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Ideas for K5 trailer hitch mounting/improvement

dyeager535

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For those that didn't read about it, my trailer hitch sheared where it bolted to the frame (pic at the very bottom of this post). So I need to take it off to repair and improve it.

I need ideas on what to do regarding bolting the hitch to the frame.

Primary goal is to be able to remove the hitch without having to mess with the fuel tank. Secondary is to make sure this doesn't happen again.

I took the tank out last night, and the hitch bolts are rusty enough that removal is proving to be...painful. The tight quarters don't lend themselves to being able to get any real tools on the bolts/nuts, and even then, the threads are fairly rusty, plus I used locking nuts. So it's a lot more work than it should be. Anyone that has dealt with a hitch that bolts up to the factory holes probably remembers the one rear bolt on each side that is positioned in a cutout in a frame cross piece, and the forward bolt that has rivet heads directly next to it. So far the breaker bar partially works, and where it doesn't, the angle grinder does.

My plan is to box this frame, so access isn't going to get better. My immediate thought is to weld mild steel bolts in place to act as studs. I wouldn't be surprised if frame thickness isn't playing some issue, I've got enough steel around that I could probably make a plate that sits on top of the frame (inside the C-channel) that the bolts could be welded to, to spread the hitch load between the front and rear bolts. This hitch is just four tabs for each bolt, there is nothing tying the front and rear bolts together except the vertical plate that drops the hitch low enough to clear the bumper. Zinc plated nuts to try and at least minimize corrosion via the nut itself? That and/or use a generous amount of loc-tite to reduce the likelihood of them loosening up, but also to try and prevent corrosion as much as possible.

I know my drawing skills suck, I'll try and explain the below image, which is not to scale obviously. The gray areas on the left image (Rear) are what I plan to gusset. You kind of have to imagine the "outside" gusseting based on the right image (Top Down)_...the four bolt tabs would be gusseted on either side of each bolt hole. The inner gusseting would be a single piece since the gas tank is in the way otherwise. The only thing locating the cross bar tube at this point is the 1/8(?") steel plate on either side that drops down from the bolt tabs. I'm assuming based on the way this hitch broke, side load is what fatigued the metal where the bolt tabs transition to the vertical, thus why I think the gusseting would add a bit more strength to prevent it again. I also think (as clearly shown in the below photo) the cutouts for the rivets make the back bolt tabs the weak point. On the "Top Down" image, the dashed lines are what I'd make as a steel plate to go inside the frame, that the bolts could be welded to, hopefully spreading the weight along more of the frame.
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And to give an idea of what it looked like after the break/what I'm dealing with in terms of hitch construction and frame design:
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How much does a new hitch cost? (you know, how many years will it take to fail again?)

I like the idea of gussets, but you'll have to check in person what will actually clear and what won't. Also, the longer you can make the mounting sections, the better (front to back). I also like the idea of plates inside the frame rails (assuming you can place them there without having to pull the tank), and bolts welded to it means no more reaching inside the frame and any rusty thread issues are where you can get to them. However, isn't this a curvy section of frame rail with rivets and stuff in the way? Maybe you could get away with 2 shorter sections, as long as they're big enough they can't spin.

As for getting it apart, can't you just take a cut-off wheel to all of the bolts from the bottom?
 
New hitch is about $200 it looks like. You aren't wrong...most people would be ok with just replacing it and moving on. But if this one failed, and it's seen pretty light and very infrequent use, it seems likely that if my usage in the future ever changes, the problem may manifest itself quicker. Plus, it's kind of a fun project lol. I like being able to work on things that aren't still attached to the truck. So much easier when the part is on the floor and I can grind cut and weld without having to contort my body. Gives me a chance to grind and repaint the hitch too.

Strangely, compared to the interference I expected to find, it seems that the gusseting should be pretty straightforward and clear of obstructions. I have to verify behind the tank, only interference I can potentially see would be the seam on the tank.

The rearmost bolt holes will be a challenge if I make a plate. The crossmember will result in needing to have it narrow or slot the plate to clear for sure, but the area is a bit wider than the bolt head, so I should be able to make something fit.

