Drive Shaft Vibrations Solved Step-by-Step

Well, against your advise I installed the shims pointy end forward giving me now a 4 degree angle at the diff versus 0 at the Trans and have low speed take off shudder. 20 mph vibes are gone at the cb though. When I get time I'm gonna rotate the shims which should put me at 0 and see what happens. This is some serious trial and error. What Is the ideal rear diff angle?

 

Now why would you go and do that? The bottom of my drive shaft angle measurement PDF sheet has ideal angles on it.

To summarize, with our two piece drive lines. First, the front output shaft flange and the rear pinion flange want to be as close to zero difference as possible, with the error leaning toward the rear diff being 0.1 to 0.3 tenths of a degree down from the front output shaft. Second, the two drive shafts want to be in a near perfect straight line through the carrier bearing (like a one piece shaft would be), with the error leaning toward the front shaft a tenth or two of a degree less than the rear shaft. Ideally, set everything to zero, then drop the diff two tenths and raise the CB an eight of an inch.

For fine tuning, every truck is different due to suspension, load, driving styles, climate, etc. There's a reason that carrier bearing is a RUBBER mount. They all shake, straight from the factory, to some extent.

Measure. Adjust. Drive. Tweak. As any pilot will tell you, trust your instruments. MEASURE. Adjust to a few tenths. Follow the formula.

 

I installed the pointy ends forward thinking that would bring my pinion down. Wouldn't they point my pinion up if I installed them fat sides forward?

 

IIRC opposite

 

What Max said. I was pretty explicit about the fat end forward. RTFM. Good wrench practice for ya! For conceptual purposes, the leafs stay the same (ya ain't gonna rotate your entire truck) and the axle changes.

 

Yeah looks like ill be rotating them next chance I get

 

Baco, your experience and sharing it here on TW is actually pretty cool. Thank you. I had to wrap my head around installing my shims bass ackwards for a while also. Totally not intuitive. Kinda a mind f*ck. Easy mistake, that hopefully won't be repeated by others. Measurements and numbers don't lie, trust your measurements. (I can hear a sidelined TW friend laughing his ass off right about now......).

Flip those shims Bacon and let us know how your tuning goes. We're all here to help.

 

subd

 

ok so i have vibes, droped drive line mesured from flanges, 3* off orderd shims, installed shims and measured again .01 diffrence thought im ok now good right (not) drove to work today and vibes like crazy! Got home and messed with shims on carrier barring and still vibes. Measured off flanges again tonight and now 1.5 degrees off : ( Im not a mathemitician! How do I go from being .01 degrees to 1.5 degrees over night?

ANY THOUGHTS?

 

Measure the t-case flange, record measurement, note if it's up or down.

Measure pinion flange, record measurement, note if it's up or down.

They need to be parallel.

Measure shafts, they need to be parallel as well, on both axis.

Don't worry about zeroing anything tools out.

Many people leave the pinion pointed DOWN a little to account for axle wrap. You may have to experiment with that a little.

Just my thoughts.

 

thanks max. just checked again zeroed on t-case flange pinion flange 1.5* down. yesterday before i put the drive shaft back in it was .01* down when zeroed on t-case. i just cant figure out how it changed so much after work & back trip.

 

Ok get this when i got home i backed in 1.5* down went out turned truck around .02* down now so i got the torque wrench back out (thinking maybe it settled or some crap) set to 75ft lb
click click uped it to 85ft pounds clickity clickity. im thinking my springs are toast or something? funny thing is with the aal it rides much much better(aal 3 weeks old) then stk with blocks. I guess ill just keep f-in with it

 

What tool are you using for your measurements? Mine was only accurate to 0.3 and was driving me nucking futz. Replaced it with the Wixey, happy now with at least consistent measurements. Also, my numbers would change after a 15min test ride. WTF. They would also change depending on if I backed into driveway or pulled in straight. I finally "pinned " my leafs (used nyloc nuts just barely snug against the leaf bushings, Ace Hardware) and with free motion of the leafs eliminated most of the changing angle madness. Sigh of relief.

