Weld the trailer hitch receiver?

[Teikas Dad]

I recently bought a used pickup to tow the trailer that I'm going to buy for my tractor. I want an 18' flatbed trailer and the only ones I can find are rated for 7000lb GVW. With the weight of my T/L/B and the trailer combined I'm right at about 4900lbs. I figured that was too close to the limit on a 5k lb rated trailer, that's the reason for going bigger.

My question has to do with the hitch receiver on the truck. The truck is a 2000 and going by the date on the Reese hitch that is on the truck, the hitch is a 2006 model. It's the universal fit type receiver hitch where there are two brackets that bolt to the frame of the truck then the center of the receiver, which is a large round tube with the receiver welded on, mounts inside the frame brackets. The hitch is rated for 5k W/C and 7k L/D. There are two flat plates on the end of the center tube that get bolted to the frame bracket with 4 bolts on each side. Here's what the center tube looks like:

This is what it looks like with the frame brackets bolted on:

I took the receiver/hitch off the truck as I want to clean it up, repaint it and I'm going to replace all the bolts with grade 8 bolts as the existing bolts were a bit rusty. After I took it apart I started thinking about welding the center tube plates to the frame brackets in an effort to strengthen the receiver. I'm not looking to increase the GVW of it, I just want to make sure that the bolts don't shear and leave my tractor and trailer in a ditch someplace. I contacted Reese and they only use grade 5 bolts so just going to grade 8 will make it stronger but I tend to overthink and over do everything.

Am I better off to leave well enough alone and just go with the grade 8 bolts or would bolting it together then welding the crosspiece plates to the frame brackets be a better way to go?

I'm going to post this on the welding thread too for all the welding experts to comment on.

Thanks

 

[Diamondpilot]

I don't think it will hurt either way.

Now if it were me I would save that hitch for another project, buy the Proper Curt Hitch for your truck, and save the headache and expense of painting and new hardware.

Curt makes the best hitches with the best finish in the industry. Putnam is good also.

Chris

 

[Scott65]

X2 on the Curt hitches.

I couldn't say for sure on the hitch you have. I would think that the attaching points aren't the weakest points of that system, so you may not gain much benefit. But you might add a lot of hassle later on if removal is necessary, possibly to upgrade to a bigger hitch, idk. But for what it's worth, I've installed a lot of gooseneck hitch kits on diesel trucks and had customers (and done it myself) pull over 20k pounds. Look up curt or B&W hitches, they are bolt on. Looking at them, you would think they would support less weight than that kit you have for your bumper pull. But I've never seen one fail

 

[Teikas Dad]

Thanks guys. I posted this on the welding forum too and got a lot of good feedback. Shield Arc posted a graph of bolt strengths and if I can break the grade 8 bolts that I've got then I've got bigger problems. I think one of those bolts could lift the entire truck based on the ratings. I think I'm going to keep it simple and stop overthinking and bolt it all together again with the grade 8 bolts.

The truck is just a weekend go to the dump, home depot/lowes and eventually to tow the tractor trailer around a few times a year. If I was working the truck, tractor and trailer on a daily basis I would take your advise and upgrade the hitch but I think for the amount I'm going to use it I will be OK.

Thanks again for the input.

 

[redprospector]

In your application I don't think it will make any difference, but the shear strength of a grade 5 bolt is greater than that of a grade 8. You are correct that the grade 8 has a far greater strength than grade 5 as far as breaking strength, and could probably easily lift the whole truck. But in this application you aren't pulling straight out on the bolts, you are fastening two plates together and will be putting a load on them in a shearing fashion.
You are also correct in saying that if you break the grade 8 (or grade 5) bolts that you've got bigger problems. Either grade you choose will hold your hitch, so happy towing. :thumbsup:

 

[Reverser]

In your application I don't think it will make any difference, but the shear strength of a grade 5 bolt is greater than that of a grade 8. You are correct that the grade 8 has a far greater strength than grade 5 as far as breaking strength, and could probably easily lift the whole truck. But in this application you aren't pulling straight out on the bolts, you are fastening two plates together and will be putting a load on them in a shearing fashion.
You are also correct in saying that if you break the grade 8 (or grade 5) bolts that you've got bigger problems. Either grade you choose will hold your hitch, so happy towing. :thumbsup:

I'm sorry, but that's incorrect.
Grade 8 is much stronger than Grade 5 in both tensile and shear strength.

 

[JasG]

I'm sorry, but that's incorrect.
Grade 8 is much stronger than Grade 5 in both tensile and shear strength.

That's what I have always found to be the case also.

Some very good information in this link, I only copied a very small section.
Grade 5 vs Grade 8 Fasteners | TineLok

Mark’s Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8’s as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, someone can figure out how much load that fastener can carry in both tension and shear.

 

[redprospector]

I'm sorry, but that's incorrect.
Grade 8 is much stronger than Grade 5 in both tensile and shear strength.

Hmm. Well, I'm not infallible, and can always learn a thing or two.
I have experienced failures in equipment with both grades in an application requiring shear strength where the grade 8's would simply be gone, and the grade 5's would be bent sharply. But if the books say they're stronger, I'll stay on the safe side and agree.

 

[crazyal]

You're not just putting sheer force on the bolts. The cross tube will want to bow in the middle since that's where the force is. This will put both sheer and tension on the bolts.