Bent my Rapid Hitch...

Well this is a new one...

I moved my rapid hitch over from '13 to my '21 and discovered it wouldn't seat in to the receiver hitch.




Perplexed and fearing the receiver had been smooshed in some un-disclosed accident, I tried another ball mount to discover that it fit just fine. Phew! Thought I was gonna have to have a little chat with somebody..

So I pulled out a straight edge to examine the rapid hitch shank with some interesting results...

Bottom Side



Top Side



It would appear that the shank has taken a bit of the bow from the last few years of service - enough that it won't fit in to a newer receiver hitch. I sent an email to Andersen to get their thoughts on it. Might be time for a new receiver on the '13...

 

Dang. What do you tow with that hitch? What’s the hitch rated for?

 

The hitch is rated for 10,000 lb/1500 lb tongue. I know they guys that designed them and manufacture them, and they handle much more weight than that, but that's the official rating. The last couple of trailers I pulled with it were pretty tongue heavy; one was a 24' enclosed for a friend that had to be loaded a certain way, making it much more tongue heavy than I would have liked. The hitch has seen some use, for sure, and the truck still handled it with aplomb.

At first, I suspected the excess tongue weight as the culprit, but then I was reminded of this general piece of material science data:



Basically, steel will weaken over time with cycles, but eventually hit an endurance limit that it can endure virtually indefinitely, so long as that stress placed on that member doesn't exceed the endurance limit.

Aluminum, however, has no endurance limit and will continue to weaken over time with cycles, eventually reaching the point at which the stress it endures has decreased so dramatically that it fatigues and fails.

I wonder if the hitch has seen enough use with enough heavy loads that the last few heavy trailers have breached the stress limit of the material and it suffered permanent deformation as a result.

 

Now thats some useful knowledge right there. Also explains how a some of our steel hitches on the farm still perform after so many decades

 

You didn't fatigue the aluminum and I doubt you loaded a trailer heavy 100K times or more. General SN curves are built from fully reversed stress applications. For a hitch, you aren't fully reversing the tongue load. There's a distinction between mean and alternating. The difference in damage due to both vary drastically. Also, fatigue-based aluminum failure will show with micro surface cracking as the dislocation density accumulates.

You somehow overloaded it beyond its yield. Maybe that misloaded car hauler took a good smack on a pothole, you dropped something heavy in the trailer at the front causing a decent dynamic spike, etc. My guess is you backed a trailer into a grade.

 

The labs we have are pretty sparse with metrology gear. Most of our testing equipment is purpose built for mechanical/fatigue based standards. The only thing worth testing on this hitch would be hardness. Sadly, the machine I bought over a decade ago was damaged during a move and now out of calibration.

@blenton could check with a nearby uni to avoid shipping to validate if the yield had actually dropped. The other easy thing would be to hit it with some dye pen to look for surface cracking.

 

Since I went full mat'l science mode in here, I'll mention that fatigue really becomes a thing when assemblies use aluminum welding. Those structures are near the top of my list for most annoying to develop because the welds/joints require a lot of attention if you don't want your shit cracking apart.

 

So that's what I'm trying to suss out - for curiosities sake and general knowledge more than anything. I got my monies worth out of the hitch and sent pics to Andersen - not to try and get it warrantied, but to get their opinion on it.

The hitch has undoubtedly been overloaded on several occasions throughout its life. Certainly no disputing that. I don't recall numbers off hand, but the guys I know that work at Andersen told me it has quite the FS built in to it; many of them grew up on farms and understand the mentality 'if it fits it gits!' It's also been on the truck for 200k miles, about 1/4 to 1/3 of that towing, rattling around on corrugated dirt roads and potholed streets. I do tow on dirt roads as well, and don't really dawdle... I'm curious how much (if any) of the failure was induced by the hitch rattling around with and without the trailer. I realize that it's not being fully cycled going down the road as you would in a laboratory, but if the hitch is banging around, it's going from loaded to unloaded to loaded again.

