Slipping Gears

Discuss light weight issues concerning mountain bikes & parts.

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Benno
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by Benno

a dirty drivetrain won't really result in the symptoms you describe. When a drivetrain is older and very dirty it tends to stick to the front chainring causing "chain suck". This is when the chain sticks to the chainring and gets jammed, usually on the chain stay. This will jam up your cranks and if pushed too hard will break/bend your chain.

Unfortunately I don't have a write up at the moment on how to adjust your cable tension. There is a simple way to test it.
* small adjustments can be made at the barrel on your shifter
- If your rear derailleur is slow to shift to a harder gear then you have too much cable tension.
- If your rear derailleur is slow to shift to an easier gear then you don't have enough cable tension.
- Make sure that your derailleur is able to get into every single gear.
- If your rear derailleur doesn't shift well up or down then you likely need new cables/housing (gunked up, too much friction)
- If your bike shifts fine for half of your gear cluster but goes out of tune for the other half, then you need to align your hanger

Also you can stand behind your bike and spin the cassette via the cranks. Look at each cog and make sure none of them are bent.
Sometimes when I get stumped on a bike I very slowly turn the cranks and watch how the chain interacts with all of the gears. Watch everything that rotates and look for smooth movement.
There is also the possibility that your drivetrain actually is worn out. The first thing to go is usually your middle ring, the chain with slip off under high torque. Perhaps you have more miles on it then you think (though usually one has less miles than one thinks ;-)

I replace my chain 2-3 times per season (about every 1000 miles). I replace my entire drivetrain every season (about 3000miles). I replace my cables/housing 2-3 times per season.
Never replace your rear cassette without replacing your front chainrings.
Light. Strong. Cheap. Pick one.

by Weenie


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paulm2322
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Joined: Thu May 30, 2013 6:59 pm
Location: Liverpool, UK.

by paulm2322

Benno wrote:a dirty drivetrain won't really result in the symptoms you describe. When a drivetrain is older and very dirty it tends to stick to the front chainring causing "chain suck". This is when the chain sticks to the chainring and gets jammed, usually on the chain stay. This will jam up your cranks and if pushed too hard will break/bend your chain.

Unfortunately I don't have a write up at the moment on how to adjust your cable tension. There is a simple way to test it.
* small adjustments can be made at the barrel on your shifter
- If your rear derailleur is slow to shift to a harder gear then you have too much cable tension.
- If your rear derailleur is slow to shift to an easier gear then you don't have enough cable tension.
- Make sure that your derailleur is able to get into every single gear.
- If your rear derailleur doesn't shift well up or down then you likely need new cables/housing (gunked up, too much friction)
- If your bike shifts fine for half of your gear cluster but goes out of tune for the other half, then you need to align your hanger

Also you can stand behind your bike and spin the cassette via the cranks. Look at each cog and make sure none of them are bent.
Sometimes when I get stumped on a bike I very slowly turn the cranks and watch how the chain interacts with all of the gears. Watch everything that rotates and look for smooth movement.
There is also the possibility that your drivetrain actually is worn out. The first thing to go is usually your middle ring, the chain with slip off under high torque. Perhaps you have more miles on it then you think (though usually one has less miles than one thinks ;-)

I replace my chain 2-3 times per season (about every 1000 miles). I replace my entire drivetrain every season (about 3000miles). I replace my cables/housing 2-3 times per season.
Never replace your rear cassette without replacing your front chainrings.


Thanks for the detailed response Benno.

It shifts perfectly up and down the cassette and front chain rings, that's why this is so annoying. Everything looks in line or me also.

Have a close look at the 2nd picture of the crank set. Is it just me or does on of the teeth look worn down on the big chain ring compared to the others? It's making me doubt wether the slip is from the cassette or actually the front chain ring!

It's annoying me that much I'm considering selling the bike and buying a different MTB. I don't want to but if it can't be solved the. I will lose patience with it. It's a shame because I think it's a great bike apart from the slip problem.

Thanks
You can't 'out train' a bad diet : )

rijndael
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Location: Haines, AK - Temporarily

by rijndael

paulm2322 wrote:Have a close look at the 2nd picture of the crank set. Is it just me or does on of the teeth look worn down on the big chain ring compared to the others?
The teeth are not designed to be identical. Their profile varies to aid in shifting.

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paulm2322
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Location: Liverpool, UK.

by paulm2322

rijndael wrote:
paulm2322 wrote:Have a close look at the 2nd picture of the crank set. Is it just me or does on of the teeth look worn down on the big chain ring compared to the others?
The teeth are not designed to be identical. Their profile varies to aid in shifting.



Thanks Rijndael, I didn't know that :thumbup:
You can't 'out train' a bad diet : )

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Benno
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by Benno

Yeah each tooth should be profiled so they are all gonna look a little different. A worn tooth/chainring, all the teeth will start forming little hooks instead of being mainly triangular. When it starts slipping on the front it really does feel like it's happening on the rear cassette but is usually not reality.
Light. Strong. Cheap. Pick one.

