Do I need to adjust pinion angle with a 3" lift?


AndyG

TJ Guru
Lifetime Supporting Member
Joined
Jul 30, 2018
Messages
8,882
Location
Alabama
Your gut instincts are telling you that something is going on.... And you know anything that vibrates can affect something... Seals, bearings and so forth... And at the minimum you want to head it off at the pass.

It could be nothing more than a transmission mount that's ready to be replaced... A good driveline shop that works with tjs will tell you quickly that a quality rubber mount is very important

From what you're describing it's going to be something pretty small.

I'm trying to think if I'm telling you right on the direction it moves when you lift it... I just went through all this on mine... And I ended up going to a CV drive shaft... But each lift and combination of components varies based on what the owner has going on.

I know that it's going to raise under torque load..

Mine would not vibrate with a passenger when I did the taller springs in the back and then when he got out it did.

if I'm telling you backward on the consequences of lift and pinion angle I stand corrected... But the reason that people do transfer case drops is to keep the transfer case parallel to the lower pinion angle....
If I'm correct.


Good luck. You will get it.
 
OP
F

Fargo

TJ Enthusiast
Joined
Oct 3, 2018
Messages
533
Location
Fargo, ND
Your gut instincts are telling you that something is going on.... And you know anything that vibrates can affect something... Seals, bearings and so forth... And at the minimum you want to head it off at the pass.

...
Good luck. You will get it.

That is exactly where I am at. The vibes are so minimal most people would just ignore it. And I am tempted to do just that. But I don't want to be stranded on the side of the road somewhere or on a trail in CO and ending my vacation early, because I neglected a small vibe.

I did get a comment from Pressurized in the 'harmonic vibrations' thread where that said:
... Typically when you lift, your diff rotates your pinion upwards a little.
So you may have been backward in your memory, or you had something else going on. Your case is kind of interesting. But it also may confirm that the pinion does infact rise when the jeep is lifted. Since your vibes went away when loaded down with a passenger it could suggest the pinion angle was improved when the jeep was lowered. But it seems backwards then, that I had vibes when loaded but none when I am alone. My issue could also be something smaller or entirely unrelated as you mentioned. Either way, I will need to do some loading and unloading and lifting and lowering on my Jeep to see what the pinion does and then get some good measurements to see if my angles are parallel or if i need a CV driveshaft. So lots of time consuming observations that I will need to pursue. Unfortunately, winter is a hard time of year to do this stuff. So I may be back in this thread next summer. Thanks again for the help.

...
I just glanced ar your post again and this comment jumped out.
I know that it's going to raise under torque load..

You know that might be the answer. If I remember correctly, the day I had the vibes it was also windy. So I had a loaded Jeep and driving into the wind. If that is the case, I would have had a constant torque load on the drive train. So if lifting the Jeep raises the pinion and torque load raises the pinion, I might just be at that edge where the extra torque load on a windy day gave me a slight vibe.
 

AndyG

TJ Guru
Lifetime Supporting Member
Joined
Jul 30, 2018
Messages
8,882
Location
Alabama
Cool, it should raise it my tech said. I'm foggy and immersed in a structural change at a remodel site we are doing.

Keep your eyes open, you know what's going on man. Good thread.

Keeping a nice jeep nice.
 
OP
F

Fargo

TJ Enthusiast
Joined
Oct 3, 2018
Messages
533
Location
Fargo, ND
Just a quick update if anyone finds this later. While I thought I had sealed Ujoints installed a few years ago, it turns out they had a grease zerk on them. So properly greasing the Ujoint took care of about 80% of my vibes. But I still had a very a minor harmonic vibe.

I then continued to investigate into the pinion angles. Putting a digital angle finder on the rear diff and lifting the Jeep with a jack, I found that lifting the Jeep another 3" caused the pinion to rotate up 1.2 degress. So approximately .4 degrees per inch. However, that is on a Jeep that is already lifted. The initial change in the pinion angle might be less.

With my angle finder magnetically attached to the rear diff at the flat spreader spots, I then proceded to adjust my lower control arms. I lengthened them about 1/8" which tipped the pinion back down 1 degree. Measuring the output shaft, drive shaft, and rear pinion, I now have angles of approximately 7.5* - 10.5* and 7.5*. Giving me 3 degrees of operating angle on both ends of the driveshaft and an output shaft that is parellel to the pinion. Those measurements are taken from on top of the harmonic balancer, the top or bottom of the drive shaft, and the flat "spreader" spots on the back of the rear axle. So its possible my angles are still not accurate if the spreader spots are not at a perfect 90 degree angle to the yoke.

So after all that, I finally went for another test drive. Getting my angles parallel fixed another 15% of the vibes. I still have a small vibe but its no longer a harmonic vibe. Its possible I went to far in tipping the pinion down. But I think its more likely that my ujoints are nearing end of life since they were not greased properly. Its also possible I am just being ultra sensitive now in listening for any little vibe.

Eitherway, I think I have solved my problem. I'll keep things posted if anything changes. Thanks for all the help.