my gears change automatically

Question
hi i have a 7 gear bicycle . the model is cignal ranger.
my bike is always on the 7th gear and when i change it to another gear, it goes slowly back to 7th gear automatically. how can i fix this?
thanks in advance!
giannis

Answer
Hi Giannis,

If the bike is a 7-gear bike, it is probably somewhat older (in the past 10 years bikes have gone from 7 to 8 to 9 to 10 gears in the back).  I am not familiar with a Cignal Ranger, but my research suggests that it is a 1999 model with the older Gripshift model of shifters.  Based on your description, it sounds like the detents (click stops) in the Gripshift grip are no longer keeping the rear derailleur from shifting all the way down to where the rear derailleur return spring wants it to go.  This is not an easy problem to cure, because it basically means that the Gripshift shifters are worn out.  
Because the Gripshift internals are mostly plastic, you will likely have to scrap the rear shifter (located on the right side of the handlebar) and get a new one.  The upside with the Cignal is that your drive system is mostly Shimano.  That suggests that most sets of 7-speed Shimano or SRAM/Gripshift shifters (not the type with what is called "1:1 actuation" but the Shimano compatible ones) will work.  Check with your local bike shop to find a Shimano compatible set of 7-speed shifters.  If you can't find any there, try E-bay.

Replacing the shifter is not especially hard, but requires some knowledge of bike repair.  If you have not worked on bikes before at all, take it to a bike shop and watch when they repair it.  If you have, here is the sequence in a nutshell: 1) Disconnect the shift cable; 2)Pull it through and throw it away; 3) Remove the rubber grip; 4) Loosen the Gripshift lock bolt; 5) Remove the Gripshift; 6)Replace new 7-speed compatible shifter, whether Gripshift or Shimano; 7) Tighten down; 8) Thread new derailleur cable back through the shifter and through the housings to the derailleur; 9) Adjust to correct tension; 10) Replace grip.

If this seems like a little too much, you may want to have your local bike shop fix it.  Sorry the diagnosis is that it probably needs to be replaced, but I have had two sets of Gripshifts wear out on me in a similar way and I haven't yet found a way to recover them.

I hope this was helpful,

Graeme