Chain slip with Shimano XT 12 speed in top gear

[dixie600mhz]

So bike has about 300 miles on it and I'm starting to experience significant chain slip in top gear. It's only happening in turbo mode. It's not changing gear, it's slipping teeth in top gear only under heavy torque.

I just double checked the b screw and its perfect. The alignment of the derailleur looks perfect and it shifts into and out of gear like a dream. Anybody else having chain slip? Am I missing something? It's only in top gear under heavy load but I can look back and watch it slip teeth when it happens while staying in top gear.

 

[steve_sordy]

If I was to ignore the mileage, I would say that this is classic sign of wear! Have you checked the chain for wear? If you use the top gear in turbo a lot, then that cassette gear could be worn more than the others. Worn chains wear gears faster than new ones because the rollers slide up and down the teeth rather than just sitting there.

I am going to check terminology now. By "top gear", I assume you mean the smallest cassette gear? In which case there are fewer teeth that have the chain wrapped around them. And with a worn chain, there are even fewer chain links taking the load than normal. Add in turbo mode and that is when they slip.

 

[dixie600mhz]

Yeah top gear as in the smallest one. I read b screw adjustment is a classic tell tale since if that's off you don't get max wrap surface area contact on 12th gear. However, this really does just sound like wear. The cassette has 300 miles and the chain maybe 200 or less. I don't use turbo that much. The chain isn't stretched either. I just measured it and it's still like brand new.

 

[flightrisk86]

I have a 2021 9.8xt and it has eaten 3 chains, with chain slip/jump happening prior in small cog.
1st check low limit setting, it is a bit different with 12sp. See manual online or youtube.
2nd check your frt chain ring - is it stamped or bullet? My OEM version was stamped and it kept bending chain links, till shop replaced the frt ring.
3rd maybe a slight tighten of your derailleur adjuster barrel
Mine might still jump in turbo small gear under load, I just don't test it anymore, had enough drama so tend to stay in 2nd ring up.

Bike shop took 3+ weeks to warranty frt ring via e13, so I'm looking at SRAM next, maybe even AXS.

 

[RickBullotta]

So bike has about 300 miles on it and I'm starting to experience significant chain slip in top gear. It's only happening in turbo mode. It's not changing gear, it's slipping teeth in top gear only under heavy torque.

I just double checked the b screw and its perfect. The alignment of the derailleur looks perfect and it shifts into and out of gear like a dream. Anybody else having chain slip? Am I missing something? It's only in top gear under heavy load but I can look back and watch it slip teeth when it happens while staying in top gear.

I'd pull the cover on the derailleur clutch and look for gunk and dirt, or a lack of lubrication. Take a look at:

CLUTCH SERVICE? Shimano 12, 11, 10 speed XTR, XT, SLX, Deore - Shadow Plus Derailleur Maintenance - YouTube

If it was 11 speed, I'd say the freehub body might be toast and the small cog was slipping around the freehub body, but I've not seen that happen with microspline (yet). It couldn't hurt to take off the rear wheel & cassette and inspect the freehub body though (both the splines and the pawls).

 

[flightrisk86]

riding on the small gear in turbo under pressure is most likely not a common practice with most riders of eBikes, so this could a wide spread issue that goes under the radar.

 

[Gary]

a chain slipping under load can be due to a number of things.
chain wear
sprocket wear
poor lubrication
dirt/grime build up
damaged components. (mech, hanger, chainlinks, sprocket/teeth, pulley wheels, hanger, cables)
poor set-up - chain not indexed perfectly causing it to ride the side of the sprocket.
Too large a gap between the sprocket and top jockey causing poor chain wrap


The top sprocket on a 12 speed XT cassette only has 10 teeth.
Which means only 5 teeth are actually making contact with the chain in use...
Yeah. Think about that for a minute...
Now with such a wide range cassette (10-51?) the derailleur's top jockey wheel has to sit a little lower (further away) from that sprocket than it can on a closer ration (say an 11-28) cassette.
So I'm sure you'll be able to see only a slight amount of sprocket/chain wear is going to reduce how firm a hold the chain actually has on that tiny little sprocket. Add in super high force from the motor and it stands to reason it will slip far sooner than a larger sprocket with greater chainwrap would or on a bike ridden with no motor.

