Two cable guides under BB, one cable?

[TDIfurby]

I am rebuilding up my 957 and have so far routed the wiring for the front brakes (no cable to the rear obviously), the rear brakes using one of the side on cable guides, and the rear mech which goes down the side and out through the swingarm, etc.

Now for the front mech I can see the cable has to go down the lower cable routing section, under the BB and back up the other side of the "seat tube" and to the front mech....  There is a plastic bit bolted to the bottom of the BB with two cable guides within it and I am not sure which one I am supposed to use?  Why are there two?  For user-choice?

I also need a mech as tried to offer up an LX one and is clearly not right.   Anyone got a mech (preferably XT) that would fit my 957?

[shovelon]

I am rebuilding up my 957 and have so far routed the wiring for the front brakes (no cable to the rear obviously), the rear brakes using one of the side on cable guides, and the rear mech which goes down the side and out through the swingarm, etc.

Now for the front mech I can see the cable has to go down the lower cable routing section, under the BB and back up the other side of the "seat tube" and to the front mech....  There is a plastic bit bolted to the bottom of the BB with two cable guides within it and I am not sure which one I am supposed to use?  Why are there two?  For user-choice?

I also need a mech as tried to offer up an LX one and is clearly not right.   Anyone got a mech (preferably XT) that would fit my 957?

You could probably use either, but I use the groove closest to the nondrive side of the BB.

[shovelon]

You need a bottom pull/top swing derailleur like the one shown here.

[TDIfurby]

Thanks - got a replacement mech sorted out now.  Just need it to arrive. 

Also thanks for reassurance there's not meant to be two cables going under the BB - did seem an odd thing to have 2 guides, 1 cable.

[Lysander]

It's a standard bb cable guide, usually meant for both gear cables, but the high swing arm means the rear mech cable isn't routed through it........when ye fit the new mech, it may be policy to do it without the chain at first, and with the rear shock removed- it'll let ye lift the swingarm up enough to roughly set the h/l limit screws on the mech- that way, with the drivetrain fully set up, ye'll only need a small turn of the screws to get it zeroed. IIRC, I used an exacto knife blade, the top blunt side, as a horizontal blade to get under the swingarm from the side.

[fyrstormer]

It's not the high swingarm that does it, it's the presence of any rear suspension at all. You can't have a loose cable wrapping around a potential pivot point like the BB shell if the position of the rear derailleur is going to be changing due to suspension movement. The cable guide is designed to work on FS and hardtail bikes, but because the rear derailleur doesn't have a fixed location relative to the cable guide like the front derailleur does, the shift cable has to run inside its housing for the full length. (yes, the inside of the swingarm does count as a housing of sorts.)

[TDIfurby]

Well, all sorted and one of the guides was definitely more suitable for the job - i ended up using the one with a slight bend in it, and it was also slightly longer than the one alongside it.

Bike is nearly ready for its first proper run.

[fyrstormer]

It's interesting that your 857 has the dual-cable guide attached to the BB shell; my 756 has one like you described, but the 857 frames I have only have single-cable guides. Must've been a situation where they used the dual-cable guides until they ran out, then switched to the single-cable guides.