Top 2 gears - hop

[MattR]

I replaced the chain on my daughters bike. Now it won't stay in the top two gears (6 and 7). It constantly hops out and back in. The rest of the gears seem fine. It doesn't matter what gear the front derailleur is on.

The back cog is 7 speeds. The chain is an 8 speed chain, but as far as I can tell they're the same. The length of the new chain might be one link shorter. I adjusted the tension on the derailleur as best as I could. The derailleur seems a bit bent as the wheels don't line up with the gears. That's my first guess as to the problem, but it used to work fine.

Any ideas on what I should look for?

Thanks for your time!

[Painkiller]

try to get a pic straight from the rear and side of what you have, do you have a freewheel or cassette?and by 6 and 7 do you mean the two smallest cogs or the two largest cogs?

[MattR]

It's a trek, so I assume it's a freehub? Two smallest gears. A photo is going to take some time, as my daughter has the bike on the other end of town.

Thanks for the quick response.

[nfmisso]

(03-31-2013, 09:28 PM)MattR Wrote:  It's a trek, so I assume it's a freehub? .....

Not a good assumption; 50-50 depending on vintage.

[MattR]

it's about 4 years old, if that helps. Not sure how else to figure it out.

BTW, this only happens when I put pressure on the crank

[nfmisso]

Best guess is that you should have replaced the chain and cassette/freewheel (depending on what it has) at the same time.

Is the chain the correct length? A long chain could be a cause to this symptom.

Further, I would guess that most of the time it is ridden in the smallest ring at the front and smallest ring at the back, which: (1) increases the wear on the chain and sprockets (especially at the back) and (2) means that the derailleur put very little tension on the chain.

[MattR]

I can look at the gears and see if they're worn. The bike has been used a lot and the chain was junk, so It could be worn teeth.

The new chain is about one link shorter.

"(2) means that the derailleur put very little tension on the chain"

Please explain? Do you mean that the derailleur isn't putting enough tension on the chain to keep it on a gear?

[nfmisso]

(04-01-2013, 03:29 PM)MattR Wrote:  I can look at the gears and see if they're worn. The bike has been used a lot and the chain was junk, so It could be worn teeth.

The new chain is about one link shorter.

"(2) means that the derailleur put very little tension on the chain"

Please explain? Do you mean that the derailleur isn't putting enough tension on the chain to keep it on a gear?

If the chain was longer that the original, the derailleur would put less tension on the chain in any given gear.

Most likely that is not the issue. If the chain needed replacement, the freewheel/cassette also needed replacement.

A quickie, though not sure fire way to see if it is likely a freewheel or cassette is to count the number of teeth on the smallest sprocket at the back. If there are 14 teeth; it is most likely a freewheel (99+% confidence); if there are 13 teeth, 90+ % confidence that it is a freewheel. If there are 12 or 11 teeth, 99+% confidence that it is a cassette.

[MattR]

I took it to a shop and they looked at for me. The derailleur and the hanger are bent. They tried to straighten the hanger. I'll buy a new derailleur.

Thanks everyone