I thought the frame had way more angle in it than I saw last night (I clearly recall the rearmost bolt tabs being angled at a decent angle, a difference from trucks) but maybe the frame has suffered some trauma. Once I get the hitch off I'll look at those rearmost tabs. I don't see alignment issues with the bumper so I don't think anything frame-wise has shifted.

I think at a minimum I'll grind the exposed threads off the remaining bolts. The front bolts as shown in the pic are kind of tight to get a grinder in, but the head is easily accessed from inside the frame, so the breaker bar works here. The rear bolts are clear access from the bottom, but with the bumper in place, as you ascertain from the photo, the crossmember makes it really hard to keep a socket on the bolt head once you start loosening it up, since both hands are on the breaker bar. Of course I broke one side loose before thinking I'd have issues, would be much easier to grind with the bolt still tight.
 
Were you using the factory tow hitch? It mounts in four places on the frame.

No clue if it was OEM/factory or an aftermarket one as I pulled it off a rig years ago, but it *used* to mount in four places. I trimmed that down to two. lol

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No? Whats the factory design look like?

I'll have to look closely, I think it's got stamped in data on it.
 
Definitely modified, Dad put those "ears" on to hold mudflaps so the trailer didn't get covered in mud when towing. And I welded the 7 pin outlet to it.

Few glimpses I see in the early 80'sChevy Brochures look like it COULD be factory. But those aren't always accurate.

Tenth to last page here, for example: https://ck5.com/forums/threads/1984.324334/
 
I pulled the factory hitch from a late 70s trailer special K5 Blazer and it was a direct bolt in for my non trailer special 78 K5. I didn't even need to drill the frame.
 
Definitely modified, Dad put those "ears" on to hold mudflaps so the trailer didn't get covered in mud when towing. And I welded the 7 pin outlet to it.

Few glimpses I see in the early 80'sChevy Brochures look like it COULD be factory. But those aren't always accurate.

Tenth to last page here, for example: https://ck5.com/forums/threads/1984.324334/
The available hitch accessories were dealer installed, aftermarket parts. No "factory" receiver hitches were designed by GM in the squarebody years. Also, be sure you are not looking at the suburban accessories. They are not the same as the Blazer/Jimmy.
 
The available hitch accessories were dealer installed, aftermarket parts. No "factory" receiver hitches were designed by GM in the squarebody years. Also, be sure you are not looking at the suburban accessories. They are not the same as the Blazer/Jimmy.

So how did that work? All the GM images I'm seeing through the 80's SEEM to show the same design hitch. Did they contract with say, Reese, to be the sole provider for trucks that got trailering packages?

Page 6 here looks the same, but to be fair, low resolution and a fair distance away https://ck5.com/forums/threads/1988.324329/
 
However, as far as why it failed in the first place, that was completely due to fatigue. The ears were bending back and forth over a long period of time until a crack started and slowly propagated all the way through the tab. This could be made worse if the hardware was loose.

Gusseting will help prevent that type of failure and it is only needed between the outer ear and vertical plate. No need for it at the square tube. However, I would not waste time on repairing that hitch. The weld is only 60-70% as strong as the base material it is attached to and it will not be something you can easily return to original strength, even with gussets, without cutting off the plate completely and rebuilding it with a new plate.

I would buy a new hitch and add gusseting as needed.
 
So how did that work?
GM would write a specification and different manufacturers would provide accessories to dealers based on region is the way I understand it. That is why accessories look similar but slightly different in different parts of the country. It is also the reason Dodge and Ford have very similar accessories from their dealer installed options.
 
My trailering special came with a home made hunk of iron the went under the fuel tank. I put a Curtis on the 77 burb.
 
I would buy a new hitch and add gusseting as needed.

I unfortunately don't have the time for that. But if it's better to replace with new, I can use this one to get the inner plate/bolts mounted so it can be easily replaced later.
 
I've gotta get it bolted back on tomorrow so I can move some stuff around. Doesnt have to be perfect, just need to get it back in and the truck up and running. But if I get the bolts all figured out, swapping out a new one later will go a lot easier.
 
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