MTB rear downshifting issue.

[LiquidNeoN]

Hi Guys,

 

I have got a very very frustrating shifting issue on my X-Large Specialized Camber Comp Carbon 2015 than I am hoping you could give me some possible causes and solutions.

 

The rear derailleur shifting down works like a charm. 

 

Shifting up causes the chain to jump and slap(not always). This is exaggerated under torque. During mid cassette shift it even sometimes causes the chain to jump off and sit between the frame and the cassette.

 

I have attached slow-mo videos of this happening.

 

https://www.youtube.com/watch?v=9WHkL8Xk8dc

https://www.youtube.com/watch?v=qVKUs1wBKn4

 

Its worth noting. The bike is stock(see attached spreadsheet) except for the items mentioned below. I have tried the following; 

• Current Cassette Sram - SRAM PG1050 10 Speed MTB
• Brand new chain - Shimano SLX CN-HG75 10 Speed MTB
  • Previous chain with 250km - SRAM PC-1051 Chain
• New shifter cable
• Tested with a different rear shifter - Shimano XT M780 10 Speed Trigger Shifter

Please help me resolve with possible causes and resolutions.

 

Thank you in advance.

[GLuvsMtb]

The only thing that comes to mind is that your chain is possibly too long, meaning that the chain is not under enough tension. Did you install the chain yourself or was it done by a bike shop? Presumably the XTRD does the same, meaning that the RD springs are still good.

[raptor-22]

Is the chain on the large or small chain ring when this happens?

 

How old is that cassette?

 

If new did this occur with the previous and current cassette?

 

Any other drivetrain noises?

 

Btw you are upshifting in those vids. Upshifting is when you go to a lower ratio. Downshifting is to a higher ratio

[LiquidNeoN]

I fitted the last two chains. I have asked specialized to send me the correct chain length.

 

The only thing that comes to mind is that your chain is possibly too long, meaning that the chain is not under enough tension. Did you install the chain yourself or was it done by a bike shop? Presumably the XTRD does the same, meaning that the RD springs are still good.

[Paul Ruinaard]

Also Specialized have been sensitive to the diameter of the loop of the outer cable under the bb. If you route the cable too tight it causes ghost shifting and general shifting issues.

 

Not sure if this is your problem but give it a try anyway. 

[LiquidNeoN]

Noted and changed the shifting direction, thx!

 

Front chainring does not effect the issue.

 

Cassette has about 500km on it.

 

I have had this problem for a while. Since I have tried to address it, it has only been getting worse.... bleh!

 

Is the chain on the large or small chain ring when this happens?

How old is that cassette?

If new did this occur with the previous and current cassette?

Any other drivetrain noises?

Btw you are upshifting in those vids. Upshifting is when you go to a lower ratio. Downshifting is to a higher ratio

[LiquidNeoN]

Are you referring to the to the cable housing where it comes out under the BB?

 

Also Specialized have been sensitive to the diameter of the loop of the outer cable under the bb. If you route the cable too tight it causes ghost shifting and general shifting issues.

 

Not sure if this is your problem but give it a try anyway. 

[Bigjim]

It sounds to me like your shift cable might be binding up - i.e. the inner cable is not sliding smoothly within the outer sheath.

 

If you downshift, the cable is placed under tension, but if you upshift the cable tension is released and the derailleur spring is responsible for the upshift process.

 

If the cable is binding, the spring may not be able to overcome the bind resistance immediately & hence the "jump" when it eventually does.

 

How long is the delay from initiating an upshift to it actually happening? - is this time consistent?

 

You say you have tried another shifter also - otherwise I would have that on my suspect list 

[River Rat]

Try tensioning the chain by turning the screw on the derailleur.

[Paul Ruinaard]

Are you referring to the to the cable housing where it comes out under the BB?

yes,

 

You need to give it  a loop under there with a little clearance from the frame - not flush.

 

I think - not sure, that this is where the cable will pivot for suspension activation.

[LiquidNeoN]

B-Tension is set correctly.

 

Try tensioning the chain by turning the screw on the derailleur.

[LiquidNeoN]

I have checked it there is a bit of slack there.

 

yes,

 

You need to give it  a loop under there with a little clearance from the frame - not flush.

 

I think - not sure, that this is where the cable will pivot for suspension activation.

[Martin PJ]

Something you may consider is to make the rear cable housing a bit longer where it feeds into the derailleur, I can see on the video that this is quite short. I know this causes problems with the SRAM rear road derailleur shifting if the housing is too short.

 

Whenever I have rear shifting problems, I change the rear shifter cable and the cable housing. This seems to sort out most issues. You mentioned you changed the shifter cable, you need to change both, if you have not done so.