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Driveline Vibes: Imminent Problems or Just Annoying?

smithz

NAXJA Forum User
Location
Denver, CO
So I hear about people trying to solve driveline vibrations in many different threads. My question is this: If left alone, will damage occur? Or do people try to fix this just because it's irritating?

I ask because I installed a Rusty's 4.5" lift a couple weekends ago. Fortunately or unfortunately the lift ended up being more like 6" (23" from center hub to stock fender flare). Now that's fine, but I went with the 4.5" so I wouldn't have the driveline issues I've read so much about. So now I have vibrations, but they aren't too ridiculous. Basically I can live with it as long as I know it isn't self destructing the slip yoke or u-joints.

Opinions? Advice? Thanks.
 
Can you explain exactly why that is? Isn't the slip yoke designed to do exactly that, slip? It seems that as long as it isn't pulled out too far, it should work the same. I'm really just trying to understand the problem better so I know if I need to worry about getting it fixed or if I can't just deal with it for awhile first.
 
Driveline vibrations put extra strain on the t-case output shaft bearings and the pinion bearings in the differential. The reason should be fairly obvious, the cyclic side loads from the vibrations dramatically increase the normal loads that those bearings usually take, so they wear out much quicker. Vibes aren't good for the u-joints either.
 
Just to make things clear. Sorry if it is obvious. Eliminating the slip yoke does not solve the problem of vibes. Vibes are caused by the normal u-joint drive shaft being at angles it was not designed for. An SYE does not do anything for vibes. The double cardin, or CV joint drive shaft that you add solves the vibes cause it can operate at higher angles. A SYE just Eliminates the Slip Yoke on the transfer case, and moves it to the drive shaft. CV drive shafts have a slip yoke. Sorry if I am being picky.
 
PAPXJ said:
Yes a SYE can help fix vibrations. You MIGHT be able to cure the vibes by just dropping the t-case and/or using axle shims.

No you do not need a SYE for the front. (It already has one)

http://www.4xshaft.com/driveline101.html

Well, I've already installed a crossmember with a 1" drop. Maybe that's not enough? Also the rear axle shims came with the lift kit and are also already installed. The u-joint angle on the diffs are pretty small. I haven't measured the angles off the transfer case. If I am remembering correctly, I think I read in a thread here that less than 15 degrees is better for a DD.

Basically, nothing really looks too extreme as far as angles go. So I'm not positive exactly what is causing it. More importantly, I'm not sure if what I'm feeling is normal or not on a lifted vehicle, since this is my first.
 
Dirt Surfer said:
Just to make things clear. Sorry if it is obvious. Eliminating the slip yoke does not solve the problem of vibes. Vibes are caused by the normal u-joint drive shaft being at angles it was not designed for. An SYE does not do anything for vibes. The double cardin, or CV joint drive shaft that you add solves the vibes cause it can operate at higher angles. A SYE just Eliminates the Slip Yoke on the transfer case, and moves it to the drive shaft. CV drive shafts have a slip yoke. Sorry if I am being picky.

Whatever you do, don't apologize! I asked the question to get repsonses because, unfortunately for me, this stuff is not obvious.

A friend of mine also theorized that it *might* have something to do with the u-joints operating at different angles then they were used to, and that they could of in effect been grooved (for lack of a better word). He's admittedly no expert, so again, he was just guessing at possibilities. Can anyone confirm or deny whether u-joints can be worn more in certain angle ranges?

Sorry this stuff isn't obvious to me, but I am learning from you guys.
 
smithz said:
Whatever you do, don't apologize! I asked the question to get repsonses because, unfortunately for me, this stuff is not obvious.

A friend of mine also theorized that it *might* have something to do with the u-joints operating at different angles then they were used to, and that they could of in effect been grooved (for lack of a better word). He's admittedly no expert, so again, he was just guessing at possibilities. Can anyone confirm or deny whether u-joints can be worn more in certain angle ranges?

Sorry this stuff isn't obvious to me, but I am learning from you guys.

Really, there is an easy way to solve this.

Get the SYE from www.performanceoffroadcenter.com and find a front driveshaft from a stock XJ to use it with.

Measure the angle of the driveshaft after you install it and put in appropriate shims to make the angle of the pinion match -2 degrees.

For example, my driveshaft is 15 degrees. The pinion is 13-14 degrees. I run a stock front driveshaft in the rear with the PORC sye I linked above.

All is well now that the driveshaft is balanced.

If you really don't want to get a sye, your t-case output angle should match the pinion angle.

For example, measure the t-case output angle by placing an angle finder on the top of the head cover on the engine (yes the head cover and t-case output are parallel) and then measure the pinion angle by placing the angle finder on the round case spreader holes on either side of the diff cover. The angles should be equal -2 degrees.

If you are using shims without a sye, I would bet your angles are fuct.

If you don't have a magnetic angle finder, get one before you proceed any further. You can't solve this without one.