The reason I replaced the hitch in the first place is that it became very rattly. The shank rattled in the receiver, the mount rattled on the shank, and the ball rattled in the mount. I bought some replacement pins to try and salvage it but realized it was beyond it's service life. So I've had a different hitch on the truck for a few months, but needed to pull one of my little 2" ball trailers with a different truck and grabbed this one off the shelf to discover the bent shank.

Doing any sort of testing on it would be interesting to me. Maybe I'll put some Dykem blue on it to look for cracks, unless there's something better/easier/more accessible. Else, I'll look for a testing facility to test the hardness. I'm trying to think of someone local that would do that for me aside from the universities.

Bring on the material science! It was one of my favorite classes in college that I had planned on pursuing. I appreciate the insight and understanding that I simply don't have. I'd be interested to hear your take on aluminum trailers; my workhorse is a 7x16 aluminum enclosed. My main impetus for purchasing it was the fact that it had almost as much payload as a similar trailer with dual 5k axles, but still on dual 3.5k axles. And where I'm at, it's cheaper to register being under 2k lbs unloaded.

 

Agreed. This bent hitch should illustrate that point rather well. On the plus side, Toyota built one heck of a truck.

Mitigating this issue moving forward...

- First thing is I told my buddy I'm not pulling his stupid trailer any more - at least not if he keeps loading it like that. The two issues with his setup are: the trailer has a dovetail, so hardly anything gets loaded on that sloped rear floor, pushing all the weight between the axle and tongue. For a gooseneck, I'd be fine with that. For a bumper pull, no way! The second issue is understandable in principle: he knows that too little tongue weight is a bad thing, so he loads nose heavy on purpose so as to avoid sway. What I've tried explaining to him is that the rear axles are so far back on the trailer that he could load evenly nose to tail and still have a heavy tongue bias.

- Second thing: I purchased a weigh-safe hitch. Actually, I purchased two weigh-safe hitches, but one of them is well machined garbage. I ordered an Adjustable Weigh Safe Aluminum hitch but it went on backorder for a few weeks. So they had the Aero-safe hitch on sale, which is an all steel setup with a lower tow rating (but perfectly adequate for normal tundra towing) that I could throw on the wife's rig when I was done with it. It appears beautifully machined and well built. Unfortunately, they should have named it the Rocky Mountain Rattler hitch; the shank rattles in the receiver (the receiver that the old Rapid hitch wouldn't fit in to), the mount rattles on the shank, and ball wobbles in the mount, and they use a 2" to 2 5/16" clamshell adapter that ALSO rattles. I literally haven't pulled a single trailer with it, and just put it back in the box. Most folks probably wouldn't care, but since I'm not sure if or how much the loose fit affected the rapid hitch over time, I chose to forgo the Aero hitch.

While waiting for the Aluminum Adjustable Weigh Safe to show up, I picked up a Curt forged adjustable hitch, and another Andersen Rapid Hitch to try out. The Curt is nice for a few reasons - it is forged steel (or forged chinesium) and has a rubber damper to mitigate the noise from the mount to shank interface. It's stout, but only has one shank depth and pushes the ball a little further from the bumper. But after only a couple of months of wintry muck, it looks beat on.

The Andersen is still shiny and polished, and lets me draw the ball in closer to the bumper. The downside is, my tailgate hits the trailer jack. Luckily, on most of my trailers, I've installed a Ultimate Trailer Jacks that let me drop the jack down and out of the way.

The Aluminum Weigh Safe showed up a little while ago, so I'll pull it out of the package and see how well it fits.

- Third - and this is a small thing - I've installed an anti-rattle bracket on my hitch to try and keep the shank from rattling up and down in the receiver. I know it doesn't do a thing in regards to overloading a hitch, but it keeps things quiet, and will hopefully help prevent some of the gouging seen on the last hitch from the mouth of the receiver.

- Fourth - I have an Andersen WD hitch that we use when pulling the camp trailer with the sequoia; I purchased some extra brackets for it. The issues is the setup is that the brackets don't always fit on utility trailers, but I can make them work if I shorten the chain on the hitch itself. That decreases the lever arm, making the WD action less effective, but it is an option.

 

This is what I was getting at about mean v alternating. In the basic premise, you aren't wrong, you are cyclically loading it when it slaps around. But in actuality the only weight is the weight of itself, and the resultant stress on the shank is minuscule. I'd put that well below its endurance limit.

