Help with Pinion Angle

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RicksterAZ

New Member
Joined
Nov 26, 2018
Messages
10
Location
Phoenix, AZ
I just did a 2" lift on my 2005 Wrangler Sport. Not sure exactly how much my original suspension was sagging but my corners changed between 2" and 2.75" after the install. My install included:
- front lower adjustable control arms
- front adjustable track bar
- front swaybar links
- rear track bar relocation bracket
- Rancho RS9000xl shocks
- 4 progressive springs

Now, to my question regarding the pinion angle and the vibration that I have during acceleration. In measuring my rear driveline geometry I have the following measurements:
Transfer case yoke: 4 degrees (pointing down)
Axle: 14.50 degrees
Rear pinion: 9 degrees (pointing up)

The measurements surprised me to be off by so much. So, what would you do to correct this problem?
Thanks
 
How can you adjust your rear pinion angle without adjustable rear control arms? I only see mention of front adjustable control arms.

You should be measuring the pinion angle in relation to the driveshaft. Put the angle finder on the rear pinion, then put it on the rear driveshaft.

The rear pinion should be 1-2 degrees lower than the driveshaft.

You need a SYE and double cardan driveshaft in order to do this though (which I'm assuming you have).

This is how you take the measurement:

img_0295.jpg
 
RicksterAZ said:
I just did a 2" lift on my 2005 Wrangler Sport. Not sure exactly how much my original suspension was sagging but my corners changed between 2" and 2.75" after the install. My install included:
- front lower adjustable control arms
- front adjustable track bar
- front swaybar links
- rear track bar relocation bracket
- Rancho RS9000xl shocks
- 4 progressive springs

Now, to my question regarding the pinion angle and the vibration that I have during acceleration. In measuring my rear driveline geometry I have the following measurements:
Transfer case yoke: 4 degrees (pointing down)
Axle: 14.50 degrees
Rear pinion: 9 degrees (pointing up)

The measurements surprised me to be off by so much. So, what would you do to correct this problem?
Thanks
Click to expand...
Before discussing angles, what rear driveshaft is installed? The factory single-cardan or an aftermarket double-cardan? It's rare to see an aftermarket double-cardan driveshaft with a SYE installed for only a 2" suspension lift.
 
Jerry Bransford said:
Before discussing angles, what rear driveshaft is installed? The factory single-cardan or an aftermarket double-cardan? It's rare to see an aftermarket double-cardan driveshaft with a SYE installed for only a 2" suspension lift.
Click to expand...
Prior to the lift the Jeep was completely original with the single-cardan joints. I set 2" as my maximum lift to avoid more expense such as the SYE and new double-cardan driveshaft.

I was surprised that my diff pinion was turned upwards as much as 9 degrees post install (I did not measure angles pre-install). I assumed with a minimal lift of 2" that perhaps I needed adjustable rear upper control arms. But seeing my angles, I would need to rotate the diff pinion down 5+ degrees but, doing that would leave me with ~10+ degree pinion angle. Seems way off for what I have done, hence my turning to the forum for advice.

I'm not even considering softening the problem with a transfer case drop. A motor mount lift would change the front pinion angle and caster which is perfect per my and the alignment shops measurements.

My increase in rear height was exactly 2" as measured from top of rear tires to lower edge of the fender extensions. I gained 3" at drivers front and 2.75" at passenger front.
 
Chris said:
How can you adjust your rear pinion angle without adjustable rear control arms? I only see mention of front adjustable control arms.

You should be measuring the pinion angle in relation to the driveshaft. Put the angle finder on the rear pinion, then put it on the rear driveshaft.

The rear pinion should be 1-2 degrees lower than the driveshaft.

You need a SYE and double cardan driveshaft in order to do this though (which I'm assuming you have).

This is how you take the measurement:

View attachment 68660
Click to expand...
Thanks for your reply. Agreed that the SYE and new double-cardan would address my issue but am surprised I need it with a 2" lift. For my rear measurement I measured the driveshaft per your drawing but the rear pinion angle I measured at the front face of the diff housing where the pinion exits the diff case. Same difference though.
 
