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MTB drivetrain - what to check/replace


NotSoBigBen
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Little Ben had some issues with his bike at the 6hr over the weekend (some 'slipping' when in the middle chainring).

 

So we checks it out last night and ja it looks somewhat worn but the chain / biggest and littlest chainring as well as the cluster looks 'ok' (to my highly untrained eye!).

 

We have a 'spare' middle chainring around so we fit it hoping for the best but no go still some slipping. So the question is do I go and buy a cluster/chain and only middle chainring? Is there some way to check which component if it's only one in the 'chain' (if you'll excuse the pun!) is causing the trouble?

 

Since as you all know this stuff aint cheap I would of course like to get away with buying just what's necessary ! It has been well looked after and the chain/cluster is about 8 months old and the XT middle chainring probably nearly a year. Many miles of hard XC and Marathon MTB has passed in that time of course!

 

This is the kit we will be moving tonight from his old (1 year!) Orbea Oiz PV to the new Specialized Carbon HT so I guess this is as good an opportunity as any to get it sorted!

 

Any suggestions would be welcomed!
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Hi BigBen

 

The most likely cause is a stretched chain which you can only check with a measuring tool or measuring a certain number of links (can't remember the formula right now).

 

If the chain is stretched it could well have caused the cluster to wear so you would probably need to replace both.

 
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BigBen, my bike is fairly new and I get the same slipping effect when pedalling really hard and I have only done 1 race with the bike so it's can't be the Crank Blades or the cassette, I think it might be my chain that stretched out...but I'm just guessing.

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You will probably find that only the chain needs replacing, but the worn cluster will wear the new chain quicker.  I'd say replace the chain, if the changes are slick and smooth and stay that way for a couple weeks leave the cluster until the next chain change.  If not, replace the cluster as well.

 

Also check that the derailleur hangar isn't bent as that could be causing the problems.
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Thanks IanJ - Should I go with the just a new chain for a start?

 

Usual advice is to always change cassette and chain together, especially if you suspect that either of them is worn.

 

Chain and cassette are items where you generally can "trade down" the food chain without sacrificing anything except maybe a very few grams.

 

(Well, true for roadie stuff anyhoo.)
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Marius - chains don't stretch.  The holes that the pins sit in wear a little and that causes the chain to become longer.  It cannot stretch after a few rides.  More than likely it is just your rear suspension bobbing about as you pedal like a maniac and that is causing the chain to bounce around.

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Marius - I think your chain is slipping because it and the cluster are new - I just fitted a new cluster and chain on my road bike, and for the first week it slipped quite a bit if I put too much power on the pedals. It is now nicely worn in and behaving well...

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Thanks guys! Useful as always when one poses a true technical question.

 

I will replace the chain tonight and should there still be an issue then go the cluster route tomorrow!
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Not sure I agree with you on that Velouria but anyway. Don't trade too far down, the XT gives markedly better shifting performance over the LX cassette under power, purely because each ring flexes alot less during shifts. Chain: Shimano 9 speed chains shift the best on a shimano cassette.

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hmm, now you guys got me worried, it's to close to the Mtb race to do anything about it now, will take it in after the race, just better not slip when I'm almost at the top of that hill....LOL

 

I think the only old thing on the bike is the cluster since that's all I took from my old Mtb..maybe it's the cluster, damn.
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BB, the XT middle chainring wears out relatively quickly in comparison to both the inner & outer.

 

The result of the wear will be what's known as chainsuck, where the chainring "grips" the chain and tries to force it around the middle blade. It is not as a result of chain wear.

 

I have recently had to replace my middle blade (in fact it was the Friday before the 6 hour) and the chain itself is still within wear limits.

 

The weight difference between LX & XT is a massive 3g.

 

 

 

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Keep with the SRAM chain, it gives better wear than Shimano also works a treat with the powerlink.

 

regarding the wear, I seem to be very heavy on the drive train, but I have found the following:

 

Life of 1 x chain about 500 - 800km depending on conditions. Muddy and long short life.  past 800km mark i need to chage Granny and Middle blade. I either get serious chainsuck or ultimatly the chain slips over the front ring. Very similar feeling to putting a new chain on old rear casette.

 

If I don't change the rear casette after 800km and new chain is put on it jumps a bit at the back for a while and then wears in.

 

Now for future ref, and I have tested this out. It works!

 

Start with everything in good order and at least three chains, then swap chains every 300km or so and thing run smoothly for way past 3 x normal chain life.

 

I think it has something to do with the fact thaqt when you change the chains you clean the old chain well and then lube it. The lube somehow settles in better and life is great!!

 

Just my take, as I was spending a bomb on drivetrains till I started doing this.

 

My 2ZAR's

 

chains are way cheaper than casettes or chainrings.
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Marius go cranck up the gears that are jumping, you will probably find that there are only about 3 or so that are jumping. Wear them in quickly and things will be kool!!

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Maybe it is just Campag stuff - but whatever was causing the chain to slip is gone, and it running nicely now.

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