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Drivetrain alignment

2K views 13 replies 4 participants last post by  sylgeist 
#1 ·
Stupid question for those of you that have done drivetrain swaps -

How tolerant can I expect the driveline to be of a crooked drivetrain? Obviously I am trying to get the drivetrain completely straight in the chassis, but I'm not sure how accurate of a measurement I need to get.

I have some vibes that weren't there before the swap, but I don't know if I should attribute them to the suspension or the drivetrain.

This is in an Unlimited Rubicon with DC shafts - drivetrain is essentially the same length as the 4.0 and tranny.
 
#3 ·
Yep adjustable arms and trackbars all around. My driveline axles actually improved after the swap due to the t-case being pointed down more.

I've had it 4-wheel aligned at a local shop.

I've tried a couple different rear pinion angles and removed the front shaft with no change. As an unrelated change I had the gears swapped from 5.13's to 4.56's and it move the vibe up 10MPH so it's definitely related to the shafts.
 
#7 ·
When you say "alignment," which axis are you referring to? Front-to-back or left-to-right? There are many variables that affect whether a crooked drivetrain is going to have negative repercussions.

Have you tried calculating your driveshaft angle? I'm not talking in one plane, either -- if the differential is offset to one side of the vehicle, this will increase the effective angle of the universal joints. As long as you're within their operating limits, it shouldn't matter where the engine is positioned.
 
#8 ·
By alignment I am referring to the drivetrain being parallel to the chassis front to rear.

My driveshaft angles are correct (confirmed by a shop when I did my suspension alignment).

I checked this weekend and DC u-joint on the t-case output is very slightly off side-to-side. I just don't see how that could be a problem when many people have their axles offset by inches from doing a budget lift. Unless I'm not understanding how those angles cancel out?
 
#10 · (Edited)
All axles are offset, very few if any are centered, it has nothing to do with budget builds, it has to do with u-joint physics and longevity.

Did the OP swap on new tires? new U-joints in the axles?, Ball joints are good? Tires are balanced or unbalanced?
 
#12 ·
Yes it does! I was just trying to get a feel for how much flexibility there would be in the amount.

The only thing that changed from last summer is the engine/trans and I didn't have this issue before so it seems like it would have to be an angle issue?

I think that is correct that the "yaw" factor is probably the spot I need to look into. Thanks!
 
#13 ·
No problem!

If you can provide some dimensions, it's easy to determine how many degrees you're off by. You may have even surpassed the maximum operating angle of the universal joints, since you're experiencing vibrations.

For the math, you'd need to provide the horizontal and vertical distances between your t-case output and the pinion yoke, from both the top and side perspectives. The "yaw angle" would also be necessary.
 
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