vibration after gears installed

[xjrockrawler21]

I just got 4.56 gears installed into a d30 and 8.25. The d30 used spicer and the 8.25 used sierra gear. The truck ran fine when i took it to a small shop to have them installed, but I never went on the freeway to get to the shop. Also before having the gears intalled i lifted the rear of the truck slightly by adding some leaves because i was having axle wrap problems.
Now i have the truck back, it runs perfect and very smooth unit i reach about 60, and the vibration stays there if increasing speeds from 60, but will go away if i let off the throttle. It is a moderate vibration that shots through out the truck, and it sounds like it is coming from the rearend or maybe the driveline.
I noticed when i picked up the truck that my driveline was extented another 1" or so, and looks like it is almost fully extended.
My question is can the driveline be out of balance because it has lengthened, because it was not out of balance or i didn't notice it when i took it to the shop. Or if the rear end was set up wrong would it vibrate all the time or just at high speeds.
Any sug. or thoughts would be greatly app.
thanks
ben

 

[xjrockrawler21]

And i just got my tires balanced and rotated yesterday. no difference

 

[MojaveDXJ]

I realize everybody's problems can be different for whatever combination of changes they have made. I However, just put 4.56 in mine as well and have a high frequency vibration at about 65. But for me, and maybe yours, the driveshaft which used to spin at a certain rate at 65, now thinks it's pushing me at between 80 to 85. And with the stock gears at 85, I used to get a slight vibration.
Maybe you're experiencing the same thing. Maybe not.
Just my .02

 

[xjj33p3r]

Did you get that fast with the new springs before you installed the new springs? It could just be a slightly off pinion angle.

 

[xjrockrawler21]

I dont think i went over 60-65 after installing the bottom two axle wrap springs. so i dont know. but can the driveline become out of balance by it being longer than it once was. And i had a driveline shop just look at it yesterday and he told me that the pinion angle was fine. and that the driveline shouldn't be out of balance.
If the rear end was set up wrong wouldn't it vibrate all the time and not just at high speeds

 

[sgtmack]

How much lift did you get from the springs? If it's more than a couple of inches try lowering the t-case. Wait. Before you try that, remove the rear shaft and drive in front wheel drive to make sure it's in the rear shaft. Then let us know how it drove.

 

[tealcherokee]

its the gears, you need to get a driveshaft made with a bigger diameter, sounds weird, but call up tom woods, theyll explain everything about it

 

[FUNKYTEE5]

It probably has to do with the higher drivedhaft rpms with 4.56's than what you had before. That'll make any slight variance in pinion angle, slop in the slip-joint, or driveshaft imbalance much more noticeable.

 

[ArcticXJ]

No matter what, the driveshaft shouldnt have been any further extended when you picked it up than when you dropped it off. Changing gears doesnt entail anything that would cause driveshaft extension.

If you added leaves, it likely lifted the rear end. But enough to cause your shaft to slip a whole inch? Not likely. And regardless, you said it was normal when you dropped it off, but extended when you picked it up. Something is certainly strange. Do you have any other details about what you had done, or what you did to the jeep?

 

[xjrockrawler21]

It has the Rubicon express sye and driveshaft(so the driveline is pretty big), and the only other thing the shop did was weld some high clearance shock mounts on.