gear change problem

andy83

sorry if this seems a really simple question but been doing my head in

have been doing a rebuild of my bike, got a 2005 GT agressor 3 frame and my set up is as follows

deore xt m770 shifters
deore xt m770 front mech
deore xt rear mech
deore xt hg93 chain
deore octalink chainset and bb (cant remember which model)

i have got all set up on bike but for the life of me i cant stop the chain jumping on the rear cassette, it usually jumps from the second smallest to the third smallest and seems like all the adjusting and i cant get it sorted. also it seems the front mech is not going across enough to get on the largest chainring.

is it something as simple as cable tension, just keep trying to adjust or have i got some incorrect parts although i dontthinkits this as they are all what are recomended to be used in the instructions in the shimano boxes apart from the chainset but all seems ok there. could it be the b tension screw is not set right??

sorry if this is a simple question but any help will be appreciated

nicklouse

followed the info on parktools?
tension and or B screw or top and bottom screws or all.

andy83

basically its just little tinkering then i take it, been following a book i have that is endorsed by park tools and is very good lol

glad to know its nothing wrong with the set up

this is my first build, do you think i should get a LBS to check it over before i start riding it??

supersonic

What cassette do you have?

Peter224

What sort of rear mech do you have?

It may be worth double checking if it's a top (more common), or low normal rear mech. The low normal spring type automatically pushes the spring towards the largest chain ring, whereas the top normal pushes it towards the smallest. Setting up your gears may vary slightly depending on the type of rear mech you are using.

if you are using a top normal you will no doubt have a barrel adjuster at the end, this along with the barrel adjusters on the handlebar shifters are great for finely tuning the tension.

Aimt to get the two screws on the rear mech done first so that it wont go over the highest and lowest cogs, then work on tightening the cable to the rear mech. Having done this, play around with the tensioners on the rear mech and barrel adjsuters.

If all fails, it me be the case where your teeth on the rear casette are worn down (if you have not already placed this). I also found that re-oiling the cables and oiling the inside of the cable outers helps, but this shouldnt be required on brand new cables etc.

andy83

SORRY ITS A BRAND NEW SHIMANO DEORE CASSETTE

ALL IK NOW BOUT THE REAR MECH IS ITS A LONG CAGE AND THE MODEL WITH THE XT RAISED, IN SILVER, THE ONE BEFORE THE NEW BLACK M770 MECH

supersonic

Everything is compatible. Sounds lie a cable problem - check for smoothness, then fine tune. An 1/8th of a turn of the adjuster at a time can make all the difference.

Also check the alignment of the rear mech and hanger, and as Nick says, the B tension screw.

MountainPete

Adjust the cable tension at the shifter end.

andy83

cheers for all your help, will hopefully get to try and sort it out later