Oscillating Harmonic Vibes

[JMT]

After the Savvy MUA, with JB SS SYE and rear Adam’s driveshaft, I get vibrations from the stock front DS at 65+mph. The vibes are only under load. I’ve fiddled with the pinion, it’s 0.5* higher than the DS. When I remove it, vibes go away. Should I change the u joints first? Anything else I should replace on that shaft? What if that doesn’t work? What would be next?

 

[Apparition]

Why not keep adjusting the pinion angle?

 

[JMT]

Why not keep adjusting the pinion angle?

I’ve tried a lot

 

[Goatman]

Have the shaft rebalanced to eliminate that question. New Ujoints can never hurt, and they are not expensive. What is your pinion angle at now? Also be sure the slip joint is indeed allowing the shaft to easily extend and contract. That could be a possible problem too.

 

[JMT]

Pinion is 9.3, shaft is 8.7. I tried the pinion lower than the shaft by up to 1.5. I also tried it up to 1.0 higher. There was no substantial difference.

 

[JMT]

Have the shaft rebalanced to eliminate that question. New Ujoints can never hurt, and they are not expensive. What is your pinion angle at now? Also be sure the slip joint is indeed allowing the shaft to easily extend and contract. That could be a possible problem too.

I know the slip joint is not allowing easy slippage. How do I fix that?

 

[Mike_H]

I did a full rebuild on my front D/S. By the time I got all the parts, it was only a few more dollars to just buy a new shaft. That will be the route I take, next time. Might look into it.

 

[JMT]

I did a full rebuild on my front D/S. By the time I got all the parts, it was only a few more dollars to just buy a new shaft. That will be the route I take, next time. Might look into it.

I thought it might be. You think just replacing the ujoints is worth a shot? In the end I’ll probably end up buying Warn small hub kit, but I’d like to avoid that if possible

 

[Mike_H]

I thought it might be. You think just replacing the ujoints is worth a shot? In the end I’ll probably end up buying Warn small hub kit, but I’d like to avoid that if possible

You could try it...I did the three joints, plus the centering ball and assembly. I think parts from denny's driveshaft were like 150ish. Then, I still had to do the work and I can't balance it at home. If you blow up a ujoint or something, fix it. If you think you need to replace all three? I'd just buy a new one. That centering ball is kind of a pain in the ass.

 

[JMT]

You could try it...I did the three joints, plus the centering ball and assembly. I think parts from denny's driveshaft were like 150ish. Then, I still had to do the work and I can't balance it at home. If you blow up a ujoint or something, fix it. If you think you need to replace all three? I'd just buy a new one. That centering ball is kind of a pain in the ass.

I’ll try swapping over a front driveshaft from another TJ on the lot and see how that goes! Why didn’t I think of that sooner?!

 

[Mike_H]

I’ll try swapping over a front driveshaft from another TJ on the lot and see how that goes! Why didn’t I think of that sooner?!

Great idea!

 

[bobthetj03]

Hope you get it figured out Jeremy. I feel your pain.

 

[Jerry Bransford]

Did you have the front driveshaft out during any point of your mods, or did you only remove it as a test to verify if it was the source of the vibes?

 

[JMT]

Did you have the front driveshaft out during any point of your mods, or did you only remove it as a test to verify if it was the source of the vibes?

I originally had vibes after doing a TT. I messed with the pinion until I gave up. Later I removed it when modifying the TCase and changing the clutch. Probably several times. However, there have been vibes since the first time when I originally did the TT. Is there a specific orientation?

 

[psrivats]

After the Savvy MUA, with JB SS SYE and rear Adam’s driveshaft, I get vibrations from the stock front DS at 65+mph. The vibes are only under load. I’ve fiddled with the pinion, it’s 0.5* higher than the DS. When I remove it, vibes go away. Should I change the u joints first? Anything else I should replace on that shaft? What if that doesn’t work? What would be next?

Get front locking hubs. Don't go into the rabbit hole. Trust me, the time, money and effort is not worth it.

 

[bobthetj03]

Before making that investment, pull the rear ds and take a 4 hi cruise just to verify. Sometimes, it's rare, but the vibes go away with one or the other ds installed, but combine the two makes the connection to the whole drive train. If that happens, you've entered "The Land of the Lost". I'll save you a seat. @psrivats, scoot over!

 

[taylormade73]

Get front locking hubs. Don't go into the rabbit hole. Trust me, the time, money and effort is not worth it.

X2

 

[psrivats]

Before making that investment, pull the rear ds and take a 4 hi cruise just to verify. Sometimes, it's rare, but the vibes go away with one or the other ds installed, but combine the two makes the connection to the whole drive train. If that happens, you've entered "The Land of the Lost". I'll save you a seat. @psrivats, scoot over!

Remember, it took me a while to get there and way too much money and parts. Only after rubicrawler install did things change enough to put hubs in. I would have done that a long while ago if it were possible. I gave up understanding these vibes and you know how much effort I put into this.

@JMT, try what @bobthetj03 said. If you can make these go away with front hubs, make that investment and save yourself the pain.

 

[starkey480]

I like my hubs a lot. Only downside is the hub decreases your backspacing by 7/8” on each side. I can’t remember what @mrblaine said is the minimum amount of backspace he will use with a small hub kit but it’s something to think about.

 

[psrivats]

I like my hubs a lot. Only downside is the hub decreases your backspacing by 7/8” on each side. I can’t remember what @mrblaine said is the minimum amount of backspace he will use with a small hub kit but it’s something to think about.

Not if you get the 5x5.5 kit. It's more spendy though. And wheels are a pain.