High speed vibes, even w/ new driveshaft

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OnespeedTRD

OnespeedTRD

Joined
Dec 13, 2020
Threads
3
Messages
39
Location
Middle TN
Looking for some help identifying a high speed drivetrain vibration, besides a new driveshaft, which didn't solve the issue.
95 FJZ80, 3" lift with 35x12.50r17 Toyos.

Some recent background info:
Was previously running 33" tires on stock wheels. Smacked a rock on the front diff a few months ago while off roading, knocked the 3rd member loose. Tightened the bolts and was able to get it home. Since I was going in there anyways I decided to move up to 4.88s front and rear with an Eaton E-locker in the rear.
Picked it up from the gear shop and they told me there was a pretty severe drivetrain vibration from the front, starting at about 60mph and got worse as I went faster. This vibration wasn't there previously. Since the driveshaft is now rotating a lot faster than before, especially on 33's, I chalked it up to an old worn out front driveshaft that just couldn't hang at those RPMs anymore.
Went home, installed the 35s and tested, vibes still there.
Removed the front driveshaft, locked center diff, tested, vibes gone. Drove it this way for a week or so waiting on a new driveshaft, no vibes whatsoever.
Ordered a new double cardan front driveshaft from Tom Wood's, installed today and tested.
First run up to 70 seemed fine, exited and U-turned and got back on the freeway and right at 60 there it was, same high speed vibe, maybe even worse than before.
It's Friday afternoon so I'll have to wait until Monday to call Tom Woods to discuss with them.

Besides a bad driveshaft, anyone know why the vibes would be there with the front driveshaft in and gone when its not? Same condition with old and new d/s.
Could be a bad balance on the new one, however unlikely.
Could it be the front gears? They're still spinning even with the d/s disengaged, so doesn't seem like that's the issue, but maybe?
Anything else I should be checking or anyone run into this issue before and figured it out?

As I mentioned, I'll be calling to discuss with Tom Wood's and the shop that did the gears on Monday, but in the meantime, if anyone has any ideas I'd love to hear them.

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You have some kind of third member damage. You said you knocked the diff apart. I would start there.
 
DIRTBIKEUSA said:
You have some kind of third member damage. You said you knocked the diff apart. I would start there.
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That should have all been fixed when installing the new gears, but good point and probably worth looking at. Everything down there is still spinning even without a driveshaft installed, but maybe something is out of whack and only shows up when under power.
 
Check if the driveshaft flanges are nice - flat and square - ie facing each other true, in alignment.

Max 7 to 8 degrees angle of pinion flanges.

And I would personally get rid of that custom double cardan shaft.
 
You could jack up all the tires. Then remove all the tires and engage drive train and throttle. If vibes are gone then it's tires.
If vibes are still there isolate the drive train by removing a driveshaft, repeat.
 
landtank said:
why did you install a DC shaft?
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Wha
blinkerfluid said:
Check if the driveshaft flanges are nice - flat and square - ie facing each other true, in alignment.

Max 7 to 8 degrees angle of pinion flanges.

And I would personally get rid of that custom double cardan shaft.
Click to expand...
What's wrong with the DC shaft?
 
Squash said:
You could jack up all the tires. Then remove all the tires and engage drive train and throttle. If vibes are gone then it's tires.
If vibes are still there isolate the drive train by removing a driveshaft, repeat.
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Its definitely not the tires. I've already isolated it to the front driveshaft. Vibrates with front driveshaft installed, no vibes with front d/s removed.
 
With a DC you have to rotate the front axel so the diff (pinion) flange and the propeller shaft are perpendicular within 1 degree+/-.
You'll need to reduce the original caster correction. Get a caster angle measurement from an aligmment, and measure the angular delta between the pinion flange and drive shaft.
Try and get the pinion flange and drive shaft to within 1 degree of perpendicular while maintianing a minimum of 1.5 degrees caster angle.
 
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OnespeedTRD said:
Should I not have?
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A DC shaft typically goes on a truck with a 4” lift and 7degrees of caster correction.

It looks like you have caster bushings and the correction for those is around 3 degrees. And stock shaft works better.
 
landtank said:
A DC shaft typically goes on a truck with a 4” lift and 7degrees of caster correction.

It looks like you have caster bushings and the correction for those is around 3 degrees. And stock shaft works better.
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Well crap. So that being the case, would a DC shaft vibrate when those conditions aren't met? If that's the case, at least its just an expensive lesson and I'm not chasing another issue.
 
landtank said:
Yes. A DC shaft isn’t a better shaft, it’s a different shaft. And each type has its use.
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Well, luckily Tom Wood has a pretty generous return policy. I'll call them Monday to discuss and get the right part ordered up.
Lesson learned, I should have called to discuss before ordering anything. Thanks to everyone here for the info and knowledge.
 