This is why 9&10t cassette sprockets are a completely stupid idea on an E mountain bike. and why drivetrains slipping under load from wear at just 2-300 miles isn't out of the question.

Simply stop putting extremely high load through the 10t sprocket (ie. up your cadence to a decent rpm and use the gearing properly) and you will get more life from it.

you'll also get more life from your drivetrain if you change gear smoothly under less load and at higher cadence. (easing off pedalling force just before each gear change)

clue: no one on conventional bikes is spinning low cadence/High torque in their smallest sprockets. So why would anyone think it's a good idea with a motor?

 

[dixie600mhz]

This isn't a case of being in the wrong gear. This is pedaling at 20mph with normal cadence and a slight headwind causes slipping. The XT setup shifts like a dream vs the X01. The slipping after 30 miles is the only gripe.

For the record it looks like you can just replace the 10T and 12T sprockets and not the entire cassette. Once I check out the clutch and all the other culprits, I might try replacing the 10T cog. The part number is Y1X498020. Looks like the same part number applies to M8100, 9100 and 7100 cassettes.

 

[flightrisk86]

Yeah, let us know if the cog swaps work, I'd rather to to a larger cog then deal with skip when I'm unknowing in the wrong gear or mode. Previous 11sp XT setup on acoustic bike allowed me to mash pedals all day with out a whipper.

 

[Gyre]

This wouldn't be the first report I've heard of a worn 10 or 11-tooth sprocket slipping in turbo mode. Definitely try the cog swap, and I'd suggest staying off those cogs until the replacements arrive.

 

[Gary]

Assuming you're riding a 29er with a 34t chainring riding at between 18-20mph in the 10t sprocket would actually mean fairly low cadence (60-67rpm). Do yourself a favour and change to a lower gear (larger sprocket) and spin a little faster.
Another option to stop you using the smallest sprockets so much would be to change to a larger chainring.

 

[TPEHAK]

This is about the mileage when the smallest sprocket normally starts slipping if you use the top gear regularly. You have to replace the smallest sprocket and check the chain wear.

 

[dixie600mhz]

So the 10t sprocket is out of stock everywhere : ( Also the Rail is a 34T front chainring max. I don't want to switch out an entire cassette after ~400 miles. This sucks.

 

[Gary]

Just continue using the cassette but stop using the 10t
You can pedal up to 30mph in 34x12 pretty easily

 

[flightrisk86]

You can pedal up to 30mph in 34x12 pretty easily

Downhill?

 

[TPEHAK]

Uphill against the wind.

 

[dixie600mhz]

I adjusted the b-screw so that the jockey is 3 to 4mm closer to the cassette than spec and it's made a world of difference vs chain slip. I can still get into 1st no problem without rubbing. 12th is much improved with little to no slip so far. It seems just getting a little more chain wrapped around 12th makes a significant difference to chain slip.

 

[RickBullotta]

I adjusted the b-screw so that the jockey is 3 to 4mm closer to the cassette than spec and it's made a world of difference vs chain slip. I can still get into 1st no problem without rubbing. 12th is much improved with little to no slip so far. It seems just getting a little more chain wrapped around 12th makes a significant difference to chain slip.

Good to hear. In my experience that’s usually the cause of poor shifting if the cables and housing are good. A slightly bent hanger is a consideration too.

also consider that depending on your suspension geometry, when sagged, the chain length/tension will be lessened. Perhaps you’re compensating for sag with the 3mm tweak.

 

[Zekiel]

Good point! Did your bike store set the b limit static or with you on the bike? 12 speeds on Sram at least come with their plastic b limit setting guide but it still needs to be set under sag.