Also, as stated previously. Measure. Adjust. Drive for a week. Seriously. I'm not sure exactly what's going on, but I have to leave my truck alone for at least a few days to let new adjustments settle in. Doesn't seem that complicated, but that's been the reality. Frustrating if you are looking for instant results like me, I feel your pain.

Max is perfectly correct on the angles. Drive your truck for a bit, fill out my PDF sheet with measurements, post it as an attachment, and we'll see where you sit in a day or three.

You also didn't mention what your shaft angles were. Those are just as important as pinion angles. Don't frustrate yourself guessing. Measure.

Oh hey. You are measuring off the flanges (front flat plate just after transfer case and last flat plate just before rear differential, where the u-joints connect), right?

 

Just read your flip truck around, torque. Our posts crossed. I also realized pin the leafs was on another thread. Here's the concept.

The three bolts on each leaf that connect thru the leaf bushings to those welded brackets on the truck prevent the leafs from moving freely and thus bind up. We see it as screwed up measurements every time we move the darn thing. The nuts that hold those leafs in are M14 x 1.5 metric, in stock if you have an Ace Hardware where you live. In theory you should remove the bolts (six total) and lube them with super grease, but I skipped that step and simply removed the factory nut and lock washer which were super torqued down and replaced them with the single nyloc nut. I HAND tightened the nut, compressing the frame welded bracket, until the bracket just snugged up against the leaf spring brushing BY HAND. You want that joint to rotate freely, and the nyloc won't vibrate loose so no worries about dropping a leaf on the freeway or something.

Totally not my idea, credit and kudos to others, but it works freaking awesome.

 

im using the harbor freight angle finder and am measuring off the t-case and pinion flanges and had have drive shaft .03* apart. i was trying hard to get it done this last weekend. have to drive to cali for a funeral on friday really wanted to take my truck instead of the wifes nissan. im not very computer literate so when i get back ill see if i can fill out the sheet and post it up. thanks for help everybody.

great thread op
at least u learned me something
now i need to learn me some more computer tech

 

Cali still a possibility. The harbor freight gauge is going to be off a bit, tap the thing a bunch until it settles down.

If you're 0.3 pinion angle is UP you'll have vibes, but 0.3 down is darn near ideal. Better than mine. Put a flat metal bar against that rear flange, stick the gauge against it with the magnets, and while holding the top of the bar against the flange pull (tilt) the bottom of the bar toward the front of the truck. If the angle number on the gauge, lessee... gets smaller, you're pointed down and that's good. If the number gets bigger you're pointing up and that's bad.

And measure your shafts. Just stick the magnet on the bottom of each shaft and write down the numbers. You want the first (front) shaft number to be just a few tenths LESS than the second (rear) shaft number. Shim CB as necessary.

Sorry 'bout the funeral. Nobody makes it out of this life alive. Make sure you're having fun in the meantime.

 

.03 is the diff between the two halves of my shaft(ha ha) .02 is the diff between t=case and pinion flange using the flat metal trick. ill have to double ck if its up or down not enough sleep past few days prob screwed that up will post back tommorrow after work.
hopefully ill figure out how to post pdf form w/#s if not ill have to suck it up and ask for help from my wife. (but not if i can help it)

 

I've been seeking the "perfect" driveline angle, The Equation that Fixes All. I have a theory, I've tested it, and it seems to work.

The theory:

1. The front output shaft flange and the rear pinion flange need a few tenths of a degree down difference (pinion down). How much is a few? Less than one degree is nice. I've heard anywhere from 0.2 to 0.7. My truck is happy at 0.5 degrees pinion down. It doesn't seem to matter exactly where it is, as long as it's within a degree DOWN from perfect zero.