OnespeedTRD said:
Looking for some help identifying a high speed drivetrain vibration, besides a new driveshaft, which didn't solve the issue.
95 FJZ80, 3" lift with 35x12.50r17 Toyos.

Some recent background info:
Was previously running 33" tires on stock wheels. Smacked a rock on the front diff a few months ago while off roading, knocked the 3rd member loose. Tightened the bolts and was able to get it home. Since I was going in there anyways I decided to move up to 4.88s front and rear with an Eaton E-locker in the rear.
Picked it up from the gear shop and they told me there was a pretty severe drivetrain vibration from the front, starting at about 60mph and got worse as I went faster. This vibration wasn't there previously. Since the driveshaft is now rotating a lot faster than before, especially on 33's, I chalked it up to an old worn out front driveshaft that just couldn't hang at those RPMs anymore.
Went home, installed the 35s and tested, vibes still there.
Removed the front driveshaft, locked center diff, tested, vibes gone. Drove it this way for a week or so waiting on a new driveshaft, no vibes whatsoever.
Ordered a new double cardan front driveshaft from Tom Wood's, installed today and tested.
First run up to 70 seemed fine, exited and U-turned and got back on the freeway and right at 60 there it was, same high speed vibe, maybe even worse than before.
It's Friday afternoon so I'll have to wait until Monday to call Tom Woods to discuss with them.

Besides a bad driveshaft, anyone know why the vibes would be there with the front driveshaft in and gone when its not? Same condition with old and new d/s.
Could be a bad balance on the new one, however unlikely.
Could it be the front gears? They're still spinning even with the d/s disengaged, so doesn't seem like that's the issue, but maybe?
Anything else I should be checking or anyone run into this issue before and figured it out?

As I mentioned, I'll be calling to discuss with Tom Wood's and the shop that did the gears on Monday, but in the meantime, if anyone has any ideas I'd love to hear them.

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Alignment? Wheel bearing? Sounds like a pretty rough hit that could have tweeked drag link or other steering component or the axle itself.
 
Update: Removed the DC shaft and installed a new standard shaft. (By the way, Tom Wood's was great with the return and got me a new shaft in a couple of days). Unfortunately, the vibes returned, but now they don't show up until closer to 70mph, and much less severe.
Kinda stumped now. If they went away completely it would be obvious, and if they stayed the same then I'd probably be thinking something is amiss with the front diff, but the change in speed and severity has me scratching my head. Maybe what I'm hearing now is the rear driveshaft?
I don't think its anything steering or suspension related as that would show up with or without the d/s (maybe).
What else changes in the drivetrain when under power (d/s installed) vs when not under power (d/s removed)?
 
OnespeedTRD said:
Update: Removed the DC shaft and installed a new standard shaft. (By the way, Tom Wood's was great with the return and got me a new shaft in a couple of days). Unfortunately, the vibes returned, but now they don't show up until closer to 70mph, and much less severe.
Kinda stumped now. If they went away completely it would be obvious, and if they stayed the same then I'd probably be thinking something is amiss with the front diff, but the change in speed and severity has me scratching my head. Maybe what I'm hearing now is the rear driveshaft?
I don't think its anything steering or suspension related as that would show up with or without the d/s (maybe).
What else changes in the drivetrain when under power (d/s installed) vs when not under power (d/s removed)?
Click to expand...
You had new gears installed.

That means the entire front axle was disassembled and reassembled. Assume nothing is correct, check everything.

Did you do this or did a shop do this?

Wheel bearings. If the shop followed the FSM, the wheel bearings may be loose. The front wheel bearings need to be torqued to 35 lb-ft on the inner nut while rotating. Then the outer nut to 45 lb-ft.

Grease in the knuckles and on the front spindles. It has been seen to have shops forget to pack grease in the front knuckles and particularly on the birfield shaft into the spindle bushings so there is a dry bushing that shows up. Usually it is a low tone hum or grind that a person can hear but it could manifest asca vibration and will show up more under power.

Have you done the proper break-in on the new gears? Low speeds, cool down times changing gear oil per the gear manufacturer recommendations for about 500 miles?

Driveshafts are properly oriented and properly phased?

Next I would listen to output bearings on the transfer case.

Change the t-case fluid to see if there is anything if concern there.
 
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