FD-M770 - pivot linkage slop

[buzby]

I recently bought a secondhand M770 Deore XT front derailleur, it's in pretty good shape (a bit of wear on the inner side of the cage but that's to be expected). However, I noticed that when the cage is swung out to the big ring against the sping tension there seems to be a bit of slop in the front pivot linkage (the figure-of-8 shaped piece that links the cage to the body). There is enough slop there that the front of the cage can rattle about a bit.

Has anyone else with this mech noticed this, or is this wear in the linkage? I am thinking of drilling the rivet out and replacing it with a bushing and small bolt and locknut, but I thought I'd check first just in case it's meant to be like that...

 

[Reluctant]

FDM770 is a top swing front mech (low clamp style). Top swings always seem more prone to developing slop in the pivots, partly,i think because there's more of them. It needs to be pretty bad before you'll get audible rattling when riding and a bit of play doesn't affect performance badly. I think you'd have a very fiddly and tough job to drill out and replace with anything that'll work better for any length of time - I'd live with it as it is.

 

[buzby]

Cheers for the reply. I've always preferred bottom swing derailleurs as they seem more robust but my new frame has a stepped seat tube with an odd diameter where a conventional derailleur would mount, so top swing is the only option.

The rattling was getting a bit annoying (on the flat I like the only noise to be the hum of the tyres and the whirr of the chain) so I took the derailleur off to have a look at it. Most of the wear was in the top front pivot (between the linkage plate and the cage). I managed to carefully grind the riveted head off the pivot pin and used a punch to drive it out. The pivot was bone dry with no trace of lubricant (as were all the others), and there was about 0.5mm difference in diameter between the pin and the hole in the linkage plate (and with hardly any wear on the pin). I suspect it has been run dry for some time, possibly any lubricant that was there originally had been washed out and it had never been re-lubed.

Once the pin was out, I went looking in my spares box and managed to find a piece of chromed brass bushing just about the right diameter, and a small hex bolt and nyloc nut to hold it in place. After a bit of fettling it was fitted (and lubricated, along with all the other pivots) and there's now no play and a nice smooth movement. The brass will probably wear out in time but it's replaceable, unlike the steel linkage plate.