Topic: Bad Vibes

[95 Lowbuck]

I've got a problem with my front DS and vibrations.
I have done a search on this Forum for some answers
but could not find any that will help.
I'm running a TrueTrac in the front which means the DS
is turning all the time.
I had it straightened and balanced with no luck.
Then I checked to make sure my u-joint angles were parallel.
Bingo, there is a 10 deg. difference and I'm not even
running a TC drop. I don't think I have a chance.
I'm don't want to point the pinion down with 10 deg. shims
and end up with a castor problem.
I am still at a loss how a TJ without the disconnect gets away with it.
I was thinking maybe a front CV DS from an XJ might help.
Has anyone tried this?

[Bounty Hunter]

How much lift?  Any aftermarket shackles?  What length?

What else have you done to change the jeep from factory?

[Jeffy]

I've got a problem with my front DS and vibrations.
I have done a search on this Forum for some answers
but could not find any that will help.
I'm running a TrueTrac in the front which means the DS
is turning all the time.
I had it straightened and balanced with no luck.
Then I checked to make sure my u-joint angles were parallel.
Bingo, there is a 10 deg. difference and I'm not even
running a TC drop. I don't think I have a chance.
I'm don't want to point the pinion down with 10 deg. shims
and end up with a castor problem.
I am still at a loss how a TJ without the disconnect gets away with it.
I was thinking maybe a front CV DS from an XJ might help.
Has anyone tried this?

Have you replaced the U-joints?  There usually aren't as many problems with the front driveshaft since it has a lot more length.  I'm sure mines out of phase since I run a 1" MML.

Problem with a CV is that you really should have the lower U-joint inline with the driveshaft.  This isn't usually a problem with a stock Jeep but when you're lifted it becomes more of a problem.  The only way to correct for this would be to cut and relocate the perches and shock mounts.  Then you'd have to cut the inner knuckles off and rotate them to keep teh caster in spec.

[95 Lowbuck]

I'm running a RE 4" lift with a CV DS in the rear so no TC drop
to affect the front DS angles.
When I had my front DS in the shop they put in new U-joints.
I have not checked this guys work though and should check the
shaft for straightness.
Right now the angle between the front DS and the D30 Pinoin Yoke
is 5 deg. (Pinoin pointed down)
Maybe I could get by with a CV DS and some 2-3 deg. shims and
live with a little less castor.

[jfrabat]

I got the same lift, but no problems...  My mechanic (the second one, anyway!  That's the one that really knew his stuff!) recommended that to put a couple of shims in the front to compensate for the lift, but it should be very small (0.5 to 1*).

Felipe

[95 Lowbuck]

Found out TJ's do run a CV style front DS.
Guess that's what I will try.

[Bounty Hunter]

5º down doesn't sound bad, your front pinion angle should stay close to correct despite your lift.  I would not install a CV front driveshaft or put shims on the front axle, I would look elsewhere for your problem.

There are thousands of YJ's lifted without that problem, look for a worn or out of balance part before doing any uncommon modifications like the CV or shims.

Your front pinion should be parallel with the front output of the transfer case, so the pinion will appear to point downward from the driveshaft.  Grab an anglefinder and compare the pinion and TC output angles.

[95 Lowbuck]

I think my problem is the difference between the TC and the D30.
With a angle finder I get a 10 deg. difference. They are not parallel.
I may have not been clear on a previous post, my pinion on the D30
is down from the drive shaft by 5 deg. but up from level.
And the output from the TC is pointing up.
But I think your right about checking other parts first like the
condition of the DS. (straightness)

[Bounty Hunter]

From the perspective of the driveshaft, the pinion pointing down and the TC output pointing up would put them close to parallel.  If they're both 5º from the driveshaft you're good to go on angles.

This is what you're after:

[95 Lowbuck]

I agree with your diagram 100%.
The condition with my YJ useing your diagram is the D30 is rotated CW 5 deg.,
and the TC is rotated CCW 5 deg. giving me a total of 10 deg. difference.
I don't have a TC drop and I'm useing stock spring shackles.
If no one else has a problem with this condition then I should
take a close look at the Drive Shaft. (which was just rebuilt and balanced)

[Bounty Hunter]

Not sure why you're experiencing problems with such a common setup.  Are you sure the front springs were installed correctly and not backwards.

Your pinion should not be pointed up.

Have you checked your caster?  Use the angle finder on a line parallel with the upper and lower balljoints.  If your caster is in check, your pinion angle should be close or spot on.

[95 Lowbuck]

So I wound up getting a CV DS and pointed the pinion to the correct
angle using 2 deg. shims. (Got rid of 80% of the vibration)
Checked run out of the DS at both ends and the middle.
The Transfercase side was .007" and the Pinion side was .015".
Should be .010" max according to the FSM.
Swaped the DS 180 deg. and the run out stayed with the Pinion Yoke
not the DS.
This was a brand new Pinion Yoke from 4wd Hardware, I wanted
to run U-bolts instead of straps.
Swaped the original Yoke back in and got .004" run out,
but still had a little vibration.
In desperation I changed out the Transmission Motor Mount, and it worked.
It was not broken but 120k miles weak.