At my wits-end with drive shaft vibrations

[xXDavidCXx]

TLDR, I have rhythmic (dynamic) vibrations above 63mph that won't go away, no matter the pinion angle.

I've tested more than 30 different pinion/ds angle combinations from above and below and I always have the same dynamic vibrations. Sometimes worse, some times better, and one time constant vibrations (could not duplicate), but never gone. I use a digital angle finder to the tenth of a degree. I measure angles on the back of the Dana 35 housing, and the slip shaft.

Relevant modifications:
Savvy double adjustable upper and lower arms.
JB Conversions super short SYE
Tom woods dc ds (balanced twice locally)
UCF belly up skid (full tummy tuck with BL & MML)
Rough Country rear coil spring correction plates
3.73 & 31 (30.5inch) tires

I Didn't have this problem before the SYE and double cardan drive shaft.

I've had the tires rebalanced and rotated - no changes

With the rear ds removed the dynamic vibrations are gone

At this point I either live with it or take the entire jeep to a shop and throw money at whatever the problem is

I'd rather fix it in my shop, what would you guys do next?

 

[afusco1222]

So, I had the same problem. I am running 4.88s, NV3550, a Ford 8.8, an UCF tummy tuck, and 34" tires. I did the same and though the driveshaft was the problem. I got two new driveshafts and had Tom Woods spin it as fast as their machine would let them. The driveshaft was not the problem. I then took the rear driveshaft out and drove in FWD only, vibes went away. I adjusted pinion angle like crazy with little to no change. I thought my 8.8 pinion being slightly offset was the problem and I adjusted the rear axle over an inch to test it (I put it back to center after) with no change. It ended up being that my SYE bearing had some play in it and my yoke nut started working itself loose. I changed from a standard SYE to a Super Short and that fixed it. Make sure your SYE was installed correctly and there is no damage to the output yoke on the transfer case. If I was in your shoes, I would start with a new output yoke (they're around $75) on the transfer case and check the torque on the yoke nut for both the pinion and transfer case.

 

[mrblaine]

TLDR, I have rhythmic (dynamic) vibrations above 63mph that won't go away, no matter the pinion angle.

I've tested more than 30 different pinion/ds angle combinations from above and below and I always have the same dynamic vibrations. Sometimes worse, some times better, and one time constant vibrations (could not duplicate), but never gone. I use a digital angle finder to the tenth of a degree. I measure angles on the back of the Dana 35 housing, and the slip shaft.

Relevant modifications:
Savvy double adjustable upper and lower arms.
Advanced adaptors super short SYE
Tom woods dc ds (balanced twice locally)
UCF belly up skid (full tummy tuck with BL & MML)
Rough Country rear coil spring correction plates
3.73 & 31 (30.5inch) tires

I Didn't have this problem before the SYE and double cardan drive shaft.

I've had the tires rebalanced and rotated - no changes

With the rear ds removed the dynamic vibrations are gone

At this point I either live with it or take the entire jeep to a shop and throw money at whatever the problem is

I'd rather fix it in my shop, what would you guys do next?

Do your testing and adjustment without the front driveshaft installed.

 

[Blackjack]

What transmission mount are you using with this combination? Did you make sure to not tighten the engine and transmission mount fasteners until everything was in its final resting position?

What speed(s) is the vibration occurring? Is it in a speed range? Does it start and get worse with additional speed? If you snap on or off the throttle does the vibration change at all?

Post some pics.

 

[xXDavidCXx]

What transmission mount are you using with this combination?

OEM

Did you make sure to not tighten the engine and transmission mount fasteners until everything was in its final resting position?

Yes

What speed(s) is the vibration occurring?

Above 63

Is it in a speed range?

No, just above 63

Does it start and get worse with additional speed?

Not that I can tell

If you snap on or off the throttle does the vibration change at all?

no

Post some pics.

 

[xXDavidCXx]

So, I had the same problem. I am running 4.88s, NV3550, a Ford 8.8, an UCF tummy tuck, and 34" tires. I did the same and though the driveshaft was the problem. I got two new driveshafts and had Tom Woods spin it as fast as their machine would let them. The driveshaft was not the problem. I then took the rear driveshaft out and drove in FWD only, vibes went away. I adjusted pinion angle like crazy with little to no change. I thought my 8.8 pinion being slightly offset was the problem and I adjusted the rear axle over an inch to test it (I put it back to center after) with no change. It ended up being that my SYE bearing had some play in it and my yoke nut started working itself loose. I changed from a standard SYE to a Super Short and that fixed it. Make sure your SYE was installed correctly and there is no damage to the output yoke on the transfer case. If I was in your shoes, I would start with a new output yoke (they're around $75) on the transfer case and check the torque on the yoke nut for both the pinion and transfer case.

