Gears slipping under load

[Bigtallfatbloke]

Gears are slipping but only when the bike is fully loaded and only when I'm on the middle cog. It's a tourer bike with 3x9 speeds shimano. I haven't touched the screws at all. Would I be right in thinking I should just tighten up the cable?
What confuses me though is why it only slips on the middle cog and not the big one or the smaller one.

 

[g3nzo]

I'd try tightening the cable first but if that doesnt fix it, it could be that the chain is on its way out. It could also be the middle ring on the chainset that's wearing out. If its had that much use then it might be time to replace a few bits!

 

[Rhythm Thief]

Sounds like the middle ring is worn to me. How old is it? Have you replaced the chain recently? If you can pull it off the chainring more than a couple of millimetres then it's worn. If the teeth on the middle ring are beginning to go "shark fin" shaped then that needs replacing too.
If the chain is worn you'll almost certainly need to change the rear sprockets too.

 

[Amanda P]

What exactly is it that's slipping? Is the chain sliding over the teeth of the cogs without meshing in them? Or is the chain slipping sideways on to the next sprocket or chainring?

Different causes, different cures.

 

[alecstilleyedye]

fwiw i had that problem after a complete (other than hubs) groupset upgrade and it turned out to be the freehub (that the rear cassette is mounted on) which was knackered. lbs won't repair non-shimano freehubs so new set of wheels it was.

 

[starseven]

Is this the new Galaxy? Unless you racked up a lot of miles very quickly the chain etc shouldnt be worn. You may need to get the LBS to have a fiddle.

 

[Bigtallfatbloke]

...thanks for the comments...
well the bike is pretty new and I have done 1300km in about 2 & a 1/2 months...so hopefully it's not due for a chain replacement...the chain is the one I got with the bike.

When I say slips I mean it makes a clonking noise and suddenly I am in a different gearto what i had hoped...so i suppose it's slipping across onto another gear and missing one out. Looking at the cogs I cannot see any broken bits and no 'sharks fin's

I will try tightening it and if that doesnt do the trick the LBS can have a look.

 

[Rhythm Thief]

Sorry, I misunderstood your problem. Sounds like you need to get the indexing sorted out. Have a fiddle with the barrel adjusters on the cable and you'll eventually sort it out (it's always more luck than judgement when I do it!) Someone more useful will be along in a bit to tell you how to do it properly.

 

[laurence]

yup, sounds like the indexing is out... normally needs a fettle after a few months.

i do it a very complex way that is no way similar to RT's above post.

i turn the adjuster in the wrong direction, to really throw it our of true and then spend hours trying to get it somewhere near right until i give up and go off for cake, leaving it pretty much, but just slightly different, to how it started.

L

 

[Rhythm Thief]

i turn the adjuster in the wrong direction, to really throw it our of true and then spend hours trying to get it somewhere near right until i give up and go off for cake, leaving it pretty much, but just slightly different, to how it started.

L

That's exactly the same as the technique I use.

 

[Tynan]

had this a few weeks ok, standard on a new bike I think, cable stretches for a while, fiddle with the adjuster thingy on the gear shifter, get it right for the middle gear and suck it and see after that

if I managed it, you'll be fine

ooo and it might need some oiling after all this rain and the factory oil all worn off

 

[Rhythm Thief]

In all seriousness ... as far as I recall from the last time I did it, you need to:

Put the chain on the smallest ring and sprocket
Click it up onto the next biggest sprocket at the back (if it won't go, turn the barrel adjuster on the cable at the derailleur anticlockwise (I think!) until it will)
Turn the adjuster so it tightens the cable until the chain begins to rub against the third sprocket
Back off the adjuster until the rubbing stops

This should, in theory, sort out your indexing for all the gears. In practice, I find it works fine for coming down the gears, but not for going back up them, or vice versa. Maybe if all your drivetrain bits are reasonably new, you'll have a bit more luck than me.

 

[laurence]

oh... and check you have no twigs jammed between sprockets at the back... as i did.

L

 

[CEE5BOY]

I stripped my bike down and the gears have been a mess since.

They jumped so much yesterday it broke off three teeth from the cassette!

http://www.parktool.com/repair/readhowto.asp?id=64

This explains it well,I `m gonna try it tonight!

This Forums MUCH better!!

 

[Gary D]

I also experienced this problem last night.
It was when I got out of the saddle to climb a hill. Using the middle ring and the 5th or 6th out of 8 sprocket on the rear.
When I started to put on pressure, the chain jumped to one or two lower gears i.e going "up" the cassette. It never seems to go to a higher gear, or down the cassette.

The only thing I can think of is it is due to cable tension? Is the cable too taught?
My theory being, is that when I exert force on the pedals, everything starts to flex a little. If that then causes the cable to be pulled tighter, the rear mech will try to change down.
I know some might say adjust it anyway, but I would like to know the cause before I start twiddling randomly

Any thoughts?

Thanks,

Gary