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OH went out on my mountain bike a month or so ago and it came back with the back derailleur completely mangled, the chain twisted and the back end generally jammed solid. I'm not sure what he did but the bike had been in the back of the car the day before so presumably something became misaligned and it just went from there.

Having spent years taking my son bike racing (albeit on a fixed wheel bike) I decided I would have a go at fixing it. I've had the chain off, straightened the twisted links and fitted a brand new derailleur. It's now all reassembled and seems to work OK on the front chain rings (there are three) but the rear ones (six) only seem to work on the middle four sprockets. Before I leap in and start adjusting all sorts of things can anyone tell me which is the most likely reason for this please?

Dear Graye,
On the deraulier spring loaded arm, between the 2 small gears, you should find 2 small screws pointing towards, or in contact with, a small plate of metal. Turn the one in contact with the metal plate a quarter turn at a time either clockwise or anticlockwise, then spin the wheel by means of the pedals whilst changing gear up and down. Repeat until you get a result. Then try with the other screw. DON'T move either more than a quarter turn at a time or you run the risk of throwing the chain off the block.

Hope it's been useful, good luck with it.

Thanks for that! I thought it might involve some delivate adjusting somewhere. I'm getting there - I've got FIVE rear gears now so just a bit more adjusting and I may get it right later today. I'm struggling as I'm having to adjust the screws AND hold the rear wheel off the ground AND turn the pedals all at once. Things will be easier when I have someone to help later.

Re fiddling with derauliers and such I usually turn the bike upside down and turn the pedal with hand and twiddle with the other.

Now that's far more sensible! I'll give that a try later. My own fault because I always used to have a bike stand to do all the adjustments on my son's BMX and hadn't really thought through how to manage without one.

Hopefully we'll be back on the road tomorrow. Thanks for the assistance!

Hi

In addition to the info already posted I would like to point you in the direction of Sheldon Brown a god to most cyclists who sadly died this year but his gold mine of a website survives.

http://sheldonbrown.com/derailer-adjustment.html

Everything you ever need to know about bike and a lot you will never need to know

mamos

That's a useful link, thanks.

I've managed to adjust mine properly now and it works well. I must admit I'm reasonably impressed with myself!

Well done Graye

I love learning new stuff

Think how much money you have save by not having to take your bike the the shop

mamos