ColoradoCorey

Thanks for the help in advance,

I have a 4.0, AX15, NP231 w/sye, D30 and D35. I had a shop install 4.56s and now I have nasty vibes. I have had both my shafts rebalanced. My drive line angles are good. I didnt have these vibes before the install. I have had the jeep up around 100 MPH prior to the swap and never felt anything. I asked the shop to look at it and they did. They changed out my axel bearings but it didnt change much if at all. They keep telling me that its a harmonic and not a vibration. Well to me a harmonic is a vibration. They also blamed it on the T-Case as well as mounts. Does any of this seem right? I have minimal experience in gears and such.

Thanks Guys!

SeriousOffroad

You want another set of eyes on it?

ColoradoCorey

I guess it wouldnt hurt, Thank you sir!

RWKHausSupply

That does happen time to time.

Harmonics change when you add 50% faster trans/TC/driveshaft/DS ujoint speeds.

One main issue I find is that a driveshaft is typically balanced to 1000rpm.
If your at 1000RPM in 4th gear (the gear in a AX-15 that is 1:1 ratio), then your at 40MPH prior to gear swap with 3.07's. Now your doing 22mph.

So even if your DS shop had a nicer machine and balanced your shafts up to say 2000RPM, I bet its safe to say that they are spinning faster then that at highway speeds.

Top speed x 336 (a constant) x rear ratio (like 4.10), then divide it by the tire height (28” tall tire) = your driveshaft speed...

Is this your problem? Maybe not. But its a VERY common issue, especially when the DS angle is close to perfect yet not perfect. It might look good but maybe it likes being 2deg lower, or higher.

ColoradoCorey

Thanks for the help Frank!

You were 100% right. I ended up getting new shims and that took away most of the vibes. I think there may be some fine tuning still needing to be done, but you definately sent me in the proper direction.

What I do find funny about this whole thing I took it to 4 wheel parts to have them install the gears (big mistake) and then back again to have them fix the vibes. They claimed it was possibly my T-Case or motor mounts or yadda yadda as well as the fact that it was a harmonic and not a vibration (Harmonics are vibrations). They said my drive line angle was "Perfect". Well low and behold it wasnt.

Well once again thanks for the help. Oh and yes the G2 gears whine something fierce lol.

mr white

Should have gone to Frank for the gears like me. :P

I'm having the same issue, still haven't found the round to it to fix it. 37s helped out but I didn't like those tires so they are for sale now lol. I just drive at less than 70 and it's fine. More than 70 and it does the weird harmonic thing when I'm on the gas. I'm assuming it's the same problem as yours.

SeriousOffroad

Glad I could help!

Thanks!!

ColoradoCorey

You know I minimized mine a huge amount with the 4* shims but like you I have some at higher speeds (not nearly as bad). The next thing Im gonna do is shore up the Drive Train with motor and t-case mounts. I dont wanna get to far into modifieng the drive line angles and such because I am gonna lift even more. And yes, I should have gone to Frank lol.

FLAWK 4 Wheel Parts!!!