RicksterAZ said:
Thanks for your reply. Agreed that the SYE and new double-cardan would address my issue but am surprised I need it with a 2" lift. For my rear measurement I measured the driveshaft per your drawing but the rear pinion angle I measured at the front face of the diff housing where the pinion exits the diff case. Same difference though.
Click to expand...

With a 2" lift you either need to choose one of two paths (and these are the ONLY two paths):
  1. Stick with the stock control arms and stock driveshaft, and drop the transfer case.
  2. Get adjustable rear upper control arms, a SYE, and a double cardan driveshaft, then rotate your pinion angle in relation to the rear driveshaft as shown in the photo above.
There is no other way to do it. The rear stock driveshaft is NOT meant to be rotated in such a way that the rear pinion angle is inline with the rear driveshaft.
 
RicksterAZ said:
...I measured at the front face of the diff housing where the pinion exits the diff case...
Click to expand...
Measure angle at two other spots to see if all match. With wheels on the ground, rotate a tire till the pinon yoke u joint cap is straight up and centered. Apply P brake and wheel chock. Place an appropriate size socket on the cap that will fit flat/square, then measure angle from the top of the socket. On the back side of the axle on each side of the inspection cover, are two flat spots. Choose an edge that will not allow the angle finder to rock, then measure.
 
For only a 2" lift, you didn't need to spend the $$$ for the adjustable control arms. You don't need a SYE and double-cardan driveshaft either to get rid of the vibrations for such a small lift. While most just drop the tcase 1/2" to 5/8", which will do it, or install a set of 1" taller motor mount lifts. They reduce the drivetrain angle in the same way a tcase drop does.

Don't go jacking around with the pinion angle with those adjustable arms. The pinion angle must (!!!) remain parallel with the tcase output shaft. Hopefully you didn't adjust those control arm lengths trying to eliminate the vibrations by changing the factory pinion angle which will still be correct with a 2" lift.

The vibrations aren't being caused by the rear pinion angle, they're caused by the steeper angle both of the rear driveshaft's u-joints are now working into. So it's the u-joints that are vibrating.

Personally I'd just drop the tcase 1/2 to 5/8" by stacking washers around the tcase skidplate bolt and positioned between the frame and skidplate. Then when/if you get to a taller lift, you can install a SYE and double-cardan driveshaft. Or if you really don't want even that 1/2" to 5/8" tcase drop, install the taller motor mounts. Like the Bombproof motor mounts with rubber (!) bushings from Mountain Offroad Enterprises.

This is how the pinion angle and tcase output shaft angle must be with your stock rear driveshaft... parallel to each other.

2joint_angle.jpg
 
You say 2" lift, but according to your numbers it sounds like you netted more to 3" of lift. You are at that magic number where other stuff needs to be done. Maybe a MML will quell the vibes, and maybe it won't. If it doesn't, then your only other options are to drop the tc skid, or SYE/DCDS/Adjustable arms. Or, lower the jeep.
 
bobthetj03 said:
...according to your numbers it sounds like you netted more to 3" of lift...
Click to expand...
Agreed. With wheels on the ground and typical weight in the Jeep, measure a rear spring from perch to top, at the forward side and rear of the spring. Share the measurements with us please.
 
Jerry Bransford said:
For only a 2" lift, you didn't need to spend the $$$ for the adjustable control arms. You don't need a SYE and double-cardan driveshaft either to get rid of the vibrations for such a small lift. While most just drop the tcase 1/2" to 5/8", which will do it, or install a set of 1" taller motor mount lifts. They reduce the drivetrain angle in the same way a tcase drop does.

Don't go jacking around with the pinion angle with those adjustable arms. The pinion angle must (!!!) remain parallel with the tcase output shaft. Hopefully you didn't adjust those control arm lengths trying to eliminate the vibrations by changing the factory pinion angle which will still be correct with a 2" lift.

The vibrations aren't being caused by the rear pinion angle, they're caused by the steeper angle both of the rear driveshaft's u-joints are now working into. So it's the u-joints that are vibrating.

