Trek Rail 7 SLX 12 Speed chain jump

[Twlpyn]

Anyone have an issue with chain jump on their SLX 12 speed.
On the smallest cog under load, it jumps in the same gear (Not up to the next)..
Almost as if the chain is too long. I have set the b screw tension properly as per marks on the derailleur and set limit screws as well.
Anyone have any thoughts?
thanks in advance.

 

[WilkyWay]

Have you measured your chain for stretch? how many miles are on it?

 

[Twlpyn]

Yes, within tolerances. Done 700k. Just cleaned and re oiled chain and no difference. Its been doing it for a while.
When in the smallest cog, the chain hangs onto the chainstay Until the pedals are powered. its almost like the derailleur needs to,be turned clockwise a few degrees to add more tension. You can do this by hand but it doesn’t stay there. Derailleur bolt is tight.

 

[WilkyWay]

Mine did similar. The clutch mechanism had seized up. Dismantled, cleaned, reassembled and wound the tension screw out a bit and all good.

 

[Davidwylie]

I had a issue similar, clutch was sticking and mech wasn't moving as it should to keep tension. Removed clutch, cleaned, re greased and tightened the tension a bit .. All sorted now.

 

[WilkyWay]

Sounds like a common issue with the XT 8100 rear derailleur.

 

[Twlpyn]

Thanks so much for your advice, sounds like that’s what’s wrong with my derailleur. I’ll give it a go and let you know how i get on.

 

[Twlpyn]

I tried what you suggested but the slack is still in the chain.
It seems that even though the b-screw is set as it should, the only thing that adds more tension to the chain is winding the b-screw in further. When set as per markings on the derailleur, the chain slides along the chain-stay protector It’s so slack.
Ive tightened the b-screw as little as possible just to tension the chain and I’ll test tomorrow....we’ll see.

 

[Twlpyn]

Well, it seems that overhauling the clutch and adding a bit more b-screw tension seems to have done the trick.
Thank you both for your useful comments.

 

[Doug Stampfer]

How do you know how many Kms your bike has done? Does the display have an odometer?

 

[Blue Moon]

How do you know how many Kms your bike has done? Does the display have an odometer?

If you have the purian display the trip, total mileage and range can be shown. If you range is showing then press and hold the minus button and it will switch to the trip, press and hold again and it’ll switch to the total mileage, press and hold again and it’ll go back to the range.

 

[Twlpyn]

It’s like Blue Moon said.

This should link you to the Bosch Purion manual.

Bosch Purion Manual

 

[Doug Stampfer]

Awesome! I didn't know half the stuff was on there. No bluetooth button to change from uphill to downhill music playlist?

 

[Branny21]

was your chain jumping on the chain ring? mine is doing that now when im shifted to the smallest cog on the cassette. I have the 9.7 thu with sram NX shifter. Im thinking the chain might be damaged somehow and i cant see it as its always jumping in the same spot.

 

[Twlpyn]

was your chain jumping on the chain ring? mine is doing that now when im shifted to the smallest cog on the cassette. I have the 9.7 thu with sram NX shifter. Im thinking the chain might be damaged somehow and i cant see it as its always jumping in the same spot.

Mine was jumping on the cassette on the smallest cog. adjusting the clutch and the b-tension screw sorted it out. Does your chain seem slack when in the smallest cog, that was my symptom, and why I needed to tighten the b-tension screw. It might affect the chainring as well.

Do you have a chain guide on your cassette, maybe that needs adjusting as well.

Adjusting the b-tension on a SRAM. 12 speeds needs a special re guide from what i recall, maybe check that.

Sorry can’t think of anything else.

 

[Branny21]

Ok so i put a new chain on and the jump went away. i didn't notice anything visually wrong on the chain but i just had the chainring fall off again and thats when the jumping started so it might of been damaged that way. This time i put RED locktite on and torqued it down.. hopefully that one does the trick and ill be able to take it off lol.

 

[Twlpyn]

Glad you sussed it out.

 

[Stihldog]

Awesome! I didn't know half the stuff was on there. No bluetooth button to change from uphill to downhill music playlist?

I’m thinking of strapping a boom box to my helmet so I can play the “Verve” uphill, and “Metallica” down hill. I just push the play button (between pause and fwd).
Had the chain jump on my 9.7. New chain, shift cable adjustment and some fine tuning (B-screw). Cleaned up every thing and re-greased where needed. 1800km and water will make some weird things happen.