Drive line vibrations.

[Goose]

Ok I have been tracking down a driveline vibration for a looong time and it's starting to wear thin.. The truck (84 J-10 ) runs smoothly untill 45 to 55 mph at this range it vibrates pretty badly it smooths out either side of this. if you put the clutch in and coast it still vibrates under full acceleration it shakes under decel it shakes with 3500 lbs in the box it shakes as well as empty.

Heres what I have done.

Angles. pinion is 7 degrees engine is 5 degrees with a 1 degree misalignment left to right ( I missed when centering the engine mounts).

Phase. I have pulled the yoke on the rear shaft and flipped 180 to make sure it wasnt out of phase. no effect pulled front shaft drove it, no change pulled rear shaft, drove it, no change.

Checked all wheels and tires for bent rims out of balance tires out of round tires. nada.

Pinion bearing has a miniscule amount of play up and down. a few thousandths, t-case output is tight all engine/tranny mounts are new.

I am begining to wonder if there is something in the front axle u-joints or somewhere else.. any body have any suggestions?

[jeepsr4ever]

Mud in the rims?
Tire bulge?
Bad U-joint?
Only while driving downthe road?

[Goose]

Rims clear of mud
All ujoints replaced
Tires don't appear to have defects.

But.. I put about 3000 lbs in the bed today (pulled a Backhoe on a trailer kept loading the fifth wheel) The vibrations seemed to go away as the suspension compressed.. I pulled the drive shaft and disassembled the yoke the splines are fine.. I think I am gonna lose my pea pickin mind with this..the truck has a 3" lift springs in front and blocks in back.

I am wondering if the lift blocks have too much angle built into them (In my world a 3" lift is not very much, truly I wouldnt have shimmed the pinion angle up at all with this lift.. these blocks are 5" long and there is 3/4" taper from front to back.. thats like 6 degrees isnt it?? (I suck at the math for this stuff) but the pinion angle is up compared to the driveshaft..

Damn I need pictures.

[Mudrat]

Have you checked the axle for square? Might be a little dog-leg in there that's scrubing the tires when unloaded and not notaced when loaded?

Not sure otherwise if the tires/rims are clean and the shaft angle is within spec

Be ineterested in seeing what the problem is.

'Rat

[Goose]

I will check that scrub angle..I never thought about it..(Its a big deal on a semi as the two drive axles "fighting" each other can be umm interesting but I never thought about it in this app.)

ARRGHHH I hate it when the problem is obvious and the cause is "Stealthed"

[LeadFoot]

I'd spin balance the tires before chasing my tail with drive shaft angles. It could be, but that syptom sounds exactly like a tire slightly off balance.

[youdidwhat]

I've always praticed the no more than 3* on drive line angles, that goes for front and rear/t-case and axle.

you said 5* on yours.

with my TJ with 3" lift, 5* caused vibes and dropping the angle closer to 3* was my answer.

I did a t-case drop which is easy enough useing large washers and longer bolts.
some people avoid loosing the clearance by doing a tummy tuck which is a kit I did not want to buy.

hope this helps

[Goose]

Well I pulled the blocks and swapped them out for a different set with less angle so now the pinion angle and tailshaft angle match.. I am going to balance the tire again. then Im gonna true and balance the shaft.. If none of this works, It will be for sale cheap or possibly the first J-10 on the moon.. (Hey Rat can you still get plastique?)




Really just kidding about the plastique ummm who is that knocking on my door??