Pivot axle bolts, grade 5 or 8?

[Moespeeds]

I'm changing out the BD pivot axle bolts, and BD want $104 for 2 bolts and the axle. I don't need the axle, and two 3/4" bolts are only worth $10 at the most. I'm going to put a couple of off the shelf bolts back in there. The original bolts were a very soft mill stock although I can't find a machine shop with a rockwell tester to verify this. So what do you guys think, go with grade 8, or put grade 5 in there? Gas brought up a good point, is the 8 possibly too brittle?

 

[Vegas]

Thought we were talking front axle still.

 

[MARV]

rolling thunder offers a few pivot bolts



Accessories - Rolling Thunder Frames

 

[Moespeeds]

I put a call into Daytec to see what they say about it.

 

[stlmikie]

That is a good idea Moe.

I put a call into Daytec to see what they say about it.

 

[Moespeeds]

Daytec told me to use grade 5, they think grade 8 might be too brittle for this application. Just an FYI.

 

[JamesofGA]

Who at Daytec told you that grade 8 would be more "brittle" than grade 5?

grade 5 bolts have tensile strength of 120,000lbs per square inch

grade 8 bolts have tensile strenght of 150,000lbs per square inch

The grade 5 bolt will break before the grade 8 bolt yields or stretches or becomes "brittle"

 

[Moespeeds]

Phil. From what I remember, a grade 8 bolt is simply a grade 5 that is heat treated to harden it. Remember, our pivot bolts r in direct shear, and there isn't a whole lots of friction on the mating sufaces to support it. What he is saying makes sense to me. Hardened bolts are less tolerant of vibration and sudden shocks in shear. You're talking tensile strength, but isn't that measured longways to determine bolt stretch?

 

[JamesofGA]

The shear strength (side to side) is 60% of the tensile strength.

Grade 8 bolts are made with a stronger alloy.

Grade 8 bolts being "brittle" is a long, argued topic but not true.

"Brittle" doesn't apply to bolts under 180 ksi ultimate tensile strength.

 

[Moespeeds]

Not really sure what to tell you, it's been many moons and many beers since my metallurgy classes in college. Daytec said grade 5, not grade 8. I did look up the "brittle" myth, and you're right, that's news to me. What Big Dog gives you is less than grade 5. There is also the problem that the grade 8 2.5" has too much shoulder, and would need to be shimmed to work, sticking out of the frame even farther. The grade 5 2.5" has the right shoulder size, and if I get a bug up my ass, I'd be able to drill and tap it for some shiny axle covers. Not much chance of doing that with the grade 8.

 

[JamesofGA]

Grade 5 are probally more than adequate for the application.

Just find the grade 5 vs. grade 8 to be a touchy subject. I had to argue with a co-worker, who has a "chemical" engineering degree, and somehow my "mechanical" degree seemed not to mater

Carry on...

 

[Moespeeds]

I did research the brittle thing, and found arguments for both sides. They claim grade 8 are less tolerant of cyclic loads. This is something I have heard before when I was in aviation. I only believe half of what I read on the internet, and you never know what the guy's qualifications are..

Read the "materials" section
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