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paulm2322
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Location: Liverpool, UK.

by paulm2322

Benno wrote:Yeah each tooth should be profiled so they are all gonna look a little different. A worn tooth/chainring, all the teeth will start forming little hooks instead of being mainly triangular. When it starts slipping on the front it really does feel like it's happening on the rear cassette but is usually not reality.


Thanks again Benno.

I have booked it into Evans for tomorrow. I will get it back next week. I have asked for the mechanic that has worked on my road bike as I think his work is great.

I will post back here when I get my bike back - hopefully slip free.

Cheers
You can't 'out train' a bad diet : )

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paulm2322
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Location: Liverpool, UK.

by paulm2322

Just dropped it off at Evans and had a good talk with the mechanic. He said the chain is worn and slightly stretched. Cassette also worn so he will fit both and then test to ensure it shifts as it should. Get it back on 4th November as they are really busy. I'll post back here on a hopefully successful fix.
You can't 'out train' a bad diet : )

Alejandro8100
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Joined: Sat Oct 26, 2013 2:04 pm

by Alejandro8100

Currently, I am also facing the same problem. I read out interesting and informative ideas. It is dead easy and pretty difficult to go wrong. This will be helpful in this regard. thanks everyone...


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Alejandro
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socratease
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Joined: Thu Oct 13, 2011 5:25 pm

by socratease

Measure the chain wear. Look up how to do this on sheldon brown or youtube. If your drivetrain is this dirty after cleaning it, I would think that your chain was worn. If it is worn much past .75 (on a park/rollhoff gauge-- I'm a lazy mechanic who likes pass/fail chain gauges, but there is corresponding wear you can measure using a ruler) it can wallow out the cassette pretty quickly. This is difficult to diagnose visually.

Does the drivetrain slip across the entire cassette? Does it slip only in your most commonly used rear gears? Does it slip only under your most commonly used front chainring? Describe the slip. Is it ghost shifting? (light to moderate clicking--feels like the chain wants to shift from one cassette ring to the other) Is it an actual slip? (the drivetrain feels fine under very light pedaling, but as soon as real power is applied, you get a loud pop.)

It looks like you have a deore crank. The chainrings are probably not worn since shimano uses high quality steel chainrings.

The other possible source of the slip would be the freehub. Shimano's entry level freehubs aren't the best sealed and sometimes slip if extremely dirty.
I've also seen shimano freehubs back out on rare occasion, which would be diagnosed by an excessive amount of lateral and azimuthal play in the freehub body.

Summary: if it does, indeed shift well (i.e. perfectly, not just "good enough") in the stand, and the freehub isn't slipping, and the slip you are getting is a large, jolting pop under hard load, your cassette and chain are likely worn out and need to be replaced.

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paulm2322
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Location: Liverpool, UK.

by paulm2322

Ok,

just rode home from Evans which is approx 3.5 to my house. I didn't encounter any problems and the gears felt stronger if that makes any sense?

I replaced the chain for a ten speed Shimano HG94 XT and a Shimano M771XT cassette - 11/36.

I will post here when I go for a longer ride and hope the results are good.

Image
IMG_5842 by p.t.mainwaring, on FlickrImage
IMG_5843 by p.t.mainwaring, on FlickrImage
IMG_5840 by p.t.mainwaring, on FlickrImage
IMG_5841 by p.t.mainwaring, on Flickr

Cheers for the replies folks :beerchug:
You can't 'out train' a bad diet : )

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Benno
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by Benno

Glad it's working for ya. I didn't notice before that you have a rack on the back. Sometimes those can throw your derailleur hanger out of alignment when they are tightened down.
Light. Strong. Cheap. Pick one.

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paulm2322
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by paulm2322

Benno wrote:Glad it's working for ya. I didn't notice before that you have a rack on the back. Sometimes those can throw your derailleur hanger out of alignment when they are tightened down.


Interesting Benno! I'll check how tight the bolts are.

He did adjust the derailleur hanger too so may never know the culprit for definite. Feels like a new bike so happy again. Never wanted to sell it in the first place!

Thanks for your time and advice : )
You can't 'out train' a bad diet : )

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Benno
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by Benno

Yes my first encounter with a rack was a head scratcher. As you have to partly remove the rack in order for the hanger alignment tool to fit on. But then as you tighten the rack back on it moves the hanger back out of alignment...
In the end it's good it's working for you again and you are happy with your bike. I feel your pain of not wanting to ride a poorly functioning bike.
Light. Strong. Cheap. Pick one.

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paulm2322
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Location: Liverpool, UK.

by paulm2322

Benno wrote:Yes my first encounter with a rack was a head scratcher. As you have to partly remove the rack in order for the hanger alignment tool to fit on. But then as you tighten the rack back on it moves the hanger back out of alignment...
In the end it's good it's working for you again and you are happy with your bike. I feel your pain of not wanting to ride a poorly functioning bike.


Thanks again Benno, great advice from you that I will remember. I'll bear the pannier in mind if things go out of alignment in future.

All the best

Paul
You can't 'out train' a bad diet : )

by Weenie


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