Tuning Question: Eliminating Ghost Shifting?
in my quest to get it all just right, I have resolved a few problems I've encountered but one continues to elude me: Ghost shifting.
I don't get a ton of it but it does seem to happen at/beyond halfway through the travel. My SS der cable housing seems at least as long as what I've seen in other photos so I don't think that is the problem.
I tried to configure the R-Der such that most/all cable tension is gone when in 12/32...in anticipation that the cable might get tighter deeper in the travel and pull it into a different gear.
I disconnected my top shock mount and cranked the bike throughout the travel arc (while on the stand of course) and found it does chatter a very slight bit deeper in the travel. But it's very very slight.
Any ideas on what I could be doing wrong? TIA
Faster is better, even when it's not.
I had symptoms similar to yours, but in my case it was an adjustment.
Originally Posted by Bikezilla
I was riding over rough terrain and the bike kept ghost shifting as the rear would cycle. I found that a simple tightening of the r derailler cable fixed the issue.
I'm sure that you would have checked that by now, but that's what the issue was with me.
You might also want to check the r deraller hanger. A bent hanger can cause ghost shifting. I also once got ghost shifting due to a loose derailler hanger.
Like Warrguru said, check the der hanger VERY carefully for alignment (as in, use a Park DAG-1). Turner hangers are soft and it really does not take much to put a drivetrain mildly out of alignment so the upper jockey pulley on the derailleur is just barely out of line with the cog it is trying to feed the chain up to.
Also like WG said, Derailleur trim is critical. I put the bike in some random gear and then stand behind the rear wheel looking forward at the cassette. Crouch down so the back of the rear derailleur is at eye level and look to see if the chain is feeding up onto the cog from the upper der pulley in a perfectly perpendicular manner. The chain should not have to jog to either side at all to feed onto the cog. Shimano makes this harder to determine by allowing the upper pulley to "float" about 2mm from side to side. SRAM does not do this. You can deviate from this theoretical direct line if you can determine in which direction the bike ghost shifts: if the chain always jumps to a smaller cog, then err on the side of the derailleur sitting a hair towards its larger neighbor.
Finally, look critically at the run of housing between the top tube and the seat stay. When you are not on the bike, this length of housing should be pulled almost tight but not quite- a little slack is necessary so the housing is not tugged out of its stops at topout. The reason you want this run as short as possible (without causing it to pull out) is so that it forms as little of a loop as possible at full compression.
Derailleurs are precision things and don't like the cables and housing controlling them to get bent all over. It would be smarter to route the cables through full length housing down the down tube and past the main pivot where there is a lot less movement. That is the way single pivot and downhill bikes are usually done.
There are other possibilities (loose der pivots, incorrect chain length, b-tension screw issues, etc) but we have hit the biggies...
I had a similar problem when I first put the bike together. I ghost shifted when hitting stuff at high speed. A longer piece of casing (at the top-tube to seat-stay junction) almost eliminated the ghost-shifting.
Originally Posted by Bikezilla
I am also suspecting that the cable routing inside the seatpost gusset might limit the movement of the cable when the shock compresses completely. If the cable is not free to move it might generate tension and induce the ghost shift.
I doubt that tightening the cable might do much unless the cable is very out of adjustemnt and slack.
Last edited by Davide; 04-27-2004 at 10:01 AM.
A few more ideas:
-UNSCEW the B-tension screw on shimano derailuers. Many people screw this in to get rid of the pulleys rubbing on the cassette, but this mostly goes away under tension anyways. The closer the upper pulley is to the casette, the tighter your shifting will be.
-Cable tension adjustment totally depends on where your limit screws are set. Beware of the "knock-on effect"- adjust them independantly. I adjust my limit screws with the cables pulled out of the stops- use your hand to push teh der. through it's range of motion.
-Use 5mm cable housing, like Jaguar brand. The newer shimano housing, even dura-ace and XTR, is 3.5mm with plastic ferruls, lots of drag. Another shimano un-improvement!
-lastly, (pretty obvious I guess) use very light viscosity lube, like pro-link, T9, or finish-line teflon on your cables. Grease or thick lube like Phil's tenacious eventually attracts grit and slows your shifting down.
By KevinVokeyJ24 in forum General Discussion
Last Post: 12-24-2004, 09:40 AM