Replace bolts on hitch - Grade 8?

[Teikas Dad]

I just bought a 2000 GMC Sierra 1500 that I'm going to use for towing a trailer for my tractor. The truck has a Reese hitch installed on it but I don't know when it was installed. The truck itself doesn't have any rust or body rot on it. The bolts on the Reese hitch where it attaches to the frame are rusty so I'm thinking about replacing all the bolts on that hold the hitch together and the bolts that attach the hitch to the frame.

Are the bolts that come with the hitches grade 5 or grade 8 bolts....or do they use something special. I was figuring on replacing the bolts with grade 8 bolts but figured before I did anything I'd check with you guys. I tried contacting Reese to get their input but they never got back to me.

 

[Diamondpilot]

I just bought a 2000 GMC Sierra 1500 that I'm going to use for towing a trailer for my tractor. The truck has a Reese hitch installed on it but I don't know when it was installed. The truck itself doesn't have any rust or body rot on it. The bolts on the Reese hitch where it attaches to the frame are rusty so I'm thinking about replacing all the bolts on that hold the hitch together and the bolts that attach the hitch to the frame.

Are the bolts that come with the hitches grade 5 or grade 8 bolts....or do they use something special. I was figuring on replacing the bolts with grade 8 bolts but figured before I did anything I'd check with you guys. I tried contacting Reese to get their input but they never got back to me.

Grade 5 is what is used.

Really check over the hitch itself. Especially the tube that makes up the main body of the hitch. They usually rust out from inside out.

Chris

 

[Teikas Dad]

Thanks Chris, will do.

 

[FTG-05]

I don't even bother buying grade 5's any more. For something like this, it wouldn't even be a question as to which to use. I use the rest of my grade 5s (and grade 2s if I find any) for non-critical trivial uses. Anything to do with a tractor automatically gets the Grade 8's.

When I replaced the Grade 8 metric equivalent (Class 10.9) on my Ford F-350's hitch years ago, I went with ASTM A-574 socket head cap screws. 170 KSI vs 150 KSI for Grade 8s.

 

[Teikas Dad]

Thanks, I tend to err on the side of caution myself. I don't want to see my new tractor and trailer laying on it's side on the road so I'm thinking for the 10 or 12 bolts that I need to replace I'm going to go with Grade 8.

 

[Shenandoah]

I just replaced the pintle hitch on my F350 and it called for grade 8 bolts. I can't even imagine trailering my tractor with a bush hog and a 6' blade on the deck knowing I had grade 5 bolts holding the hitch on.

Grade 8 will allow for a far greater clamping force at the bolt connection due to the minimum tensile strength of the steel (150,000 psi vs 105,000 psi). I torqued mine to 150 ftlbs.

 

[oldnslo]

If I remember correctly grave 5 bolts have a higher shear strength that grade 8 but the tensile (stretch) strength of grade 5 is lower that grade 8. If this is true then grade 5 bolts would be a better choice for your hitch since this application induces higher shear forces.

Is my memory correct?

 

[Shenandoah]

If the joint will have flex, a grade 8 bolt is not the best choice as it will be less ductile than a grade 5 bolt. However, there are certain instances where you want the joint tight and the clamping force of a grade 8 bolt far exceeds a grade 5 bolt. The hitch I just described, as an example, is one of those instances.

 

[Teikas Dad]

I did finally get an email back from Reese. They have replacement bolts available and they indicated that they use Grade 5. I'm still thinking Grade 8 will give me some additional peace of mind when towing.

 

[FTG-05]

If I remember correctly grave 5 bolts have a higher shear strength that grade 8 but the tensile (stretch) strength of grade 5 is lower that grade 8. If this is true then grade 5 bolts would be a better choice for your hitch since this application induces higher shear forces.

Is my memory correct?

No, you remember incorrectly.

Shear is typically given as .6 tensile strength. Hence, the higher the tensile strength, the higher the shear strength.

Example chart provided below.