Rear mech problem

steelo

I have just followed many instructions on how to re-set the rear mech. I now have a problem which I cannot workout how to solve.

The rear mech works fine from the smallest cog shifting up to the 3rd largest cog. However, on the 2nd to last click the chain doesn't move, on the last click it will jump the 2nd to last cog and sit pretty on the largest cog.

On the way back down, first click and the chain doesn't move, 2nd click it will drop 1 cog and continue to be 1 cog out all the way down to the 3rd smallest whereby the last click the chain will skip the 2nd smallest cog and sit back at the bottom.

I just can't get my head round why its happening.

How do I solve this?

My bike is an '07 rockhopper with a shimano LX rear mech and Shimano Deore SL M511 shifters (according to the spesh website).

nicklouse

tis an odd one.

so to sum up. the mech has full movement up and down but is sticking while over the big cogs.

is the mech hanger still straight?

top jockey wheel not catching on the big cogs?

steelo

Jockey wheels not catching.

Mech has full movement, I have re-set limit stops and moving the rear mech by hand while pedalling gives full indexed movement.

I'm wondering if its necessary to be able to index all rear sprockets while in the middle chainring? Am I worrying about 1 or 2 gears that can be avoided by changing the chain position on the front instead?

nicklouse

you should be able to get all gears at all times. ok some we should not use.

but are you saying that this problem does not happen the same when in a different front cog?

as if it does work fine in say the granny ring then it rules out my next sugestion.

steelo

Okay, starting with the rear mech in the lowest gear position (biggest sprocket) and the front mech is in any position (tried all 3). One click to the rear deraillieur should drop the chain to the 2nd sprocket - no such luck. It seems that the spring in the rear mech has no springiness to it.

As it is a normal mech it should rely on the spring to bring it to the smallest cog as the cable tension is slackened - am I right?

Shifting from highest gear position (smallest sprocket) seems fine but on occasion will need 2 shifts to move the chain 1 sprocket and then it shifts 2 sprockets on the last click.

AAAARRRRGGGGGGHHHHHHH!!!!!!!!!

nicklouse

so it is a cable problem. replace the inner and outer.

it is either dirty or more likely been damaged somewhere.

steelo

I have slackened the cable and cleaned it along its entire length by sliding the sleeves and squirting de-greaser, then re-lubing. I now also encounter more slipping and 'dodgy' gear changes when i'm pedalling and putting power down.

I've had enough, i've lost the will, i've been beaten - bike maintenance is obviously only for those who have a PHD in the damn subject!

RSMarco

Steelo,
Do as Nicklouse say's and try replacing the cables. I have put a lot of effort into understanding what can effect the action of the rear mech and I now have enough confidence to set up correctly (thanks to the likes of Nick..!).

Read the Park Tools link on Nick's sig, really useful..!

Good luck

Marco

MarvintheAndroid

Agree. Most probably caused by friction in the last section of outer cable nearest the mech - this often has extreme curvature or angles to pull through.

Marv

steelo

I feel so much better now!

I took my bike to the LBS this morning and told them about my ongoing issues with the rear mech and I asked them if they would show me their procedure of solving rear mech issues. Turns out I had made some schoolboy errors that meant no matter what I did to the rear mech I had no chance of correcting the gear changing problems.

Firstly - the rear wheel was not sat in quite straight.

Secondly - the rear mech hanger was bent out of alignment.

Thirdly - due to issue 2 the limit stops were not set correctly.

Fourthly - I had not used nearly enough lube on the chain or gear cable to be make the system work efficiently.

But the guys in the shop were very helpful, showed me what to do step-by-step (albeit they used a £70 park tool for checking the hanger alignment) and gave me some tips about how to clean and re-lube critical parts of the bike. Now I have a rear mech that works how it should and I have a bit more knowledge about troubleshooting rear mech issues!

In summary, don't knock LBS staff, they are worth their weight in gold (or mine are anyway)!