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Hi all,
I am setting up my rear gears (1st time for me), all parts new, and I am at the B-Screw adjustment stage. Now I get the principle of the adjustment but turning the screw fully in and fully out moves/changes nothing, the guide pulley stays in the same place.
Now I can see that the stop that dictates how far the pully can move is either rising or decending as I turn the screw but nothing else is moving with it? Is it my cable tension, would that effect it? or do some rear deraileurs just do this and not move?
Please go easy as this is my first ever attempt at this and just want to get it right 😀
(not sure if its connected, but I had the shifters in the correct gear when tightening the cable but should I have done anything with the cable tension adjuster on the shifters also? should they be set somehow before I tighten up the cable?)
Muchos gracias 😀
shimano mech? it tends to do **** all on them
The B-tension screw adds tension to the spring that tensions the chain. It won't make the pulley move much if at all.
Sometimes, if you have a really big cassette, this can help keep the pulley off the bottom of the sprocket, but not by much.
More tension in your chain might make your gears more secure (ie less likely to bounce out of gear on rough bits) but coudl make your shifting stiffer.
What were you expecting it to do?
As for the barrel adjusters - what I do is wind them in almost all the way, then pull the cable tight and tighten up the cable clamp bolt on the mech. You can never pull the cable tight enough, so I can then wind the barrel adjuster out to take up the slack.
yeah Shimano XTR M971 rear mech.
[url=
here (YouTube)[/url] even in this video (3mins 20secs for the B-Screw) nothing moves either, but on other web sites it seems to make a difference? 😕
do it in the biggest sprocket position and with chain of middle or big ring (yes you shoudl not do cross over, but for set up..
also did you size you chain correctly?
I just put set mine in the middle....
molgrips, it seems that the b-screw is supposed to move the guide pulley closer or further away from the cassette.
I'm running a 11-34 cassette and long cage deraileur. Nothing moves at all with the screw adjustment?
When you say more tension on the chain, do you mean tension via the cables etc or take a link out of the chain to increase the tension?
Cheers
OMG that video is ridiculous. Well, not the video itself but the voiceover and stupid music are 🙂 Sounds like someone trying to sell you crap aftershave on Eurosport.
rootes1, I think I sized the chain correctly, but it maybe one link too long as it seems a little slack possibly?
What about the setting of the cable adjusters at the shifters, should I have done anything to them before doing up the cable?
molgrips, it seems that b-screw is supposed to move the guide pulley closer or further away from the cassette.
Well not really. See the derailleur is spring loaded, so that the bottom loop of chain is not just slack and hanging about. Turning that screw just puts more tension in that spring. This could lead to the pulley being in a different position relative tot he sprocket, but in practise there's not enough travel in the screw to make it do much of anything.
I've set up dozens of mechs, and the b-tension screw makes barely any difference at all. Just screw it most of the way out and leave it.
Btw, when I say chain tension, I am talking about front-to-back tension. The cables and adjusters etc control the [b]side-to-side[/b] position of the jockey wheels and that then controls your shifting.
>I've set up dozens of mechs, and the b-tension screw makes barely any difference at all.
Funny, I've found exactly the opposite...it's not a huge adjustment but it does have an effect if your chain length's correct. It's definitely not for sorting the chain tension.
On sram mechs the b tension screw moves the derailleur alot, shimano it doesnt seem too.
As for the shifters, i usually just leave the cable adjusters wound all the way in. I only use them to tweak things if im out on a ride and the cable has stretched a bit and its not shifting proper.
I usually start with the adjuster on the mech wound about 3 turns out, then just pull the cable tight with my fingers. Gives you a bit of lee-way to alter things if the cable is too tight or slack
easyer to tell if B screw works/adjust when the mech is in the biggest cog postion.
molgrips has it. The effect is subtle but it can stop rubbing on bottom gear. If that's not happening and the shifting is OK then carry on!
>On sram mechs the b tension screw moves the derailleur alot, shimano it doesnt seem too.
I think that's 'cos the mechanics of the two mechs are a little different - IIRC when the back end of the bike's bouncing around an sram mech tends to stay roughly where it is, whereas a shimano mech tends to bounce/rotate around (and slap the chainstay on a full-sus).
Ensuring the chain is the correct length goes without saying. Just long enough not to jam if you end up in the big ring and biggest sprocket by mistake. Also, if you have a FS, it helps to haev a little more slack so if you end up in this gear and hit a bump you don't break something.