Vibration help?

[briboki]

I need some help trouble shooting a vibration.

My XJ is a 99, np231, aw4, 3.55s and 8.25 rear. 115k miles.

I started with:

2" OME coils
2" OME light duty leafs
OME shocks
JKS LCAs
JKS trackbar
JKS quick disconnects
235/75 Duratracs on stock wheels

Vibrations 30 to 40 mph while on the gas, and vibes 60 to 75 mph on/off gas. No steering wheel vibrations. Loud humming sound, and vibrations felt in the floorboard and seat.

Steps I took to solve it:

--Professional alignment
--Confirmed front DS properly aligned with pinon
--Removed front DS, vibe still present.
--Rebuilt front DS with spicer parts since it was out.
--Removed rear DS, didn't notice any vibes
--Shimmed rear pinion so it was parallel to Tcase output. Still had vibes.
--Replaced both rear ujoints. Still had vibes.
--Had tires rotated and balanced (2k on them), still had vibes.
--Replaced transmission mount. Still had vibes.

I installed a Tom Woods SYE and Tom Woods rear driveshaft. Planning to lift it higher when my kid gets bigger, so the SYE was on the list anyways.

--Rear axle is shimmed properly, so pinion angle matches driveshaft angle.

30 to 40 mph vibes gone. Highway speed vibes still present.

--Went to discount tire and spoke with the manager. They balanced each of the tires. Said one of them was on the edge of being unacceptable, so they replaced it (3k miles on the set so far). Manager drove it on the highway, said he couldn't notice anything wrong (vibration wise). I was at work and didn't have the opportunity to ride with him. He stated the humming was just what duratracs do.

I bought a used HP30 and 8.25 rear with 4.10's installed. Installed all new brakes on the "new" axles. Verified DS angles are still good. Same speed related vibrations (60 to 75mph). Higher RPMs have made no difference. Very loud humming noise like before. All symptoms exactly the same before/after swaping the axles.

I'm thinking it's the tires. Either something is wrong, or I'm a wimp and the Duratracs are acting normal.

Thoughts?

 

[psullivam]

tires.

where you located?

 

[briboki]

South West Longmont.

 

[puttzer]

Have you checked motor mounts??

I did not notice the vibs after axles, but might not have paid much attention as mine vibrates also.

 

[puttzer]

One thing I just thought of, I had problems with my Tom Woods drive shaft, had to have Northern Colo driveline grease the CV ball and rebalance shaft, fixed alot of my problems.

 

[briboki]

Have you checked motor mounts??

I did not notice the vibs after axles, but might not have paid much attention as mine vibrates also.

They looked good visually. Also did the put it drive, give it a lil gas while holding the brakes down while dad watches under the hood test.

I guess it may be worth it to have the rear shaft checked.

Did your Duratracs hum on the highway? I've always run BFG AT's on previous vehicles.

 

[puttzer]

They looked good visually. Also did the put it drive, give it a lil gas while holding the brakes down while dad watches under the hood test.

I guess it may be worth it to have the rear shaft checked.

Did your Duratracs hum on the highway? I've always run BFG AT's on previous vehicles.

Try putting your front driveshaft in the back, yes Duratracs make noise.

 

[DutchVDub]

Well I'd say its either your tires or your rear driveshaft. Remove your rear again and see if that gets rid of the vibes again. If you want to swap my rims/tires on your rig one night and see if that makes a difference you're more than welcom too. They shouldn't rub on the street with your 2" lift (their 32's) and don't vibe at highway speeds. They do wobble a bit at 45mph though.

 

[briboki]

Well I'd say its either your tires or your rear driveshaft. Remove your rear again and see if that gets rid of the vibes again. If you want to swap my rims/tires on your rig one night and see if that makes a difference you're more than welcom too. They shouldn't rub on the street with your 2" lift (their 32's) and don't vibe at highway speeds. They do wobble a bit at 45mph though.

Thanks for the offer.

Pulled the rear and put the front on the back today. Much smoother. Going to have the rear shaft rebalanced.