Just to make sure, rivit replacment sizes.

[koda6966]

I'm replacing all the leaf spring hangars and such, and need to bolt down a new crossmember.

Using the existing holes, the bolts I would need are 7/16 correct?

 

[Explorin94]

You are correct

 

[RatDog8o8]

I would get at least grade 8 bolts, just for the extra strength. I know the grades are not for "shear forces", but IMO every bit of toughness helps.

 

[hoosier1104]

And use some LockTite on those beaches.

 

[Explorin94]

I would get at least grade 8 bolts, just for the extra strength. I know the grades are not for "shear forces", but IMO every bit of toughness helps.

Depends on where they go. If it is a place like that where there could be some movement I would rather have a grade 5 that would atleast give and stretch and not just snap. Cause then you are screwed.

 

[RatDog8o8]

Yeah, that's true.....more flex to 5s. LocTite, or maybe even double-nutting if room....just a thought.

 

[Mac]

Depends on where they go. If it is a place like that where there could be some movement I would rather have a grade 5 that would atleast give and stretch and not just snap. Cause then you are screwed.

Yep, kind of agree that grade 8's are over used, when they do go, it's like a hard pretzel, just snap. The shop manual does say to use the grade 8's when replacing rivets.
Dave of the Nord

 

[Snoranger]

According to their strength ratings a grade 5 bolt will fail before a grade 8 bolt will even deform.

Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.

http://www.rockcrawler.com/techreports/fasteners/index.asp

 

[Mac]

According to their strength ratings a grade 5 bolt will fail before a grade 8 bolt will even deform.

I don't think anyone will disagree on the strength ratings but even in that part you quoted, grade 8's have their place. Spent 10 years designing and doing the fab drawings for steel structures to be bolted together in field, These were 40 ft tall and a 12' x 14' base and having 40-60K lbs of equipment in them They were all bolted together with grade 2 A-307 bolts, per long time existing customer specifications.
Dave of the Nord
Edit: Why the grade 8's are brittle
Determining Bolt Grade

Bolts of different grades are marked on the head to show what grade bolt they are.

Grade 2


Grade 2 is a standard hardware grade steel. This is the most common grade of steel fastener and is the least expensive. Grade 2 bolts have no head marking (sometimes a manufacturer mark is present).

Grade 5


Grade 5 bolts are case hardened. This means that the outside part of the bolt has been hardened but that the bolt was not heated enough to harden the inside portion. This creates a bolt that is fairly hard but not as brittle as a fully hardened bolt. Grade 5 bolts are the most common bolts found in automotive applications. Grade 5 bolts have 3 evenly spaced radial lines on the head.

Grade 8


Grade 8 bolts are fully hardened. This means the bolt has been hardened all the way through. This creates a bolt that is very hard but somewhat brittle. Grade 8 bolts are more likely to snap off than bend under extreme loads. Grade 8 bolts are often found in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head.

 

[koda6966]

I'll be going with grade 8, only thing I really use 5 for is bumpers and whatnot.

 

[koda6966]

Should I dick around with heavy duty washers? I double the bolts will slip through the holes or anything these are just to make me feel better. I'm going with grade 8 yellow zinc for the bolts/nuts and just regular medium strength zinc for the washers.

 

[lil_Blue_Ford]

I always ream/drill the holes out to 1/2 inch because sometimes the hole from the factory is a little bigger than 7/16. Grade 8 for suspension, I usually use either ungraded or grade 5 washers and grade 8 bolts with locktite. Only in certain applications do I bother with the grade 8 washers and those are more pull-through than shear. Suspension bolts are a shear application or if I have to really crank on a bolt to tighten it down.