2. The front drive shaft wants to be a few tenths of a degree up (shallower angle) than the rear drive shaft (steeper angle). How much is a few? EXACTLY THE SAME NUMBER AS YOUR PINION ANGLE. On my truck, my pinion is 0.5 degrees down, so the difference between my front shaft and my rear shaft is set to exactly 0.5 degrees also, with the CB being physically UP from perfect zero so that the front shaft is shallower than the rear shaft. Washers, shims, chewing gum, whatever it takes to make that number match your pinion offset.

The test: They just paved a long section of road near where I live. I had a local tire dealer swap my BFG All Terrains for a set of road radials with silky smooth street tread. I installed my custom fabricated aluminum shims to set my rear pinion flange to absolute zero offset from my front output shaft flange (perfectly parallel angles). I adjusted my carrier bearing so that my two drive shafts were perfectly in line, zero offset angle. I drove my truck to fresh pavement, and swore a freaking blue streak that after all that effort, the vibes were HORRIBLE. Yeah ok. That didn't work, but why?

The solution: Went back to the driveway and swapped shims and washers and spacers around. Set rear pinion to 0.5 down, set second shaft 0.5 down from first shaft. Drove to freshly paved road. Drove again. Punched it. Slammed on the brakes. Tested every speed I could in 5mph increments. Took a corner way too fast and slide off the road into a ditch. Felt like a fool. Back on the pavement. Not a single vibration to be felt, anywhere, any speed.

My thoughts: Pinion wants to be down to account for axle wrap under load. All of our trucks experience axle wrap, even mine with those beefy expo leafs I have. So as the rear pinion rotates up, IF YOU SET THE REAR DRIVE SHAFT OFFSET TO THAT SAME EXACT ANGLE, voila, everything rotates under load into perfect alignment. Flanges are parallel with each other, shafts are in line with each other, and down the road you go. The front drive shaft doesn't change much as it's bolted to the frame through the carrier bearing, and the transfer case / transmission doesn't change much as it's bolted to the same frame, so those points remain relatively fixed (within rubber mount tolerances anyway). What moves around is the rear axle rotation under load and suspension travel, so the relationship between the rear pinion offset and the first to second drive shaft offset becomes critical as that rear axle moves up and down and rotates. When they perfectly match, everything is in tune. And since everything is just a few tenths off of one another, and as the suspension does its job, all those pesky u-joints get lubed nicely as you drive.

My results: I'm done experimenting, my truck is staying the way it is, 0.5 degrees all around. I put my BFGs back on this morning and was back to the comfortable hum of All Terrains to lull me into slumber down the road.

 

thanks tscot and max for all your input. i went out this morning before work and checked my t-case to pinion angle three times (moved truck each time)
t-case to pinion 0* or .01 up so i orderd 3.5* shims today, should be here when i get back from cali. shiming the cb has helped but still have to play with that some more. but i wont give up tell i gots it. i will post results when i get her fixed. long weekend for turky day should have it done then.

thanks again to everybody that helped on this issue.
Its bugged me for too long now hope is in site.

 

...well it looks like i'm gonna give up on this for now

Seems like nothing I do is giving positive results. Only different results.

I rotated my 2 degree shims and seems like the low speed shudder is gone but i still get vibes always from 15 to 20 mph.

I'm even beginning to wonder if I have another problem all together although the vibes only started after adding the 1" blocks in the rear. These blocks are only temporary anyway, I just don't know how long.

With holidays and another child coming within the month I have to put my truck on hold. The blocks were free (I made them using a piece of OL leaf and a piece of a regular leaf) and I only put them on to get rid of the bro lean from 5100s @ 1.75 which gave me closer to 2" of lift up front.

I think I'll just suck it up and deal with the vibes for now until i get my tax return and can either put the 3 leaf progressive AAL or a deaver pack in the back along with some OME 885x springs and UCAs in the front.

Boy when people say to do it right the first time with a lift, take their advice. At least i only have $150 bucks invested into this lift so far so no loss, and i'll still be using the billies but what a headache this has been.

I'll work on the vibes again when I get the proper leaf setup in the rear.

BTW, thanks for all the help guys!!!