A better way to think about this would be you apply a trailer, it puts 750lb onto the ball and you go driving down the road. The road dynamics will undoubtedly fluctuate that load, but this may be 750 +/- 50lb (I'm making up numbers). The shank stress from the 750lb apply and removal is quite high, therefore the damage accrued is far more of a bite into the damage tally (this is just a metric of 0:new --> 1:failed) than the damage which those 50lb flutters offer. BUT I'm going to stop there because I don't know the material props, I don't actually know the loading, I don't actually know the resultant stress, etc. It's important you realize I'm speaking generally.

I've only ever used that for machining. Unsure if it will actually flow into micro surface cracks like dye pen does. Would guess that it's too viscous. The cracking should be visible to the eye, though. It should look like the surface is getting cloudy.

It's a cool field and where I spent my grad school years. Unfortunately, it's also the field I now use the least.

This could get pretty unruly/lengthy quick. Ha! I'll say this - most people don't understand how to design a welded joint (steel or aluminum). Those mfgs which typically produce steel structures and carry over those steel-minded build principles to aluminum assemblies will generally execute some design aspects incorrectly. If you want a boring read, US20220144159A1 is a patent I put out about optimizing a flatbed aluminum design to mitigate weld fatigue failures.

On the big heavy haul trailers, their spreaders (or stingers, or hydraulic tag axles, or whatever you want to call them) will have a hydraulic release for the times you either back into a grade or come down a grade and flatten out. It's a tremendous moment. And going back to your bent shank, it took a big load to make that happen.

One question - why not get the B&W tow and stow instead of the Andersen loyalty? It's steel.

 

Awesome! I’ll give the patent a read when I have a minute. Like I said, it’s usually very interesting to me even if I’m still grasping at comprehension.

That’s also why speaking generally about it makes sense helps a lot, but makes me want to dig a littler deeper. Your general explanation of the loading scenario makes perfect sense, and your reasoning for putting the stresses below the endurance limit are logically enough for me to follow. I like asking questions in the form of suppositions; if I’m wrong I’m perfectly happy to wrong as long as I learn why.

I looked at the B&W tow and stow several times and am not at all opposed to it. It looks like a great hitch. In fact, I almost pulled one off the shelf last summer when I was at a trailer dealer buying my smaller enclosed. I like the Rapid Hitch, but I like what works more than the brand stamped on a thing. Somewhere in my selection process, though, there was something that put it lower on the list. Either the tongue weight rating for the 2” shank versus was lower (1000 lbs vs 1500 lbs) or the whole assembly had more slop to it. Maybe both. But the lower tongue rating would have been a big factor for my use case and discounted it.

I suppose I should insert some sort of disclaimer here to follow the MFG recommendations for tongue weight, but obviously the truck has no *apparent* issue with exceeding it, even if the attached accessories do have an issue. For the readers out there in tundra land, I’m not trying to debate the limits, but rather show what can happen when you do exceed them. Even if not exceeding the limits, it is nice to have some overkill built in (one of the same reasons I run LT tires over p rated tires). I was happy to discover such a failure and pay for another hitch (or hitches) without incident. I now consider them wear items as they should be.

Concerning trailering and backing into grades - you are absolutely right about that scenario creating a tremendous moment. I’ve seen WD hitches cause frame damage to either the trailer or tow vehicle traversing large v’s or dips that send the tail of the trailer and nose of the truck in the air. Simply supported traditional ball mounts can get beat on pretty hard with the trailer pitched up a grade. I do my best to avoid or mitigate those situations, but they are sometimes unavoidable. Last summer I was pulling a virtually identical trailer that I had to back up a fairly steep grade that transitioned from a level road almost without a ramp up, it seemed. But I wasn’t using the Andersen at the time (one of the very few times I had a different ball mount hitched up).

 

My WDH always rattled in my receiver even when it was new until I wrapped some stuff around the shank (not sure exactly what you call it - I got a roll of it from my dad).

 

Tape

 

Wouldn't just normal driving with too much weight cause this issue as well? You are cycling load by hitting bumps in the road.

