gears jumping

[busdennis]

hi
its a new giant bike with a 50 34 double up front an 11 28 cassette at the rear, mainly 105 stuff.
all was well for the first 500 miles but now the gears are jumping, it only happens on the 34 front ring when putting heavy pressure on the pedals (hill climbing) jumping between the 4th 5 th and 6th cog at the back, it caused me to fall the morning.

should the bike be serviced after 500 miles? (is this enough time for cables to stretch etc) or is there a common cause?

denny

 

[simon.r]

It's quite possible that the cables have stretched slightly. It probably just needs the tension tweaking slightly - use the barrel adjuster on the rear mech. If you can get the back wheel off the ground and spin the pedals while you're turning the barrel adjuster you can easily see the effect it has.

 

[Maz]

Are you saying the bike is new and you've done 500 miles on it?
Most bike shops will service the cables for you for free, if you've just bought it from them.

 

[paxterg]

How do you adjust the tension on a Deore Shadow rear mech? There is no barrell aduster on the mech!

 

[simon.r]

How do you adjust the tension on a Deore Shadow rear mech? There is no barrell aduster on the mech!

There's probably an adjuster on your gear shifter (where the cable exits) which does the same job. Same as above, lift the back wheel and spin the pedals while turning the adjuster and you'll see the effect it has. If there's not enough adjustment at the gear shifter, make coarse adjustments by undoing the cable-fixing clamp and tightening / loosening the cable, then fine tune using the gear shifter adjuster.