Anyone rebuilt a Shimano rear mech?

[ishaw]

I've got two lunches xtr rear mechs, both broken in different places. In theory I can make one good one from the pair, but unlike sram x0 rear mechs, you can't simply take them apart.

Has anyone successfully removed the pins that hold the parallelogram together, or have any thoughts on how to? Are they simply pressed in, or do they unscrew?

Pics below of the bits I mean. I'm hoping it's possible as it seems a shame to throw them away.

I'm willing to experiment on one, hoping to learn and repair one, just don't know where to start.

 

[xerxes]

Re:

Looking at the pictures, the pins obviously aren't designed to be removed, they're pushed into a "blind" hole.

However, I think it could be done; here's how I might try it:

1. Drill a hole in the blind side using a bit smaller than the pivot pin, down to the pivot pin; this will leave you a sholder for the pivot pins to but up against when you put them back in from the open end.

2. Use a parallel pin punch that fits the holes you drilled in the blind end to drive the pivout pins out through the open end.

3. When you reasemble, you may need to deform the open end again to hold the pins in; you might be able to do this by using centre punch just slightly to the side of the hole.

It will probably be quite fiddly to hold the mech for drilling and punching etc. and obvoiusly you would have small holes at the end of the pins when you've finished.

 

[mattr]

I've done it with older mechs (open holes at both ends of the pin)

Trying to splay the end of the pin with a punch is an exercise in futility, especially without proper press tools.
Do what shimano did first time round and splay the body of the mech to grip the end of the pin. A cheap, wide bladed screw driver works well.

 

[ishaw]

Re:

So essentially I need to create a small hole in the blind end to push the pins out.

I'm not sure what you mean by splay the ends. Can you dumb it down for me.

I'd plan on using loctite when refitting as well.

 

[xerxes]

Re:

Trying to splay the end of the pin with a punch is an exercise in futility, especially without proper press tools.
Do what shimano did first time round and splay the body of the mech to grip the end of the pin. A cheap, wide bladed screw driver works well.

That's what I said:

3. When you reasemble, you may need to deform the open end again to hold the pins in; you might be able to do this by using centre punch just slightly to the side of the hole.

I'm not talking about trying to deform the pivot pin, it's steel and will be way to hard, but the alloy body of the mech by using a punch to make 1 or more dots around the hole.

 

[My_Teenage_Self]

if you look at your pics, the 4 'crosshairs' around the pin are just punched into the soft alloy and are all that's holding the pin in.

Once the pin is back in, you'll need to replicate this by bashing the alloy with a punch, but it won't need to be as neat as the shimano ones, and you shouldn't need locktight.


HTH

 

[drcarlos]

Worst bit of all that is working out where to drill on the blind side as ideally it needs to be bang in the middle but as you'll be doing by eye it just needs to be where it's 'all pin' behind if you know what I mean. Also hopefully the pins are hardened as that will stop the drill bit when it hits that.

Carl.

 

[mattr]

Re: Re:

That's what I said:

Sorry, must have read it too fast.

 

[ishaw]

Re:

Thinking this through a bit more, do you think it is possible to get the pin out without drilling the body?

I'm wondering if a small easy out would allow me to screw it out?

 

[mattr]

You run the risk of damaging the pin sufficiently that it won't go back in