[Hunter]

I've had a bolt break on my suspension pivot twice now, and replacing it leads me to a few questions about the strength of bolts.

So generally, most suspension pivot bolts are stainless steel...right? I understand the need to be corrosion resitant, but stainless steel bolts generally have a pretty low strength, when compared to a grade 5 or 8 bolt. Is there another specific reason why the qualities of stainless steel is desired in this application? What other material options are there for replacing pivot bolts (titanium...)?

And of course nothings easy...the bolt I need is a left-hand thread, M8, 1.25P, ~23L. Mission impossible.

 

[zebrahum]

WTF are you doing to these bolts? How can you be snapping more than one M8 pivot bolt? Save the money on Ti bolts (probably won't help anyway) and buy a torque wrench.

Are you breaking them by tightening them or while riding? If you're tightening them and they break, you're either going to hard or too frequently, possibly both. Again, torque wrenches can be had reasonably cheaply. If they break while riding, then there's something wrong with your rig and you really need to get it looked at.

Relax hulk, your pivots won't fall out. Try some blue locktite when you install the bolt in the first place.

 

[Hunter]

I've got a torque wrench, and it works just fine thanks. This bolt has broken twice while trail riding, nothing too crazy in my opinion. I know of a few others who have broken this same bolt on the same frame, and I proposed this same question to the manufacturer...waiting for an answer.

 

[zebrahum]

What bike?

There shouldn't be sufficient shock loads on most bolts to break them. Do your pivots have any play in them? There's something wrong in the design or in the way it's maintained. Try using your torque wrench. Preventative maintenance goes a long way. Or perhaps are you simply beating the **** out of a bike that doesn't deserve it.

 

[syadasti]

What bike?

There shouldn't be sufficient shock loads on most bolts to break them. Do your pivots have any play in them? There's something wrong in the design or in the way it's maintained. Try using your torque wrench. Preventative maintenance goes a long way. Or perhaps are you simply beating the **** out of a bike that doesn't deserve it.

The swingarm is attached on each side of the main pivot instead of a standard yoke design with a single axle bolt at the main pivot.

Mcmaster has class 8.8, 10.9 or 12.9 bolts, I didn't look closely to see if they have the size/type you need though http://www.mcmaster.com

 

[Hunter]

The swingarm is attached on each side of the main pivot instead of a standard yoke design with a single axle bolt at the main pivot.

Mcmaster has class 8.8, 10.9 or 12.9 bolts, I didn't look closely to see if they have the size/type you need though http://www.mcmaster.com

Yeah, its a bit of an odd design on the Chumba, and they've had some trouble with it - that bolt seems to back out occassionally, and has snapped on some riders. I tried the McMaster thing the first time it broke, but no luck finding a hardened, left-hand thread metric bolt - looks like a special order item. I'll see what Chumba comes up with.

After the bolt broke this time, I replaced all the pivot hardware and bearings, torqued everything according to spec, blue loctite, etc. I've broken that bolt about once a season, so we'll see how long it lasts this time.

 

[zebrahum]

Sounds like a pain, have you asked if Chumba has any ideas?

 

[DesuL]

I have my own ideas on the bolt. But what it comes down to is it is most likely being put under some hard tensile strength that it was not designed on the computer to be put under. Someone mentioned that some bolts back out, this would lead to the force int he wrong place and SNAP! I don't want to speak for Chumba they may have a great fix on it, but there are LOTS and LOTS of grades of bolts, some are brittle some are not. In my line of work (not bikes but metal) we deal with different bolts for diff places. I know where you can get that screw, but you should be able to get it offline. Other then that call a place called TACOMASCREW in SEATTLE,WA 98108. We get almost everything from them and I get all my lil screws that are crazy metric LH thread. I don't have a phone number but if you call and they have it I would be happy to walk down and get it for you (its a block away) and I can mail it to you. But see if Chumba can do something. Feel free to PM me and I will go see if I can get ahold of it for you.

Dave