Help - BAD one-wheel death wobble hitting bumps between 25 and 40 mph

[sydude]

Howdy y'all, I hope you guys are all keeping well and sane during the zombie apocalypse I'm trying to figure out WTF is most likely going on in the front end of my Bronco, and I'm hoping someone here has some helpful insight.

Symptoms: SOMETIMES hitting a random kind of bump between 25mph and 40mph or so causes that wheel (and ONLY that wheel) AND the steering wheel to go into a NASTY sawing/shaking wobble... and the only way for it to go away is to let off the gas and let the truck decelerate down to about 15mph. Hitting the brakes makes it worse. It doesn't happen at any other speeds, hitting small or big bumps HARD at higher speeds is fine. The truck feels solid steering and suspension-wise at speed. Also, sometimes hitting the same bump at same speed doesn't cause it to wobble. I guess it just needs to hit bumps a certain way. It can happen to either wheel, but it's definitely happened more often on the left wheel. This occurs maybe once every 75 miles of around-town driving.

Current front-end setup: Fully heimed Southwest Performance standard width C&T beams and radius arms, Bilstein 9100 remote reservoir coil-overs with Southwest Performance fabricated towers and brace, and ambulance upgrade stock-type steering setup with a dropped pitman arm.

Things checked out: The ball joints, tie rod ends and all fasteners were checked and nothing checked is worn-out or loose. Also, I have TONS of caster.

Notable items:

1. The camber/caster alignment bushings do not seat all the way in - the taper on the upper ball joint's fills out the taper on the cam bushing BEFORE the cam bottoms out, about 1/4" of an inch. See the picture. I don't know why that is, and it's the same on both sides. I've tried different cams, same result. I'm guessing the spread between the ears on the beam were made closer from cutting and turning the beam?

2. My coil-overs don't have a lot of miles on them, but they are nearly eight years old and they've never been rebuilt, so I'm not sure if they've lost their nitrogen. It doesn't feel like the wheel is bouncing up and down when I'm getting the death wobble, but it's entirely possible.

Ideas?

Thanks

S

IMG_6268.jpeg (132.78 KiB) Viewed 1451 times

[sydude]

By the way - when I refer to the 'left' wheel I mean the driver's side wheel.

[AussieRod]

First:
Check for abnormal wear on the tyre tread. US trucks/Broncos have a short tie-rod on the LH side on the longer beam, which makes the tyre go through different angles compared to the RH tyre on steering lock. (More so the speed/rate of turn difference between left and right wheels). This abnormal wear can affect dynamic balance, even though the wheel assembly will balance up ok on a machine, loaded balance with an uneven tread surface can cause wobble.
Check wheel balance. Sometimes a weight comes off and while that might not be noticable through the steering wheel, it can have some effect on the behaviour of the wheel at certain speeds.
Check the gas pressures in the front shocks. The affected wheel will not be properly dampened by a shock with little or no gas to help the shock function.
I'd also consider having the alignment checked as well, it's possible something has moved or got bent enough to create the condition you are experiencing at certain times and bumps.
Good luck.

P.S: clean off that bloody rust and put some paint on that front suspension!

[Cricket]

Just as a point of reference: I have the SWP Beams and radius arms, and they have the same issue with the alignment cams, exactly how you describe it. I have tried different brand ball joints with no difference. It almost makes me wonder if it was a jig issue or some difference between knuckles on model years. I also have a heavy duty factory steering setup, but no drop pitman arm. Along with that, home fabbed coil towers and King 3.0 C/O's. My Caster is pretty much on spec, but with fairly aggressive camber depending on where the shocks are set. Toe'd in just slightly.

I have not experienced the death wobble issue with all the similarities in my setup. There is the typical TTB shuffle from the camber changing over bumps, but it is pretty stable at speed.

The drop pitman arm on these C&T kits never made much sense to me because the suspension pivot geometry remains stock, but I have not spent the time to cycle it with both setups. If your uniballs are still tight, then I would start prying on different steering parts to find and loose joints or fasteners, Starting at the steering box all the way to the outer tie rods and ball joints.

[LvSteve]

Take a close look at the beam pivots. Then move to steering linkage. Take a close look at the mounting for the radius to the beam.
May be a good idea to check the charge on the front coilover shocks
This is not a new problem with any 4x4 of any brand.

[funinthesun95]

What Tires, how old are they?

[S00TLYFE]

Take a close look at the beam pivots. Then move to steering linkage. Take a close look at the mounting for the radius to the beam.
May be a good idea to check the charge on the front coilover shocks
This is not a new problem with any 4x4 of any brand.

Agree 100% with this, i would check beam pivots for cracks and move on from there

[MOSS2]

Too much caster can make it wobble too. If hitting the brakes makes it worse perhaps its because your caster increases when the front dives. Since you have coil overs maybe try increasing ride height and see if it changes or lower ride and see if it gets worse. How much is Tons?

[sydude]

Thank you ALL for your help & suggestions... ultimately the problem simply came down to low nitrogen pressure. It was down to 150 or so, so I charged the left shock back up to 225 psi and the death wobble is GONE!

[funinthesun95]

nice