Shimano 105 triple rear derailleur problem

[Derk Drukker]

Hi!

I help my neighbour building a decent bike using a new Merckx alu frame and his old 8 speed 105
triple group.

I installed the derailleur, but something strange happens: I put the chain on the big chainwheel and
on the smallest cog and pull on both chain ends, so the 2 derailleur wheels make a vertical line (
one is above the other), in order to get the correct chain length. So far so good, BUT: in this
position, the part of the rear derailleur (cage?) that holds the 2 small wheels touches the frame.

The one thing I noticed is that the so called "B-tension adjustment screw" and the round ring it is
part of (the part in between the derailleur and the frame) can be turned freely from one limit to
the other limit without feeling any resistance.

I have a 9 speed Ultegra derailleur lying around, that also has this B-tension adjustment screw of
course, but this one can't be rotated as easily.

Could this be the cause of the problem and if so, is there anything I can do about it?

NOTE: on his former 20 year old frame , I saw a sort of a metal part that was attached to the
dropout tab, so the derailleur was placed lower than normal. Does this make it clearer?

Thanks in advance! Derk

 

[Ted Bennett]

In article <[email protected]>, Derk Drukker
<[email protected]> wrote:

> Hi!
>
> I help my neighbour building a decent bike using a new Merckx alu frame and his old 8 speed 105
> triple group.
>
> I installed the derailleur, but something strange happens: I put the chain on the big chainwheel
> and on the smallest cog and pull on both chain ends, so the 2 derailleur wheels make a vertical
> line ( one is above the other), in order to get the correct chain length. So far so good, BUT:
> in this position, the part of the rear derailleur (cage?) that holds the 2 small wheels touches
> the frame.

Sounds like the chain is too long.

Your method is incorrect, probably. That method will only roughly give the correct length, which is
the length that wraps around the big-big combination plus one link, measurement taken with the chain
NOT through the derailer.

> NOTE: on his former 20 year old frame , I saw a sort of a metal part that was attached to the
> dropout tab, so the derailleur was placed lower than normal. Does this make it clearer?

Modern derailers are somewhat fussier about the distance from the wheel axle to the derailer's
mounting bolt.

--
Ted Bennett Portland OR