I have a Shimano Deore XT rear derailleur. At the moment it moves easily between the bigger cogs but doesn't move every time I change gear between the smaller cogs. For example, when moving from smallest to next smallest it doesn't do anything, when I go down another gear it then moves but is always one behind for a period until in the middle gears. Which screw do I need to adjust at the back to get it to work properly?

Could be just an over-tight cable.. or the limit screws at the gear end over-tightened so that the selector does not transverse the full width of the gear cluster cassette...

Derailleurs have a return spring in them that will always return them to the smaller cog (whether it is front or rear). The derailleur cable resists this spring tension. If your front der. is on the large ring and will not shift to a smaller ring then it could be a couple things. First, too much cable tension preventing the spring from returning the derailleur to a smaller cog. Second, you low limit screw is set too far in so the derailleur cannot travel back to a lower gear. This will be evident if you shift to a smaller cog, the derailleur does not move and the cable becomes slack. Third, something else is preventing the derailleur from moving, perhaps the derailleur was moved when installing the new crankset and it is getting hung up on a tooth of the large chainring, there could be some foreign matter lodged in the derailleur spring preventing it from operating, the spring could have broken so there is no longer enough tension to move the derailleur back to it's "home" position. Good luck.

Go through theadjustments at some point but first determine if you have excessive friction in the cable. It is ON LYspring tension in the derailleur that makes it seek out to the smaller cogs. The cable just controls how far.

http://www.sheldonbrown.com/cables.html

http://www.parktool.com/blog/repair-help/categories/derailleur-systems

What I was taught to do is shift to the highest gear, suspend the bike so you can access the rear derailleur and turn the crank by hand. It should go to the highest cog. If not, make sure there is no residual tension on the cable (or disconnect it from the derailleur completely) and pull the derailleur gently to see if it moves that last little bit. Keep rotating the crank. By repeatedly pushing the derailleur in to the largest cog and letting it spring back out to the smallest cog you can rapidly assess the limit screw adjustments to make sure it CAN reach each end gear without crashing the spokes or the frame with the chain. Reattach the cable and procede with the adjustments as prescribed in teh online resources.

These are among the simplest design for shifter on the market. If the cable is taut it WILL pull. Perhaps the cable is broken, grossly loose or rusted inside the housing.

If the model is incorrect look for yous at http://techdocs.shimano.com/techdocs/index.jsp

Procedures... http://www.parktool.com/blog/repair-help/categories/derailleur-systems

check out this link; I had the same problem and this is great.

www.cs.hmc.edu/~geoff/deoredx/index.html

Possibly the right one, but I doubt it.

Load-induced upshifting is usually due to the indexing adjustment being off due to normal expected cable stretch over time.

You might need to adjust the tension of the rear derailleur cable. Get a bead on how the gear selected and the two derailleur pulleys line up as viewed from directly behind. They should all be in the same vertical plane. If the pulleys are slightly outboard of the selected gear you can expect random upshifting to the next highre gear (smaller cog).

Turn the barrel adjuster at the derailleur about 1/4 turn CCW as viewed from behind the bike. This will make the cable a small bit tighter and you should see the pulleys move inboard to be better aligned with the selected cog. Try riding it and see if it gets a little better, then try another 1/4 turn. Don't go overboard with it though.

Hi,

This one's easy enough.. If you move the derailer through it's full stretch you will see that part of it will be blocked in each direction by a small screw. These screw adjusters are to stop the chain from running over the end gears, and sometimes if they're too tight they can stop the chain from reaching the gears in the first place.
A small screwdriver is all you should need, turn the bike upside down, loosen these screws completely and then change gear to one end first until it runs smoothly on the chain and then do the same with the other.
These are designed to be adjustable so you can add or remove gears/change wheel sizes etc and then readjust to run smoothly..

Hope this helps..

Here is a link to a tech sheet for a Shimano Deore rear derailleur. It is not your exact one, but all Shimano derailleurs are more or less the same. Make sure you have thoroughly cleaned your drivetrain with a degreaser (like Simple Green) and a brush to clear all grease and debris before making adjustments. The second step is to shift into your highest gear (the smalles cog) and then release the cable in the derailleur, pull taut and retighten it. Check again to make sure you can not get into low gear, because it may have been a problem with cable tension, which you just fixed. If it still does not, then adjust the "L" setting on the derailleur so that the jockey wheel on the derailleur will move just ever so slightly past the last cog on the cassette when the shifter is fully engaged.

Hope this helps,
matt

ok this is a little hard to explain in words but the important thing is to make sure the chain is on the biggest cog, pull the cable through the deralier tight and fasten. don't pull it too tight however. you may need to fine tune using the h/l screws but if it was in tune before then it shouldn't need too much adjustment.

Try this first:
Shift into the small ring and release the cable. Pull it tight (with pliers) and re-tighten the cable. It should shift now. If it doesn't, the solution is a little time consuming, so i apologize in advance.
First, flip your bike onto the bars and saddle. Now shift into the small chainring and your lowest cassette cog (the largest in number of teeth). Release the cable from the front derailleur and set the adjustment knob for the front derailleur to its center point. You should find it on your shifter. Now adjust the "L" setting on the derailleur while turning the crank so that its stop sets it in a position where it just skims the chain but does not touch it. Now pull the cable taut and re-clamp the cable. Shift into the middle ring and shift the rear derailleur to its highest and lowest gears, making sure the chain does not rub the front derailleur. If it does rub (it will be in either the lowest or highest cog on the cassette), adjust the front derailleur by way of the adjustment knob to clear the rub. Then shift into the big ring and you should have no problem. Set the "H" stop if necessary.