CAUTION!!: Double Check Trailer Hitch

[rving2015]

Thanks Bigben for the update.

[DocMike]

BigBen,

I have studied your picture and it is hard to believe that could happen to metal. I have yet to start towing but your warning has me checking. I have a question, did the metal that "tore" was it the metal that makes up the extension (part 12 and 13 in the attached schematic) or the actual chassis frame that the extension bolts onto?

Vegas Chassis.pdf

Hopefully the attachment will open as it is the chassis schematic for my Vegas 24.1.

Doc

[bigben]

Michael - it is the extension. Spent some time at a local business that does mostly fabrication for heavy trailers and custom hitches. The business was very helpful. The term tore is basically what they used. They had some takes on how and why but it is preliminary.

Working with Morryde to have these professionals affix the repair. Local guys will give me a better idea of how this might have happened. Waiting now to hear from Morryde to see if I've got to pursue an uglier method to have these guys do the work. They are the right ones to do the repair.

I'll keep everyone updated.

[DocMike]

BigBen,

Thanks and good luck.

Doc

[bevedfelker]

Looking at the picture I too have a lot of questions. I sure would like to hear the local business theory on how and why it tore.

I took courses at Penn State in my Mechanical Engineering program in Strength of Materials and Metallurgy. In the Air Force I also attended the University of California Aircraft Accident Investigation program. All these courses had extensive laboratory time especially in testing various metal alloys under both compression and shear stress.

Every sample I've ever seen that fails in shear had fairly ragged tear out. The picture at post #1 looks more like what you would expect when a bad weld at a joint fails under shear. The shear tear looks very smooth and even.

In the question DocMike asked if this was a failure of the extension plate number 12 or 13 in his attached drawing, I would suspect that the plate was made by welding two smaller plates together. The welds then could have been ground down, primed, and painted. Looking at it would have looked like one continuous plate. If the weld was defective I could see it failing in stress through the bad weld yielding a very smooth stress tear. It makes no sense to me that a continuous plate failing in stress would have torn so smoothly through its lattice structure. Smooth tears like that are more common in failures through a joint.

[JamieGeek]

Crap! I need a bolt! Looking at the diagrams DocMike posted and my pics: I had mentioned that my bumper appears to be held on with only 3 bolts (2 on one side and 1 on the other) it would appear to me that those 3 bolts also hold the hitch on. e.g. I need that 1 bolt on the other side.

My reasoning: Look at the diagrams, specifically items 8, and 9 on the first page. These appear to be right-angle brackets that the hitch is bolted to (the three bolts on the diagrams(14) look like they are the three bolts holding the extension to the frame). Next time I'm at the camper (tomorrow) I'll have to look closer at that arrangement.

Wow and we've pulled a car now for over 2000 miles...

[bigben]

bevedfelker - gotta begin by saying, my surgery was knee surgery so it is very difficult for me to get down and look. But I believe this is a formed channel that bolts on top of the original frame as an extension - no welds. The local company tells me that the "extension looks in good shape as it is bolted onto the orginal chassis". That is why the tear - and that looks to be the right descriptor - is a bit of an anomaly.

As the local technicians work on correcting the issue, I'll keep everyone updated. For now thought - Check, Double Check and Triple Check.

[bigben]

JamieGeek - I am not sure from looking at the PDF and your pics. I'd give the folks at Thor Warranty/Service a call and ask the question directly. If they cannot answer to your satisfaction, I'd ask to be referred to Morryde.

[bevedfelker]

Ben -- so again. What part failed? The extension, the Ford frame or the side of the hitch. When I talked about welds I did not mean welding the extension to the frame. What I meant was they did not have an extension that was long enough. So they took two piece of channel, laid them end to end on the ground, and surfaced welded them together. Then they ground down the welds, primed and painted it, cut it to length, drilled the mount he's, and bolted it to the Ford frame.

But when you said the company said the extension looks in good shape so that sounds like it is not the extension thst tore -- now it sounds like it was the Ford chassis, or the side of the hitch that bolts to the chassis.

[bigben]

Ed - very specifically it is the frame extension that "tore". As best I can determine, the frame extension is a formed piece of steel channel that sits over and is bolted to the original Ford chassis. The reference to the extension looking good means that the extensions look correctly affixed to the Ford chassis. The part that the local company will help with is determining what sort of stressors caused the tear.

