Chain dropping off big ring

[Jimmy Welch]

Bit of a odd one when I'm in the big ring on the front , as I go up the rear cassette when I get just over half way up the chain drops into the small ring on the front if I drop back down on the rear it goes back up to the big ring . It's a 105 mechanical groupset .

 

[richardfm]

Has it always done this?

 

[Jimmy Welch]

No just started last couple of days

 

[Paulus]

It could be that the chain is worn.
Throughly clean it and lube it and see if it still does it.
Also check the front mech adjustment.

 

[Jimmy Welch]

Yeah the chain is about 200 miles old , but the mech is a possibility I recently changed the front gear cable and so had to re index the front although it did go in and out of both rings fine , what's should I be looking for ?

 

[vt2]

I had something similar and decided it was time to change the large chainring, but was having trouble sourcing a new one. Looking closely at the chainring there was a buildup of hardened crud that was lifting the chain above the bottom of the tooth profile. Once the crud was removed, the problem of dropping the chain was resolved.

 

[Jimmy Welch]

On Friday last week my chain link sheared off while out on a ride and I fixed it by the road side I think I may have put the chain on back to front , that could be the reason couldn't it

 

[boydj]

Yeah the chain is about 200 miles old , but the mech is a possibility I recently changed the front gear cable and so had to re index the front although it did go in and out of both rings fine , what's should I be looking for ?

You probably need to slacken the cable slightly. There should be just a touch of slack in the cable when it's on the small ring, otherwise there is too much strain on the cable when the chain is on the big ring.

 

[Sharky]

On Friday last week my chain link sheared off while out on a ride and I fixed it by the road side I think I may have put the chain on back to front , that could be the reason couldn't it

Don't think so, but has the chain been jumping only since you repaired the broken link?

Presume the quick link was same speed as the chain? Any stiff links on the chain?

 

[Jimmy Welch]

I'll take the chain off and give it a soak and check the links

 

[fossyant]

Check the chain ring - could be worn.

Ultegra chains are 'directional' - just ensure the printing is on the outside. Most other chains aren't directional. It's supposed to increase shift speed - I've no idea if it does, but I got the chains cheap in the Wiggle fire sale.

 

[Ming the Merciless]

Yeah the chain is about 200 miles old , but the mech is a possibility I recently changed the front gear cable and so had to re index the front although it did go in and out of both rings fine , what's should I be looking for ?

Here’s your answer. It started happening after you made this change.

 

[Jimmy Welch]

Always the place to start isn't it

 

[Dogtrousers]

You probably need to slacken the cable slightly. There should be just a touch of slack in the cable when it's on the small ring, otherwise there is too much strain on the cable when the chain is on the big ring.

To add a bit more speculation to this...

If the cable's too tight the front mech cage will be sitting a bit closer to the centreline of the bike than it should be when in the big ring. If the chain is on the low gear (inboard) sprockets at the rear, this may not be a problem. But when changing up to the higher gears at the back, the chain will move across a bit, come in contact with the front mech cage, and drop down into the little ring. That's my theory.

 

[Jimmy Welch]

To add a bit more speculation to this...

If the cable's too tight the front mech cage will be sitting a bit closer to the centreline of the bike than it should be when in the big ring. If the chain is on the low gear (inboard) sprockets at the rear, this may not be a problem. But when changing up to the higher gears at the back, the chain will move across a bit, come in contact with the front mech cage, and drop down into the little ring. That's my theory.

I think your right I've just soaked the chain new quick links , put it right way round cleaned each tooth on chairing and it's still doing it ill go and have a look at the front mech tension