I'm having some issues with driveline vibrations after installation of my lift, which is at about 4.5" in the rear via an S10 bastard pack (XJ main leaf + first 3 S10 leaves). Replaced trans mount, u-joints seem OK (Jeep has 153k), installed a t-case drop and it helped a bit, but after reading up on proper drive line geometry I think the issue may be that my pinion angle is off. After installing the lift it's rotated upward rather than parallel with the t-case output:



The vibration occurs mainly between 25 and 40 mph and between 50 and 55, especially when accelerating or trying to maintain speed into a strong headwind, which makes me believe the pinion is rotating further upward under load.

So, the point of this thread, I'm hoping to correct or at least reduce the vibes with shims and I'm wondering which ones I"ll need to get the pinion angle in line.

I grabbed an angle finder and took some measurements, but I'm not certain whether or not I'm doing this right, so here are some pics to show what I found.

T-case angle as measured at the driveshaft yoke shows 5 degrees:



rear axle measured at the yoke shows 9 degrees:



rear axle measured at the little flat spot on the bottom of the pumpkin (Chrysler 8.25) shows 7 degrees:



Which measurement for the pinion angle is correct? If I use the ds yoke I should need a 4 degree shim. If I use the flat spot on the axle housing I should need a 2 degree. Thoughts?

 

For a single u-joint driveshaft (like you have) you want the transfer case and pinion angles equal, meaning they are parallel. This keeps the entire rotation in phase.

This would be the ideal set up, but you also have to consider the driveshaft angle too, the difference between the pinion and driveshaft. Too much angle here will cause vibration too.

I can't tell in your pic (and can't recall from memory) if that flat area on the housing is parallel to the pinion. Are you wanting to shim the pinion up, and reduce that angle? I find that to be only a band-aid, and while it will remove some vibration, it also creates a phase problem.

 

Actually I was hoping to shim the pinion down to get it closer to the same angle as the transfer case output, to reduce vibrations from the two being out of phase. If that makes sense.

 

^ Yes I think this should be the first thing to try.

 

here is a link for ya http://www.cherokeetalk.com/forum/f6...-angles-13941/

 

you are only off 2 degrees. I doubt this is going to do it. maybe, but I dont think so. you hay have a better chance dropping the t-case down a little more. The joint at the case is at the highest angle.
This sounds stupid, but make sure all of the u-joints are tight and do not bind. maybe even take the shaft out and really feel the joints. you just changed the angle they have been running at for however many miles and they may not like it.

 

i have the same set up and the same problem allthough ill probably get a sye before trying to fix it.

 

Is your trans mount good? just curious as the mount now holds the load at a different angle not that you have a T/C drop and could be causing noise/vibrations too, just something to check.

But I would think you need to shim the pinion down to match the angles. but 2* isn't a big deal. when you load the back up with gear or hook up a trailer the pinion will rock down as you load the back with more stuff.

 

2* off can be a big deal depending on how much axle wrap he has upon acceleration. Ideally the transfer case output yoke is suppossed to be parallel with the axle yoke, but that doesn't take axle wrap into consideration. Set the axle yoke 1-1.5* lower then the transfer case yoke,that way upon acceleration and maintaining speed the axle yoke will point up slightly and be perfectly in line. Of course it will nose back down upon deceleration, but that's not as big of a deal and generally doesn't produce vibes since there is no torque being applied.
Now if you had a double cardan shaft you would want the axle yoke to point directly at the transfer case output shaft "parallel to the driveline". Then take the 1-1.5* change into account and set it slightly lower. Like stated above check both u-joints, and your tranny mount. Wouldn't hurt to get the driveshaft balanced. Another thing that causes driveline vibes is a bad pinion bearing which is very common.

 

is it me or is the drive shaft in kinda far in the rear cone,maybe try sticking a couple of washer between crossmember and drop kit see if it helps a little more . Also dont look like the ujoint been greased in a while

 

Shaft is pulled out some from its original running position. You can see the clean spot. I agree with the angle changing, but he gets a vibe at cruising speed also. Typically the change in angle is most pronounced on take off, where you have the most torque.
I guess we could answer that easily,
If you let off of the throttle and coast at highway speed where you have the problem, does the vibe go.away?
Actually, to add, downshift the trans to third and see if it still vibrates, this will drop the rear pinion angle down, with the load of decel.
If in both cases you still have a vibration, its the t case angle.
Now for fun, have you run without your front shaft? Isolating the rear.

 

X2 good idea

 

Thanks for the responses guys. I will pull the ds to check the u joints more closely, and grease them. Been meaning to, need to get more grease. If I decide to replace them will I absolutely need a vise or will a large c-clamp work?

I replaced the trans mount after the lift and it did help with the vibes a little. The old one had gotten a bit soft.

I forgot to mention I swapped the rearend from a D35 to an 8.25 at the same time as the lift. That's the original DS I'm running, if the rear end was lifted any less I think it would be to long. The slip yoke is barely pulled out of the t case. Could that be affecting anything?

My rear springs are so stiff I doubt I have much axle wrap, if any. I'll try the downshifting into 3rd and see what happens and also try running without the front shaft.

I appreciate you guys trying to help me figure this out without just telling me to get an SYE. If I ultimately need one that's fine, but I like to figure out why I'm having a problem before just throwing money at it. :-)

 

old thread, no answer...,