[Chance]

Originally Posted by DocMike

BigBen,

I have studied your picture and it is hard to believe that could happen to metal. I have yet to start towing but your warning has me checking. I have a question, did the metal that "tore" was it the metal that makes up the extension (part 12 and 13 in the attached schematic) or the actual chassis frame that the extension bolts onto?

Vegas Chassis.pdf

Hopefully the attachment will open as it is the chassis schematic for my Vegas 24.1.

Doc

Thanks Doc, I had no problem opening attachment on an iPad.

It's really good information to have, and somewhat surprising too. I did not expect they started with 158-inch wheelbase and stretch it 30 inches instead of starting out with longest WB chassis and stretching less. I guess it makes sense to lower costs, and simplify rear.

Would be better if Ford offered longer versions of these E-Series chassis. They make the F53 motorhome chassis in many more lengths.

[bevedfelker]

Ben -- ok. That makes more sense. So somewhere on the extension the channel tore, even though the channel looks like it was correctly mounted to the Ford chassis. So the tear in the extension channel is not through any of the mount holes. Is that correct?

And looking at the picture it looks like one of the legs of the C-channel tore away from the web. Normally C-channels are rolled using a die. The curved fillet between the legs and the web is normally the strongest part of the channel (due to the heating and tempering). I'm thinking this channel might have fabricated by taking three pieces of steel plate and welding two pieces to form the legs on to the piece that becomes the web. This would certainly explain why the leg would tear from the web so evenly (if one of the welds was not a good weld).

[bigben]

Ed - once the repair is done we'll have confirmation but based on the local company experiences (and they have been fabricating and working on frames at least 30 years), the only time they have seen this type of tear is from a strong down force on the end of the hitch. Versus a rear pull on the hitch. When the tech gets to work on it, Morryde and we will have a better understanding.

Specifically, the tear is on very end of the extension channels where the hitch is attached. The local company thought the frame and frame extension bolt on looked right.

[bevedfelker]

That downward force is exactly what I was thinking too. There is no way force being exerted toward the rear could have causes that leg to fail on the channel. It had to be downward and there had to be something wrong with the joint between the extension's leg and web.

[Chance]

Originally Posted by bevedfelker

Ben -- ok. That makes more sense. So somewhere on the extension the channel tore, even though the channel looks like it was correctly mounted to the Ford chassis. So the tear in the extension channel is not through any of the mount holes. Is that correct?

And looking at the picture it looks like one of the legs of the C-channel tore away from the web. Normally C-channels are rolled using a die. The curved fillet between the legs and the web is normally the strongest part of the channel (due to the heating and tempering). I'm thinking this channel might have fabricated by taking three pieces of steel plate and welding two pieces to form the legs on to the piece that becomes the web. This would certainly explain why the leg would tear from the web so evenly (if one of the welds was not a good weld).

Ed, if that channel was formed from a flat plate, it was most likely not heated or tempered. They never do that. For that thickness plate (about 1/4-inch thick or less) it's bent cold. And that's it. Normally nothing else is required. It's very common. I had it done all the time.

We are most likely talking about mild steel with 36,000 PSI yield which is also what the frame of most F53 chassis are made of.

[Chance]

Originally Posted by bevedfelker

That downward force is exactly what I was thinking too. There is no way force being exerted toward the rear could have causes that leg to fail on the channel. It had to be downward and there had to be something wrong with the joint between the extension's leg and web.

A downward force is just one way to cause this kind of failure. Indeed a heavy trailer tongue weight is one way.

But as I stated before in a previous post, you can also get a downward pull at the end of the extension channel every time the dinghy tries to run into the motorhome before its brakes kicks in and reduces the stopping force -- which can be quite high.

[bigben]

Chance - you guys have now bounced way beyond my limited understanding. Based on my conversations with the local company and the service manager from my purchasing dealership, this issue is rare. But a rare problem of this nature definitely pops up on the list of things to visually inspect.

Update on the repairs - going ahead next week. Yeah. More to follow.

[bevedfelker]

With it being channel, that's hard to bend 2 90 degree bends on a brake. That's why I thought the legs might be welded. And the tear sure looks like what you would see on s bad weld.

[DocMike]

Wow, this is getting complicated.

Doc

[bigben]

Doc - my recommendation for you still stands and is simple. I don't know the engineering piece but I understand the make it right/prevention piece. Visually inspect the hookup. I wish I would have known about the possible failure point earlier myself. Then I could have eliminated a risk early on.

And I still love my Thor Challenger. So far everyone has stood up to be counted for the repairs.