R7000 rear mech cable route (warning - potentially difficult content)

MattFalle

Thistle: you do realise that the cable is clamped up the wrong way don't you?

Ben6899

This actually kept me awake last night.

MattFalle

The MFs haven't slept for days. There are liads of the fekkkers, all mooching around, wondering what's happening.

seanoconn

Rumour has it Thistle has taken the rear mech apart but didn’t get anywhere and has now lost the will to live.

So probably no closure today 😕

david37

he should at least do the decent thing and have a warning in the title that this content is damagingly difficult

thistle_

Some progress has been made.

Thanks @pilot_pete for confirming that it's attached correctly to the frame. I tried it using the other peg against the stop and the jockey wheel/chain would be rubbing against the underside of the chainstay.

@i.bhamra the mech comes with a length of the special outer and that's what I've used, I couldn't get a piece of standard stiff in the short space.
Thanks for the offer @dannbodge, I still have some left so I think I'm ok for now.

Limit screws are fine, they were wound out generously for testing but now set almost correctly.

So... it seems like there's a bigger problem:
The (internally routed) cable was gunked up at the BB and in the down tube because the sleeve had split. All cleaned up, new cable and sleeve installed, long nosed ferrule put on and cable clamped correctly.
Shifting's great apart from going into the smallest cog. Turns out the nipple of the cable is slipping out of the shifter when it gets to a certain point and then gets stuck.
It could be the shifter, but I'm also wondering if the new mech puts less tension on the cable because the old mech shifted fine with a gunked up cable

Hope you can all sleep easier tonight for knowing all that

MattFalle

You did realise though that the cable was clamped up wrong on the mech though, yah?

MattFalle

what gear are you leaving the shifter in when taking out initial cable slack before clamping off the cable into the mech?

If, as it should be, smallest cog, there shouldn't be any "new" slack to cause your cable shenanigans..

thistle_

MattFalle said:

You did realise though that the cable was clamped up wrong on the mech though, yah?

Yeah that was deliberate. I tried it in the "correct" place and it didn't work, tried it on the other side and it was better.
It's now in the correct position.

Shifter is set the be in the smallest cog when I set it up. Shifting to a bigger cog is no problem, when it gets to the smaller ones the shift is sluggish so there's some slack in the cable allowing it to come out inside the shifter.
Sluggish could be partly due to the tight bend at the rear mech.

masjer

Thistle, I think you are correct about there being less tension in the spring with the newer design rear mech.
Since the cable is going slack (in the shifter) whilst changing down to the smallest cog, it indicates that there's still too much friction in the cable. Has the outer cable been replaced from under the handlebar tape? Also, is the bottom bracket cable guide worn and is the cable routed correctly under any lugs on the BB guide?
If you still have problems, sometimes a thin coating of silicone grease on the inner cable can improve shifting by lowering cable friction.

nibnob21

Begs the question, what was wrong with the 5800?

MattFalle

new shifters to match new mech?

nothing weird like pull ratios making it go weird?

new inner coming out of the shifters?

thistle_

nibnob21 said:

Begs the question, what was wrong with the 5800?

Now you mention it, it was slow to shift onto the smallest cog...
I assumed it was because of all the play in the pivots.

@masjer the guide under the bb30 is fine, I took it out and cleaned the mud out of it, plus the inner wire is in a sleeve through the guide to keep it crud free. The outer under the bar tape seemed fine when I pushed the new wire through, but I could try replacing it anyway.

MF: it's not pull ratios, going from small to big then half way back it's perfect.

I'll have another look at it at the weekend.

MattFalle

Take it to the guys at Bici e Libri: they'll sort it for you.

johngti

Do what MF says, @thistle_ I’ve heard great things about the place

thistle_

Will i get 49p coffee?

masjer

Yeah, I'd replace the outer under the bar tape. It goes through a tight(ish) bend out from the shifter and can certainly cause extra friction when worn.

johngti

thistle_ said:

Will i get 49p coffee?

You’d have to stay quiet about it but I don’t see why not

MattFalle

You've got to get past the handsome bloke on the door first but I'm sure it'll all be tranquillo.

thebigman

So the old mech was sluggish going into the smallest cog and the new one is, that would suggest the mech wasn't the problem and it may be cable related..

thistle_

To bring closure for all those who need it (and in case it helps someone else):
Cable replaced, no better
Outer and ferrules replaced, no better
Inner plastic tube thing for internal cabling replaced, no better
Long nosed ferrule added at the mech, no difference

Took it all apart after a test ride and the new cable was chafed/fretted.

Turns out the plastic cable guide thingy in the shifter had worn and was snagging the cable. Not worn through (so wasn't obvious) but had made enough of a groove to cause a problem.

Made a temporary one while waiting for the replacement to arrive and it works a treat. It's still working after 50 miles so I'm not going to replace it for the sake of it, but the proper parts are here now for when the cable next needs replacing.

I've left the loop at the end of the chainstay as it was - a small tight loop - although I trimmed a couple of mm off it so it was a neater curve. I found some images of the same mech on a new bike with a similar frame and that was how it was done.

So the R7000 mech is fine and it now shifts beautifully.