How often , change rear mech ?

bing gordon

How often would you or should you think about changing the rear mech ?.

I have tried no end to get it to shift correctly but nothing works. it seems sluggish going going up through the gears not quite biting .you can get it to bite on some rings then it then starts skipping on the others. This has caused a couple of chain snaps when under force.
The bike has had a new cassette / chain in the past 6 month and new cabling and housing and a m8 who knows his stuff set it up but within a few weeks it starts off not quite getting hold either up or down.He checked the shifters and said there fine.

Could it possibly be the spring in the mech ? if so, can this be replaced ? its about 4-5 years old , dura ace 7800.

chaymck

I have just replaced a 105 mech after 4 years - it started to stick. No amount of degreasing, cleaning or adjustment would help. First time I've ever changed a rear mech.

chaymck

It may be worth checking the jockey wheels first- to much play?

bing gordon

chaymck wrote:

It may be worth checking the jockey wheels first- to much play?

I stripped it all down and degreased it all . There's no play in the wheels but could they be at fault if worn ? i can't tell if they are or not.
To me it seems the moving left/right is the fault that's why i replaced the cabling/housing first.

keef66

How freely does it move when the cable's not attached / no chain running through it? And are the jockey wheels sitting absolutely vertical when viewed from behind?

All my rear shifting problems have been down to either cable problems or a bent mech hanger. Sometimes even newly installed cables can be the cause if there's a badly seated outer somewhere, or an outer not cut quite square or cleanly.

bing gordon

keef66 wrote:

All my rear shifting problems have been down to either cable problems or a bent mech hanger.

ummm funny you should say that, I never though to take a proper look till you mentioned , the hanger does look like its slightly leaning into the bike, not much but it seems that ways.
Just spent 10 mins on youtube and It seems to be pointing to the hanger been at fault. I've Watched a few youtube guides and it seems another gadget is needed and it aint cheap .

http://www.parktool.com/product/deraill ... auge-dag-2

Is it needed or is there a cheaper way ? i watched a guy screw another wheel into the thread and gauge off that but that's all abit to much for me.

bing gordon

I've got the bike in the kitchen while the other 1/2's at work . I flipped the bike over and dropped the rear mech and took a look just to see if i could see any bending of the the rear mech hanger.
Once the wheel and rear mech is off it looks ok, . i then took the rear hanger off to take a look to see if its bent which it wasnt.

The thing that worries me on the youtube video is , when the guy bends it back into place are they actually bending the bike forks socket for the hanger or the hanger itself ?? that hanger is a short stubby thick piece of alley and i cant see that bending as its not long enough to flex without the bike bending with it.

amaferanga

Buy a new mech hanger. They don't cost much and shifting can be affected even if the mech hanger doesn't look bent to the eye. If it turns out it's not the mech hanger though then you have a spare anyway which is worth having as they can be a bugger to get hold of quickly if you have one break on you.

bing gordon

amaferanga wrote:

Buy a new mech hanger. They don't cost much and shifting can be affected even if the mech hanger doesn't look bent to the eye. If it turns out it's not the mech hanger though then you have a spare anyway which is worth having as they can be a bugger to get hold of quickly if you have one break on you.

yeah I'll do that, seems to me gear shifting on a bike can be one of those long elimination process's to find out whats the root cause ,


and a costly one.

keef66

I've bent steel frames back into alignment (where the hanger was part of the frame and not replaceable) but with alu and carbon frames the replaceable hanger is designed to be sacrificial, ie it will bend / break thus saving the frame. I wouldn't really recommend trying to straighten an alu hanger.

An LBS would be able to check the alignment of the hanger for you; it might save you the cost of the hanger if it isn't in fact bent.

cycleclinic

With shifting probelm it is mostly down to a bent hanger or sticky cables. Mechs go wrong rarely. If the cables do not move freely in the housing then change them. Get the hanger checked at LBS. some will do it for nothing as it does not take long. If it is bent then they can charge you for straigtening it. Yoiu really need a allignment gauge to check out hangers, it is difficult to do by eye.