"Droopy" chain problem...

[Kevin Groome]

Hi - another newbie to this forum with an annoying road bike problem... My Trek Madone 5.2 Triple has a Shimano Ultegra rear derailleur.
With the largest front and smallest rear sprocket combo engaged, when free-wheeling the chain flops onto the frame lower bracket - is this normal?
I have tried adjusting the B tension screw and I have even removed a chain link to increase the tension without success. All the gears engage properly and the chain slack problem only applies to the above combo.
Any suggestions would be much appreciated.<br />
Kevin

[DaveM]

You say this happens when you "freewheel". Just to confirm, I think you mean that it only happens when you are rolling, but not pedaling (coasting). If so, it sounds like your freehub is not spinning freely. It is getting dragged forward by the wheel slightly which takes the tension off the chain. This could result from wearing freehub or a bent axle which is rubbing on the inside of the freehub body. I'd take off the wheel and cassette and check it out a little.
BTW, you may have made your chain too short now. Not a big issue, but be careful going into the big-big combination, you could tweak your rear derailleur.

[on.looker]

Hi,

I am also having the same problem when I am pedaling backwards. I have replaced my freehub to accommodate a new 9 gear cassette. The freehub spins correctly until I tighten down the axle to eliminate any free play and provide a freely rotating rear wheel. I have found that a rubber dust/water seal that sits on the freehub side of the axle is the culprit. At the moment the “cup side” of this rubber seal is facing the bearing retainer of the freehub. If I use the tapered side, the other side of the seal, it will get squashed when I tighten up the axle. Either way, this seal is causing enough friction to interfere with the freehub’s rotation thus the saggy chain.

Is this normal and I should just let both parts wear in?
Have I used the correct side to seal the bearing retainer?
Is the seal the correct size for this freehub it worked fine with the older and shorter freehub?

Thx,

[xerxes]

Assuming that it's all assembled correctly, it could be just a bit tight as it's new, it's difficult to tell without actually having a look. Also make sure it's well lubricated and the seal is not "dry".

It may also be that your chain is a bit too long. Shift the chain onto the largest sprocket at the rear and the largest chainwheel at the front. Is there still a lot of slack in the chain? If so, pinch the chain together to calculate how many links you could remove without having the rear deraileur cage pulled too far forwards and under too much tension.

If you want to calculate chain length more accurately, take a look here: http://bikeride.com/calculate-chain-length/

[JonB]

^He's right, could easily be that.

I got a new bike a few years ago from a very good bike shop, but the chain was really a bit long. I use Alex's chain length calculator and took nearly 3 complete links out of it. Rock gardens were not much of an issue for the chain anymore (certainly not now I have a chain device )

[on.looker]

Hey thanks for the replay guys,

I am pretty sure the problem is with the dust seal and the freehub bearing retainer. The freehub rotates freely until the axle is tightened down to remove any wheel wobbles while maintaining smooth rotations. There must be a slight size different between the old and new bearing retainer in the freehub. Does this axle seal come in different sizes?

I have not seen anything on the net that even addresses this axle seal.

Thx