rear derailleur bolt stuck

Hi mechies :)

I've been having trouble with the rear derailleur on my commuter mtb, but I'm not sure what's wrong. It skips and gets stuck and does a lot of weird stuff, and there is quite a bit of sideways play compared to the frame. I took it off today to look closer at it, and the jockey wheels are worn but not exceedingly so, but are pretty wobbly side-to-side. So I'll probably be changing those, which should help shifting precision. The derailleur itself seemed good, tight spring and smooth action, but the mounting bolt was a major hassle to get off and on. It was so stuck that I had to really yank on the allen key to budge it. Is this bolt usually this tight? The sideways play was less once I got it yanked into place again, but it seems to me the derailleur is supposed to be able to pivot around the mounting bolt, apart from the separated plate actually facing the frame. At the moment I don't think anything can pivot around the bolt without a lot of force.

Should I take it off again and disassemble it, so that I can grease up whatever is stuck? Or isn't this really a pivot point in normal action? I'm a little leery of disassembling it since I know there are springs and stuff inside. This is a Shimano Deore der, by the way.

If the spindle won't turn independently of the derailleur body, how did you get it on/off? I must not be understanding your issue.

Shimano specs torque at 8-10 Nm, so it shouldn't have been that tight unless maybe the threads are a little corroded? How does your derailleur hanger look? Maybe put a little anti-seize on the threads when you reinstall it ...

I've never tried to disassemble that part of a derailleur. I just put a drop of oil in there (and all the other pivot points on derailleurs and brakes) after I wash my bikes. Exploded diagrams are here - you didn't say which series your derailleur is. There are no springs on the spindle, but you'd need a cerclip tool.

I'm not sure what the spindle is. The mounting bolt holding the derailleur to the frame will turn independently of the derailleur body, but only with a lot of force. To put it this way, I would have stopped yanking on the allen key if I hadn't been absolutely sure that that was the only way to remove the derailleur. And I know it's not the threads, they're fine.

I'm not certain if the derailleur is supposed to be able to pivot smoothly around the bolt during normal use, but it looks like it. At the moment it can only pivot around it if a lot of leverage is used, which doesn't happen during normal use.

Thanks for the link! The Park Tool guide to overhauling rear derailleurs shows a spring if you remove the plate which is directly between the derailleur body and the frame, which is why I'd rather not take it apart if I don't have to...

http://www.parktool.com/blog/repair-...lleur-overhaul
(about 3rd page down)

Oakleaf has a good suggestion with the antiseize.

Most SRAM derailleurs I know are not designed to pivot in use.

Most Shimano derailleurs I know are designed to pivot in use, and you'll get better shifting if you can figure out what's keeping yours from doing so. I've taken this pivot apart in the past, it's a little tricky to wind up the spring on reassembly but after a few tries I got it. Might help to have the Shimano TechDoc exploded view for your derailleur as a guide.

Trivia: The lower pivot is the "A" pivot. For nearly the last half a century it's been a sprung pivot in 99.9% of derailleurs. When Shimano added a spring to the upper pivot (in the 1970s?) it became the "B" pivot. That's why, to this day, the screw that adjust the angle of the derailleur body at this pivot is called the "B-tension screw"! (Some Campy derailleurs adjust at the "A" pivot but I don't think Campy calls it that.)

Quote:

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Originally Posted by dianne_1234

When Shimano added a spring to the upper pivot (in the 1970s?) it became the "B" pivot. That's why, to this day, the screw that adjust the angle of the derailleur body at this pivot is called the "B-tension screw"!

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What a cool piece of trivia. I always wondered - thanks for that! :)

Thank you ladies. You are briliant, as always :)

Updating to say - I took the derailleur off again, pulled off the c-clip and removed the body screw plate and seal. The spring inside wasn't going anywhere even though I pulled on it hard, nor was the bolt. Full of salt and corroded gunk though. I guess that's what winter riding does to a bike. After a lot (a lot!) of oil and spraying and squeaking and working back and forth until the whole thing was pretty warm, the bolt deigned to wiggle slowly out. It was a close fit, and the inside of the hole was just visibly plated. Scraped it out, trying not to make gouges, greased it up well and lo and behold, the bolt went in again and could be turned by hand.

Reinstalled I could see the derailleur pivoting a little around the bolt when I re-adjusted the gears, so I'm hoping this will solve the mysterious sticking problems back there. I still have the sloppy pulley wheels to replace, but I think they just cause imprecision.

I like taking things apart :)

If those jockey wheels are worn, you should also check your chain and cogset, as they may too be worn and cause skipping. A worthwhile tool to have is that Park chain wear checker. It fits over a link and then the other end rests in another link, and if it goes all the way into the link, the chain is worn and should be replaced. Of course, if the cogs are also worn, they should be replaced along with the chain. The derailleur cable is another item that should be changed every year, and if the bike is subjected to a lot of harsh weather/dirt the cable housing should also be replaced.

Hopefully the cleaning you gave that pivot point will help the derailleur's upper pulley track under the cogs and tension the chain properly. I do most of the work on my bikes, and would never think to open that up myself.

I have that chain checker, it's brilliant :)

I've been keeping track of the wear on the drivetrain, but just casting an eye over the jockey wheels, and since the teeth aren't excessively worn I haven't thought about replacing them until now. The sideways play was quite a lot - but I kind of suspect I at some point may have cannibalized some parts from another bike... My commuter bike is sort of put together from the odds and ends leftover from other bikes :D

Anyway. New jockey wheels it is. But the shifting is already better.