They transfer case yoke was new with the SSSYE, but I'll inspect it along with checking nut torque.

 

[xXDavidCXx]

Do your testing and adjustment without the front driveshaft installed.

Sure as shit, taking out the front drive shaft made the problem go away. Smoothest the jeep has been at any speed, ever

So now what? Balance the front shaft? Could the problem still be in the transfer case yoke torque? Both yokes were removed during install, but if the rear is good, then can I assume the rear yoke is good too?

 

[mrblaine]

Sure as shit, taking out the front drive shaft made the problem go away. Smoothest the jeep has been at any speed, ever

So now what? Balance the front shaft? Could the problem still be in the transfer case yoke torque? Both yokes were removed during install, but if the rear is good, then can I assume the rear yoke is good too?

Rule out the basics, then start adjusting the front with a known good driveshaft that is well balanced. Start taking out caster until the vibes go away if possible. If they do but the steering has suffered to the point of intolerance, then you get to decide what to live with, less money, more vibes and or crap steering. If you can't solve it, then a hub kit will, sadly.

 

[LONGJP2]

Rule out the basics, then start adjusting the front with a known good driveshaft that is well balanced. Start taking out caster until the vibes go away if possible. If they do but the steering has suffered to the point of intolerance, then you get to decide what to live with, less money, more vibes and or crap steering. If you can't solve it, then a hub kit will, sadly.

Does the MML contribute to front vibes. Thinking about removing mine (to see) and hopefully the rear will stay happy.

 

[mrblaine]

Does the MML contribute to front vibes. Thinking about removing mine (to see) and hopefully the rear will stay happy.

Only one way to find out. What other adjustments have you tried before you arrived at the conclusion the MML is the culprit?

 

[xXDavidCXx]

Rule out the basics, then start adjusting the front with a known good driveshaft that is well balanced. Start taking out caster until the vibes go away if possible. If they do but the steering has suffered to the point of intolerance, then you get to decide what to live with, less money, more vibes and or crap steering. If you can't solve it, then a hub kit will, sadly.

I assume this is all with the rear ds removed, correct?

 

[Blackjack]

Does the MML contribute to front vibes. Thinking about removing mine (to see) and hopefully the rear will stay happy.

MML improves the rear driveshaft angle by negatively affecting the front. Most of the time it works fine sometimes it does not.

 

[Blackjack]

I assume this is all with the rear ds removed, correct?

No. Now that you know the rear is fine just leave it alone and just make changes so that the front starts behaving. It you drive on the front shaft you change the power path and as such the drivetrains behavior.

 

[psrivats]

Sure as shit, taking out the front drive shaft made the problem go away. Smoothest the jeep has been at any speed, ever

So now what? Balance the front shaft? Could the problem still be in the transfer case yoke torque? Both yokes were removed during install, but if the rear is good, then can I assume the rear yoke is good too?

Given all that you have described in this thread, you are likely looking at a front hub kit. Won't be cheap. But check/test the things that Blaine said to do and in the sequence he mentioned.

 

[mrblaine]

I assume this is all with the rear ds removed, correct?

No, you have the rear dialed in, now you need to dial in the front and make it play nice with the rear one installed.

 

[LONGJP2]

Only one way to find out. What other adjustments have you tried before you arrived at the conclusion the MML is the culprit?

I've played with the front CAs a few times, but probably not enough to say the vibes can't be dialed out. Newer TW driveshaft (balance rechecked by TW).
Just thinking that removing the MML should reduce the front angle.

 

[xXDavidCXx]

Update:

Dropped the front shaft off and they reported back it's in all kinds of bad shape, though never really caused much issue till I did the rear DCDS conversion.

 

[xXDavidCXx]

So, before I put on the refurb front shaft, I have a bit of constant vibration at 65-67 mph. Ds and pinion are w/in 0.5 deg of each other. Does not seem load related.

So this means tires, hubs, something else off balance? Not angle related, correct?

 

[xXDavidCXx]

I put the front shaft on, and no changes, so everything is back to "normal". Whatever small amount of vibration I do get is inconsistent and only noticeable from 65-70.

Case closed.

 

[xXDavidCXx]

Additional info

After replacing my grenaded harmonic balancer, the vibes at 65mph are gone.