Adjusting front axle pinion angle

bobthetj03 said:
No, I have not. I'm saving my caps right now for the SYE/DCDS. Once I get this done I'll post my results as to whether it fixed my vibe or not. Gonna be a couple months away.
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I just did the SYI in mine and I still have it. I'm in the same boat as you, 04 LJ with a 3 inch lift, 33's and 4:88's. With the front shaft out its fine. I rebuilt the stock front shaft, bought a Tom Wood shaft, and now a Denny's driveshaft. Same vibe, same harmonics. I noticed today that the shaft has some run out on the end near the transfer case, I'm wondering is the front yoke may be causing me some issues.
 
jeepndogs said:
I just did the SYI in mine and I still have it. I'm in the same boat as you, 04 LJ with a 3 inch lift, 33's and 4:88's. With the front shaft out its fine. I rebuilt the stock front shaft, bought a Tom Wood shaft, and now a Denny's driveshaft. Same vibe, same harmonics. I noticed today that the shaft has some run out on the end near the transfer case, I'm wondering is the front yoke may be causing me some issues.
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I wouldn't rule it out. I purchased a new front yoke and will replace it when I do the SYE just to rule that out.
 
Sorry to revive an old thread and I know this is a common question, but I want to be sure I adjust correctly. Visually, it looks like my rear pinion angle is slightly higher than my drive shaft (see attached pic).

I get a shuddering in the rear end when starting from a stop. Otherwise, has no problems. From reading through the thread, I believe this is exactly the orientation that I don’t want so I need to adjust it to lower the pinion (ie lengthen the lower control arms or shorten the upper).

Given that both my upper and lower arms are adjustable, does it make much difference which I adjust? The lower arms are almost fully threaded in so lots of room to extend. I haven’t looked too closely on the uppers, but I believe they have some room as well.

Appreciate the help!

0FC31195-2D3C-4895-A9D4-893AB03D8D79.jpeg
 
John9999 said:
Sorry to revive an old thread and I know this is a common question, but I want to be sure I adjust correctly. Visually, it looks like my rear pinion angle is slightly higher than my drive shaft (see attached pic).

I get a shuddering in the rear end when starting from a stop. Otherwise, has no problems. From reading through the thread, I believe this is exactly the orientation that I don’t want so I need to adjust it to lower the pinion (ie lengthen the lower control arms or shorten the upper).

Given that both my upper and lower arms are adjustable, does it make much difference which I adjust? The lower arms are almost fully threaded in so lots of room to extend. I haven’t looked too closely on the uppers, but I believe they have some room as well.

Appreciate the help!
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That's pretty far off, you'll probably have to adjust both.
 
Anyone think I should order a transfer case drop or a motor mount lift instead? Aren't they playing the same role to correct the pinion angle? If so I'm contemplating just adding the lift first and wait it out to see if I get any altered drive vibes instead of just ordering one when I install my new 2.5 lift, didn't think it's too big of a deal being it's at a 2.5 different and not like a 3.5 or 4 lift


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Nicholas said:
Anyone think I should order a transfer case drop or a motor mount lift instead? Aren't they playing the same role to correct the pinion angle? If so I'm contemplating just adding the lift first and wait it out to see if I get any altered drive vibes instead of just ordering one when I install my new 2.5 lift, didn't think it's too big of a deal being it's at a 2.5 different and not like a 3.5 or 4 lift


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I’m not an expert on it, but would think you have a good chance of not having any problem with the 2.5” lift. I’d put it on first and make the mods later on if you have any issues.
 
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mrblaine said:
The front and rear drive shafts are opposite in forgiveness when it comes to angle. The rear will almost always have an issue if it is adjusted slightly higher. It is very forgiving if it is too low though.

The front is the opposite. Get it slightly low, probably going to let you know about it. Lose some caster and get it too high, it pretty much doesn't care.
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What's the simple theory behind this?? Anyone know? Thinking back to learning dynamics during my degree, we learnt all about in/out of phase etc, but nothing that would explain this.

I ask because a) I've got a HP Dana 30, so assume the same applies but would like to be sure, and b) knowledge is fun! I love this forum.

Side note; while I've got you @mrblaine, I was told on another thread you may know why LP front diffs exist? I can't think of any positives? It was brought up as my export model is factory Dana44 rear and HP Dana30 front. Again, just curiosity.
 
JoshNZ said:
What's the simple theory behind this?? Anyone know? Thinking back to learning dynamics during my degree, we learnt all about in/out of phase etc, but nothing that would explain this.

