CBI rear bumper swing out 'death wobble'

[LawnDart]

Personally, I would ditch the swing out. It's not necessary at all.

In an expedition build carrying capacity matters. They're bigger, heavier, and not as nimble as a rock crawler or daily driver. I warn people doing steel bumpers it fundamentally changes how you interact with the rear of the vehicle and how it affects performance. As stated there is no free lunch, and if you add something, it affects something else.

Personally I can't live without the swing arm on the trips I go, just carrying 10 gallons of extra fuel is critical, and I can't fit a fullsize tire in my setup now underneath.

So I don't think the "swing arms are not necessary" blanket statement is necessarily fair, as it's user needs dependent. But it will affect the vehicle, as it was never designed for one originally from the factory.

I think the OP needs to have his rear alignment checked since the problems seem to have appeared having the lift installed

Kinda spitballing, but I wonder if the shop that did the original install cocked up on the tracking bar, set it too short, and the lift just made the problem worse. This could be a big multi-faceted issue that is a combo of a lot of little issues as has been discussed.

 

[Taco04]

That design has a really large span with only 2 mounting points on the ends plus the fact that it cantilevers out makes for a lot of load on that arm and it’s mounting points. Obviously something is setting it off and causing this harmonic issue. Being you are stage 7 the first thing I would check is the rear pinion angle which can easily cause vibrations in the rear if it’s set up wrong. You may just need to adjust the rear upper control arms and your spare tire will stop trying act like a harmonic balancer.

 

[bartvonwolf]

I get the same "death wobble" with my CBI. Only on conrete corregated highways when theres a seam every 10 feet.

This right here describes my issue exactly. I can drive on I-80s smooth paved roads without this issue all day long. But when I merge onto 580 southbound and hit the concrete slabbed stretch of hwy, the vehicle bounces like hell. I am glad I am not the only one who has experienced this.

This is exactly why my off road truck is old.

I agree with this, and this is why I always wheeled in my old Trooper. HOWEVER, old also creates issues with reliability. And when you are alone with your family 40 miles down a dirt road in the middle of the desert after driving 60 miles into the middle of nowhere, this becomes a concern.

In an expedition build carrying capacity matters.

I agree, but I have more or less come up with a plan should I decide to ditch the swing-out. One of the main things I hate about the T4R is the damn hatch. A real overlanding vehicle should have doors. You can open and close them regardless of what is hanging off the back, if done right, and you can carry a lot more. My plan would be to ditch the swing-out, add a rear ladder than can also carry two 4 gallon gas jugs, and move the spare underneath. I think with some minor cutting, I could get the spare to fit underneath. The drawback here is if you need to get your spare out while stuck in 15" of mud or snow, it will suck. It also makes the spare more vulnerable to damage. But this can be fixed with a lightweight skid plate perhaps.

Kinda spitballing, but I wonder if the shop that did the original install cocked up on the tracking bar

Well, by shop you mean me. I installed my lift. I did not encounter any issues when doing so, but that doesn't mean some adjusting could still be needed. As I said, I come from an old school Trooper that was leaf sprung and as simple as they get. The 4Runner has a LOT more going on underneath than I am used to.

That design has a really large span with only 2 mounting points on the ends plus the fact that it cantilevers out makes for a lot of load on that arm and it’s mounting points. Obviously something is setting it off and causing this harmonic issue. Being you are stage 7 the first thing I would check is the rear pinion angle which can easily cause vibrations in the rear if it’s set up wrong. You may just need to adjust the rear upper control arms and your spare tire will stop trying act like a harmonic balancer.

If you can, can you describe what specific adjustments in what way would be needed?

Thanks,

Bart

 

[HOJeepster]

Don't over think it...we have a spare tire hangin way over the rear axle...the stock 4runner wasn't designed to carry this additional weight. Anytime you add extra weight, its going to whack things out. I personally find that when I have more weight in the back with the overland springs, the better it rides. It's just all part of the mix.

 

[Taco04]

Well, by shop you mean me. I installed my lift. I did not encounter any issues when doing so, but that doesn't mean some adjusting could still be needed. As I said, I come from an old school Trooper that was leaf sprung and as simple as they get. The 4Runner has a LOT more going on underneath than I am used to.