Personally I'd just drop the tcase 1/2 to 5/8" by stacking washers around the tcase skidplate bolt and positioned between the frame and skidplate. Then when/if you get to a taller lift, you can install a SYE and double-cardan driveshaft. Or if you really don't want even that 1/2" to 5/8" tcase drop, install the taller motor mounts. Like the Bombproof motor mounts with rubber (!) bushings from Mountain Offroad Enterprises.

This is how the pinion angle and tcase output shaft angle must be with your stock rear driveshaft... parallel to each other.

View attachment 68733
Click to expand...
OK, sounds like a reasonable approach. I have not adjusted the rear diff pinion angle yet, and will not per your recommendation. To be clear, my goal with the stack of washers and/or MML is to match the TC angle of 4 degrees to the existing and fixed diff pinion angle of 9 degrees. Correct?
 
bobthetj03 said:
You say 2" lift, but according to your numbers it sounds like you netted more to 3" of lift. You are at that magic number where other stuff needs to be done. Maybe a MML will quell the vibes, and maybe it won't. If it doesn't, then your only other options are to drop the tc skid, or SYE/DCDS/Adjustable arms. Or, lower the jeep.
Click to expand...
You are correct and thanks for reading my original post so carefully!:) When I looked at my numbers to write Post #4 I realized that I did get 3" of lift at drivers front. Again, these were the original springs in this 2005 vehicle so I'm guessing there was sag built into my pre-lift measurement along with the variable of the new spring stiffness. My plan to add a front winch will adjust that number down.
 
RicksterAZ said:
OK, sounds like a reasonable approach. I have not adjusted the rear diff pinion angle yet, and will not per your recommendation. To be clear, my goal with the stack of washers and/or MML is to match the TC angle of 4 degrees to the existing and fixed diff pinion angle of 9 degrees. Correct?
Click to expand...

You are over thinking the exact angle measurement. You are just trying to get rid of vibrations.

If you go with dropping the skid plate i would personally add as few washers to stop the vibration.

If you go with a MML. And your vibrations are gone. I would not even measure the angle. Nor try to drop the skid to get them perfect.
 
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Boinked said:
You are over thinking the exact angle measurement. You are just trying to get rid of vibrations.

If you go with dropping the skid plate i would personally add as few washers to stop the vibration.

If you go with a MML. And your vibrations are gone. I would not even measure the angle. Nor try to drop the skid to get them perfect.
Click to expand...
X2. I have an angle finder but haven't used it to measure pinion or driveshaft angles in years.
 
k-huevo said:
Agreed. With wheels on the ground and typical weight in the Jeep, measure a rear spring from perch to top, at the forward side and rear of the spring. Share the measurements with us please.
Click to expand...
You are correct in that the driver front corner did lift 3" from where I started with these 15 year old original springs.
Rear spring bucket measurements:
Drivers front - 8.5"
Drivers rear - 10.25"
Pass front - 8.375"
pass rear - 10.0"
 
RicksterAZ said:
You are correct in that the driver front corner did lift 3" from where I started with these 15 year old original springs.
Rear spring bucket measurements:
Drivers front - 8.5"
Drivers rear - 10.25"
Pass front - 8.375"
pass rear - 10.0"
Click to expand...
By the way, these are measured from the retaining lips of spring buckets
 
If he does install only a MML, and let's say that does cure the vibes, what does the MML do for fan alignment with the fan shroud? Raise the fan shroud up?
 
So on my lift I used 3" taller springs and new shocks, a 2.5'" taller rear track bar bracket and re-drilled the front track bar mount to center the front axel. To align the rear shaft and pinion I used a set of cam bolts after opening up the "slots" on the rear upper control arm mounts on the axel. My question is my Transfer case angle is 7 degrees down and the pinion is about 5 degrees down trying to "match to same angle" as the transfer case output, to cancel out any vibrations. Would it also work if I raised the rear pinion to 7 degrees up, to match the 7 degrees of down angle the transfer case sits at? The angles would be opposite but equal if you get my drift. Does this theory make any sense?
 
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