Noisy drive train Shimano XT 1x12

thebluevoice

Hi!

When in the lowest several gears my drive train is making a right racket, whirring away.. Touching the derailleur or cranks and I can feel the vibration.. The sound seems to come from both the rear and crank area - but I think that's because the sound is being transmitted through the frame..

The derailleur, chain, chainring are 9 months old and I'm pretty sure it didn't do it when new..

So far I've replaced the bb (it was dead anyway) and regreased the jockey wheels to no effect.
Checked the b gap and indexing. Shifting is good. Clutch on or off no difference.

However, if I push the derailleur arm forwards a little the noise stops.
Pushing it towards or away from the bike or twisting has no effect.

As pushing it forwards a little (maybe 10mm) reduces the chain tension a bit I was wondering if it has something to do with chain tension?

Any ideas? Cheers!

steve_sordy

Look closely at where the chain enters the lower mech arm. The sides of the mech arm should be slightly flared as though to guide the chain into the jockey wheel. That may be its purpose, but I reckon it's to allow for the range of angles (when viewed from above) that the chain is at with the mech arm. If the mech arm has had a bang then the flared bits may have been knocked inwards, causing the chain to rub at either end of the cassette range.

If the mech arm has had a bang (dead easy on a 1x12), then the mech arm may be dented, twisted or bent. See if the upper and lower jockey wheels are in line with each other. They should be, but it is amazing how far out they can be and still shift OK, as long as the upper jockey wheel is in line (usually is).

Whatever you find, attempt to correct the problem. You will probably have to remove the mech to do it, set the gears so that the chain is in the smallest cog before removing the mech (makes things easier later). Once you have done your best on the mech, refit and set up the gears again. If you are careful and fully tension the inner wire before clamping it, you should not have to reset the gears. Don't be tempted to adjust the outer limit screws, they almost never need adjusting once correctly set.

If you are still having problems then it may be that the mech hanger is bent. It doesn't have to be bent far for it to cause problems. Mech hangers are designed to bend so that the impact on the mech doesn't break the mech, but bends or snaps the hanger instead. Sometimes both items get bent in the same impact! If you don't have a mech hanger alignment tool (£30-£50), then your LBS should be able to align the hanger for not much money as it is very quick to do. Shortly after my first 1x12, I had it reset on three occasions by the LBS at £10 a go. So, I bought the correct tool, and did it myself from then on. It is quick and easy to do, once you have the tool!

Good luck, let the Forum know what was the cause of your problem and how you fixed it.

thebluevoice

Thanks Steve, I will probably invest in an alignment tool It all looks ok though lol
I've had to fit a new chain as it had worn waaay too much (unexpected as only lasted a few months unlike on my 10 speed chains which always lasted well over a year!)
This has helped a little bit but now it may be worn cassette and ring doh!