I have the dreaded "Jeep shakes on take off" syndrome

The large SAE bolts holding earlier TJ skidplates like yours are long enough to drop the tcase as recommended. The smaller metric bolts they started using around 2003 are not.

If you ever need new tcase skidplate bolts, Grade 5 is fine. No need for Grade 8. :)

The bolts are free from work!
Anyway, tonight I "temporarily" lowered the skid plate by approx. 1" and took a short drive. It seemed to work. I went ahead and ordered an Actual lowering kit, as I don't want the look of 6 stacks of washers.
The factory bolts were not long enough after all. What I bought were 4 (5/8" x 7/8") steel bushings and installed one on each of the four corners (Temporary), and drove up and down my street. Vibration was gone.
Thanks for the info!
 
You could get some 1" square steel tubing cut to length and painted. It'll look more "factory-ish" than actual t-case drop spacers.
 
I went through this and the place I bought my tj had thrown four tires on aluminum wheels. To find out the tires were wore funny.flat spots all over the front tires. Not sure if I want to go through that again.
 
Bringing an old question back up. I have the same problem. My Jeep shakes at take off.
I have a long arm 3.5 lift
Any suggestions?

F3FFFBFA-BD4E-44DD-A767-8E576810E697.jpeg
 
With that type of driveshaft, the pinion angle needs to match the transfer case output angle. I’m guessing based on that picture that there is a TC drop? The pinion angle looks a bit high, but that could just be the perspective in the photograph. I would adjust the pinion angle until it matches the TC output angle.

You can drop the rear DS and drive around in 4hi to see if the vibrations go away. If they do then it probably is related to the rear DS. Just make sure to leave it in 4hi when you park and use the parking brake so it doesn’t roll away.
 
Actually no, since with the stock rear driveshaft you have to keep the pinion angle as the factory set it. The rear pinion angle must remain parallel with the tcase output shaft with the factory driveshaft.

Why is that, I do not see in the Service Manual where it says anything about the pinion angle needing to be parallel with the T-case output shaft. However I do see where the difference between the T-case output angle and Axle input to the pinion should be within 1 degree (U-joint cancellation).
In the manual, if the U-joint cancellation angle is not within 1 degree, the manual states to use a cam kit for the rear axle upper control arms to adjust the rear pinion angle, It does not say anything about adjusting the location of the T case output shaft.
Dropping the T-case is one way to get there but why is not rotating the pinions another way?
Heck when you drop the T case the two are no longer in parallel anymore anyway.

Not trying to be an A$$ just wondering why since it seems to be the conscience here on this forum.
 
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The service manual is not written for a lifted Jeep.

Why would the jeep being lifted matter if the driveline is still stock, the operating angles still need to be within factory specifications to operate correctly.
 
You can get away with the stock shaft if you install a small suspension lift. You might need to drop the transfer case with spacers. You will not need to drop it as much as what is included in most kits sold. I believe Jerry has a very good example of DS angles etc. You can also go look at the Tom Wood site. He also goes into great detail on the angles. I think Stu Offroad offers some good write ups for the DS do's and dont's.
 
Why is that, I do not see in the Service Manual where it says anything about the pinion angle needing to be parallel with the T-case output shaft. However I do see where the difference between the T-case output angle and Axel input to the pinion should be within 1 degree (U-joint cancellation).
In the manual, if the U-joint cancellation angle is not within 1 degree, the manual states to use a cam kit for the rear axel upper control arms to adjust the rear pinion angle, It does not say anything about adjusting the location of the T case output shaft.
Dropping the T-case is one way to get there but why is not rotating the pinions another way?
Heck when you drop the T case the two are no longer in parallel anymore anyway.

Not trying to be an A$$ just wondering why since it seems to be the conscience here on this forum.
If the two angles of the pair of u-joints in the stock shaft are within 1 degree of each other, how close to parallel are the two shafts? ;)
 
If the two angles of the pair of u-joints in the stock shaft are within 1 degree of each other, how close to parallel are the two shafts? ;)

Wouldn't that depend on the lift? So the output of the T-case and pinion do not need to be parallel with each other, they need to be within their respective specified operating range (3 degrees) AND have a Cancellation angle of less than 1 degree.

So, what is wrong with using adjustable arms or a cam kit to rotate the rear axle to achieve a good cancellation angle, as opposed to lowering the T case that is my question.
 
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If you are talking about the centerline of the T-case output shaft and pinion yoke then 1 degree , so the output of the T-case and pinion do not need to be parallel with each other, they need to be within their respective specified operating range (3 degrees) AND have a Cancellation angle of less than 1 degree.

So, what is wrong with using adjustable arms or a cam kit to rotate the rear axel to achieve a good cancellation angle, as opposed to lowering the T case that is my question.
You're picking fly shit out of the pepper for some reason. Most won't be able to look at a rear non DC driveshaft and see that the joints are within 1 degree and they will look pretty parallel. Whatever the angle of the two joints is, it will be achieved by setting the angle of the two shafts, output shaft on the t-case and shaft on the pinion.

I also promise you that the angle numbers you describe can be achieved without them being parallel and it won't work very well so it is easier to tell folks to work on the parallelism and go from there.

There is nothing wrong with using arms, there is a bunch wrong with the cam kit at the uppers. I've yet to see one that worked very well and that didn't totally screw up the "slots" in the upper mounts.
 
You're picking fly shit out of the pepper for some reason.

No, I am asking why it is recommended not to rotate the rear axle as opposed to dropping the t-case, if there is a bunch wrong with cam kits on the uppers then that is one reason.

Whatever the angle of the two joints is, it will be achieved by setting the angle of the two shafts, output shaft on the t-case and shaft on the pinion.

