Driveline Confusion

[Backdraft]

Alright, time to re-hash this old subject once again. I lifted my jeep 4 inches recently, the rear springs (rustys 4 inch full packs) give me right at 4 7/8 inches. I was having some driveline vibe issues and now have 4* shims in the back and a 1 inch t-case drop. When I put a magnetic angle finder on the t-case and the pinion my angles are exact, meaning they are perfectly parallel to each other (angle reading on finder is 85.5* on pinion and 85.5* on t-case). Driving this thing down the freeway gets me some vibes at 35-45 then they go away, then at 60 theres a small vibe that returns. Its not a bad vibe, just a low underlying, buzz of a vibe. Also around 45mph when i get off the gas and coast theres a small roar comming from the rear end which suggests axle wrap. I have removed my rear swaybar and have a custom cut driveshaft under it. My problem is Ive chased this vibe down forever and am jut tapped dry of ideas. The only thing I can think of would be the driveshaft. When the shop cut it, they cut it a little too short and there is about 1 5/8 inch of spline engagement. The driveshaft IS balanced and is the same one I was using before the lift(no vibes, but less than ideal engagement). Other than the driveshaft and u joints(rear is new, front isnt, neither have ANY play), the only thing i can think of is axle wrap which was mentioned to me once before, but it doesnt seem like the cause considering I dont romp on the gas at all during acceleration. Im seriously considering getting a SYE and CV driveshaft in a couple weeks when money permits, but would like to solve this problem without shelling out 600 bucks.Anyone with a clearer brain and expierence chasing this bug feel free to chime in with yer opinion. And sorry its such a long read.

Thanks

Mike

Disclaimer: My skill with dealing with lifts is extremely minimum, and I dont practice K.I.S.S. very often

 

[meangreenjeep]

It is possible to have your output/input angles parallel and perfect and still have vibes...due to an overall operating angle that single u-joint shafts can't hide. I drove like this for at least 2 years without problems...just irritating vibes that come and go. How high is your tolerance for vibes?

 

[Georgia Mike]

Try going to a 2.5 degree shim instead. This will allow for rotation of the axle under load,and will put you just about right at even under normal driving conditions

Edit:I'd seriously consider the SYE,or at least go get your current shaft lengthened a bit for more output shaft contact.

 

[Backdraft]

I replaced 2.5* shims with the 4* and it actually helped it a little. With the 2.5* I didnt have any vibes until I got to 60 and they were a bit worse than what I have now at 60mph.

As far as my tolerance for vibes goes, I have none. Im a perfectionist, but if I have to live with it for a couple weeks I really have no choice.

And with the SYE, I am seriously considering getting it, but with losing a job 3 months ago, and starting a new(better) one this comming tuesday I wont have the funds availible to throw at the SYE until after a couple weeks pass. The driving Ive got to do with the new job is moderate (around 200 miles a day) and it looks like the vibes will irritate the crap outta me, but its a means to an end of sorts. The first thing Id like to do is locate a stock driveshaft locally if possible or have mine lengthened to stock or just a hair longer than stock specs. If this doesnt work, itll be ime for the SYE. Im just a poor boy trying to save a buck if I can....lol

Anymore opinions are welcome

Mike