This is my first time using this forum, so please excuse me if I posted this in the wrong category.

I have a 2008 Scott Voltage YZ 25 and recently, the bolt that holds the rear derailleur to the frame sheared off. The rear derailleur is a Shimano Acera, but I can't find a model description more specific than that. I searched for exact replacements with my model of bike and rear derailleur, but get no results for them, almost like it's too old and different to be kept in stock anywhere. I've tried ordering a new bolt off of Amazon, but the circumference was slightly too large and the length wasn't quite long enough. With none of the other bolts for sale listing any measurements, I don't want to go on a wild goose chase ordering bolts until I find one that works.

The bolt that sheared off is about an inch and a half long with a circumference of 1.178 inches (1 and 11/64 inches). There's a shackle at the end of the threads, but I'm not sure if it's necessary for a replacement. Is it possible to get a new bolt like this or will I have to do something like fit a new rear derailleur?



The hanger for the rear derailleur

that looks like the pivot bolt for the derailleur - the hanger looks fine. So, this is a derailleur-specific part (as in, a plain bolt - even of the requisite length and thread - won’t work) rather than a frame-specific part. I think you’re looking at a new derailleur, unless you can find a used example on eBay to cannibalise for parts. Quick look on eBay, there a few used ~$20, and new ones online for $25-40
How did the bolt shear? I’d be concerned that the hanger itself took a hit and might need some attention/realignment

This bolt should work https://www.ebay.com/itm/231301900800 , but for the price of the bolt and shipping, you would probably be better off buying a new derailleur. Almost any Shimano 8 speed derailleur will work.

I'd second just getting a new derailleur. Repairing a $10 der. with a $20 part makes no sense and you run the risk of it not fitting or there being other damage you can't see. Any 8,9,10 derailleur will fit and you can use other brands like microshift too. Shift quality with a new part may improve also.
Here's one for $20 new.
https://ebay.us/m/5gxN0U

It appears that you had an unfortunate failure. Generally, the hanger itself should break before the frame or derailleur (by design). I would replace the derailleur and potentially also the hanger

The derailleur will have a model number on the back side. Something like RD-M360 or RD-M3020

Typically one wants the hanger to bend in order to save the rear derailleur. However RD hangers lately tend to be as much or more than the RD that they should protect. In this case the bolt broke. Which also protects the RD. However it's likely still just as inexpensive to replace the RD as has been suggested.

And you also should have the hanger alignment checked to be certain it is a tad askew which might cause your shifting performance to be poor or do strange things that mimic other issues.

If you have the alignment tool. Or the smarts to know how to make your own you can do that yourself. But a LBS will probably check it for less than the tool will cost you if you have to buy one.

​​​ You're excused!​​​​
Bicycle Mechanics will have been the better place for this thread. Welcome to BF.

I forgot to mention - if you replace the derailleur with the same one, consider saving the old one. Especially given your history, you might get into a spot down the road where your derailleur is worn/broken but your bolt is still good. You could get a free swap out of it.

Wow, thank you for the quick and helpful replies everyone. Honestly I'm not used to forums being so active so I wasn't thinking about checking back quickly. I'll go ahead and buy a new rear derailleur. I actually wasn't aware of how cheap they were, especially compared to that bolt dsaul sent. Once again, thank you for help.

I honestly have no idea how it sheared. I hadn't ridden the bike in a while due to the old tires finally giving out, so I wanted to do a proper little tune up with the chain and gearing before riding again. I cleaned up the chain and then gently rode the bike down the driveway through the gears to see how it affected the shifting. Then I adjusted the H-limit screw on the rear derailleur and tried adjusting the indexing with the barrel adjuster and noticed it was threaded all the way out. I started messing around with the tension of the cable to adjust the barrel adjuster and the first time I pulled on it, the whole derailleur just fell out. I don't know if it failed during a ride before I got new tires and friction was keeping it on, or if my gentle ride was somehow the nail in the coffin.

If I misunderstood and you meant "how" as in "where" did the bolt shear, then you can see right below the shackle and threads where it's broken. It's a surprisingly clean break; nearly straight across.

Ah alright, I tried to do a thorough sweep of the site, but somehow missed that page. Thank you.