Ghost Shifting - HELP!

[Steve Snowdon]

I've been experiencing a maddening 'ghost shift' on my bike recently. When I go to climb a hill and start to apply some pressure, the chain seems to jump off and back onto the selected gear cog (it almost seems to perform a lightning quick shift down to a tougher gear then back up again), resulting a heart-stopping moments of loss of momentum. Is this due to cable tension? Could it be a misaligned rear derailleur?How do you fix this?

[VLAD (the Friendly Vamp)]

Its a misaligned rear mech.You have to turn the little thumb screw at the end of the cable on the rear mech so that the rear mech cogs align with your casette cogs.

[Steve Snowdon]

There's a barrel adjuster at the end of the rear derailleur cable but this just seems to alter cable tension. Do you mean the limit screws that are on the derailleur itself? Maybe a trip to a local bike shop is in order...

[martyn gall]

Yeah Vlad is suggesting turning the screw to alter the cable tension this may be the cause but it may also be some dirt/crud in the cable guide under the bottom bracket which sounds likely giving that its happening when you give it beans.  What happens is that when you give it some the bike naturally flexes and if everything is clean on the cable guide the cable will move over it no probs and keep the correct tension if dirty the cable can grip and cause the shifting probs you describe.  Never had this myself but read it on Sheldon Browns website so worth checking

[JonnyBB]

just look for a guide on how to calibrate your rear mech using the barrel adjuster, it can be quite complicated otherwise...but not really a LBS job.

[coolboarder]

Steve, read the thread on 'Re-indexing campag' its right below this one.

[Steve Snowdon]

Martyn I never thought about potential cable-fouling - thank you for that one. Sheldon Brown's website is an awesome resource (and it's a real downer that the man himself isn't with us any more) but I have the feeling that if I go footling around with my Dura-Ace I am going to wreck it.I will have a look and make sure everything is squeaky clean tonight. If not - then cable adjustment might be the answer. Where's a YouTube clip when you need one???

[Jorrin Peereboom]

You mean any of these? http://www.youtube.com/results?search_type=&search_query=rear+derailleur+ adjustment&aq=0&oq=rear+der

[John Cooper 4]

Mine started to do this yesterday on a hilly 10 mile tt training loop . So annoying when you've spent some time setting it all up.Sure gets the adrenalineflowing when you are out the saddle on a hill in front of impatient driversI have also had this problem before  where mud and crud gets stuck and dries in the cable guide groves under the bottom bracket. The increased friction prevents the cable returning accurately to indexed positions  I'm going to remove my inner cables today and apply a smear of oil then I'm going to check the cable runs particularly where the outer cable nipples enter sockets on the frame. Check all the cables have nice gentle curves and there are no sharp kinks or anything that could cause friction on the inner cables.Clean and grease the BB cable guide runs Then i'll reset the transmission alighnment and hopefully all will be silent and smooth once more.

[Jorrin Peereboom]

IMO the whole cable groove thingy under the BB is a piece of shit engineering solution anyway - kind of like 'oh, it's under the BB, nobody will see it anyway'. I can't over the fact some truly top end bikes still use this method. Even my 1977 PX10 has a better solution by running an inner/outer combo over the top of the BB! My Kestrels and BP have internal cabling and the Porsche's cables run over the toptube and seatstay so doesn't have it either, but I do have these plastic blighters on the Breezer, the Klein, Cube, Dave Quinn and Specialized. The Spesh is now owned by wifey and she only rides it when it's sunny anyway, the Cube is dead, the Quinn is only a commuter, so this leaves only the Breezer and Klein to get wound up about. I am changing the way the cables run on the Breezer anyway as for some reason it has a plethora of options - it actually allows me to run 4 cables all the way from front to back. Not yet sure how I will do this with the Klein yet.

[John Cooper 4]

quite agree. Can't think what bike frame manufacturers were  thinking about. Even my 70's gas pipe Carlton had above BB guide braized to the BB crude it may be but it doesn't collect crud and rust the cables.Surely it can't be that hard to design a BB cable guide that doesn't collect mud and water. I prize my Ribble 653 for the through the top tube cable routing. Such a clean solution rather than have crude cable clips sticking up out of the top tube to tear your shorts and damage your fragile bits. It would be an interesting thread to  see how cyclists would design a frame from scratch

[Steve Snowdon]

Definitely going to get stuck into the cable guides at the bottom bracket area later on. Sounds as though a squirt of WD40 or GT-85 into the cable guides below the bottom bracket before every ride might be good practice to adopt - then again, would this not encourage dirt to stick and build up more? Interesting point about alternative cable routing options - I might suggest that to a custom frame builder and see what the response is. How come these little plastic doodads that seem to adorn really expensive bikes haven't been enhanced by the addition of Teflon-coated cable grooves or similar to reduce friction? Maddening stuff - talk about spoiling the ship for a ha'p worth of tar