I ask because a) I've got a HP Dana 30, so assume the same applies but would like to be sure, and b) knowledge is fun! I love this forum.

Side note; while I've got you @mrblaine, I was told on another thread you may know why LP front diffs exist? I can't think of any positives? It was brought up as my export model is factory Dana44 rear and HP Dana30 front. Again, just curiosity.
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Its simple, drive shaft angles off = vibration

Low pinion diffs are built because they were used primarily on the rear. It wasnt until the mid-60s when the high pinion became popular with it being used by Ford in the front of their 4x4 vehicles. Why have 2 different dana 44 gear sets, castings for the housings, etc., basic economics for Dana until Ford had Dana mass produce the HP diff.
Tim
 
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JoshNZ said:
What's the simple theory behind this?? Anyone know? Thinking back to learning dynamics during my degree, we learnt all about in/out of phase etc, but nothing that would explain this.

I ask because a) I've got a HP Dana 30, so assume the same applies but would like to be sure, and b) knowledge is fun! I love this forum.
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Never actually considered the why behind it. I only know it from experience.

Side note; while I've got you @mrblaine, I was told on another thread you may know why LP front diffs exist? I can't think of any positives? It was brought up as my export model is factory Dana44 rear and HP Dana30 front. Again, just curiosity.
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The positives is that in most situations or applications there aren't enough negatives to warrant a different housing.
Export model TJ? If so, it came with a LP from the factory and someone swapped in a HP.
 
astjp2 said:
Its simple, drive shaft angles off = vibration
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But why can a driveshaft angle OK if it's high on the front, but bad if its high on the rear? and vice versa


astjp2 said:
Low pinion diffs are built because they were used primarily on the rear. It wasnt until the mid-60s when the high pinion became popular with it being used by Ford. Why have 2 different dana 44 gear sets, castings for the housings, basic economics until Ford had Dana mass produce the HP diff.
Tim
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Got it, assumed that was the case but wasn't confirmed last time. Thanks!
 
JoshNZ said:
But why can a driveshaft angle OK if it's high on the front, but bad if its high on the rear? and vice versa
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rear axle pinion wants to tip up when you try to go forward and front wants to tip down, so that is why
also read the tom woods article I posted a link to above.
 
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@mrblaine, yea, probably an unnecessary question, but worth an ask. I'm happy with "it just does"

Re the export model. Im 99% sure that TJs sold in NZ came factory with a Dana 44 rear and a HP Dana 30 in the front. @Kiwi TJ, I'm assuming yours is the same?
 
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JoshNZ said:
But why can a driveshaft angle OK if it's high on the front, but bad if its high on the rear? and vice versa
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In the rear, there is some axle wrap that will raise the pinion and weight transfer under acceleration also changes the pinion angle. The same is true in the front with regard to torque lean and weight transfer causing the front to rise.

Why they vibrate is due to how a CV works in that you want the driveshaft pointed to keep it square to the pinion. If there isn't a CV in the rear due to a SYE, or fixed yoke, then the two angles are moving out of the proper angle they need to be to each other to stop vibrations and shaking.
 
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JoshNZ said:
@mrblaine, yea, probably an unnecessary question, but worth an ask. I'm happy with "it just does"

Re the export model. Im 99% sure that TJs sold in NZ came factory with a Dana 44 rear and a HP Dana 30 in the front. @Kiwi TJ, I'm assuming yours is the same?
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Does the front axle have slots for the lower control arm bolts or round holes?
 
astjp2 said:
rear axle pinion wants to tip up when you try to go forward and front wants to tip down, so that is why
also read the tom woods article I posted a link to above.
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OK cool, I guess all the times I've read about setting pinion angles, people mentioned accounting for wrap, people also mention that the front can be above/the rear can be below, but specifically linked the two.

But yea, makes a lot of sense
Thanks
 
JoshNZ said:
Holes.

I have adjustable control arms if your question is towards pinion angle.
Or does this define where the axle may have come from?
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Although Jeep had the low pinion axle from the TJ in production when they switched to the LP axles in the XJ, they still made them the same as the other XJ axles with holes since the rear mount is slotted at the unibody. It stands to reason that they would do the same for the TJ and keep the slots that all other TJ's have even if they were to build a TJ specific front HP 30. Since you have holes, I highly suspect that you have a HP 30 out of an XJ. If you run the VIN on the site that is posted from time to time to get the build sheet, that would tell us one way or the other.
 
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