slbaseballdad

ok, here are the symptoms.

pretty serious vibration 55mph to 65mph.
up to 55 and after 65, smooth.
vibration comes and goes with suspension compression. example: driving on a road with waves.
measured on the fins of the differential and transfer case, Diff is 7 degrees up, transfer case is 5 degrees down.
truck has what looks to be a 6" lift.

new ujoints both ends of the drive shaft.
no broken shims as there are none.
lift blocks are square.

since the diff will torque up under power, I figure the diff should be 4 degrees up instead of 7.

hows my thinking?

slbaseballdad

bump

PerryB

Thats correct. Four degrees would probably be about right.

slbaseballdad

ok, measured off of the outputs and got a different answer. I think that should be more accurate.


Transfer case is 6.5 degrees down and rear pinion is 5 degrees up. sounds about right I think after rear end torque.


can someone confirm?


Now, looked at the pinion into the transfer case and there's some up and down play. not much mind you. maybe a 1/16 of an inch play.


I added a 3/4 inch spacer to the rear end pinion thinking that the lift pulled the drive shaft out too much. the pinion into the transfer case still shows a shiny area 1/2 inch long indicating it has not always been exposed.


I pushed it in to cover the shiny area and then measured how much more it could push in. another 1.5 - 2 inches.


current thought then is "drive shaft isn't long enough causing wear on the splines in the pinion to the transfer case" valid?


solution: lengthen drive shaft and new pinion and balance drive shaft


what say the knowledge base?

Especial86

iTrader: (1)

Sounds like you need tapered blocks to rotate the rear pinion up about an inch or 2..
You can also buy shims..
That should help the slip yoke in the transfer case sit further inward.
You might want to consider getting rid of that driveshaft spacer too, it shouldn't be necessary.

PerryB

Deleted

PerryB

That will put the driveshaft slightly further into the T-case but will probably cause a high speed vibration due to the front and rear angles being too far out of sync with each other. They want to be at inverse angles, so if the front joint is 4 down the rear should be 4 up. I've been there and done that with this issue.

Especial86

iTrader: (1)

Yes exactly, you want to zero out the difference. Rotating the pinion up at the rear diff on the leaf spring perches with tapered blocks would do just that.. The driveshaft length should not be an issue at all.

slbaseballdad

I researched that the rear pinion should angle up just under the transfer case out put so that when under power, the pinion would torque upward therefore in alignment.


transfer case points down 6.5 degrees and rear pinion is up 5 degrees. seems good there under the above assumption.


also researched that "sometimes" the front pinion "could" pull out of the xfer case in a lifted scenario to the point that the splines are less than desired engaged on the output shaft. possibly causing a vibration or premature wearing of the splines.


I already have a high speed vibration that i'm trying to get rid of.


sounds like i'm hearing now that the angles should be the same at rest. confused.........

PerryB

Your 1 to 1.5 degree undershoot on the pinion angle is a good number. If the shaft is too short, take it to a driveline shop and have it re-tubed. They do it all the time.