Drive shaft vibes, pinion up or down?

I have some vibrations that I know are driveline angle related they get a little better when under acceleration and worse on deceleration/coasting do I need to angle my pinion up or down?

I've taken flange measurements and everything seems to be within 1-1.5° of parallel and straight as far as I can tell but still have vibes coming in most noticeably after 55mph and remaining strong up to 75mph where they reduce slightly beyond 80 but never fully smooth out.

Not noticeable below 45mph.

 

Do you have a center bearing lowering kit on it now? This will help with lift angles

 

Yes I do, and I have reinforced the carrier bearing using the urethane injection method.

 

Umm, I’m pretty sure it’s up/positive…
Is it a new vibration from a lift or something? Maybe a weight on your driveshaft fell off?


Not that you asked but I ran into this too after my lift. You probably know but if you don’t mind spending money, maybe grab a pair of 1° slotted shims from headstrong off-road, try one way for a week or two and if that fixes it great and if not try the other way. Skinny side forward to face the pinion up.
I used a 3° shim then added fender washers with longer bolts on the cb to get the entire d/s and pinion close to same operating angle.

 

Not new it's been around for a long while and I can't seem to be rid of it.

I have wedges angling the pinion down (fat end forward) right now IIRC, I think they're 2° wedges and this got the TC and Diff flanges pretty close to parallel but didn't do much to change vibes so either I'm not getting good readings with my angle gauge, which is possible, or I have another issue.

I have carefully looked over my drive shaft and can't see any remnants of a broken weight tack weld or any area of missing paint so I doubt I threw a weight but also possible I suppose.

I'm using long bolts and 1/8" stainless structural washers to be able to fine tune my carrier drop and have played with different heights and where it's at now seems to be it's happiest spot, appropriately 1° angle difference between front shaft and back shaft.

I've about memorize the driveline vibes thread and angle finding/adjustment steps in it and it just ain't working for me.

Maybe I have thrown a weight?

Was hard to tell before as I had so many different vibes but over the last year or two I have gotten newer tires, Archive Garage Hammer Hangers with cross tube, done my front wheel bearings, got stouter springs etc etc and every little change has helped it seems but I still just can't seem to get rid of my vibes.

I've been meaning to pull the rear shaft and drive in FWD to confirm after these changes but haven't had a chance yet.

The first time I tried that it didn't change much as it was actually my shistey old KO2's that wouldn't balance but I've effectively eliminated everything other than driveshaft at this point.

Most days I can live with it, some days jiggling like a paint shaker on the highway drives me close to madness.

Guess what kind of day today was.

 

Even I still have good and bad drives lol. For the most part mine are more good then not.

I thought I’ve seen your name in the hammer hanger thread and many other places as well lol.
Sounds like you have lots of things going on under there. Maybe it’s just the truck at this point? The leaf to axLes not tightened and lined up, really I’m just throwing suggestions out there at this point. Sorry I can’t help more. You’ve done everything I would have done or suggested (not that I’m an expert by any means, I’ve just read the driveline thread a lot and personal experience)
The only people I know that have gotten all their vibes to go away ended up with a single piece driveshaft. I think someone was selling a tom woods one in the b/s/t. Or, is there a driveline shop near you that might not charge an arm and leg to diagnose it?

 

TC and Diff flange angles in reference to eachother means nothing unless the center joint is at a near zero, and due to how the 2 piece driveshaft is phased on our trucks aligning the joints with a zero center deg and equal and opposite tc and diff is not proper.

For a proper running angles you must make the TC and center or center and diff at equal and oppsoite angles, with the 3rd joint at a near zero. With how suspension cycles this is best to do with the TC joint at a near zero then make the center / diff at equal and opposing angles at ride height.

Unfortunately with how flat our leaf springs have to be you get quite a bit of axle wrap which makes for take off vibrations, but if joint angles are proper at ride height you shouldnt have vibes at speed.

 

Can you elaborate on what you mean by the third joint at a near zero?

Are you saying my front shaft shouldn't be inline with the rear shaft?

So front shaft parallel to the ground inline with the TC flange then the diff flange inline with the back half of the driveshaft?

Meaning I need to raise my carrier bearing and angle my pinion flange up?

 

you gotta get out and do measurements and see where you are at. The easiest way would be to zero your angle finder on the bottom side of the shaft between the tc and center carrier, then take your angle finder and place it on the bottom of the pumpkin of the rear axle. If its zero this will let you know that the working angles of the center joint and the rear joint are equal and opposing. Then you can measure the working angle of the joint at the tcase

Its bad practice to reference off the ground for driveshaft angles. Reference off a surface (theres a great flange on the tcase) of your driveline as the driveline is what needs to be oriented properly to itself, not the ground. You do not want the shaft to be (both pieces) inline with each other as the phasing (how the u joints are oriented rotationally along the shaft) is not setup to cancel out vibrations via the front most and rear most joint. It can only do so via the front and center, or center and rear.



https://www.waterousco.com/media/wysiwyg/pdfs/content/J3311-1-DSSP.pdf

page 16 (labeled 13) Multiple shaft installation through page 17 (labeled 14) will be in your interest.