Mountain Biking - Shifting....
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07-11-03, 10:08 PM
Sometimes when I shift it won't shift, and when I press it again it shifts down/up two gears at once.. Is there a reason this happens? I just got a new rear cluster, could this be the reason? It doesn't happen all that often but it does getting annoying.. I'll shift and think it changed gears to see it really didn't, click it again and it'll switch two, then i'll have to downshift to get to the gear I wanted.
Mad Dog JR
07-11-03, 10:19 PM
sounds like its out of adjustment, has the bike ever had its cables attended to?
i would get things adjusted right first before you go replacing parts if its not needed. when was the lat time you had a tuneup?
07-11-03, 10:28 PM
I just got it back from the shop. They put a new rear cluster on it, put new derailleur cables on, and adjusted the rear derailleur. The reason I got the rear cluster is because my old one was worn out and causing it to skip on every gear.
Mad Dog JR
07-11-03, 10:35 PM
hmm, maybe take it back to the shop to have them look at it again. if they adjusted them properly it shouldent be doing whats its doing. it might not do it on the bike stand so maybe even have them "test ride" it so they can see the problem.
07-11-03, 10:52 PM
There's nothing I can do to look it over to find the problem?
Mad Dog JR
07-11-03, 11:00 PM
well, there is. im not expert but if you look strait down the chain/cassete/derailer they should all line up. meaning the chain at the derailer pully and the chain at the casset should be in the same place. if its not most likely its out of adjustment. maybe some one other than myself can shed some light on the topic ;)
07-12-03, 12:18 AM
Do you have a replaceable deraileur hanger? If so look at changing it. Also get a mech to check the alingment of the dropouts to see if everything is aligned...
07-12-03, 01:32 AM
No, I do not, but the derailleur hanger was recently bent back into shape.
So many things involved. I'd start by checking the cable tension. 99% of my shifting/indexing problems have been fixed by that alone.
The hi/lo screws on the rear der. From my experience I've found you can have quite a variance of screw adjustment between the point where you think the chain will slip off and the other extreme where moving the guide wheel the other way can cause the chain to rub against the gears and possibly cause shifting problems as well?
I might be wrong with what I now mention, so please correct me if I am. The spacing between the rear cogs is equal for all cogs on the cassette? A wrongly adjusted hi/lo screw setting may not be too much of a problem on the inner/outer cogs, but the same error in adjustment would be present on all the cogs? If the chain can drop from the innermost cog to the next one down or can 'climb' from the outermost cog to the next one up you might not notice any problems there. But the chain might run rough on the other combinations because of the adjustment error and that too could cause shifting problems? Just thinking aloud here...
If you got a new rear cluster (cassette), you should probably get a new chain also. Your chain may be worn a bit, stretched, and not meshing well with the new rear gears. I put a new chain on my bike recently and it is smooth!
07-12-03, 03:59 PM
I did also get a new chain, sorry I forgot to mention that.
07-12-03, 08:13 PM
Okay, here goes. This may be long, but I'm bored so there:
Put the bike into a stand or a rack or hang it from the seat. Something so you can pedal and do some mechanics stuff.
I'm gonna have you completly redo your rear derailleur.
Shift into the middle chainring (up front) and the smallest cog.
Undo the rear shift cable and pedal the bike a wee bit.
Bend down and look at the bike from the rear. The upper jockey pully should be directly below and in line with the smallest cog. (In the same verticle plane)
If it's not, play around with the limit screw on your rear derailleur (RD). There are two of them. One is the inside stop the other is the outside. Play around and find out which one moves the rear derailleur in it's current position. Remember which one is which, because later, we're gonna adjust the other one. You'll actually see the derailleur move in as you screw it in. Adjust it so the rear derailleur lines up with the small cog.
Turn the barrel adjuster on your shifter and the rear of your RD in all the way, then out 1 full turn.
Pull the rear shift cable snug (not too tight) and tighten it down.
