Dissent Off-road Rear Bumper Tire Swingout Wobble

[Yung4Lo]

I have an early design rear bumper that I bought in 2021 and have some serious wobble when I’m driving. I went back through and made sure all the bolts were still there and that everything was torqued down.

Does anyone else experience this? I did the same shake test to another LC100 that had the same exact bumper and his wobbles the same. I have a 35in tire so maybe that’s why…

Anyone have a solution? The wing stiffeners that attach the wing to the frame seems like the culprit.

Here is a video of the wobble.

 

[hoser]

A video of the bottom and the mounts would be useful. I imagine multiple bolts are loose or something is cracked. Same on both sides?

 

[OEMGUY0720]

The rattle appears to be from lacking rigidity brackets more than the swing arm. I can already imagine how it moves and the noise it creates when you drive it. Any underside rear bracket to frame pictures?

 

[pavell]

Use some thick rubber washers as isolators. ?

Or shove some old cut up radiator hoses up between the area that is rattling ?

 

[NearJetties]

I don’t remember where I saw it but I think it has to do with the tire holder mounting bracket crushing in a bit when trying to tighten. Adding metal sleeve spacers (from McMaster Carr probably) added the necessary rigidity. Don’t quote me on that but I remember seeing that recently and I believe that was the solution

 

[Yung4Lo]

The rattle appears to be from lacking rigidity brackets more than the swing arm. I can already imagine how it moves and the noise it creates when you drive it. Any underside rear bracket to frame pictures?

I tend to agree with you. It actually isn't the noise that bothers me. As a matter of fact, I don't hear it at all because whatever noise it makes is drowned out by my wind noise, Revel cat back exhaust, 4.88 gears, and 35in Falken's.

What bothers me is the significant disturbance I observe through my rear view driving down the freeway/washboard roads. It's most anxiety inducing when it hits resonance frequency.

I reached out to Dissent and they sent me an exploded isometric view of a newer Rev bumper, telling me to torque all my bolts again and to ensure that the wing stiffeners are still there, which they are.

I've marked up the model view Dissent sent me with some comments. Most of the force induced by the tire travels through the swingout and into the hinge bolt, depicted below in blue. I think what's occurring is that the corner of the bumper deflects downwards in the -Z direction (towards the ground) because there aren't enough connections between the bumper and frame. I've highlighted in green the hole locations that bolt to the frame. There are 3x holes on each half of the bumper (left and right) for the bottom of the frame rail -- in the view below, you can only see 2x for the left side, and 1x for the right side, but it's basically just a straight line pattern of 3x holes. So in all, there are 12x holes used to bolt the bumper to the frame.

Honestly, I think it's just a design flaw. I believe the wing stiffeners needed to be bigger with more gusseting. The wing tip as well as the corner of the bumper near the hinge bolt are cantilevered too far out from the nearest bolted interface. I know it's steel, but the geometry lends itself to be more compliant.

I'm not here to complain and criticize, I'd just like to know if anyone's found a simple solution to this problem. It's unnerving watching my 105lb wheel oscillate as I drive. I am going on a coast to coast trip next month and I don't want the oscillations to cause fatigue failure. The last thing anyone needs is a wheel smashing through their windshield at 75mph.

 

[seanz0rz]

My aluminum Dissent bumper does not do that, something is loose or broken. How about a video from underneath?

 

[OEMGUY0720]

I tend to agree with you. It actually isn't the noise that bothers me. As a matter of fact, I don't hear it at all because whatever noise it makes is drowned out by my wind noise, Revel cat back exhaust, 4.88 gears, and 35in Falken's.

What bothers me is the significant disturbance I observe through my rear view driving down the freeway/washboard roads. It's most anxiety inducing when it hits resonance frequency.

I reached out to Dissent and they sent me an exploded isometric view of a newer Rev bumper, telling me to torque all my bolts again and to ensure that the wing stiffeners are still there, which they are.

I've marked up the model view Dissent sent me with some comments. Most of the force induced by the tire travels through the swingout and into the hinge bolt, depicted below in blue. I think what's occurring is that the corner of the bumper deflects downwards in the -Z direction (towards the ground) because there aren't enough connections between the bumper and frame. I've highlighted in green the hole locations that bolt to the frame. There are 3x holes on each half of the bumper (left and right) for the bottom of the frame rail -- in the view below, you can only see 2x for the left side, and 1x for the right side, but it's basically just a straight line pattern of 3x holes. So in all, there are 12x holes used to bolt the bumper to the frame.

Honestly, I think it's just a design flaw. I believe the wing stiffeners needed to be bigger with more gusseting. The wing tip as well as the corner of the bumper near the hinge bolt are cantilevered too far out from the nearest bolted interface. I know it's steel, but the geometry lends itself to be more compliant.

I'm not here to complain and criticize, I'd just like to know if anyone's found a simple solution to this problem. It's unnerving watching my 105lb wheel oscillate as I drive. I am going on a coast to coast trip next month and I don't want the oscillations to cause fatigue failure. The last thing anyone needs is a wheel smashing through their windshield at 75mph.

View attachment 3972044

1-2 inch (25-50mm) deflection is a lot tbh for automotive standards.Hopefully Dissent works with you to get this fixed.
@seanz0rz curious to know how long have you had your rear bumpers?

 

[seanz0rz]

1-2 inch (25-50mm) deflection is a lot tbh for automotive standards.Hopefully Dissent works with you to get this fixed.
@seanz0rz curious to know how long have you had your rear bumpers?

It was installed in late November, 2019

 

[Yung4Lo]

My aluminum Dissent bumper does not do that, something is loose or broken. How about a video from underneath?

I wonder if they designed the aluminum version with thicker plate as well as additional gussets for added stiffness — the assumption being that aluminum is “weaker” than steel, thus requiring additional design features in order to stiffen it up. You also have to think that aluminum is 1/3 the mass of steel, which means there’s less inertia in the aluminum assembly when compared to steel.

How heavy of a 5th wheel do you have?

 

[seanz0rz]

I wonder if they designed the aluminum version with thicker plate as well as additional gussets for added stiffness — the assumption being that aluminum is “weaker” than steel, thus requiring additional design features in order to stiffen it up. You also have to think that aluminum is 1/3 the mass of steel, which means there’s less inertia in the aluminum assembly when compared to steel.

How heavy of a 5th wheel do you have?

Stock 18" wheel with 275/70r18 BFG KO2, and a trasharoo. Other side has a flat shelf with 2 20L NATO cans.

You have a crazy amount of movement. Way more than reasonable. I'd look for frame cracks or other serious structural issues.

 

[plainjanefjc]

I’ve got the same bumper with zero wobble. Looks like some loose bolts under there

 

[Yung4Lo]

I’ve got the same bumper with zero wobble. Looks like some loose bolts under there

do you have one of the newer revisions though? I know they increased the stiffness in the design of the newer ones.

 

[Yung4Lo]

Stock 18" wheel with 275/70r18 BFG KO2, and a trasharoo. Other side has a flat shelf with 2 20L NATO cans.

You have a crazy amount of movement. Way more than reasonable. I'd look for frame cracks or other serious structural issues.

Yeah I have a feeling something else is going on as well. Hard to believe that Dissent would sell a bumper that wobbles this much.

 

[plainjanefjc]

do you have one of the newer revisions though? I know they increased the stiffness in the design of the newer ones.

Previous owner installed around 2022 I think. I just know it ls rock solid and it’s been used a lot on some rough roads with a spare tire and a storage box or fuel on the other side.