There, so you can rotate the rear drive shaft as opposed to dropping the damn T-case and loosing some lift height and the recommended way is to use adjustable arms as opposed to cam kits.

I also promise you that the angle numbers you describe can be achieved without them being parallel and it won't work very well so it is easier to tell folks to work on the parallelism and go from there.

Yeah, I know, so what won't work so well for the TJ, that is what I would like to know. Is there an angle that the rear should not be rotated past? Not arguing just want a reason besides "just because".
 
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No, I am asking why it is recommended not to rotate the rear axel as opposed to dropping the t-case, if there is a bunch wrong with cam kits on the uppers then that is one reason.
That may be what you are asking now but saying that parallel isn't right when the two shafts should be within a very narrow degree of separation between the two is most assuredly picking the fly shit out of the pepper. I don't know where you get that dropping the t-case is ever recommended by anyone that knows anything except as a budget option instead of fixing it correctly with a SYE, DC driveshaft, and adjustable arms.



There, so you can rotate the rear drive shaft as opposed to dropping the damn T-case and loosing some lift height and the recommended way is to use adjustable arms as opposed to cam kits.
You aren't losing lift height, you are decreasing your break over angle and screwing up your ground clearance which has the same effect as losing lift height but they are not the same thing. That's how you pick the fly shit out of the pepper when it matters.



Yeah, I know, so what won't work so well for the TJ, that is what I would like to know. Is there an angle that the rear should not be rotated past? Not arguing just want a reason besides "just because".
The rear drive shaft and the front one for that matter should not be rotated past any angle that induces vibrations.
 
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Has anyone used cam bolts or adjustable length control arms to raise the rear pinion angle? It should not have been with the factory rear driveshaft still installed.

Adjusting the pinion angle should not be done with just a 2" lift.

Actually no, since with the stock rear driveshaft you have to keep the pinion angle as the factory set it. The rear pinion angle must remain parallel with the tcase output shaft with the factory driveshaft.

drop the tcase as recommended.



That is just from this post

You aren't losing lift height, you are decreasing your break over angle and screwing up your ground clearance which has the same effect as losing lift height but they are not the same thing.

I know that also, but depending on the situation one might be more important that the other. For example where we take our Jeeps, break over angle is really not much of a concern but ground clearance it since we are in rutted out trails most of the time, no fly shit there.

The rear drive shaft and the front one for that matter should not be rotated past any angle that induces vibrations.

Now you just answered the question, you can rotate the rear drive shaft if needed as a way to correct drive shaft angle problems, hence vibration problems.
So is there problems with rotating the pinion to bring the angles in spec so there is no vibration if say a 4" lift is installed and someone still has the stock drive shaft on a TJ?

As a side note, when we installed a 6"" lift on my 88 Bronco, 15 years and ~ 150,000 miles ago, we rotated the pinion to bring the drive line angles back to factory specifications. No ill side affects, but that is a Bronco with a DC and slip yoke, and it is still going just fine.

That is why I am asking, (still no fly shit), folks here with more experience on TJ's that I.

What I am getting is that rotating the pinion using cam kits on the uppers might lead to problems down the road so not recommended due to past experience.

Rotating the pinion using adjustable arms is one way to bring the drive line back to specification so that there are no vibrations.

Lowering the transfer case is another way to bring the drive line back to specifications so that there are no vibrations, AND it is a budget friendly way to do it.
 
What I am getting is that rotating the pinion using cam kits on the uppers might lead to problems down the road so not recommended due to past experience.

Rotating the pinion using adjustable arms is one way to bring the drive line back to specification so that there are no vibrations.
But you're forgetting the actual reason for the vibrations. With enough suspension lift height you can have the drivetrain angles exactly what they should be and still have vibrations. The reason is once your suspension lift gets high enough, even when the pinion and tcase output shafts are precisely parallel to each other assuming the factory driveshaft, the angle between the tcase output shaft and driveshaft, and the angle between the driveshaft and pinion angle, become excessive for the u-joints and they then vibrate. U-joints are what cause the vibrations... operating at angles that are excessive for them.

Raise that engine/trans up via a suspension lift high enough and the angles the two u-joints shown below will become excessive and the u-joints will vibrate. Even if the tcase output shaft and axle pinion shaft are exactly parallel to each other.

Once the lift height becomes great enough there's no way to eliminate the vibrations caused when the u-joints are operating at the resulting excessive angles. Even when the tcase output shaft and pinion shaft are parallel through any means you desire. That's when you need to go to a CV driveshaft which no longer requires the tcase output shaft and pinion shaft be parallel to each other.

The max operating angle for a 1310 size u-joint, which is the size most of our driveshaft u-joints are, is 30 degrees. Once that angle is created by a suspension lift you're going to have vibrations even when all of the other angles are exactly where they should be.

83545
 
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Thank you Jerry,

I do understand where the vibrations are coming from (in my Bronco example that is why the Axel has to be rotated) and the velocity differences in the drive line that cause them and that is what I am getting at.

I know that the operating angle limit of the TJ U-joints is 30 degrees, the operating angle being the angle between the t case output yoke and drive shaft and the drive shaft and pinion yoke separately (ass opposed ot he U-joint cancellation angles which is different).
With that said with the TJ, since the drive shaft is short, a 4" lift will bring the operating angle out of range, requiring a different solution to vibrations such as a CV shaft and of course rotating the rear end will not change the operating angle of the drive shaft and T-case, it will still be greater than 30 degrees.

That picture suggest that it is required that the T case and Axle be parallel to each other, regardless of the vertical distance between them. My question is why can the axle not be rotated (with the factory shaft set up) to bring the angles back together to prevent vibrations as opposed to lowering the T case for a 2" lift if the operating angles are less than 30 degrees.
I am not disputing, just looking for a reason.
 
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