Yes, another death wobble case but only under braking.

[jdub]

My Jeep Cj7 has a dana30 up front with a 4'' spring under lift with shackle reverse set up.

Recently I have rebuilt the front axle from the rotors/hubs out. Everything is new, I went to the 6 bolt hubs. Rotors weren't surfaced at all upon installation.

The end of the steering shaft is a fixed joint-not stock. Box is 2 years old. I have changed out the steering stabilizer.

My question is why at >45mph and medium braking the tires start to shake side to side? Tires are well balanced. It doesent seem to come up into the steering column- so I don't think it is in that area or steering box.

I have worked on almost everything that would be a culprit, with the exception of pulling tierod ends off and looking at them individually. Is it the suspension system? It happens while descending hills more is my suspension wrapping and causing a kind of hop? My tires sway back and forth about 4'' I could see it being shocks, the fronts might be wearing out or the shackle reversal can be the culprit for axle wrap.

Any suggestions would be very helpful.

 

[Chevycrew]

Has anything with the suspension been changed recently? I ask because that shackle angle is horrible. It looks as though the shackle mount needs to move around 2"-3" forward.

 

[Tacoma]

gah! that IS a terrible shackle angle.

 

[Chevycrew]

It also looks as though the pinion has been rolled upward. How are the alignment specs compared to factory? I think I have the specs if you need them.

 

[bryson]

If your brakes set it off, I'd recommend you turn the rotors...

Also, I can't tell very well from the pics, but I'd imagine from looking at the front spring hangers relative to the shackles, you need to give it more caster (turn your pinion down with shims...)

 

[Chevycrew]

I dont have cj specs, closest i have is fsj. But most older solid axles are all similar.

Roughly +4 degrees caster, this is the upper ball joint back 4 degrees from vertical. Camber should be around 0 to 1 degrees, this is the amount the upper ball joint is towards the center of the vehicle from vertical.

I set all my rigs this way, my wife runs 40" mtrs with no stabilizer and no shake at any speed.

 

[jdub]

I've always been a little suspect of those shackles. I think that the lack of turning the rotors and the weird reaction that the suspension is creating is a chain reaction.

I have changed everything but the springs, shackles and shocks.

To move the shackle mount forward do you just drill a hole in the frame? Shim it so the shackle bolt doesn't pinch the frame?

 

[jdub]

would proper shackle placement be the next step and see if it helps caster?

Do the rotors need to be removed to be turned?

 

[Chevycrew]

Does the vibration/shaking only happen when braking? If so, I would remove and have the rotors turned.

But the shackle angle still needs corrected, and the alignment brought into spec.

There should be a sleeve for the bushing installed in the frame. You can either move the stock one, or get a new set and drill holes, and install them.

Rotors: removed from axle- yes, removed from bearing hub- depends on the machine.

 

[jdub]

Cool, thanks. Cj's don't have pressed on bearings. It is all loose, so yeah, it would need to come off.

I look down at the tires when it is doing it (at braking at 45) and it is moving the tires back and forth side to side Only at braking does it do this. This jeep is solid and straight from 0 to 70, it's the slow down. I put new to me used rotors on but didn't get them turned. It did the side to side motion on the old rotors though.

 

[jdub]

Would welding these to the under side of the frame forward 3-4'' be a bad idea?

 

[bryson]

Would welding these to the under side of the frame forward 3-4'' be a bad idea?

They would be easy, cheap and they would give you more caster at the same time, but it will lift the front of the Jeep a little bit as well. They will lift the front approx. half of the vertical difference between the new shackle mount height, and the old shackle mount height.

 

[DaveB]

My scrambler satrted doing a similar thing on our last wheeling trip. My death wobble would kick in at 45 doing a right turn. I had rotated the tires and the right front wheel was the cause of the problem. I had to swap the spare onto the right front position to get it to stop.

 

[jdub]

Ooooh, I do need to do a tire swap soon. I'll try that.

Huh, good info bryson.

Thanks guys.