Bumper Pulled Off Bronco

[geargeek]

Starting in the video below at 15:50, apparently a broken Bronco was being towed in by a Raptor, and at some point the Raptor gave it a hard yank, completely detaching the aftermarket front bumper, winch and all.

My observations from studying the video:

• the driver's side frame horn mount is completely separated from the frame horn
• the passenger side frame horn mount is intact, but the bumper separated from the bolts and flat nuts
• the aftermarket bumper does not use the factory nut plate behind the frame horn mount, but rather bolts from behind to attach to flat nut inserts on the bumper
• the aftermarket bumper has two recovery points which appear slightly inside of the frame horns (not inline)
• there are no frame horn reinforcements installed

My speculation (I could be wrong):
I expect a tow rope was connected to one of the recovery points, so when one side failed the other quickly followed. From the way the metal was bent on the outer part of the driver's side frame horn (16:33 in video), it appears to me that the passenger side bumper connection failed first, causing an extreme twisting load on the driver side frame horn mount.
Edit: A witness said they used a flat strap to connect to both recovery points, so I was wrong about that part.

My opinions and takeaways (again, I could be wrong):

• drivers should have discussed no hard hits (not sure if tow rope was kinetic, but still)
  • Edit: A witness said it was a flat strap, not kinetic; and confirmed it was a very hard hit.
• a bridle connecting to both recovery points might have prevented the issue, spreading the force more evenly
  • Edit: A witness said they used a ~30' strap to connect to both recovery points, so the bridle didn't help.
• the aftermarket bumper's method of attachment to the frame horn mount does not appear very robust
• frame horn reinforcements should have been installed for a bumper-mounted winch, but probably would not have helped in this case, as it appears the bumper failed first (although he'd maybe only have to replace a bumper and not weld a new frame horn mount).

Of course, Matt's team got him out (with a bridle to a-arms connected to a kinetic rope and no hard hits).

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[orion]

Unless your bridle is long, 30 degrees or less, it actually puts more stress on each tow point. I just learned this the other day...



Yes, hard hits are stoooopid, never do it and frame horn reinforcements are a must unless your wheeling curbs at the mall. Just do them in case you need to be recovered, not just for a winch I would say...

 

[geargeek]

Unless your bridle is long, 30 degrees or less, it actually puts more stress on each tow point. I just learned this the other day...

To clarify, a bridle of any length/angle puts more inward stress on each tow point, but it still considerably reduces the in-line and total stress compared to not using a bridle unless your angle is 120 degrees or greater.

Agreed you should ideally use the longest possible bridle to minimize the inward pull. The big question is how much inward pull the recovery point can withstand (certainly less than an in-line pull).

I do like Robert Pepper’s rule-of-thumb of trying to keep the included angle at 20-30 degrees or less. But it’s still guesswork with no published in-line vs. inward stress rating data on the recovery points.

My Bronco’s front and rear recovery point spacings are 31 and 43 inches, respectively. In the table below, I calculated the bridle lengths required to achieve various angles for those spacings.

The table also shows the forces for an 8,000 lb recovery (perhaps what might be required for a slightly bogged, fully loaded 6,000 lb Bronco). If I was using my 10 ft tree strap as a bridle attached to the rear tow hooks, I’d be at 40 degrees angle, and I’d have 4,257 lbs total force on each recovery point, with the inward component of that being 1,456 lbs. If I instead decided to pull from just one recovery point (no bridle), I’d have 8,000 lbs total force on the one recovery point, but 0 inward component. In that case, I’d personally still go with the bridle.

(Note that if just pulling from one tow hook, it's never going to be a straight in-line pull - if the car rotates just 20 degrees during the 8,000 no-bridle scenario below, the outward force on the tow hook would reach the same 1,456 lbs as using my 40 degree bridle. A bridle pull is also more stable and balanced.)

 

[swamp2]

...apparently a broken Bronco was being towed in by a Raptor, and at some point the Raptor gave it a hard yank, completely detaching the aftermarket front bumper, winch and all.

My observations from studying the video:

• the driver's side frame horn mount is completely separated from the frame horn
• the passenger side frame horn mount is intact, but the bumper separated from the bolts and flat nuts
• the aftermarket bumper does not use the factory nut plate behind the frame horn mount, but rather bolts from behind to attach to flat nut inserts on the bumper
• the aftermarket bumper has two recovery points which appear slightly inside of the frame horns (not inline)
• there are no frame horn reinforcements installed

My speculation (I could be wrong):
I expect a tow rope was connected to one of the recovery points, so when one side failed the other quickly followed. From the way the metal was bent on the outer part of the driver's side frame horn (16:33 in video), it appears to me that the passenger side bumper connection failed first, causing an extreme twisting load on the driver side frame horn mount.