I can't believe I typed all that, but you are being too nice.
 
On a two u-joint driveshaft (non CV) the angles of the two joints need to be less than 3* different or there will be vibrations. The only way to solve vibes is to measure the angle of the two u-joints and then either change the shims in the rear or change the lowering of the transfer case. A slip yoke eliminator makes the driveshaft a little longer, which helps the angles, and also normally uses a CV (actually double carden joint) driveshaft. With the CV shaft only the bottom, or pinion, angle is important and it needs to be 0*, or the pinion should point straight at the output shaft of the t-case. This makes it easier to handle lift since normally the pinion will need to be pointed upward without any lowering of the t-case, which is much better for ground clearance as well as solving angle (and vibration) problems.

While we're on the subject, the reason for vibrations is because a u-joint spins in a slightly oval pattern (rather than perfectly circular) and if the angles are off the two oval patterns aren't in sinc so they work against each other and cause a vibration. A double carden joint has two u-joints which by design operate at exactly the same angles and so there is no vibration, as long as the third u-joint at the pinion is at 0* angle. It is good to actually set the pinion angle with a CV shaft at 1* down, that way as power is applied and the pinion rotates up slightly the angle will be at 0*.
 
You guys kick a55.

So I'm understanding the issue much better now, and it makes sense. Given that it's visually very obvious that the angle from the driveshaft to the transfer case and to the rear diff's pinion is not even close.

So if I were to get the SYE you mentioned above, why would I need a front drive shaft to use with it? (sorry if this is a stupid question). Is one of their CV driveshafts what I would need to get with the SYE? Also if I make this change, do I have to worry about the lift settling later on?
 
I'm at 3" and have VERY slight vibes. I can only BARELY notice them under heavy acceleration and very quick hard deceleration. I realize that even slight vibes are putting undue stress on the driveline but how much? In my case will I ever even notice the damage?
 
smithz, as mentioned you need to get an angle finder and find out where you are now. You can try angle shims between the springs and the spring perches first, then if you still have vibes try a transfer case drop. After the t-case drop you will have to correct the angles again. If this works it's the cheap fix. I have shims only on my 88 XJ with 3.5" lift with no vibes. If this doesn't work or if you elect to go SYE/CV you will need the shims anyway to correct the pinion angle. If you get lucky a stock front driveshaft, which is already CV, will be the correct length and will save you some scratch. If you change the lift at a later date you will again have to correct the pinion angle, but that's all provided your driveshaft is still long enough.


Dragline, driveline vibes usually occur at a particular speed rather than during acceleration/deceleration. It's just me but I would be unable to ignore the vibes and would be trying to track the problem down and fix it. End of lecture.
 
If the angles are just barely good enough to not vibrate, they can be thrown off enough during acceleration by the torque rotating the pinion up slightly. This situation means the pinion should come down a degree or two so that as it rotates up slightly during acceleration the angles will still be alright.
 
smithz said:
So if I were to get the SYE you mentioned above, why would I need a front drive shaft to use with it? (sorry if this is a stupid question). Is one of their CV driveshafts what I would need to get with the SYE? Also if I make this change, do I have to worry about the lift settling later on?

You don't need a front driveshaft to run with it, it's just the cheapest option.

What you want is a driveshaft with a double cardan joint on the t-case end and a single joint at the pinion. If you want to spend a little more money I would recommend one from Tom Woods.

Your lift will probably not settle enough to throw the angles out of whack.
 
Things are making more sense now.

So I got an angle finder last night, and as you guessed they were setup more like you described for a CV driveshaft, not a stock one. So basically I reversed the shim that I installed with the lift kit (came with it) and now it's looking more correct. I think I've got close to 15 degrees at both u-joints. I couldn't really find a good spot on the rear diff to acurately check the pinion angle though. I used the flat ridge on the passenger side of the diff which looked pretty close to parallel with the pinion. I *think* it's better than before, but it's not night and day. There are still some vibes, especially when accelerating. I'm hoping it will be ok until I can spend the dough on the SYE and CV driveshaft, which from what I've gathered from you guys is really the ideal setup.

I found a decent DIY writeup for installing a JB SYE and Tom Wood's driveshaft (for other noobs wondering how all this sh1t works). http://jeepin.com/features/sye/jbsye.shtml

Thanks you guys for taking the time to answer my questions and explaining this stuff to me. NAXJA rules!
 
smithz said:
This deal from Rusty's seems like a pretty damn good one compared to all the separate prices I've seen. It's an Advanced Adapters SYE with a Tom Wood's CV driveshaft for $480 + shipping. I still need to call and make sure it comes with everything needed.

Has anyone used this combination? Is this a good price for this stuff?

http://rustysoffroad.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=AACOMBO1&Category_Code=SYE

Also call Tom Woods and see what he can do for you as a whole kit.

Also, check the naxja vendors section and call everyone in there. Most of them will be able to sell you the same stuff, probably at just as good a price.
 
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