Now, while pedaling, shift up one gear. If the derailleur shifts up once, great! If not (while pedaling the bike) turn the barrel adjuster on the RD out (counter clock wise) until it shifts into the 2nd cog. Keep turning it until it starts to "want" to climb into the 3rd cog. Then turn the barrel adjuster back in (clockwise) until it stops "climbing" into 3. Usually about 3/4 to 1 turn back in.
Look at the back of the bike again. The derailleur should now be directly in line with the 2nd cog.
Now, check the inside stop. Shift all the way to the biggest cog. Try to overshift and force the chain off to the inside of the big cog. If you cannot, GOOD!
While pedaling, and shifting back and forth between the largest cog and the 2nd largest. turn the limit screw in to where the chain will NOT go into the largest cog.
If the chain doesn't want to easily go into the biggest cog, the limit screw is in too much. Turn the limit screw out until you can shift into the big cog.
Now, run through all the gears while pedaling. Up and down. Each shift should be crisp and clean. If it's slow to shift up from the small cogs, turn your barrel adjuster out in 1/4 turn increments.
If it shifts UP well, but is slow to shift back down, turn the barrel adjuster IN by 1/4 turns. Find a good compromise between the two.
Now, as a final check. Shift into the small cog in the back. Check the cable tension. Where the cable is exposed (between stops - no housing) you can pull on the cable. It should be taught, not tight, but not sloppy either.
Now that you've adjust the rear, go through and check how it shifts in each of the front chainring combos. Fiddle with the barrel adjuster till it's the best compromise!
07-12-03, 10:39 PM
Damn.. Now I think I really screwed it up. Before it was only messing up in 6th and 7th gear now it is messing up from 4th gear and up.
Just read up on the Barnett's Manuals and see what you can do. They have a pretty good explanation on RDs. Don't worry about messing up, coz we all do it at least once trying to tune our bikes. Remember, "bike tuning isn't a chore, it's an opportunity."
07-13-03, 01:31 AM
I read up about it on the barnetts manuals, and it still is a little off.. Maybe I just should of left it.
I'd persevere myself. a2p described the steps involved very well. Providing you get the hi/lo stops set right the main solution for solving the shift problem will be in the cable tension. Once you know which stop screw does what take some tools on the road with you and do a series of tweaks as you go along. The cable adjustment is the simplest to do.
You mentioned you had a rear der hanger bent back into shape. From where I sit, it should have been replaced - assuming it's a bolt on? Could it possibly be out of alignment ever so slightly, to the point that the rear der is running askew?
07-14-03, 01:44 AM
It was part of the frame, so the derailleur hanger could not be replaced. I did however go out today and adjust it as I rode. I was only adjusting the barrel adjuster, but I pretty much got it. The only problem with it now it when I am trying to downshift from the 7th gear I have to push the shifter twice before it shifts into 6th.
It might well be a good time to check the cable where it joins the rear der. I don't know how important it is generally, but my rear der fitting instructions said to run the cable over the top of the bolt and not underneath it. Maybe that is useful to know, maybe not.
The cable might need to be pulled tightish over the bolt before it is locked into place. Some folk use pliars to give it a good pull before the bolt is tightened. I tried that and my shifting was a little unpredictable. Eventually, I settled on pulling the cable by hand and getting enough tension on it to be useful but not so much that the cable is as taught as highly strung wire. That seemed to help a lot and all other problems in shifting were then corrected on the adjuster.
Is the cable routed ok around the frame? That is, there are no 'pinch' spots as it were. I recall Sheldon Brown documented the correct cable routing. Does the cable fit securely onto the frame using the lugs it might have on yours?
07-14-03, 01:20 PM
Yes, the cable is routed ok around the frame. I can't really mount over the top of the bolt, because it will end up slipping loose. I have been using pliers to pull it tight.. Maybe I have been pulling it too tight. Thanks for your help.