If you can, can you describe what specific adjustments in what way would be needed?

Thanks,

Bart

First your track bar will only make it pull to one side or the other it shouldn't cause any real vibrations unless its way off. Since you installed your own suspension I can assume you checked to see that the upper and lower links were the same length as the factory links? If not, I would recheck them. Also is it possible that it is sitting low enough to ride the bump stops when loaded down?

Don't over think it...we have a spare tire hangin way over the rear axle...the stock 4runner wasn't designed to carry this additional weight. Anytime you add extra saurce, its going to whack things out. I personally find that when I have more weight in the back with the overland springs, the better it rides. It's just all part of the mix.

The Runner frame does flex a lot but it should not cause the rear to vibrate like a guitar string either. In the past, I have run ome 895's and ome sport struts with an 8-gallon water tank underneath my rear bumper. The bumper also had 2 full fuel cans, spare tire and Front Runner grill on the spare; plus, trash container with as much firewood as it could physically hold. It was way under damped and sprung. It rode like a pig but had zero problems other than bottoming out and never had any vibrations at any speed. This even included bouncing off my hydraulic bump stops until the landing plates decided to say “adios amigo” more than once! I have also run it in a lot of other various combinations, down lots of corrugated roads and have never had harmonic problems at any speed! Obviously, something is still leading up to this as not everyone is having these problems while running a rear bumper with carriers….

 

[bartvonwolf]

Yeah, I followed Icon's instructions carefully, and insured the lengths were the same as stock when I installed. I still think this might simply be a combination of the exact wheelbase of the vehicle, combined with the sheer weight of the shit hanging off the back, and the unfortunate way some concrete roads are laid out. The combination is just right to cause this hideous oscillation. From this lengthy discussion, I have gathered the following issues:

A) The tires may need to be properly balanced
B) I may need more HD springs to account for the load
C) I may need to make some adjustments to my Icon Suspension
D) There is no solution, the weight and configuration of my vehicle will always produce this problem under the aforementioned circumstances

Bart

 

[Dropzone]

Toyota has used a similar rear suspension on 4 generations of 4Runners.
Lifted they all need to be properly adjusted.

Link angles are going to be changed when you lift it, stock length may not always cut it.

 

[bartvonwolf]

Toyota has used a similar rear suspension on 4 generations of 4Runners.
Lifted they all need to be properly adjusted.

Link angles are going to be changed when you lift it, stock length may not always cut it.

So, how does one "properly adjust" the suspension? What would I look to change? No one seems to be able to answer that question.

Thanks - Bart

PS - Been driving with the spare in the cargo area all week. The problem is pretty much completely gone with it not hanging off the rear end any more. I am thinking the best option is to just get rid of the swing-out all together.

 

[mikey's2010SR5]

Seems like a design flaw in the bumper... I have not heard of this complaint for shockworks or 4x4 labs owners....

I have it too. I just break the rhythm as [MENTION=124732]LawnDart[/MENTION] said. Nothing you really can do about it.


Sent using 1s and 0s.

 

[LawnDart]

I have it too. I just break the rhythm as [MENTION=124732]LawnDart[/MENTION] said. Nothing you really can do about it.

I'm trying to be of two minds about this.

On one hand I think what could be a very big culprit here is the fact that the OP is using the stock Icon springs, which are overloaded at this point, which means they're now too soft and translating up/down movement along the bumper like a tuning fork. Rear wobble is always more dramatic that front wobble (front bumper).

The OP's ride needs new springs regardless of if it makes the vibrations better either way, there could be a tire imbalance, something could be set wrong on the rear suspension. All we know is there's likely something that's causing a problem that the wobble is manifesting itself as a symptom.

On the other hand, and I tell people very bluntly, when we do big steel bumpers, sliders, roof racks, etc it's always a compromise, and the vehicle suffers as much as it gains. I hate to say that, but you add bigger and better tires, gas mileage goes down, road noise goes up, but you can handle tougher terrain. Roof rack? Carry more shit, but more wind noise and decreased MPG. rear bumper? better protection, more weight, more stuff that needs maintenance.

