What's wrong with the rear cassette on my bicycle?

Peter Principle

Normally a bike chain has tension, and the rear casette has free rotation wrt the rear wheel. Yesterday I noticed that when I was coasting, the rear cassette would tend to rotate forward (i.e. the cassette would rotate clockwise if viewing the bike from the starboard side). This would produce slack in the "top" of the chain where it runs from the rear sprockets toward the forward sprockets. Shortly, the rear cassette would seem to regain its free rotation and the slack would "snap" out of the chain.

(If that doesn't make sense, let me know and I can MS Paint some diagrams.)

Anyway, for those who can decipher my poor description, I'm just wondering what's going on and how I fix it.

mts

the cassette doesn't do tension, the derailler does. assuming it is not a single speed or a fixie.

how old is the bike?

How old is that chain? Chains stretch over time, though if it si a ton of slack the derailler is off kilter and needs to be adjusted or replaced

Peter Principle

mts wrote: »

the cassette doesn't do tension, the derailler does. assuming it is not a single speed or a fixie.

how old is the bike?

How old is that chain? Chains stretch over time, though if it si a ton of slack the derailler is off kilter and needs to be adjusted or replaced

I forgot to give the stats on the bike. It's a Trek 820, 21 speed. I bought it back in 2007, store it indoors. Everything on it (relevant to this problem) is original.

I'll have to do something to get a better look at it, because as far as I can tell - and admittedly riding a bike and trying to see what's going on with your gear system can be difficult - it really looks like the slack is coming from a failure of the cassette to freely rotate when I'm coasting.

Midshipman

Make sure that there isn't any debris between the last inside gear and the wheel. If there is any, it could be catching and dragging the cassette along with the wheel on occasion. Also make sure that if you have a spoke guard that it isn't rubbing with the cassette. A couple months ago I had a new rear wheel put on my road bike and the spoke guard from the old wheel didn't play nicely with the clearance on the new wheel and was dragging the cassette along.

It also wouldn't hurt to oil the freewheel mechanism.

Sporked

Peter Principle wrote: »

mts wrote: »

the cassette doesn't do tension, the derailler does. assuming it is not a single speed or a fixie.

how old is the bike?

How old is that chain? Chains stretch over time, though if it si a ton of slack the derailler is off kilter and needs to be adjusted or replaced

I forgot to give the stats on the bike. It's a Trek 820, 21 speed. I bought it back in 2007, store it indoors. Everything on it (relevant to this problem) is original.

I'll have to do something to get a better look at it, because as far as I can tell - and admittedly riding a bike and trying to see what's going on with your gear system can be difficult - it really looks like the slack is coming from a failure of the cassette to freely rotate when I'm coasting.

This. Pull the wheel off, play with the cassette, look for obvious obstructions. If it doesn't spin smoothly, and lubing it doesn't help, take it to a bike shop. Not that it's likely, but if the freewheel mechanism freezes up and goes all hipster fixed gear on you, it will be a most unpleasant surprise, probably with you ending up on the ground.

Bartholamue

If you haven't had it tuned up since you got it, I think it's time to do so.

Peter Principle

The place I bought it from charges $60 +parts to do a tune up. Reasonable?

BlindZenDriver

There is likely no reason to bring it in for service as it's likely you can fix the issue with a little oil or WD40.

Here is a site that should tell you all that is needed: http://sheldonbrown.com/freewheels.html#lube

And if you really want to get into the details and take the freewheel apart here is one with more pictures:

http://www.parktool.com/repair/readhowto.asp?id=45

The two sites in question has guides for pretty much anything related to bike maintenance so if you got the time you can really go crazy :-)


PS. The $60 + parts is perhaps on the pricey side but it depends how much they do. Try and google for local bike clubs - they will likely have a forum where you can learn if it is a good bike shop or not.

itchbay

That seems pretty reasonable to me. Usually, what's involved with that is checking the derailleur, the brifters, the cables, wheels, cleaning the chain, re-wrapping the bars, etc. It's time-consuming. I try to get a tune-up once a year, although I've had to skip it this year for financial reasons.

If my bike was doing what yours is doing, I'd consider it time to visit the shop. Of course, I've been living with it not going from 6th to 5th without visiting 4th first for a while now.

mts

60 is on the high side of reasonable. If it is a high quality shop that does high end stuff its probably fine

Peter Principle

Disassembly and oiling didn't seem to correct the problem.

I brought it to the bike shop today, they're going to replace the chain and cassette. $50 + tax.

Red Raevyn

Did they tell you what was wrong, or are they just replacing parts in lieu of doing real diagnosis? (I hate places that do the latter).

Peter Principle

Red Raevyn wrote: »

Did they tell you what was wrong, or are they just replacing parts in lieu of doing real diagnosis? (I hate places that do the latter).

Appears to be the latter, although the proprietor did show me that there was wear on the 'force' side of the gear tooth.

Rook

My bike has just started to do the same thing, hopefully it's a different problem, but the bearings in my rearhub were screwed anyways (2nd hand) so it wasn't super surprising that it went. New wheel time.