It's worth looking at for sure. Too tight can pull the rear der in a bit but then you could compensate for that at the barrel adjuster I guess. a2p described the initial barrel adjuster position very well. For my SRAM XOs, the distributor told me to screw the adjuster in completely and than back it out 1 whole turn. I then pulled the cable hand tight and locked it down. That meant I could make small 1/4 turn adjustements until I got the indexing to run smooth.
Two other things come to mind: 1. Is the b-screw set correctly as well? 2. Is the front der cage set correctly as well? The front mech is usually 1mm clearance above the big chainring. For me at least, setting both front and rear mechs correctly are complementary to each other.
07-16-03, 01:26 PM
I can't find the B-screw I have looked over the whole derailleur to find it.
07-16-03, 02:02 PM
It's the screw on the back of the derailleur that presses against the derailleur hanger.
07-16-03, 08:34 PM
Is this right?
07-16-03, 08:41 PM
Thanks, now what effect will it have when I turn it Clockwise? How about Counter-Clockwise?
07-16-03, 10:01 PM
When you are in the largest cog, if you notice the upper jockey pulley dragging on the cog, turn clockwise. This will increase tension and eleviate it rubbing the cog. What it does it changes the effective position of the derailleur and pushes (pulls? rotates?) it back further to avoid.
Think of two tangential circles stacked and meeting. You are moving the center of the lower circle down and back, causing the tangential points to seperate.
Does that make sense. After I read it again, it doesn't to me either, but at lease I know what it does. Can't explain it, but I know!
07-16-03, 10:04 PM
hey trek, do me a favor.
Shift your bike into the middle chainring and the smallest cog. Take a picture of this directly from the rear. I want to see the vertical alignment.
Now, without adjusting anything. Shift into the big cog and take another pic. at the same angle.
Methinks your derailleur hanger is STILL bent. If it's shifting well in the lower (smaller) half of the cassette, but hangs up in the upper half, that's usually a good indication.
07-16-03, 11:18 PM
Here's the first I hope it's at the angle you wanted, if it isn't let me know and i'll take more:
07-16-03, 11:35 PM
Here's it in the biggest cog, I thought the bigger picture size would help:
07-17-03, 10:10 AM
From the pic of the first one, things look spot on regarding your stop setting. I'm not sure, maybe someone else can provide their opinion, but it appears from looking at the lower jockey pulley that there may be a slight counter-clockwise twist to your derailleur. The lower jockey pulley seems a bit "outbound".
I can't tell from the second pic., and that's my fault. I didn't clarify.
I need to look at it directly from the rear so I can check the vertical alignment.
Your second photo is too much of a side view.
07-17-03, 10:20 AM
alright, let me take another and i'll post it, it's just hard to balance the bike and take the picture at the same time.
07-17-03, 10:42 AM
How's this? lol i'm not sure if thats what you want, let me know.
07-17-03, 10:54 AM
Yep, that's what I needed. It appears to be lining up correctly.
Is the slow shifting only from 7th to 6th or is it all the way through the gears?
Try turning the barrel adjuster IN (clockwise) a little, like 1/8 of a turn and see if that helps.
07-17-03, 11:02 AM
When I turn it all the way in and then turn it out 1 turn like you said before it won't allow me to shift into the biggest cog. Should I just keep turning it out until it allows me to shift into the biggest cog? Should I make any adjustments to my B-Screw? Thanks
07-18-03, 08:16 AM
Shift into the smallest cog, then turn it all the way in and back out. Then, set the cable tension. I just pull the cable snug with my hand and then tighten it down.
Shift once, and turn barrel adj out until it "climbs" into 3rd gear then back in just to the point where it stops "climbing" onto 3. If you look at the derailleur it should be lined up directly under the 2nd cog.
Then shift through the gears. If it won't go into 7th, but does in all the others, try unscrewing the limit screw a tiny bit. 1/8 - 1/4 turn.
Go through the gears again, (many times) and see how that works. Remember, small turns of the barrel adjuster (max 1/4 turns).
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