Is my rear pinion angle okay?

DGJ

New Member
Joined
Jun 2, 2021
Messages
18
Location
Austin Texas
Hello, Does this pinion angle look ok? 2004 TJ non- Rubicon. 2.5” lift with Moog factory length control arms. TC case dropped about 3/4 inch. Trying to eliminate driveline vibration.

DEF15B6C-55D4-47A9-B6EB-2C30FC4B9FE4.jpeg


607E75A5-A02C-44FD-9A76-634072CF96DE.jpeg
 
Looks like it is pointed up too high. Should be near parallel to the tc output angle. Maybe slightly lower.

Do you have a smart phone? Search and download free inclinometer/angle finder app. Can use a spare socket on the u joint caps for a flat surface to use your phone to take measurements.
 
  • Like
Reactions: rasband
Did you replace the upper controls with Moog too? Are the axle side bolts tight on the upper arms? If there is a slot on the upper arm axle mount, is the bolt in the middle of the slot?
 
I was thinking the pinion was a little too high. Yes, the uppers and lowers are Moog. Bolt holes were not worn and everything is tight. I went ahead and ordered a set of adjustable upper control arms for the rear that will be here Wednesday. I will lower the pinion angle some and see what happens. Vibes showed up after re-gearing to 4.56. Front and rear driveshafts have been balanced and have new u-joints. Hopefully my issue is pinion angle.

I can feel the vibe starting at about 46 mph and the intensity increases with speed. Vibes are more noticeable if I am accelerating or going up hill. Gets bad above 65. You can feel it coming up through the body of the jeep.
 
With the stock driveshaft transfer case drive shaft and axle pinion should be parallel not have the axle pinion pointed up. With an SYE and double cardan drive shaft the pinion should be parallel with drive shaft, otherwise angled up to point at the transfer t-case output shaft.
 
Vibes are pretty typical at 2.5” lift. I’m surprised that a 3/4” TCase drop didn’t get rid of them. On my 2.5” builds I’ve always used a 1” MML to solve them. I don’t remember my pinion ever looking that high. Moog are just factory length, right?
 
  • Like
Reactions: TheBoogieman
For a non-cv shaft it looks too high. It should be roughly parallel with the transfer case shaft. Since yours is angled with the TC skid drop the pinion should be just slightly pointed up, but you’re pointing above the TC.

Courtesy of Tom Woods:

D8C30442-404C-40DA-A4C5-8AEBE10D29CA.jpeg
 
Some say to install both upper and lower adjustable control arms not be
just upper or lower. Changing the length of only one set of arms will slightly alter the wheelbase and adjusting top arms only could cause diff contact with gas tank on TJs but is it really an issue in most instances???
 
Update - Installed adjustable rear control arms. I lowered pinion angle quite a bit. The flat spots on the back of the the rear differential are now at the same angle as the harmonic balancer on the TC output shaft. Unfortunately the vibration is still there. Comes on at 40 mph and gets pretty intense as you get up to 60+mph. The vibration intensity increases when you are accelerating our going up hill. When you let off the accelerator the vibes are reduced significantly. The new pinion angle completely eliminated the 1st gear shudder I had when taking off from a dead stop. First and second gear are soo smooth. Wish I could stop this high speed vibe.
 
Given that the vibrations increase under load I would suspect the U-Joints. They are cheap and easy enough to replace. You could pull the rear shaft and drive in 4hi if you want to confirm it's driveshaft related.
 
  • Like
Reactions: Matt888
If you' ve done a 1" plus transfer case drop the next cheap thing is 1" Motor Mount Lift if you've isolated the drive shaft as the problem.
 
Pulled rear drive shaft and ran it up to 65mph on the highway. Vibes are gone. It is either rear drive shaft or possibly new gears.
 
Pulled rear drive shaft and ran it up to 65mph on the highway. Vibes are gone. It is either rear drive shaft or possibly new gears.
Check for excess play in the output shaft and the yoke. Also with the shaft out and in 2WD put it in gear and see if the output “wobbles” like its bent.
 
Update - Installed adjustable rear control arms. I lowered pinion angle quite a bit. The flat spots on the back of the the rear differential are now at the same angle as the harmonic balancer on the TC output shaft. Unfortunately the vibration is still there. Comes on at 40 mph and gets pretty intense as you get up to 60+mph. The vibration intensity increases when you are accelerating our going up hill. When you let off the accelerator the vibes are reduced significantly. The new pinion angle completely eliminated the 1st gear shudder I had when taking off from a dead stop. First and second gear are soo smooth. Wish I could stop this high speed vibe.
Got any pics of the adjusted pinion?
 
My next move would be to replace U joints if you don't know when they were last done, and if it's still there add a MML or increase the t case drop.
 
Here is an updated pic of my pinion angle. I played with pinion and transfer case angles all weekend and have reduced the vibes the best I can but it is still there. However, on the way home from the grocery store I had a load in the back (couple cases of water, 40lb bag of salt and other grocery items) and I noticed almost all vibes were gone. Is this just from additional weight in the back or possibly slightly different angles due to compressing the rear spring? This gives me hope. What should this tell me?

C51FD0DF-94E2-4DAC-9472-D45018FB6155.jpeg
 
If the vibes go way when you compress the suspension, that my be telling you that your pinion is likely a little too low when at normal ride height. Hard to tell from the pic, but it doess look a little low there.
 
  • Like
Reactions: JMT