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Will grade-5 leaf spring u-bolts be strong enough?
- Thread starter akxj01
- Start date
5-90
NAXJA Forum User
- Location
- Hammerspace
I believe most U-bolts are bent from SAE5 stock (or equivalent) anyhow, and you're dealing with 1/2" stock. You're better off with the lesser heat-treatment, since SAE5 will stretch and deform more before total failure than SAE8 will (which makes it more likely that you'll get out and home.) Yes, SAE 8 is stronger, but it also fails rather more dramatically - oops!
stxcherokee
NAXJA Forum User
- Location
- Corpus Christi, Tx
Grade 9 all the way.. sorry I work for Fastenal
Thanks. I didn't think of the point you just made.
Don't trust Grade 5 bolts for this kind of application. The idea that Grade 5 are better because they "give" is a fallacy that keeps being passed around as gospel. I was an engineer and have two engineering degrees if that is a consideration. There are two common strengths associated with bolts, Yield Strength and Tensile (or ultimate) Strength. Yield Strength is where the bolt begins to deform, but does not fail. Tensile is when complete failure occurs. For Grade 5, Yield is 92,000 psi and Tensile is 120,000 psi. For Grade 8, the Yield is 130,000 psi and the tensile is 150,000 psi.
So the Grade 5 will completely fail before the Grade 8 begins to deform. The myth arises because people assume that because a Grade 8 is a harder alloy, it is more brittle. Hardness and strength are not the same thing.
Don't gamble, use the Grade 8's where they belong, or Grade 10.8 in metric sizes.
So the Grade 5 will completely fail before the Grade 8 begins to deform. The myth arises because people assume that because a Grade 8 is a harder alloy, it is more brittle. Hardness and strength are not the same thing.
Don't gamble, use the Grade 8's where they belong, or Grade 10.8 in metric sizes.
5-90
NAXJA Forum User
- Location
- Hammerspace
Hm. Thanks for the correction. However, the idea of "yield before failure" would still apply in some cases, right? Just not this one?
What are leaf spring U-bolts, usually, then? All of the ones I've seen don't have any grade markings on them, so it's a bit hard to tell. And all of the threaded rod I've seen has been equivalent to SAE5...
- Location
- Southern Maryland
apologies for the detour, but where are you guys buying grade 10.8 suspension hardware in lots of 1-4? all I can find is lots of ~20...
8Mud
NAXJA Forum User
- Location
- Central Germany
I use grade 8 (non coated) 1/2", having said that, elastic, plastic and shear fall somewhere in the yield and tensile curve also.
It is sometimes hard to tell what will perform better in a specific application without testing.
I'm not an engineer. But I've done my fair share of re-engineering.
Dodge used to employ a bunch of good old boy, practical engineers. I've studied many of their solutions , that sometimes go against engineering basics, but have survived the test of time.
Grade 5 IMO has too much stretch and is too easy to over torque (axially) past the elastic.
The older grade 8 chromate coated bolts tend to crack. The galvanized grade 8 tend to crack. Though they say they have cured this with new methods and techniques.
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8Mud
NAXJA Forum User
- Location
- Central Germany
From what I can glean, Grade 5, 1045 rod (U-bolts) are standard for most truck applications, up until 9/16" diameter U-bolts.
