Steering Stabilizer or Sway Bar with RFS?

[Noiseydiesel]

'94 7.3 idiT CC Dually
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After doing the 4X4 mod and installing the Dana 60 on a Reverse Front Shackle set up,
Going down the road is pretty stable. Until. I hit a rough patch in the road on the left side and about a foot later, a rough patch in the road with the right side.
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It is a fun amusement park ride. Left side bounced up, then the right side bounced up and forced the left down. Left rebounded, came up and forced the right side down, non stop.
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Steering wheel was not amused and veered right and left and right and left. I was impressed and buried the brake pedal with no one behind me and got the speed down as fast as possible and it smoothed out. I just got the drive line vibration worked out, this is next on the Hit Parade.
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So what say's the brain trust?

 

[u2slow]

Sounds like death wobble. Whats your caster angle at? Is your pinion pointing more upward than before the RSK?

 

[94NAIDI]

When you installed the Dana 60 for the “4x4 mod” did you also install a track bar and track bar bracket? Also, did you add any lift to the truck while doing the RSK and Dana 60 swap? When I did mine, I had to purchase a longer adjustable track bar to prevent bump steer. Nothing as severe as you are describing. But I bet not having a track bar at all could cause such a severe reaction.

 

[Clb]

Are the shackles loose?

Example
My straight axle yota gets death wobble if the bushings aren't nice and snug.

 

[Noiseydiesel]

Shackles are new. New as in less than, lets be generous, 6,000 miles.
As is/are the shocks, springs, differentials, Allison transmission, transfer case, engine, turbo, injectors, injector pump, fuel pump, water pump, paint job, led lights, rear bumper. . . Am I missing much?
As for the track bar, I made a custom mount under the engine cross member and kept it as near level as possible, matching the other linkage geometry. Funny part on that one is on most, semi-major bumps, the truck steered better without it. I am suspecting a sway bar would alleviate most of my problem. However, I am getting tired of laying on the ground in a gravel driveway.
Caster angle is good question. I am aware that Ford used these axles on other/similar models and in order to keep my life sane, I have tried to keep it as close to "stock" as possible. While it is a decent looking machine, I believe I should have left it 2WD with the Allsion and a Truetrac rear diff. No, not going back. This exercise in excess is just too much fun to stop now. Wjhat ever the angle might be, it went down to the alignment shop after building the front end, tie rod ends, ball joints, (everything) and was signed off on.

 

[u2slow]

Factory tries to use as a low a caster setting as is manageable/repeatable without side-effects. 1-3 degrees is common. This small amount can be 'erased' with age - spring sag and bushing compression.

When you start modifiying the suspension and/or different wheels, bigger tires, etc... may need more caster to keep things under control. 5 degrees is a good baseline. Slightly longer shackles is an easy way to add.

 

[Clb]

Are they loose?
I don't care if they are 300k old as long as there is side pressure on them...
And the pins are not sloppy.
I didn't read the rest.

 

[Noiseydiesel]

Everything is new.
Everything matches the identical model with the mono beam axle.
I am going to add the sway bar back into it and see what happens.

 

[Clb]

Tight or loose....
I officially give up.

 

[Noiseydiesel]

Tight.
"Officially Giving up"?
Ho-No-Sir.
Your stuck with THIS albatross around yer neck.
She wanted the no ECM diesel.
Dodge is overpriced.
That made it a Ford for an option.
And the engine went kaflooey with 126 on the clock.
Might as well do the trans at the same time.
Add the Truetrac to the rear
Naturally it had problems after the build.
Stuff in an Allison.
Drop the 2WD brackets, add the 4X4 with the RFS
Add the Dana with the eLocker and the BW1356.
Paint this pig and that was done wrong.
Shake rattle and roll are now all coming to town.
There is more but the brain had long forgotten at this moment in time.
Sell? That option she decided to forgo when it went kaflooey saying that it would be cheaper for me to build it.
Now that it is close to done, she once said to me that it would be all that I desired in a truck.
2023 F450 is pushing 1200 Ft Lb torque and a 40K towing capacity. and only a bit more than i have spent on this one.
Then she cheated on me and moved to heaven without me leaving me this over priced albatross. It is no longer a case of stop spending money but now a case of completion.
Dang the torpedoes?
Dang the Wallet!!
So, NO. Giving up is NOT an option.

 

[u2slow]

Everything is new.
Everything matches the identical model with the mono beam axle.
I am going to add the sway bar back into it and see what happens.

Blindly matching stock - but also the RSK. Doesnt seem like a sound strategy.

As I said before, get the caster figured out. RSK in particular may have changed the level/angle of the leaf spring, which is a direct change to the caster angle.