 

[dixie600mhz]

mmmmn, I set the b screw with the bike on the stand up off the ground. Now I'm curious to see how sag effects it. It's working a treat for now.

 

[Zekiel]

My difference between static and with sag was just a few mm so it might be GTG.

 

[dixie600mhz]

Another 30 miles in and the slip is back. It's definitely chain slip. Check out the video. Ignore the rust and the sandals. It was a spur of the moment gopro clip just after washing the bike tonight and was about 35C outside.

 

[Oldrider]

Could Rick Bullotta be on to something when he mentions chain length? Have you checked if your chain is too long?

 

[RickBullotta]

Another 30 miles in and the slip is back. It's definitely chain slip. Check out the video. Ignore the rust and the sandals. It was a spur of the moment gopro clip just after washing the bike tonight and was about 35C outside.

I can't ignore the rust. ;-)

Even a slightly binding chain link could jump around when wrapped around a 10T cog.

 

[dixie600mhz]

This chain is lubed after every other ride. That rust was after a 30 minute wash in blistering heat and lubed right after.

The clutch feels tight and no binding. There's 118 link pins in the chain right now. If I make it shorter it will def be too short. The chain was replaced after a pedal strike at 200 miles (200 miles ago) and is the exact length defined by the shimano guide and the previous chain.

The derailleur looks straight. Gears select crisp. Chain is not stretched. I can't see any wear during inspection. Looks like I'll get less than 400 miles to that top gear.

I'm still trying to replace that single gear but can't find the part in stock anywhere.

Just happy the video confirmed its chain slip. I was starting to think hub, front chainring or something with the motor.

 

[Mcharza]

From the last picture you can clearly see that the smallest gear has been worn.

 

[Jubby]

I was having chain slip as well as grinding and drivetrain noise also.
Turns out Shimano had a factory issue with hubs not being greased properly. My mechanic took mine apart cleaned and greased with Shimano white grease and all noise and chain slip has gone!

 

[Phantomx0_1]

I have a 2021 9.8xt and it has eaten 3 chains, with chain slip/jump happening prior in small cog.
1st check low limit setting, it is a bit different with 12sp. See manual online or youtube.
2nd check your frt chain ring - is it stamped or bullet? My OEM version was stamped and it kept bending chain links, till shop replaced the frt ring.
3rd maybe a slight tighten of your derailleur adjuster barrel
Mine might still jump in turbo small gear under load, I just don't test it anymore, had enough drama so tend to stay in 2nd ring up.

Bike shop took 3+ weeks to warranty frt ring via e13, so I'm looking at SRAM next, maybe even AXS.

How many miles for 3 chains I'm just at 1k miles still on orginal chain and it's about 0.5 on the wear indicator have you done 10k miles?????

 

[Phantomx0_1]

This chain is lubed after every other ride. That rust was after a 30 minute wash in blistering heat and lubed right after.

The clutch feels tight and no binding. There's 118 link pins in the chain right now. If I make it shorter it will def be too short. The chain was replaced after a pedal strike at 200 miles (200 miles ago) and is the exact length defined by the shimano guide and the previous chain.

The derailleur looks straight. Gears select crisp. Chain is not stretched. I can't see any wear during inspection. Looks like I'll get less than 400 miles to that top gear.

I'm still trying to replace that single gear but can't find the part in stock anywhere.

Just happy the video confirmed its chain slip. I was starting to think hub, front chainring or something with the motor.

View attachment 60566 View attachment 60567 View attachment 60568 View attachment 60569 View attachment 60570 View attachment 60571

How have you done that to a cassette in 300 miles POWERING up step hills in turbo?

I have 1k miles on my orginal chain and cassette with hardly any wear and I ride in the Welsh mountains ⛰

 

[Phantomx0_1]

Another 30 miles in and the slip is back. It's definitely chain slip. Check out the video. Ignore the rust and the sandals. It was a spur of the moment gopro clip just after washing the bike tonight and was about 35C outside.

Knackered cassette from the pics below. That's some serious wear in 300 miles ?.