a no brainer for me. Actually to think that all human energy is channelled into propulsion in the operation of a bicycle, with all things being equal, as you seem to propose is far out. 90 percent of the energy expended by a light bulb is heat.
"The usual cause of the problem, believe it or not, is the cable guide that the derailer cable uses to get around the bottom bracket. As you pedal the bike, the frame flexes from side to side. This causes the gear cable to get tighter and looser with every other pedal stroke."
the concept - that a steel truss, mounted on flexible wheels/axles, with the next reality interface - rubber tires - contacting a less than adhesive surface FLEXES!! is not believable
I have thought about this flex problem and the shifting troubles mentioned in the other posts - friction at the bottom bracket, friction in cable housings, stretchy cables, etc. The ideal solution would be an indexed rear Derailleur. I have never heard of such a thing but it seems like it could be done.
A little research finds an indexed front dr US patent # 6,629,903
"Ron" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Quoted message said:
I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not really sure what to adjust ... cable tension or rear derailleur alignment, or both?? Any help would be appreciated ... maybe a recommended procedure to identify the problem and eliminate this issue?
Thanks!
Try diacletic grease (found at auto stores) and put some where the rear derailleur cable goes under the crank, through the plastic guide that is there. Diacletic grease won't hurt plastic. Dis this on my wifes mountain bike, it was doing the same thing.
If they look at you funny try asking for dielectric grease instead.
Steel, aluminum, and carbon fiber are elastic. They stretch and return under ANY force. Sheldon's argument is that the dirty guide makes the cable slip-stick, causing it to store the little deflections on each pedal stroke until the rear mech has been pulled significantly out of position. Those of us with recent friction shifter experience will recall it doesn't take much cable pull to start up some chain noise, and in some cases to cause a shift.
Ken
<[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
"The usual cause of the problem, believe it or not, is the cable guide that the derailer cable uses to get around the bottom bracket. As you pedal the bike, the frame flexes from side to side. This causes the gear cable to get tighter and looser with every other pedal stroke."
the concept - that a steel truss, mounted on flexible wheels/axles, with the next reality interface - rubber tires - contacting a less than adhesive surface FLEXES!! is not believable
Wrong. Chain and cassette replaced when the crankset was replaced. Again, it shifts fine ... up or down ... at all times. This only occurs during hard climbing out of the saddle.
On 24 Apr 2006 12:21:23 -0700, "[email hidden]" <[email hidden]>
Quoted message said:
I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not really sure what to adjust ... cable tension or rear derailleur alignment, or both?? Any help would be appreciated ... maybe a recommended procedure to identify the problem and eliminate this issue?
http://sheldonbrown.com/autoshift.html may contain some relevant information. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts.
has the bike sat out in the rain? check each link for shrinkage its possible a stretch of 3-4 links shrank and no longer mate with the cassette or CR while the remainder are of a similar length. skip skip skip then run count the revolutions between each skip quick now - how many crank revs equal one chain revo?
I've been fighting this problem since "re"building up my frame this winter (w/ a new crankset, rings and cables). The f and r derailleurs are Dura-Ace 9sp. - 53/39 front rings and 12-27 rear cassette (if it matters). The bike shifts well in most instances, but will shift on it's own under load, such as climbing hard out of the saddle. I'm not
A worn cassette and/or chain will not cause *shifting* under load. The chain may slip, but gear will stay the same, since the derailer is still at the same position.