Dykem won't do it. You need a dye penetrant to be able to get into the cracks.

 

That is one I picked up but haven’t tried yet.

And, yes, I leave the hitch in the receiver almost all the time. I tow frequently enough that it’s more an inconvenience every couple of days to stop, dig out the hitch, mount it up, back up the rest of the way to the trailer, and hitch up, than just back up, hitch, and go. I know it’s not always the easiest on gear to leave them on all the time, but that’s also one reason I went with aluminum over steel. (I’ll wait for someone to pint out the dissimilar metal issue with steel next to aluminum 24/7). Also, in the winter, it keeps the receiver from icing up to the point that I can’t get the hitch mounted.

Tried that. It turns in to a big mess. This what I find to actually work. I’ve used it on my steel hitches but haven’t tried on the aluminum. I’m a little worried it might mar the hitch, but if it keeps it from getting beat up and rattling around, it might be worth it.



https://www.etrailer.com/Hitch-Anti~Rattle/Gen~Y-Hitch/GY28XR.html

Etrailer had their own anti-rattle clip that I might be trying as well. It’s supposed to be easier/tool free to remove to swap hitches.

https://www.etrailer.com/Hitch-Anti~Rattle/etrailer/e38FV.html

 

Looked at the B&W tow and stow again - 2” shank only has 1000 lb tongue weight capacity. That would have pushed it down the list for me.

 

For a Tundra? Don’t think the hitch is rated for more than that is it?

 

Overkill is the order of the day… Compared to the other options I was considering, it had considerably less capacity. Not saying one should or shouldn’t, just that it wouldn’t suffice for me judging by the hitch in the original post.

Edit - forgot to add that according to an email between Toyota and a forum member on a different forum years back, Toyota rates the hitch above a Class 4, which means something over 12,000 lbs trailer/1200 lbs tongue.

 

Gotchya. It's a stout unit, but if those 200lbs are that important, then fair point.

The OEM hitch structure is a thing of beauty. I look at it every time I'm under there and can't find one thing I would've changed.

 

Go back to post #12 and search some of those terms. I bet a few diagrams will help clear up what I was saying.

The thing to remember is the truck has a suspension, as does the trailer, and road inputs are basically consumed by those pieces. These aren't rigid systems. If they were, towing would constantly feel like it does when you slam the brakes when hooked up, take off hard, or hit a giant pothole. What you feel is your ass end weighted down and the two units largely moving in unison (IE low alternating loads). It takes a lot to overcome gravity.

 

That is more or less what I was asking about and I do understand the concepts in the post. I'm trying to wrap my head around certain scenarios and if it would load the hitch more than normal. I guess the example I have in my mind is driving down the road and the truck hits a bump which causes a momentary unloading and than a sudden loading. Is that sudden loading more than just the static load?

 

This is hard to convey over text...

I think you're confusing road dynamics COMPLETELY removing tongue load v a PORTION of the tongue load. Complete removal would unload the suspension entirely, like the trailer was momentarily weightless at the ball. That doesn't really happen as the system is pretty much always preloaded to some degree.

To answer the other portion, yes, dynamic loading can play a role. The term here is impact factor. There's a whole lot that goes into it, but for simplicity and approximate rigid bodies, the difference between splat and bounce can be estimated as 2-3x factors for the input load. Again, the suspension will eat up a lot of that impact energy making the alternating portion less of a damage tally blow.

All of this talk now has me convinced to strain gage a basic drop hitch. To one line summarize: I have a work proj which I made a 50KHz high-fidelity amp to digitize a strain signal and send to an edge filter to capture impulses. Was intending to only capture axle loads but I'll throw a setup onto a hitch when I get back to that proj (won't be soon).

 

Judging by the amount of rattling and banging with my old hitch, I’d be very interested in the results. I’d also be interested to see if the anti-rattle devices make a difference in that area, or if they just reduce the noise. Happy to send one your way when you decide to get after it.

 

I've used several different anti-rattle devices with my hitch mounted dirtbike carrier and some work, some do not. Also, the one that worked well with my 2006 Tundra did not work on my 2020 Tundra.