Duff T-Rex Evolution Vibration

[dsmelfi]

Hey all,

I just installed the Duff Evolution radius arms and I'm getting a vibration when accelerating at lower speeds. Clutch in and it rolls smooth.. higher speeds are no issue. I feel like it's a drive line angle issue, but I cant tell. With the bubble level on my phone, I get a different reading depending on where I measure, one set of measurements is right within the 1-2 degree range (drive line and u-joint) but if I do the drive line to flat surface on the pumpkin face, I'm closer to 3°.

I have 4.5" WH front coils, and what seem to be 4.5" leaf springs from PO (measured 10.5" from top of tubes to frame in back) and the PO also had installed 6° shims.. the new arms gave me right at 4° of caster after the alignment, toe is within spec..and she handles and drives better than ever other than the vibration.

My question is; by installing the new arms, is it possible I need to go down to a 4° shim? Just by looking, it seems closer to 0. I've attached a pic, but not sure that helps.

I have a digital angle finder coming in the mail so I'll get some better numbers soon. Any thoughts are appreciated in the meantime.

Thanks!

Any ideas are appreciated!

 

[gnpenning]

Is the vibration in the front or rear?

Basic checks that need to be verified, is it in 2h, hubs unlocked?

Do the front axles turn when driving.

What tires, how long on the vehicle, when were they last balanced?

Remove front drive line and drive.

Do you still have a CV rear drive line? How old and have you double checked all joints, pivot and splines?

You can do these while you are waiting on the angle finder and it's all free.

 

[DirtDonk]

It looks like the pinion is pointed a bit high in the rear, but the pic is hard to tell for sure really.
Can you gauge the difference in pinion angle vs driveshaft angle?
Did the vibration just start after installing the arms? That would be strange, except for our Broncos love to throw "coincidental failures" at us at the most confusing moments!
Was the lift installed previously? Or at the same time as the arms?
If previously, how long ago was it installed?
Are there shims between the leaf springs and the spring perches?
Stock axle housing and spring perches? Or aftermarket?

And last, can you take a pic of the rear pinion directly from the side? Whether just in the front of the tire, or just over the top. Looking directly down the line at the u-joint.

Paul

 

[dsmelfi]

The vibration started after the alignment was done.. It also ran across my mind that this could just be a "coincidental failure".. Bronco life eh!

The only thing I changed was installing the new arms & coil retainers, the WH 4.5" front coils were installed about a year ago and everything else has been on the truck for at least 30k miles.. plus whatever the PO had into it. There is also a front Hellwig sway bar.

There are 6 degree shims already installed.

Stock housing and spring perches as far as I can tell.

The truck is in 2H with the front hubs unlocked.

Tires have been on the vehicle for 30k miles, 35" falkin wildpeak M/T.

Looks like the driveshafts are from WH, High Clearance HD front and rear.

Going to grab the angle finder this afternoon and will report back once I can check the angles.

 

[dsmelfi]

I feel like a moron.. but it's still hard to get a good measure on the angle for the axle. The driveshaft is easy, but the angle finder doesn't have anywhere flat to sit on the axle.. I'm open to thoughts there, but before I go further down this road, I noticed something else.

I took a closer look at the radius arms adjustment bolt, and the flat edges are about 13° out of sync, which I think could be the issue. I didn't watch that closely when the alignment was being done, but when I looked today it was clear they are not set to the same angle. 70.4 on the driver side and 57.1 on the passenger side.. and thinking back, the vibration started after the alignment. I figure I'll split the difference and get them both set close to each other and see if the vibration stops, then head back to the alignment shop to recheck the numbers and adjust if necessary.

If that fails, I'll be back to checking the angles.

Thanks for the help so far, I'll report back.

 

[73azbronco]

are the fins of the pumkin level with output shaft? use that?

 

[Yeller]

Key to what I’m reading is “goes away with the clutch pushed in”. Unless the hubs are locked and your driving it in 4 wheel drive, it is coincidental to the arms being installed and aligned. I’d be double checking pinion angle and checking u joints. By money is on a unjoint or CV kit biting the dust in the rear driveshaft.

If the hubs are not locked and the transfer case is in 2wd, the vibration is not in the front drivetrain. Could even be a motor mount, on the throttle at low speed, high torque and it is moving pushing stuff where it is not supposed to be.

 

[dsmelfi]

Quick update.. I got the arms dialed back in so they are at the same angle and the vibration reduced considerably. I mostly feel it now when down shifting so there is still something going on, but I would say it's 90% better than it was.

On to the u joints and cv.. thanks again for the help!

 

[DirtDonk]

The double-cardan yoke and centering ball can have some strange side effects when they go dry or get worn.
Downshifting does force the rear pinion lower, so if a pinion angle is already slightly low, going lower will cause a vibration. But in your earlier pics, it sure did not look low from here.
Did you ever get a reasonable facsimile of an angle measurement between the rear pinion angle and the driveshaft angle?

Paul

 

[dsmelfi]

Alright.. I was just able to measure the angles, best I could.. and it looks like 18.6° on the driveshaft and 15.6° on the pinon.. so right at 3°. Should I move to 8° shims?

 

[DirtDonk]

So that's 3 degrees lower on the pinion than on the shaft? Pointing below the centerline of the shaft?
If so, is there some way to fab up a temporary shim to test the theory? Get the pinion pointed up slightly more towards the centerline?
Just thinking that it would be a shame to go to the work and expense of thicker shims, only to find out it's something else.
Perhaps by sliding something extra into the thick side of the existing shim, then tightening the u-bolts down and drive it just far enough to check.

Trying to remember if a degree at the spring perch equals more than one degree, or less than one degree change at the pinion.
Maybe someone here remembers the ratio of change. If it's less than the angle of the shim, then that 8 degree shim might just put you in the sweet spot.

And don't forget to grease the joints. Like right now! And at all four locations.
Grease them up, and see if it changes the vibration even if only for a couple of miles.

Paul

 

[dsmelfi]

Thanks Paul. Yes, pinon sits lower than the shaft and everything has been greased, twice just to make sure! The female zerks up in the cv were all full, but the lower ones at the pinon were pretty dry. The front end is all greased as well.

Not sure if feel confident wrigging up a temp solution.. my fab skills are pretty crude.

I have a set of WH extreme duty u bolts that Ive been wanting to install, so I'll grab a set of 8° and hope for the best.. otherwise maybe it's time to rebuild my shaft..

I'll update with my findings.

 

[Yeller]

3 degrees will vibrate, especially downshifting. So you are headed the right direction.

 

[dsmelfi]

Quick update.. I got the 8 degree shims in yesterday and it's rolling much smoother now! There is still a very small vibration when going very slowly, which may have always been there and now I'm just paying more attention, but it seems like the major vibrations are all gone.

I will note that when I got the u bolts off, the top of my leaf has TB3.5 on it, so what I thought was a 4.5" lift in the back was incorrect. Maybe the added shim was giving me the 11.5" from tube to axle? At any point, does it make sense that having 3.5" springs in the back and 4.5" coils in the front would require 8 degree shims? or should I be worried that something else is still wrong?

 

[DirtDonk]

Can’t say anything else is wrong at this point, but it’s very common for the modern leaf packs to lift higher than rated.
Two common unfortunately

So, in your case, the previous owner may have known this already and compensated with the taller front coils, or found out after installation and swapped in coils as the simpler and less costly option.

Glad to hear the vibration is mostly gone. Curious as to whether your current low speed vibration is still driveline related, or perhaps Tire related?