Need Help Diagnosing a Mechanical

[retrofit]

My wife reports that on her last couple of rides there has been a sound and movement that occurs when her left foot/crank arm is at the 12 to 1 o'clock position. She said it feels like the crank "slips" forward a bit when the sound occurs. She also says it doesn't happen when she is out of the saddle or climbing.

I had her demo for me and I can hear the metallic "clink" and it does appear that the her foot ticks forward. Though it doesn't seem to happen with every pedal stroke, it is relatively consistent.

The crank is not loose and the bottom bracket has less than 100 miles on it.

Components are Ultegra 6500 9-speed with an unknown number of miles, but likely a lot (purchased 2nd hand). Wheels/hubs are 2004 era Campy Scirocco G3.

I suspect it's a problem with the free hub body, but I'm not sure at this point. Paw tips are shiny; two springs appear in good shape, one is has a slight bend. Is it possible that the paws and or paw springs are worn out and therefore occasionally slip?

Any ideas?

[gone]

The pawls slipping seems the most likely culprit.

[Ken Robb]

cleat moving a bit?

[David Kirk]

cleat moving a bit?


This was my thought too - what kind of pedals are being used?

Dave

[retrofit]

cleat moving a bit?

This was my thought too - what kind of pedals are being used?

Dave

Checked that out--cleat is firmly attached. She uses SpeedPlay Light Action.

[Ithadan]

Is the pedal tight in the crankarm?

Finding it tough to believe the freehub is the culprit with it consistently happening between noon and 1 in the rotation.

[Ken Robb]

when my Speedplay cleats got worn they did not hold the pedal as tight as when they were new. When she stands to pedal her weight (slight though that probably is) she jams the cleat down tighter onto the pedal than when she is seated. If the cleats aren't nearly new I would swap them and see if that fixes the problem.

[retrofit]

Is the pedal tight in the crankarm?

Finding it tough to believe the freehub is the culprit with it consistently happening between noon and 1 in the rotation.

Yep. This bothered me as well…

when my Speedplay cleats got worn they did not hold the pedal as tight as when they were new. When she stands to pedal her weight (slight though that probably is) she jams the cleat down tighter onto the pedal than when she is seated. If the cleats aren't nearly new I would swap them and see if that fixes the problem.

To test this I clipped in her left shoe (bike was on repair stand) and tried to make the cleat shift. In trying to (awkwardly) apply sufficient torque to make this happen the crank arm nudged forward. This, despite feeling securely tightened on the BB spindle. Yet, I was able to consistently repeat the nudge.

Now I'm going to clean the octalink splines on the crank arm, inspect, and remount with recommended amount of torque (need to look up). Oh, and reassemble her rear hub.:p

Thanks for all the suggestions folks!

[dustyrider]

Loose cassette?

[lhuerta]

This, despite feeling securely tightened on the BB spindle. Yet, I was able to consistently repeat the nudge.

Now I'm going to clean the octalink splines on the crank arm, inspect, and remount with recommended amount of torque (need to look up). Oh, and reassemble her rear hub.:p

Thanks for all the suggestions folks!

If the crank was firm then it is not the crank nor is it the BB. Sounds like slippage in the freehub, unless you are misinterpreting the slip with what might be jump/skip of the chain. Specifically, are you sure the chain isn't worn and that the chain isn't skipping on rear cogs? Also, inspect your chainrings for bent or worn teeth, which may also yield a skip in chain.

Are you really not able to reproduce skip other then between 12-1?

Lou

[Mark McM]

Checked that out--cleat is firmly attached. She uses SpeedPlay Light Action.

Did you check all the bolts? Once in a while the 3 bolts holding the base plate of a Speedplay cleat to my shoe will loosen, and I'll discover it when I feel a fore/aft movement at the same place in my pedal stroke. Unfortunately, you can't really check these bolts without removing the outer plates of the cleats (4 bolts).

The base plate bolts seat against thin (and soft) plastic ledges on the base plate, so correct bolt tension is important - too tight, and you'll crush the plastic ledges; too loose, and the joint can loosen allowing the cleats to shift.

Another reason I'd suspect this is the particular point in the pedal stroke - there can be much highly total forces on the drivetrain at other points in the pedal stroke, but the top and bottom of the circle are where the pedaling forces are primarily fore-aft, producing the shear forces that can cause the cleat the slip. The lack of the click when standing may be that when standing pedal forces are primarily vertical, with little fore-aft pedal force at the top of the circle.

[Mark McM]

To test this I clipped in her left shoe (bike was on repair stand) and tried to make the cleat shift. In trying to (awkwardly) apply sufficient torque to make this happen the crank arm nudged forward. This, despite feeling securely tightened on the BB spindle. Yet, I was able to consistently repeat the nudge.

Upon reading this, disregard my first suggestion.

If the crank arm is shifting on the spindle, I'm sorry to say that it is likely that the splines on the crank have been damaged beyond repair. You may be able to stop the movement temporarily by re-tightening the crank bolt, but the reversed loading that cranks often seen will eventually loosen the bolt, allowing the cranks to shift again.

This type of failure is not uncommon, and is the reason that there are two versions of Octalink (V1 and V2). V1 was originally released with Dura-Ace and XTR groups, which use cold forged cranks. The metal in these cranks was strong enough so that the small contact area of the short V1 splines was sufficient to handle torque loads. But Shimano found out they weaker metals on their lower level cranks wasn't strong enough with the short splines, and resulted in failures like the one you're experiencing. To address the problem, Shimano introduced Octalink V2, which had longer splines to increase the contact area on the splines.

[retrofit]

Upon reading this, disregard my first suggestion.

If the crank arm is shifting on the spindle, I'm sorry to say that it is likely that the splines on the crank have been damaged beyond repair. You may be able to stop the movement temporarily by re-tightening the crank bolt, but the reversed loading that cranks often seen will eventually loosen the bolt, allowing the cranks to shift again.

This type of failure is not uncommon, and is the reason that there are two versions of Octalink (V1 and V2). V1 was originally released with Dura-Ace and XTR groups, which use cold forged cranks. The metal in these cranks was strong enough so that the small contact area of the short V1 splines was sufficient to handle torque loads. But Shimano found out they weaker metals on their lower level cranks wasn't strong enough with the short splines, and resulted in failures like the one you're experiencing. To address the problem, Shimano introduced Octalink V2, which had longer splines to increase the contact area on the splines.

You nailed it. This is indeed what has happened. After cleaning the crank splines and placing the crank on the spindle without the crank bolt, there was a significant amount of play. After installing the crank bolt, I advised my wife that the crank bolt would eventually loosen and the problem will return.

In the short term, I may try to find another crank arm; in the long term, its a good time time to get her a Campy group, like the rest of the family.:)

On the plus side her freehub body, axel, and pawls got a cleaning and fresh grease!

Thanks again to everybody for their responses.

Stan