3" lift vibrating from the rear help?

i have installed a rusty`s 3" lift on my `99 xj and had a bad vibration in the rear. Well i installed a trans drop and that seemed to help it some but it is still vibrating ...especially when i get off the throttle around 40 mph or right as i get back into it(the little bit of slack you know)....i have a couple questions...first if i install a slip yoke eliminator do i need to also buy a new driveline/or can i modify the stock one to make it work(i mean by using a new u-joint or something....not by cutting the shaft and installing a new end)? also is this mod worth the cost?finally does anyone have any suggestions on using shims to correct the pinion angle(the pinion seems to be pointed up ) i haven`t checked the exact angles yet(it has been sleeting all day)....but i do know on my last lifted truck the pinion pointed toward the front. more than up...i did contact rusty`s and the guy i spoke with said the pinion on mine (with the chrysler rear) needed to be up.....any opinions would greatly be appreciated.......thanks

I am running a Rubicon express 3.5" lift with a 1" t-case drop and 4 degree shims and I still have vibrations from 30-40mph. My 2000 Xj will be getting an Advance Adapters SYE and a Tom Woods driveshaft installed this week to eliminate the vibrations, once that is done I will put the t-case back in it's original position.
I have never heard of adapting your original driveshaft to work with an SYE but I may be wrong. From all the research I have done it seems that any post 96 XJ will need an SYE to correct driveline vibrations (something I found out after I bought my lift) RE makes a cheap SYE refered to as a Hack and Tap that uses your existing t-case shaft but I chose to go with a heavy duty unit for my jeep even though it cost more. You might as well try the axle shims first because they are very cheap compared to the SYE, and if they don't solve the problem then you know what comes next...$$$


Silver Bullet

Silver Bullet said:

I am running a Rubicon express 3.5" lift with a 1" t-case drop and 4 degree shims and I still have vibrations from 30-40mph. My 2000 Xj will be getting an Advance Adapters SYE and a Tom Woods driveshaft installed this week to eliminate the vibrations, once that is done I will put the t-case back in it's original position.
I have never heard of adapting your original driveshaft to work with an SYE but I may be wrong. From all the research I have done it seems that any post 96 XJ will need an SYE to correct driveline vibrations (something I found out after I bought my lift) RE makes a cheap SYE refered to as a Hack and Tap that uses your existing t-case shaft but I chose to go with a heavy duty unit for my jeep even though it cost more. You might as well try the axle shims first because they are very cheap compared to the SYE, and if they don't solve the problem then you know what comes next...

Silver Bullet

Click to expand...

how did you know what shims to use?
or did you just guess at it?
should the pinion and the tran. yoke be parallel?

A friend of mine reccomended the 4 degree shims from his experience with XJ's,check out 4xshaft.com for info on drivelina angles.

Silver bullet

xjhm said:

how did you know what shims to use?
or did you just guess at it?
should the pinion and the tran. yoke be parallel?

Click to expand...

I'm also running rusty's 3" spring pack on my '98 and there were some angled shims already mounted to the pack itself. These shims gave me a zero angle on the diff input end. The vibes I get are something that I can live with until I can afford an HD SYE and DS.

so does my pinion need to be aligned with the driveline? right now it is pointing down away from the centerline of the shaft........if the end of the pinion was raised about an inch, it would be really close......

how thick would a 2degree shim be would it raise the rear any higher?
it is about an inch and a half higher than the front after running the springs for a week..........where is a good place to order shims........local parts stores don`t have any....

I ordered my shims from RubiconExpress.com and I had them in about three days.

found a pair of 2 degree shims.......so am i correct in thinking the pinion needs to be a degree or so down from being in line with the driveshaft?

xjhm said:

found a pair of 2 degree shims.......so am i correct in thinking the pinion needs to be a degree or so down from being in line with the driveshaft?

Click to expand...

Hang on a minute - you are just guessing. I have a '93 and put a 3" lift from Rusty's in it about 9 months ago. You need to try to match the angle of the pinion with the angle of the the slip joint by measuring the angle of the u-joints. Go to Sears and buy an inexpensive protractor. I picked one up for less than $10 under their craftsman # 939840. It has a magnetic base that helps measure the angle over the u-joint cop. Rotate rear axle until the cap is on top, then measure. Do the same thing off u joint at the front. It should be as close as equal as possible (within 1 to 2 degrees). The difference between these two angles will indicate how much you need to shim it.

My new rear springs that came in the kit came with (3 degree?) shims already installed. On the 93, I took them out to get within 1 degree and vibrations GREATLY decreased. Check out the diagrams on madxj:

http://www.madxj.com/

Another problem I had was vibrations while braking. My old yoke was bottoming out causing some binding: I fixed this by buying a YJ yoke off of Quadratec. Ed Stevens has a great section explaining this on:
http://members.aol.com/Stvns/XJhelp3.html

Do you have the tires you plan on running installed on the XJ? After tinkering with all of this and lengthening drive shaft (not a necessity, but I wanted full engagement and float out the slip yoke arrangement, and had to put new u-joints in it anyway), when I installed the 31 inch tires and got rid of the stock "doughnuts", it made a HUGE difference and got rid of my vibes.

My advice, for what its worth, is to start with the inexpensive corrections first, then if that doesn't work, go to the more spendy fixes. If I bought a SY eliminator first, and that didn't take care of the vibrations, I would be furious at myself for trying to fix something that did not need to be fixed.

Be patient with it and try to do a search on this forum for past threads for other possible solutions. I know this comes up all the time on this forum and there are some great people who you can learn a ton from.

Good luck

i understand the need to take measurements.........but what angle do i need to shoot for between the driveline and the pinion? i have read that the pinion needs to be parallel with the output shaft on the transfer case...but i have also been told that the chrys. rear needs to be angled up........my xj is a `99 auto....231 case please help!!!!!!!!!! thanks

I can oly speak from my experience. As I understand it, the angle of the drive shaft is not the critical issue, nor whether your pinion is pointed up or down, only that output shaft and pinion are parallel. My pinion points slightly up, but I did not plan it. If you do buy the SYE, you run right to the yoke of the u-joint on the tail shaft and THEN you must have the pinion pointing directly at the tail shaft.

Did you mark your driveshaft before you disassembled it? If not, you could have put things back together 90 degress off, which would effect balance of the drive shaft and cause vibes.

Hope that helps

2XJ

xjhm said:

i understand the need to take measurements.........but what angle do i need to shoot for between the driveline and the pinion? i have read that the pinion needs to be parallel with the output shaft on the transfer case...but i have also been told that the chrys. rear needs to be angled up........my xj is a `99 auto....231 case please help!!!!!!!!!! thanks

Click to expand...

You are not shooting for AN angle between the pinion and the driveshaft, as a numeric quantity we can give you. The deal with vibrations is that there is an angle between the transfer case output and the front end of the driveshaft, and there is an angle between the rear end of the driveshaft and the pinion. If these two angles are not the same (or very close to the same), the u-joints operate "out of phase" and the result is vibration.

In theory, the two angles should be identical. That means that the pinion should be exactly parallel to the transfer case output shaft. HOWEVER ... under load (acceleration), the differential tries to rotate the pinion upwards. For that reason, most people advise setting the pinion angle about 1 degree down relative to the transfer case, so that they are more parallel when the drive line is under load.

There is no magic number that anyone can give you off the top of their head. You MUST get an angle finder and measure what the angles are now, then work from that.