The only way to get a perfectly tuned experience is to leave the vehicle bone stock and live with it the way it was designed originally.

Especially when you get into the big heavy overlander setups it's best described as:

"Travel to new places. Meet new people. Crawl all over and inside your vehicle diagnosing, squeaks, rattles, and electrical issues!"

I hope the OP reaches some compromise her, as I just hung out with someone rocking the 4x4Labs bumper and we talked about the same stretch of I5 road going up to washington and he mentioned he gets the same wobble, it just happens.

 

[bartm]

Just bought 5th gen 4runner with a CBI bumper and experienced the same problem described by Bart. Driving around 70mph on concrete slab highway, the whole car subtly wobbles up and down. The feeling is similar like if the engine was stalling in a stick shift car. First I was freaked out thinking something is wrong with my engine, or transmission, than I thought it's suspension. After like a week of driving I finally figured out it was the spare tire on the CBI swing arm. I went to my mechanic, he agreed it shakes a lot. I asked him to find a way to attach the top of the jerry can holder to a ladder that is mounted to the rear gate. I will keep everyone posted. Wish me luck

 

[Jeremy556]

I asked him to find a way to attach the top of the jerry can holder to a ladder that is mounted to the rear gate. I will keep everyone posted. Wish me luck

Don't do that.

The ladder is attached to the body, which is isolated from the frame via rubber body mounts to allow independent movement. If you rigidly attach your frame mounted bumper swing out to your body mounted rear hatch, you are going to break the hatch.

ETA: Also, your spare is riding super high, you should lower it. That will make a huge difference as you are shortening the lever that your spare is connected to.

My spare is a 34" and I still mostly see out of my rear window

 

[mtnbiker49]

Don't do that.

The ladder is attached to the body, which is isolated from the frame via rubber body mounts to allow independent movement. If you rigidly attach your frame mounted bumper swing out to your body mounted rear hatch, you are going to break the hatch.

ETA: Also, your spare is riding super high, you should lower it. That will make a huge difference as you are shortening the lever that your spare is connected to.

My spare is a 34" and I still mostly see out of my rear window

Yeah his spare is stupid high. Lowering it should help, along with making the truck look better. These aren’t baja vehicles.

However, I don’t think you’ll get rid of all the wobble. That is a ton of weight with a lot of leverage on the hinge and latch. Check for broken welds too.

 

[unsub1]

So, is the consensus that the wobble is about the same, all things being equal, with single or double swingout configurations?

 

[Xtremluck]

So, is the consensus that the wobble is about the same, all things being equal, with single or double swingout configurations?

Or any metal bumper on the market with a swing out spare

 

[lefty721]

Or any metal bumper on the market with a swing out spare

Not true. My shrokworks swing out doesn't wobble at all. This think is build like a shit brick. Only complain it's waaay too heavy.

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[EddieV4runnin]

Not true. My shrokworks swing out doesn't wobble at all. This think is build like a shit brick. Only complain it's waaay too heavy.

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You ever had any issues with the tire on the carrier getting caught on any rocks while on the trails?

 

[unsub1]

Or any metal bumper on the market with a swing out spare

Since your bumper is my basic goal.... anything you'd do differently? (if you could do it again now?)

 

[Xtremluck]

Since your bumper is my basic goal.... anything you'd do differently? (if you could do it again now?)

Absolutely not, its one of the best upgrades I've done on my truck. It allows me to carry bikes up technical trails, is an essential component of my camp kitchen setup and offers extra protection which I've definitely used. The only thing I would wish for is a bit more clearance. The other newer bumpers in the market seem to have much better departure angles.

 

[lefty721]

You ever had any issues with the tire on the carrier getting caught on any rocks while on the trails?

Actualy no.. I removed the swing out arm and the spare as it was way too heavy. The truck sat like a boat with the OME 890. You can even see in the picture is squats. Plus it's my daily. It's a pain to open the swing out everytime I open the trunk. I just replaced with LC coils so I might throw it back on to check how she sits. I don't think the tire will be caught. You can adjust the height BTW. In the picture I have it on the lower point for better rear view.

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