Installing front and rear derailleurs - cable tension question
I've watched several videos on derailleur adjustments, and I'm starting to understand things better. I'm installing new derailleurs, and am a little thrown off at how at the initial set up in terms of how much tension to put on the cable and what position the derailleur should be in when you clamp the cable down.
For instance, the front derailleur moves laterally - almost vertically or diagonally from left to right - do you move the derailleur cage to a specific postion, and then clamp the cable down, or do you leave it in its starting position, and then clamp the cable down? Also not sure what to do with the rear - for the initial installation, do you leave all of the tension out and then do your adjustments, or do you clamp the cable down after moving the derailleur cage into a specific position before doing the adjustments?
Also, if I'm running a 2X8 setup, what position should the shifters be in when I start the installation?
Thanks for any feedback you can give. This is my third or fourth attempt at initial derailleur installation, but my friend has previosuly done everything for me. I'm trying to get out of that beginner phase and figure things out for myself, but getting started is a little confusing!
Just for the record, I'm installing a Shimano Alivio on the front and Shimano LX in the rear with Alivio shifters.
Last edited by getagrip; 07-16-2012 at 08:23 AM.
First off, you need to make sure that your limit screws are properly set. If the high limit is set properly then you wind the barrel adjuster(s) in most of the way and pull the cable snug. You don't want to preload the derailleur at all, it should stay right there, in the same place as if you set the H limit, and not move until you hit the shifter. Sram systems, for example, actually have a tiny bit of cable slack in the system when at the highest gear if set properly. Fine tune the tension adjustment through your barrel adjuster(s). If you can't get an acceptable level of adjustment or if you start using too much barrel (too much threaded out barrel can lead to the adjuster being more easily damaged) then wind the barrel down and pull through some more cable at the pinch bolt.
Originally Posted by getagrip
Two things to note: first, every time you pinch the cable you can damage it. The strands become deformed and it can lead to breakage. Pinch the cable as few times as you can, sometimes it's handy to have a spare cable or two on hand in case you mess up. Second, make sure you stretch the cable so you seat the housing properly. That usually means that you sort of grab the cable and pull it by hand or you have to let it seat naturally which takes time and requires more times adjusting your shifting. I guess this only applies if you are changing the housing, but if you are using new shift cables then you should always change the housing. Think of them as a pair and you'll get much better shifting for longer.
Don't you hate it when a sentence doesn't end the way you think it octopus?
Click the shifter out till it is slack. The RD will be at its lowest position...set the low limit screw....
Originally Posted by getagrip
Screw the adjusting screws till they are about half way...
Route the cable and force the housing into the stops....
pull the cable tight by hand and do it up.....
This should put you within 1/2 a turn of the adjusting screw...if not bang on.
The first few times I did this, I had the cable overtight, even when just using my hands to remove the slack. I find it's OK to have a little bow/curve/slack in the end of the cable when first tightening it...you can always make it tighter w/o damaging any useful part of the cable, but the inverse doesn't apply.
Originally Posted by jeffscott