Skipping gears in the rear and chain rubbing in the front

[SaveTheClockTower]

I replaced my front and rear derailleurs and I'm having some problems with both. the derailluers and shifters are Shimano.

In the rear, I'm having problem with it skipping gears. The bike is 6x3 so I will call the lowest gear 6 and the highest gear 1 to avoid confusion. I place the chain on 6 and start to pedal, it will automatically shift to 5 on its own. When I shift once, it will skip 4 and go straight to 3. Shifting is then fine from 3 to 2 and 2 to 1. When I get to 1, there are sill 2 more gears on the shifter but they keep the chain on 1.

The front derailleur isn't moving enough to move the chain to the largest cog and it rubbing against the chain when on the middle cog. It seems to be running smooth on the smallest cog. Looking down from above, the der. seems pretty much parallel with the cogs. I tried to position the der. close to the teeth of the largest cog, 2mm as stated in the tutorial but that seems to be too close.

[DaveM]

It sounds like both shifter cables have too much slack in them. You probably need to go through the adjustment procedure for both deraileurs. Start with the rear: http://bikeride.com/part/rear-derailleur/ and then do the front.

[SaveTheClockTower]

(03-09-2010, 02:48 PM)DaveM Wrote:  It sounds like both shifter cables have too much slack in them. You probably need to go through the adjustment procedure for both deraileurs. Start with the rear: http://bikeride.com/part/rear-derailleur/ and then do the front.

I've been messing with this thing for over 2 days now and it's still not shifting right. I adjust the inner and outer screws on the rear derailer and the cable tension but it doesn't seem to want to shift to the largest cog, in fact, it seems like it won't reach that far. Also, the jockey wheels don't ever move when I shift, they always stay in the same position. Based on the tutorials, every time he shifts gears the jockey wheels are moving to a new angle. Could the chain be too tight? I measured it out as instructed in the tutorial, leaving 2 extra links.

Could another problem be the angle that the derailer is screwed into the frame? I tried adjusting the angle but it doesn't seem to have any effect.

[Joe_W]

Well, you said you changed the front derailleur? Maybe you installed one that is not compatible with your setup?
http://www.sheldonbrown.com/bbsize.html

[DaveM]

(03-11-2010, 10:43 PM)SaveTheClockTower Wrote:  the jockey wheels don't ever move when I shift, they always stay in the same position.

That sounds weird, but I don't know what would cause it. Even if the chain is short, the angle should change. Is it getting so tight when you go to the bigger cogs that the two pulley wheels are almost in a straight line between the front and rear cogs? The should be vertical in middle gears and the lower pulley should be behind the upper when you're in smaller cogs.

Maybe you could post a pic of what it looks like when you're in the small rear cog and when you're in the largest cog you can reach.

Also, it's hard to diagnose when we're not clear on what all the problem is. Is it shifting fine except you can't reach the largest cog? Or are you still having trouble with the individual shifts not staying in place? The limit screws and the cable tension change different specific things. They're interrelated, but you've got to adjust things one at a time or you're just "twiddling" around and it's hard to tell what each adjustment changes. Note that a bent derailleur hanger will make getting the adjustments right very hard. Do the two pulleys sit in a vertical line perfectly parallel to the cogs or is there an angle?

[cyclerUK]

To start with, disconnect the cables and try moving the derailleurs by hand.
If you can't move them by hand then neither will the cables.
Be careful when moving the derailleurs as the springs are very strong and it's easy to trap a finger.
You will have to turn the pedals/cranks to allow the chain to move between gears.
Make sure the rear derailleur is vertical when viewed from the rear, and parallel to the sprockets when viewed from above.
See the first photo on this park tools page. This is obviously out of line and should be straight up:-
http://www.parktool.com/repair/readhowto.asp?id=39

Also the small screws are "stops" and NOT for adjusting the derailleur.
The screws are only there to limit the ends of travel to make sure the derailleurs don't shift to far.
If a "stop" screw is in to far then the derailleur won't move over enough though.

Regarding the jockey wheels staying in the same position - have you got the chain routed through them correctly?
Scroll down to bottom of page:-
http://www.parktool.com/repair/readhowto.asp?id=25

And lastly make sure the cable is clamped in the correct position on the derailleurs. Usually there is a small slot where the cable goes.

[JohnnyCO]

Check the limit screws on both derailleurs. With the chain removed and set the screws so the front derailleur cage is right in the middle of the outer ring and then do the same for the inner chainring. Do this while looking from above. This will get you in the ball park and will let you know if the derailleur is even compatible. Do the same for the rear derailleur while looking from the back of the bike, line up the guide pulley to each of the high gear and the low gear. Make sure you have correct chain length and then fine tune with barrel adjusters. Good Luck