Chain skipping under load after bike service

[pagheca]

I took my bike in for a service. Everything seemed fine, but yesterday I finally had a chance to ride it again and noticed that, as soon as I put some torque on the pedals (going uphill or accelerating), the chain starts slipping over the cassette sprocket. It's also quite dangerous, I lost my balance several times while climbing.

I'm going to contact the bike shop that did the work, but in the meantime I'd like to hear your thoughts on what could be causing this. I really don't understand it.

It never happened before the service. Now it happens every time, almost as if the cassette teeth were worn out... but why now? What could have changed?

I took a few photos and noticed two things:
1) There's a small lever that I'd never noticed before. What is it for? How should it be set? Up or down (as it is)?

2) The cassette teeth look very uneven. Is the cassette simply worn out? If so, again, why did the problem only start after the service and not before?

Any help would be greatly appreciated. Thanks!

 

[RustyMTB]

Lift the lever up & try again.

 

[pagheca]

Lift the lever up & try again.

thanks, but do you think this is the problem or just to try? I do not want to make the situation worst...

 

[RustyMTB]

You may not improve it but you won't make it worse.

 

[cozzy]

B screw has been turned in too far. You don't have enough chain wrap.

 

[pagheca]

B screw has been turned in too far. You don't have enough chain wrap.

that's what I was guessing: not enough chain wrap... thanks Which is the B screw?

 

[RustyMTB]

Which is the B screw?

On Shimano derailleurs, the B screw adjusts the distance between the mech & the cassette. Adjusting it is involving & if you don't know where the screw is, the rest will be a challenge. You can look up the process on Youtube or take it back to the bike shop. However, the lever mentioned earlier is your clutch, whose purpose is to add tension to the chain. It appears the shop turned the clutch off, probably to remove the rear wheel & did not turn it back on.

Turning it on will likely improve the shifting & is the first thing you should do. The second thing is adjust the gears at the shifter by turning the barrel adjuster. Turn it away from you to tighten the gear cable & toward you to slacken it until you achieve smooth shifting. Only then should you move on to B screw adjustment.

 

[skizzian]

the B screw is the one by itself - easy to see with the long thread pushing against the derailleur hanger
the plastic lever is the clutch switch - you want it ON when riding
if it still slips it might be a worn cassette in the smaller gears