Hi

The Pivot Bolt that holds my Rear Derailleur to the bike frame has snapped. It's a Shimano XT Deore M751 (or similar number). My bike is a 2008 Specialized Rockhopper, 24 gears, 8 speed.

I went to the bike shop and they want to fit an inferior derailleur (non XT) for £55 - this includes labour and part. Now I'm no expert, but this seems like alot of money.

I asked if they had a replacement bolt and they said shimano don't supply them. I'm thinking of buying a 2nd hand shimano cheap derailleur off of Ebay, just so I can use the bolt.

Would appreciate any views on my thought processes here, as I am no expert at fixing bits on my bike.

Cheers,

Fi

I'd have thought spares would be available - they were the last time I snapped one.

The TechDoc for your mech is HERE and the relevant part, if available, can be sourced via Madison.

I have a few knackered old XT 8-speed mechs here, the bolts should be ok though. If you PM your address I'll drop a bolt in the post. Note that they are a bit tricky to re-assemble, because of the internal spring.

Thanks to everyone for the advice....

I didn't realize I would need to take apart and rebuild the derailleur itself. I thought I would just be able to pop the new bolt in the hole of the derailleur and screw it into the frame.

So am I right in thinking that this won't work? and I have to take the chain off the derailleur and take a spring out to pull it apart, then pop the bolt in and put the spring back in that keeps it all together?? Do I need any additional parts like washers?

As you may have guessed I have never fixed parts of my own bike. The most mechanical thing I have ever done is changing my break pads! Do you think this might be a bit much for novice? I have a good bike maintainance book (The Zinn one) which might have instructions on how to go about it. As a regular commuter (I have started touring a bit too), I probably should start learning - as it's costing so much to keep taking it to the bike shop!

I have spent almost £200 having it serviced (twice) and replacing bits on it, and it's only a 2008 model! AND it still makes a strange clicking sound (somewhere near the front of the bike) - which the previous bike service didn't fix.

The weird thing is, the same bike I had before (2006/7 model) never had one thing wrong with it for the 1 1/2 years I had it.

The part I was thinking of was this one but I will probably take up the offer of a free pivot bolt - then I can have a go and if it all goes horribly wrong I can go out and buy a new derailleur and not feel I've wasted more money:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=350257914667&ssPageName=STRK:MEWAX:IT

Replacing a rear derailleur (DR)  bolt is not a terribly common operation, but it's not quite as simple as you put it and the whole operation is much easier if you take the DR off the bike. You won't need any extra parts, as long as you don't lose the circlip or spring as follows. 

It's pretty easy taking the DR off - just stick a 5mm hex key down the bolt and undo it (remove the rear wheel and pull the DR backwards as you do this, else the spring will make it 'snap' around as it comes free. Easy for you in this case, as the bolt is already broken. You don't need to split the chain, because you can unbolt the jockey wheels and take one side of the cage off (make sure you put the wheels back in the right order, as the upper and lower are different). Be careful if you remove the gear cable though - it may be difficult to refit and you'll have to set the gears up afterwards.

Once you've the DR in your hands, getting the bolt out is a bit tricky. First off there is a circlip keeping it in the DR, and this circlip needs to be pushed off. You can then push the bolt out of the DR - at which point the internal spring (which coils around the bolt) will fall out.

To reassemble it with the new bolt, you have to  ensure both ends of the spring sit in the holes provided. The catch is you have to 'wind it up' a bit to do this, and you'll find this requires fairly strong hands (plus it's the kind of thing where you wish you had 3 hands).  It'll probably take a few attempts to get it back together (serious frustration can occur) at which point you need to push the circlip back over the end of the bolt, to keep everything together.

Finally,  you can then screw the DR back onto the frame hanger, making sure the B tension screw (the little screw in the DR, near the pivot) is sitting nicely against the little flat on the hanger.

It does sound like it might be a bit advanced for your current experience to be honest - though it's one of those jobs that is best learnt by doing.

You might also like to browse through the tech articles on here and on the Park Tool website, if you're planning to do more of your own maintenance.