My opinions and takeaways (again, I could be wrong):

• drivers should have discussed no hard hits (not sure if tow rope was kinetic, but still)
• a bridle connecting to both recovery points might have prevented the issue, spreading the force more evenly
• the aftermarket bumper's method of attachment to the frame horn mount does not appear very robust
• frame horn reinforcements should have been installed for a bumper-mounted winch, but probably would not have helped in this case, as it appears the bumper failed first (although he'd maybe only have to replace a bumper and not weld a new frame horn mount).

Thus is the 2nd or 3rd complete detachment I've seen of an aftermarket bumper. Gives me very little confidence in them. Failure points need to be engineered purposefully and sequentially from lines to shackles to bumper hardware/hooks/loops and finally bumper mounting. It obviously depends on appropriate lines and shackles, but there is just no way the whole bumper should come off like this.

 

[Tofudude]

MORR recovered DV8's own Bronco and just towing it bent the bumper mounts. (DV8 Bronco) ARB included some hefty brackets to reinforce the bumper mounts. I would hope DV8 would have included something similar by now.

 

[monsterfd]

This is pretty overblown. This guy didn’t use bumper reinforcements. He was at united by bronco, so was I. I have a dv8 bumper and a winch and did a ton of recoveries no problem. I used ADD reinforcements. I’ll post videos of my rescues later.

 

[TLO]

Unless your bridle is long, 30 degrees or less, it actually puts more stress on each tow point. I just learned this the other day...



Yes, hard hits are stoooopid, never do it and frame horn reinforcements are a must unless your wheeling curbs at the mall. Just do them in case you need to be recovered, not just for a winch I would say...

I'm rock climbing circles, they call this kinda setup the European death triangle. Lol
At 45 degrees or so, there is a multiplying force pulling the sling/anchor point towards each other...
It's easy to visualize if you just strung a line straight across the tow hooks and then tried yanking on the rope from the center.

 

[TLO]

This is pretty overblown. This guy didn’t use bumper reinforcements. He was at united by bronco, so was I. I have a dv8 bumper and a winch and did a ton of recoveries no problem. I used ADD reinforcements. I’ll post videos of my rescues later.

I have a stock bumper but an RC high mount winch.... I definitely want to add the reinforcements to my setup.
Does the bumper need to be removed to drill and mount them?

 

[Snacktime]

Lot of it was the angle pulling downward on the mount. Then add in the additional leverage of how much farther out the recovery point is from stock. It's just a combination of things that even frame stiffeners might not have even worked.

I am planning to redo my winch setup here shortly. I am noticing my frame horns flexing which means they will eventually break off.

 

[CitrusBronco]

I agree with your assessment @geargeek
Poor bumper attachments, compounded by poor tow/recovery technique.

I think it’s important for more people to see this, maybe change your title to just “Bumper pulled off Bronco.”

This is what is worrying about the aftermarket bumpers. They don’t build them for strength, just looks. Most have poor frame attachments and even worse the built in recovery points are weak.

 

[geargeek]

I think it’s important for more people to see this, maybe change your title to just “Bumper pulled off Bronco.”.

Thanks good suggestion. Title changed.

 

[MillerAndCheeto]

I have a stock bumper but an RC high mount winch.... I definitely want to add the reinforcements to my setup.
Does the bumper need to be removed to drill and mount them?

Yes, the bumper needs to come off first.

 

[geargeek]

This is pretty overblown. This guy didn’t use bumper reinforcements. He was at united by bronco, so was I. I have a dv8 bumper and a winch and did a ton of recoveries no problem. I used ADD reinforcements. I’ll post videos of my rescues later.

What exactly is overblown?

FYI the person who lost the bumper was being recovered from the bumper’s recovery points, not from winching.

 

[monsterfd]

What exactly is overblown?

FYI the person who lost the bumper was being recovered from the bumper’s recovery points, not from winching.

The welded recovery points are on that bumper, the bumper is bolted to frame horns. You recover to anything bolted to the bumper without frame supports will tear the frame horns off. It’s the weakest link in the chain

 

[geargeek]

The welded recovery points are on that bumper, the bumper is bolted to frame horns. You recover to anything bolted to the bumper without frame supports will tear the frame horns off. It’s the weakest link in the chain

Thanks for clarifying - I think everyone that posted in this thread agrees that frame supports should be used with that bumper.

From the video evidence, the flat nuts definitely pulled out of the bumper on the passenger side - this could have started due to bending of the frame horns before they failed, or it could have just been very high twisting forces on the bumper. With that bumper, the recovery points are offset and in front of the frame horn connection, so any recovery force is going to create a twisting force on the bumper and frame horns. By comparison, the stock bumper has the recovery points directly attached to the frame horns, so they will withstand higher loads (even without reinforcement).

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