Drive line vibrations after 4" lift

O

OSUBEAVER

Member
vehicle info: I have a 1979 Scout II, 4 wheel drive, 345 v8, I assume standard transfer cases in front and year (I'm not exactly sure, d20 I think in the rear?). All stock, has been in my family since the car lot, I bought it from my parents about 9 years ago. Major work: transmission rebuilt. New lower main engine bearing and oil pump. All other work is standard, and not major.

I read a few posts about drive line vibrations, but nothing was exactly what I am experiencing. Thank you in advance for your help.

the problem: I recently installed the Rough Country "bolt on" 4" leaf under axle lift. Everything before the lift was perfect - all lubricated, no vibrations at any speed (in both 2wd and 4wd). Now with the new kit, I have a drive line drone/vibration (really more of a sound than vibration) that comes at about 25 mph then again at 40mph. If I kick it into neutral while the vibration is happening (at 25mph), the drone/vibration is still there -however when I rev it while gliding, it will go away. I went to a shop, and they recommended 2 degrees more in my rear leaf spring shims (Rough Country came stock with 3 inch shims - I now run a 5 degree shim). Here is exactly what has been done:

1. Installed 4" Rough Country lift - noticed drone/vibration.
2. Installed 4" shackles front and rear. Drone/vibration still there.
3. Replaced 3 degree shims with 5 degree shims on the rear leaf springs. Drone/vibration still there.

Thanks again for your help - I really hope I can get this fixed for my annual memorial weekend camping trip!

Jon
 
You May have too great an angle on the drive line. Can you tell if it's coming from the front or rear? I'm not sure of this but I think there should be a difference of angle between the front and rear universals of 2 to 5 degrees.

Rob gimmel
 
Just to clarify your equipment...your axles both front and rear are Dana 44's. Your transfer case is a Dana 20. You only have one of those. Its the unit which allows selection between 2 wheel (rear only) and 4 wheel drive in either hi or lo range, which then engages the front axle in addition to the rear.
 
The vibration/drone denititely feels like it is coming from the rear. Do you have a good way I can measure the angles? When I "eyeball" the angle between the rear transfer case and the tranny looks darn well near perfect. Thanks for helping me out,

jon
 
The angle on the pan rail should be the same angle as the drive coming out of the transfer case. On the differentials you May have to pull the yoke and measure off of the seal surface. There are others here that May have better information.

Rob gimmel
 
I did a near identical mod a few years ago. I had some issues like you're having. Nothing terrible, but kind of bothersome. So let me ask some questions.
-did the rear drive line ever become separated at its spline/slip joint? If yes, did you make sure to phase the yokes exactly as they were originally? If not, you'll have vibration. Fixing it is easy. Look at the u-joints. Both of the forged yokes should be lined up, so that if you laid the shaft on the workbench, it would have two flat spots to rest on and not roll away. This is important because throughout the shaft's rotation, the speed is not constant when its placed at an angle (xfr case to axle, for instance). By using two u joints, the speed difference is canceled out. One joint zigs, the other zags. As long as both angles are equal yet opposite, there will be no vibration (well, in theory anyway).
-have you looked closely at the front axle? Sometimes a hub will stick in the "locked" position and spin that half of the differential as well as the front drive line. Same thing applies here as far as u joints go. They must be in phase. Even freewheeling (one hub locked) will cause noticeable vibration if there is a phase issue.
-have you changed u-joints? I found that the original units had "worn in" during use as a low rider. The extra motion caused by the added lift will amplify iffy joints, or a draw attention to a drive line that wasn't in perfect balance to begin with.
Adding shims to the rear end to lessen the increased drive line angle could actually cause more vibration. Toyota mini trucks used to also lower the xfr case to equalize the shimmed axle angle (an unrelated rant for another forum). Remember, you need equal, opposite angles at each end. When angles get beyond what the u joints were designed for (your situation should be fine), there are offset u joints, and cv joints that can solve these issues.
Check all of your u joints. If they move at all up and down or side to side, replace them in pairs. Also inspect the drive lines for dings or dents or missing balance weights.
My problem turned out to be a sloppy set of front joints and a sticky front hub. That mess was freewheeling happily and causing me grief even though both hubs indicated "free."
hope this helps. Let us know how it works out.
 
Thanks for responding dealbreaker -

I don't think anything was separated during the lift, everything was still together - I did notice that the drive line looked like it was pulled out (I could see the fresh metal where it was always in as a low rider, in fact it still is out a little). Is that enough to mess that up?


I did look closely at the front axle. I rolled it front at back wards in neutral to make sure it wasn't spinning, then again with the motor running and the tranny engaged. The front drive line didn't spin.


Interesting about the u-joints. I played with the rear ones to see if there is any play, and they felt tight and normal. Perhaps I should replace them still? I have not checked the front, I will do that tomorrow. Also about the shims: I read on another forum where a guy said you should never run shims, should I take them out all together? What is weird is that the Rough Country bolt on comes with the 3 degree shim in the rear built in. Did you take that shim out and drop the transfer case? I forget what I saw when I was looking under there, something running perpendicular to the body frame that made it look like a real pain to drop the transfer case (I have heard that dropping the case is preferred). Also, I'm not to sure how I could tell if a balance weight is missing from the drive line, I suppose something could have fallen off when I was banging the leafs into place.

