Oh bugger! Rear Derailleur...

[Funtboy]

After months of procrastination, I gave my bike a proper service. It is now clean and shiny and runs really well EXCEPT I seem to have caused a problem with the rear derailleur. This was the one thing that was working fine before!

Now it jumps up and down the down gears of its own accord. It seems to be concentrated around the smaller cogs but there is no hard and fast rule and it happens the most when I'm using the middle front cog (of 3). It misbehaves a bit when I'm using the big front cog but not as much.

I am gutted.

Here's what I did in my service - I'm not sure if it is all relevant but here goes.

Tuned the front derialleur by simply tightening the cable (thanks Mickle and Lee) - previously it was rubbing on higher gears on the middle cog and struggling to get onto the higher cog)

Took the front cogs off and cleaned them. Put them back exactly as they were.

Took the back wheel off to clean it - may have not been very delicate with it. I did notice that when I put it back on, a bit of the derailleur seems a bit loose. I can't describe which bit though unless I take it off again. It may or may not be significant.

Half-arsedly attempted to get the rear cassette off with a lock-ring and chain whip. Didn't really know what I was doing and gave up. Please God I didn't mangle some of the teeth - might that cause this problem? Please say no!

One other thing, the stand I used clipped onto the back triangle and over the gear cable. Not sure if I mashed it at all.

Sorry for such a big post. Does anybody recognise the problem? I've had a quick look on the net and was slightly intimidated.

Thanks in advance,

Dunceboy

 

[Oldlegs]

I sounds like the bike stand crushed the cable outer so the inner is'nt moving freely. A new cable would be one thing to try - they only cost a couple of £'s.

If you are unconfident on getting the gears right it's probably best to let an LBS have a look at it.

 

[Mr Pig]

Not sure if I mashed it at all.

Translation: Pretty sure I mashed it! ;0)

 

[Funtboy]

I sounds like the bike stand crushed the cable outer so the inner is'nt moving freely. A new cable would be one thing to try - they only cost a couple of £'s.

If you are unconfident on getting the gears right it's probably best to let an LBS have a look at it.

It changes freely but jumps a lot. And it sometimes jumps as I'm changing. Does that still fit the bill? To be honest, I'd rather suss out the problem myself rather than rely on an LBS. How much would an LBS charge me for that, do you think? Everything else on the bike is tuned and lovely.

 

[jayce]

check the cable take the mech off check its ok put it all back together then adjust as needed and check the chain that should sort it out ..

 

[swee'pea99]

Like Oldlegs sez, fust thing to do is see if the cable's running freely. Easy enough to find out - just detach it from the rear mech, then hold the end of the (now free) cable while you 'change gears', and just get a feel for whether the cable's moving free and easy. Chances are, you have crushed/distorted the cable housing somehow, and the cable's moving, but jerkily....sticking, then lurching thru', then sticking...

If it's not running smoothly, find out where and change (at least) that bit of housing. If it is, it might be a problem with the mech or teeth, but that's less liekly (and a lot more hassle/$ to fix, so definitely plan

 

[Funtboy]

not[/I] running smoothly, find out where and change (at least) that bit of housing. If it is, it might be a problem with the mech or teeth, but that's less liekly (and a lot more hassle/$ to fix, so definitely plan

I can change freely up and down the gears but they jump up and down across a certain range of cogs at the back. Also the cable housing looks okay. I will do what you say though and dismantle again. I am horrified that I may have bent the teeth with the chain whip but the teeth look okay.

One thing I've noticed is that the middle front cog seems to have a very slight sideways swerve (I hadn't noticed it before). Maybe the front cogs aren't completely true.

Oh well, I'll give it a bash!

 

[jayce]

do what i do get someone to go through the gears while ur down by the rear mech and look at it from all angles

 

[PatrickPending]

make sure the mech has sprung fully forward - I've found taking the rear wheel off, and replacing, (for which you push the rear mech back a bit to remove the wheel) more often than not the rear mech stays back a bit and poor shifting results. I hope this description is more or less intelligible

see link for a description of rear mech ovehaul

http://www.parktool.com/repair/readhowto.asp?id=76

 

[Funtboy]

Cheers. Will give it shot when I get a chance.