Greasable Leaf Bolt Strength and Usefulness

I have a greasable bolt from MORE (http://www.mountainoffroad.com/more.htm[) that I want to put on my rear leaf eye connection to the shackle, but the factory hardware is class 9.8 while the MORE bolts are grade 5. Is this safe? I see that the tensile strength of grade 5 is 120,000 psi while the class 9.8 is 130,500, which seems to be negligible, but I'm just checking to see if people have real world testing. Also is there any benefit to get 14mm greasable bolts to turn all the leaf spring bolts into greasable points? Thanks.

Personally, I wouldn't do it..but I'm a sissy. Now, that being said, the 8% or so difference in ultimate strength won't likely exceed the safety factor originally designed into the suspension components.... The yield strength (realistically the important value) of a grade 5 is 92 ksi., where the yield strength of the M9.8 bolt is 104 ksi. (88% USEABLE strengh compared to the factory). If your not bottoming out the suspension either way (your springs act like a buffer to control the load going into the bolt) you will likely be ok.

...ok... so I just looked at the link, and I interprit the info as there is a hole drilled down the axis (as well as across the axis) of the "greasable" bolt. That should take a nice chunk out of your yield strength... the more I read, the less I like the idea. Out of curiosity, what is the "problem" that you are trying to overcome with a greasable shackle bolt?

If I were you (and I REALLY wanted a greasable conenction there) I would forget about the greasable bolt and drill/tap a zerk fitting into the leaf directly.

The grease hole won't make any difference whatsoever.

First, a spring eye bolt (regardless of which end of the spring) doesn't act in tension, so tensile strength is not important. It also doesn't act in torsion, so torsional strength isn't a concern. It acts in shear. If you can find the relative shear strengths for grade 5 and metric fasteners, compare them. I don't think there's going to be much difference.

The key factor in shear is cross-sectional area. The longitudinal hole for grease is small. It will reduce the cross-sectional area slightly, but probably not enough to matter. The cross-drilled hole that lets the grease out into the sleeve won't make any difference whatsoever, because it's not located where shear is acting on the bolt. If a spring mounting bolt is going to shear off, it ain't gonna happen in the middle of the bushing sleeve, it's gonna happen at one of the ends.

Nice synopsys Eagle.
Good to see that some people understand statics and stress.

Thanks for all the input. Hehe, I was expecting someone to just chime in with some real world testing, like "I have grade 5 bolts in my leaf eyes and I wheel the hell out of my rig and no problems ever."

So I'm away from home and don't have access to my engineering books, but I think a lot of material strength charts in machine design books are based on the ultimate tensile strength. Everything else is just a ratio of the UTS, like here
http://www.roymech.co.uk/Useful_Tables/Matter/shear_tensile.htm

and here
http://www.roymech.co.uk/Useful_Tables/Mechanics/stress.html

Assuming this type of ratio shear strength is in the ballpark, I was curious just to calculate the difference in force each bolt could take before yielding in double shear with the leaf eye separating from the mount. I haven't checked any of my calculations, but it seems like a 10% decrease in force using the greasable bolt. The 10% is probably not a big deal, especially with the safety factor when the factory decided to use class 9.8 bolts.

I also looked at someone's revolver shackles yesterday and Teraflex uses a grade 5 bolt in the assembly.

Oh my other question is the usefulness of turning this shackle bolt into a greasable one...



If it will help, does anybody know of a source for 14mm zerked bolts?

Thayer said:

Thanks for all the input. Hehe, I was expecting someone to just chime in with some real world testing, like "I have grade 5 bolts in my leaf eyes and I wheel the hell out of my rig and no problems ever."

Click to expand...

I have Daystar brand greasible bolts in my leaf eyes and I wheel the hell out of my rig with no problems ever.

Seriously, no bull, honest. And it's pointless to have a greasible bolt inserted through the steel bushing sleeve on a set of main eyes - all you're doing is greasing up the metal to metal contact area. The only upside is that the bolt is less likely to freeze up inside the bushing when/if you ever try to remove it.

:twocents: