Premature u-joint wear

Flexlex · Nov 24, 2023

Hey everyone, I have a 2000 Wrangler Sport with a 1.25” rancho suspension lift. Stock Drive shaft. U-joints on the rear driveshaft tend wear out once a year. The angle at the t-case is 6 degrees (measured with digital angle finder on top of output shaft). Rear pinion angle is 10.9 degrees (measured at flat spot next to pumpkin).

I think this means I need to bring the rear pinion down closer to the ground.

I purchased some adjustable upper control arms without thinking it through. They don’t adjust shorter than the stock ones, they only get longer. Will adjustable lower control arms help? The rear tire in the wheel well looks about right. Can anyone suggest a brand of uppers that adjust shorter than stock?

Pics below

Jerry Bransford · Nov 24, 2023

The rear pinion angle is supposed to be the same as the transfer case output shaft angle. They need to be parallel to each other. Do you have adjustable length control arms in the rear?

It needs to look like this.

Flexlex · Nov 24, 2023

I have adjustable upper arms but they won’t adjust the pinion down (get short enough)

Flexlex · Nov 24, 2023

Jerry Bransford said:
The rear pinion angle is supposed to be the same as the transfer case output shaft angle. They need to be parallel to each other. Do you have adjustable length control arms in the rear?

It needs to look like this.
View attachment 476605

The lift came with new lower arms but they aren’t adjustable. The upper arms look like stock ones.

Modoc Guy · Nov 24, 2023

If you’re looking to truly adjust the rear differential, you’ll need adjustable upper and lower control arms.

And the more lift you have, the less you’ll be able to keep the transmission tail shaft and differential center lines parallel.

That’s why we adjust the pumpkin to decrease the running angle of the u-joint at the differential. But you may also need to decrease the angle at the tail shaft too, because it’s not the total angle difference between tall shaft and differential, it’s the angle at each u-joint.
Neither u-joint can safely run at too great an angle.

That’s where motor mount lifts come into play, helping to decrease tail shaft angle.

And you said your lift is only 1 1/2”, which isn’t much. But the photo you posted shows what looks like a much higher lift.

Have you measured your lift height to confirm your assertion? IIRC, stock is 8” and 12”, rear and front respectively.

With a 1 1/2” lift, you could probably get away with only changing differential angles, but with more lift, you’ll need more adjustment at both ends of the driveshaft.

And yes, the double carden u-joint set allows for more misalignment, but not any more than the total of both u-joints.

Just be mindful adjusting the dual adjustable control arms. It’s easy to move your differential center point in the wheel well with those, and that starts messing with track bars and other things connected to, or near the differential.

That’s my 2 cents. And somebody smarter than me will correct me if I’m wrong about any of this!

TheBoogieman · Nov 24, 2023

I'd question the brand of u-joints you're using? I've been more than 7 years on my Spicer non greaseable ones. I have stock control arms too.

Flexlex · Nov 24, 2023

Modoc Guy said:
If you’re looking to truly adjust the rear differential, you’ll need adjustable upper and lower control arms.

And the more lift you have, the less you’ll be able to keep the transmission tail shaft and differential center lines parallel.

That’s why we adjust the pumpkin to decrease the running angle of the u-joint at the differential. But you may also need to decrease the angle at the tail shaft too, because it’s not the total angle difference between tall shaft and differential, it’s the angle at each u-joint.
Neither u-joint can safely run at too great an angle.

That’s where motor mount lifts come into play, helping to decrease tail shaft angle.

And you said your lift is only 1 1/2”, which isn’t much. But the photo you posted shows what looks like a much higher lift.

Have you measured your lift height to confirm your assertion? IIRC, stock is 8” and 12”, rear and front respectively.

With a 1 1/2” lift, you could probably get away with only changing differential angles, but with more lift, you’ll need more adjustment at both ends of the driveshaft.

And yes, the double carden u-joint set allows for more misalignment, but not any more than the total of both u-joints.

Just be mindful adjusting the dual adjustable control arms. It’s easy to move your differential center point in the wheel well with those, and that starts messing with track bars and other things connected to, or near the differential.

That’s my 2 cents. And somebody smarter than me will correct me if I’m wrong about any of this!

