Correcting the rear pinion angle (1 Viewer)

[lumbee1]

I've got some mild vibration at 45 to 52mph from the rear of the truck. I pulled the rear driveshaft to verify and I've got a DC front driveshaft.

To correct pinion angle, it appears I have several options:
Install adjustable upper control arms. Rotate the top of the axle forward for proper pinion angle but keep the original lower control arms.
Install adjustable lower control arms. Rotate the bottom of the axle backward for proper pinion angle but keep the original upper control arms.
Install extended lower control arms and adjustable upper control arms to put the axle further back and proper pinion angle however replaced both upper and lower is very expensive.

I'm not trying to spend $800 to fix a mild vibration but I do want this fixed. Adjustable lower control arms means a portion of the rod is threaded and technically weaker. The lower control arms are also subject to impact.

Upper control arms seems to fix the problem easily and cost the least but move the axle slightly forward.

Another option:
I made my own adjustable panhard bar. Cut the ends off the OEM lower control arms and weld them to a cromoly tube that's slightly longer. Either made or purchase adjustable upper control arms. This would be the best of both world and shouldn't be all that expensive.

 

[CrabCake]

Delta is about to sell some of their new super strong lower control arms...they only sell in stock length as they say that if you do adjustable lowers, it will put the tire into the sheetmetal, so they recommend adjusting with upper arms only. I have adjustable uppers on mine installed by the PO and seem to do the job just fine with a lift/tire similar to yours.

Per @Delta VS web site...

Somebody is bound to ask "but why are they stock length??" Because when flexed out with 35" tires, stock length lower links are already pushing the back of the tire into the back of the wheelwell, that's why. If you install longer lowerlinks you WILL get significant tire-sheetmetal interference. Pinion angle should be adjusted via adjustable upper links if you have the need for adjusting things.

 

[landtank]

how tall is the lift? If around 4" then the best option in my opinion is an extended lower control arms. During lifting the rear axle moves forward and the pinion moves slightly upward.

Extending the rear arm takes advantage of the forward movement and subtracts some of the driveshaft slope to lessen the angle at the t-case.

Installing a 2" block on the rear bump stop will eliminate rubbing even if running 37" tires.

If you are higher than 4" it might be time for a rear DC shaft. In that case adjustable uppers would be the easiest to get the angles right to run smoothly.

If you end up with the DC/Adj UCA setup, once set, I'd weld the arms in place. People have had the threads strip out on both arms simultaneous.

But don't discount a bad slip yoke!! They are common on our rear shafts.

 

[lumbee1]

how tall is the lift? If around 4" then the best option in my opinion is an extended lower control arms. During lifting the rear axle moves forward and the pinion moves slightly upward.

Extending the rear arm takes advantage of the forward movement and subtracts some of the driveshaft slope to lessen the angle at the t-case.

Installing a 2" block on the rear bump stop will eliminate rubbing even if running 37" tires.

If you are higher than 4" it might be time for a rear DC shaft. In that case adjustable uppers would be the easiest to get the angles right to run smoothly.

If you end up with the DC/Adj UCA setup, once set, I'd weld the arms in place. People have had the threads strip out on both arms simultaneous.

But don't discount a bad slip yoke!! They are common on our rear shafts.

3" lift in the rear, 35" tires, and 2" block already installed on the rear bumpstops.

It's not the slip yoke for sure. My previous 280K rear driveshaft was covered in scratches and somehow the flanges were out of phase at an angle. The vibrations were noticeable and I was able to source a new, balanced, OEM driveshaft. The new driveshaft has mild vibrations at the same 50mph as the previous driveshaft.

 

[landtank]

what you describe is the typical rear pinion alignment after lift problem, but you don't usually see that until 4+" of lift. Did you measure your lift height or are you stating the label on the kit you bought? It's not uncommon to see a larger amount of actual lift over the advertised label especially if your truck is on the lighter side.

Other things to look at are bent Lower Control arms. They can shorten the distance from the frame to the axle putting some angle in the axle's position causing the u-joints to work though an odd alignment. Also make sure the axle is centered in the fame and not favoring one side. This can add a compound alignment issue.

Lastly, don't underestimate the effect of all 3 things ( pinion, LCA and offset) even if out small amounts, accumulating into producing this vib problem.

 

[lumbee1]

what you describe is the typical rear pinion alignment after lift problem, but you don't usually see that until 4+" of lift. Did you measure your lift height or are you stating the label on the kit you bought? It's not uncommon to see a larger amount of actual lift over the advertised label especially if your truck is on the lighter side.

Other things to look at are bent Lower Control arms. They can shorten the distance from the frame to the axle putting some angle in the axle's position causing the u-joints to work though an odd alignment. Also make sure the axle is centered in the fame and not favoring one side. This can add a compound alignment issue.

Lastly, don't underestimate the effect of all 3 things ( pinion, LCA and offset) even if out small amounts, accumulating into producing this vib problem.

Awesome response. This gives me something to look into.