105 rear mech compatibility

Garry H

Hello all

Can anyone tell me if it's possible to run a short cage 105 rear mech with an otherwise Sora 8 spd groupset? Bloke in shop said it would be ok, but I'm having a mare trying to adjust it. Runs ok on the 4 smallest sprockets, but after that chain does not quite sit properly. Any advice would be apreciated.

Smokin Joe

Garry H wrote:

Hello all

Can anyone tell me if it's possible to run a short cage 105 rear mech with an otherwise Sora 8 spd groupset? Bloke in shop said it would be ok, but I'm having a mare trying to adjust it. Runs ok on the 4 smallest sprockets, but after that chain does not quite sit properly. Any advice would be apreciated.

Check that you have not run the cable through the wrong side of the clamp on the rear mech. I did that once with a Campag and it took me ages to discover why some of the gears would not index. The cable should run wheelside of the clamp.

Garry H

Smokin Joe wrote:

Garry H wrote:

Hello all

Can anyone tell me if it's possible to run a short cage 105 rear mech with an otherwise Sora 8 spd groupset? Bloke in shop said it would be ok, but I'm having a mare trying to adjust it. Runs ok on the 4 smallest sprockets, but after that chain does not quite sit properly. Any advice would be apreciated.

Check that you have not run the cable through the wrong side of the clamp on the rear mech. I did that once with a Campag and it took me ages to discover why some of the gears would not index. The cable should run wheelside of the clamp.

Na, that's not it either. Is it at all possible that the chain may be too long or too wide? I can't think of any other reason

John.T

It does sound like a cable problem. The mech should work with no problem if set up right. It uses the same cable pull as the Sora. Make sure the cable is set in the grove correctly as only a small error can upset things.

Garry H

John.T wrote:

It does sound like a cable problem. The mech should work with no problem if set up right. It uses the same cable pull as the Sora. Make sure the cable is set in the grove correctly as only a small error can upset things.

It's dead in the groove. I'm perplexed. Wish I'd left it well alone now

andy advanced

are you using a 10 speed 105? if you are the cage will be too narrow for the 8 speed chain. disconnect the cable, set the limit stops correctly then reconnect the cable and adjust tension from there, i think your chain will chatter on the mech cage though...anther thing is have you checked your mech hanger? it could be bent?

Garry H

andy advanced wrote:

are you using a 10 speed 105? if you are the cage will be too narrow for the 8 speed chain. disconnect the cable, set the limit stops correctly then reconnect the cable and adjust tension from there, i think your chain will chatter on the mech cage though...anther thing is have you checked your mech hanger? it could be bent?

Cheers Andy, I had wondered about the possibility of the chain width, but was told it would not be a problem. I've tried comparing the 105 cage to the Sora cage and they look to be the same width. Works fine with the Sora Mech, and hanger is ok. Ho hum, guess I'll just need to buy a better bike

keef66

I'm assuming that 10 speed technology works by using narrower chain and more closely grouped sprockets than 8 speed. If it's a 10 spd mech it will shift in slightly smaller increments than you need for the 8 speed cassette, and by the time you've done 4 sprockets the cumulative difference is too great. You can't alter the incremental advance; it's determined by the construction of the mech.

If it's an 8 speed 105 mech it should work OK

nicklouse

keef66 wrote:

I'm assuming that 10 speed technology works by using narrower chain and more closely grouped sprockets than 8 speed. If it's a 10 spd mech it will shift in slightly smaller increments than you need for the 8 speed cassette, and by the time you've done 4 sprockets the cumulative difference is too great. You can't alter the incremental advance; it's determined by the construction of the mech.

If it's an 8 speed 105 mech it should work OK

sorry NO the mech is a dumb thing it only moves as far as the shifter tells it to.

as long as the shifter is correct for the cassette then any shimano mech will work ( yes even an MTB one).

Swannie

andy advanced wrote:

are you using a 10 speed 105? if you are the cage will be too narrow for the 8 speed chain. disconnect the cable, set the limit stops correctly then reconnect the cable and adjust tension from there

This sounds like it would fix the problem to me.

Additionally, is the arm on the dérailleur different to that on the original? You might need to change the chain length if it is shorter.

Good luck!

andy_wrx

WotNicksaid.

I ran 9sp 105 f&r mechs with Sora shifters perfectly satisfactorily.
Many otherwise-Sora bikes come from new with Tiagra rear mechs as a selling point, many otherwise-Tiagra bikes come with 105 rear mechs.
They're compatible.

keef66

Nicklouse. Course you are correct an I am being an idiot in confusing cause and effect. It is indeed the shifter that determines the amount of movement per click.

Garry H

Swannie wrote:

andy advanced wrote:

are you using a 10 speed 105? if you are the cage will be too narrow for the 8 speed chain. disconnect the cable, set the limit stops correctly then reconnect the cable and adjust tension from there

This sounds like it would fix the problem to me.

Additionally, is the arm on the dérailleur different to that on the original? You might need to change the chain length if it is shorter.

Good luck!

I have considered that the chain length may be too long for the 105 Mech, so will try taking a couple of links off that.

For all of you that asked, it's a 10spd 105 mech. But I don't think that it makes a difference.

Also, thanks for all your sugestions. First time I've posted on here and looks like I've come to the right place at least.