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Discussion Starter · #1 ·
Where to start: 1999 TJ 3" Lift 1" Body Lift on 35's Has Slip Yoke Eliminator and an Adams double cardan drive shaft and Ford 8.8 rear end.

Use of jeep has changed: We now tow it behind the RV and go on long trips. The 4.88 gears made the Jeep notsogood for the 30 mile run into town. 2500 rpm = 50 MPH.

Re-geared to 4.10 front and rear. The man I hired to do it was less than confidence inspiring. Immediately upon his completion I took it in to the expert shop that I should have taken it to in the first place. There was quite a bit of correction that took place in the rear. Amazingly the front checked out. Now both gear sets are in proper trim. I get a driveline vibe under acceleration and at at cruise beginning at 50 mph. It intensifies as you speed up toward 70.

One of the problems corrected was a bent pinion yoke (it was replaced) also it LOOKED like the adams driveshaft was bent but a quick check on the lathe and it is completely true.

in an effort to quelch the vibe - I adjusted the pinion angle a tad. It MAAAY have gotten slightly better - hard to say. My pinion angle with the 4.88 gears had no vibration at all and it was dead nuts 11 degrees at the pumpkin and 11 degrees on the shaft. I am now 11 degrees on the shaft and 13-14 on the pumpkin - I am afraid to keep going that direction (15 degrees on pumpkin - 11 on shaft) because DANG 4 degrees? When it wasnt vibrating before?

We have removed the front driveshaft during testing...it's clearly in the rear.

Any IDEAS that my bone head has not considered?
 

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To clarify the series of events, you had vibrations directly after having the 4.10 gears installed and then took it to another shop to have them fix it? Now you still have vibes at highway speeds?

Sounds like the original installer fudged it bad enough to warrant all new gears and bearings.

The gears have a hardened coating. If the are setup improperly, that coating will wear off sending metal throughout the entire axle.
 

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Discussion Starter · #3 ·
exactly what I feared
 

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That coating comes off when you break the gears in and work harden them. I would dial your pinion back to 0 and check again. If the vibes get better then it's not your gears. Gears don't cause vibration unless the pinion nut is loose or the pinion preload is too tight. In that case the bearings wouldn't last long anyway.

Keep working your pinion angle. Are the u joints positively good in the driveshaft? Sometimes things don't show themselves until a change had been made.
 

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Something just isn't sounding quite right. 2.5k RPM's and 50 MPH, with 35 in tires. I personally have 33's, 4:88 gears, and nv3550; 5sp, and at 2.5K RPMs, I'm doing + 60-ish. with 35's I probably would be doing + 65-ish
 

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I'll share this just in case:
Recently regeared my JK to 4.56. Although I was completely thrilled with the new performance, I was getting new vibes that I never had before. Did a little research which lead to me checking the torque on my wheels. Since my aftermarket wheels are lug-centric and not hub-centric they need to be torqued correctly. Upon checking I realized that my driver's side rear was way over torqued. Removed all my wheels and put them back on making sure to torque them properly... it fixed the vibes and I'm happy again. Might be worth a shot.
 
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