The rear coil from cup to cup is 9.5”, the front coil is 14” but the front has what looks like a 1” spacer which would make it 15”

Flexlex · Nov 24, 2023

TheBoogieman said:
I'd question the brand of u-joints you're using? I've been more than 7 years on my Spicer non greaseable ones. I have stock control arms too.

View attachment 476611

I’ve been using the same ones

TheBoogieman · Nov 24, 2023

Flexlex said:
I’ve been using the same ones

Any t-case drop, MML? Any driveline vibes?

Flexlex · Nov 24, 2023

TheBoogieman said:
Any t-case drop, MML? Any driveline vibes?

Not sure how to tell, I did have an AX15 installed recently but these u-joints issues have been around since I bought this 20 years ago. I have not done those mods though.

Flexlex · Nov 24, 2023

Flexlex said:
Not sure how to tell, I did have an AX15 installed recently but these u-joints issues have been around since I bought this 20 years ago. I have not done those mods though.

Maybe a very slight vibration but not very noticeable.

TheBoogieman · Nov 24, 2023

Flexlex said:
Maybe a very slight vibration but not very noticeable.

Any vibes are bad. You could lower the skid with a couple of thick washers and see if it goes away.

https://www.4x4xplor.com/t-casedrop.html

Flexlex · Nov 24, 2023

TheBoogieman said:
Any vibes are bad. You could lower the skid with a couple of thick washers and see if it goes away.

[URL]https://www.4x4xplor.com/t-casedrop.html[/URL]

View attachment 476621

Makes sense, any idea how far to go to change the angle by 4-5 degrees?

Blackjack · Nov 24, 2023

From the looks of your muffler did your driveshaft leave the chat once? Maybe post some pics of it.

Flexlex · Nov 24, 2023

Blackjack said:
From the looks of your muffler did your driveshaft leave the chat once? Maybe post some pics of it.

Yes, long time ago. Exhaust is probably my next project.

Blackjack · Nov 24, 2023

Flexlex said:
Yes, long time ago. Exhaust is probably my next project.

Did you have the shaft checked for straightness and balanced after that?

Flexlex · Nov 24, 2023

Blackjack said:
Did you have the shaft checked for straightness and balanced after that?

Was replaced with a new one.

Blackjack · Nov 24, 2023

Flexlex said:
Was replaced with a new one.

So is it the front or rear ujoint that gives you the most trouble?

PurpleTJAZ · Nov 24, 2023

For what its worth ......I was having a similar problem on rear drive shaft u-joints wearing out about once a year. I consulted someone who is a "wizard" of sorts on TJ' s and he recommended switching to a "high speed" grease. I started using Lucas 10301 in the green tube. Problem gone!

Flexlex · Nov 24, 2023

Modoc Guy said:
If you’re looking to truly adjust the rear differential, you’ll need adjustable upper and lower control arms.

And the more lift you have, the less you’ll be able to keep the transmission tail shaft and differential center lines parallel.

That’s why we adjust the pumpkin to decrease the running angle of the u-joint at the differential. But you may also need to decrease the angle at the tail shaft too, because it’s not the total angle difference between tall shaft and differential, it’s the angle at each u-joint.
Neither u-joint can safely run at too great an angle.

That’s where motor mount lifts come into play, helping to decrease tail shaft angle.

And you said your lift is only 1 1/2”, which isn’t much. But the photo you posted shows what looks like a much higher lift.

Have you measured your lift height to confirm your assertion? IIRC, stock is 8” and 12”, rear and front respectively.

With a 1 1/2” lift, you could probably get away with only changing differential angles, but with more lift, you’ll need more adjustment at both ends of the driveshaft.

And yes, the double carden u-joint set allows for more misalignment, but not any more than the total of both u-joints.

Just be mindful adjusting the dual adjustable control arms. It’s easy to move your differential center point in the wheel well with those, and that starts messing with track bars and other things connected to, or near the differential.

That’s my 2 cents. And somebody smarter than me

Blackjack said:
So is it the front or rear ujoint that gives you the most trouble?

Seems like the rear one fails more than the front

Premature u-joint wear

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