Thank you so much for your advice-

jon
 
The xfr case mod in the toyota situation is a hoaky fix at best. I would never advocate doing this to a Scout. I have 4" Skyjacker springs and shackles that are about 1.5" over stock, and 33" tires. After fixing the hub problem, and changing out all of the old joints, my problem went away. Pretty sure you can beat this too.
The balance weights are usually a nut or washer welded to the outside of the shaft tube. Primitive, but it works. Look for a weld with nothing attached. Dents too. If the shaft "jump ropes" even a little, you'll feel it.
The part about the new section of spline visible could contribute to the condition above. Pulling the spline apart lessens the amount of surface area used to keep the shaft from "jump roping." that combined with the extra lift could create what you're feeling. Push up and down on the slip joint and note the movement. You should not see much if any play here.
It is possible you have the shaft operating out of its sweet spot. If you can jack the body up to unload the rear springs, watch to see how much the shaft comes out at full droop. This is obviously a dangerous condition, so if it looks like there is a chance the shaft could come apart at full droop, you're probably due for a custom shaft. There should be at least 3" of spline engagement when the wheels are on the ground.
 
X2 on the yokes on the shaft being aligned properly.

Is your rear driveshaft a cv shaft or non-cv shaft?

If non-cv, the yokes on the t-case & axlemust be parallel. By this I mean the t-case yoke should be pointed toward the rear of the vehicle, while the rear yoke should be pointed toward the front, (not at the t-case).

2joint_angle.gif


Since you added shims in the rear, I'm assuming the rear yoke has been rotated upward, pointing it toward the t-case.
If this is the case, you need a cv shaft.

cv_angle-1.gif


*note-there should be a slip yoke on the shafts in the picture.
 
Dealbreaker- checked everything you said to. No play on the yoke. 3 u-joints had a little wiggle except the one at the very front of the rig. Probably should replace them?

Mochamike- those pictures you sent really helped out. I have a conventional two joint drive shaft, not a cv joint. I assume I should just take my shims out altogether and run flat on my leafs?

Dealbreaker- did your Skyjacker come with shims in the year? If so do you know how many degrees they were? I'm trying to debate if I should reverse the 3 degree shims that came bolted stock on the rear leafs or just take them out. Thoughts?

I attached pictures of my rear drive line setup. Would seeing the front help to?

Thanks for everyone help so far...

Jon
 

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Yes, ditch the shims.
However it might be too much of an angle for your joints to handle.
If that is the case, you need to leave them in & get a cv shaft.
 
My springs did not come with any shims. Looking at your pics, its apparent that the rear angle is much less than the angle at the xfr case. The shims are doing the opposite of what you want. Have you run the rig without shims (using the new springs)? If yes, and still getting vibration, I would consider installing your 2-degree shims but fat end of the wedge towards the rear (reverse of what you have). The shims installed as they are now are not helping your problem.
Also, check the crossmember mount under the trans. If its a worn out rubber stocker, it could be allowing the driveline to wander around at certain rpms. You want it to be tight, but still compliant. Using a jack, gently lift on the trans to see if the rubber allows it to move off the crossmember. Ihon sells good replacements.
Mocha Mike is spot on about the cv joint. In my other Scout, I installed a 700r4 trans and np241 xfr case. This shortened the driveline to the point that a cv was the only option. At that point, you need to shim the pinion gear right at the xfr case (like you're trying to do now).
If you have a drive shaft shop in your town, I would Mark the slip joint where it is now, and have the guy look it over. If the engagement is insufficient, he'll tell you. If the splines are played out, there's only one fix. Also, he can check the balance. Bad joints won't balance.
I don't think you have exceeded the limit with what you've done. But this kind of lift will bring into light problems you never sensed before.
 
Great advice everyone. I removed the shims and got two u-bolts away from finishing and test driving, but they stripped out bad. When I get it back together I will take it for a spin and let you know. The angle now definitely looks parallel to the transmission, so I'm hopeful it will return things to how they were before the lift. We will see.

Thanks and I will keep you all updated.

Jon
 
Ok shims out, purchased new u bolts and got it together. Problem solved! There is still a very very faint drone at the same rpm's I mentioned early in these posts, but they go away fast and almost sound normal (I'm probably hypersensitive now to those sounds). I think you guys were saying that some small sounds will be normal with a 4 inch lift anyways, right? I think I'm going to buy new u-joints and put them in just to be safe.

Thanks for the expertise - 4 months of frustration finally comes to an end.

Jon
 
Cool. I still think you'll notice a difference with new joints. They are common wear items and need to be replaced like brakes and tires. Plus, a lift stresses them more than stock height did.
You'll never forget the sound of bad joints!
Glad you got it going.
 
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