Vibration Help

[Diabolic]

I'm trying to isolate the cause of a vibration in my 94 Bronco. It has a 6" lift and 33" tires. The vibration starts at 65mph and just gets worse the faster it goes. I have 2 driveshafts, both completely rebuilt and balanced. Both behave the same way. Rear tires removed, still get vibration on Jack stands 65+mph. If sounds/feels like a bee buzzing. I don't feel it in the steering wheel, but it resonates in the cab and in the floor/dash. I know for sure it isn't the tires, driveshaft. That leaves the brake drums, transfer case, and rear differential. Neither are cheap. Is there any way to isolate one from the other?

[kingjason]

I'm trying to isolate the cause of a vibration in my 94 Bronco. It has a 6" lift and 33" tires. The vibration starts at 65mph and just gets worse the faster it goes. I have 2 driveshafts, both completely rebuilt and balanced. Both behave the same way. Rear tires removed, still get vibration on Jack stands 65+mph. If sounds/feels like a bee buzzing. I don't feel it in the steering wheel, but it resonates in the cab and in the floor/dash. I know for sure it isn't the tires, driveshaft. That leaves the brake drums, transfer case, and rear differential. Neither are cheap. Is there any way to isolate one from the other?

Just because your driveshaft's are balanced does not mean they are not causing your issue. If they are not set up at good angles they will still vibrate. The rear would be the most likely culprit since it is shorter. Plus running it in 2wd would eliminate the front one anyways. Does it have a duel cardan in the back?

[Tremor14]

i want to see video of the truck at 65mph on jackstands!

[Tremor14]

has the top been off the truck?

[Diabolic]

Yes, it has a double cardan in back at the transfer case. I took it to 4 Wheel Parts, they installed the 6" lift, and they said it was perfect. The pinion points almost directly at the transfer case. Maybe a 2 degree downward angle at the very most. I have 2 rear shafts and they were both rebuilt and balanced. Both begin to vibrate at exactly 65mph.

[Tremor14]

whats in the rear end?

[Diabolic]

When I lift off the gas the vibration stops completely.

[Diabolic]

[Tremor14]

its the ring&pinion fool.

[kingjason]

My 90 Bronc did the exact same thing I just never messed with it.

Honestly that angle on the back looks to straight. Hard to believe I know. Do you have correction wedges at the back? The ideal driveshaft angles are where the front has the same degree of angle down as the rear has up. Throws them out of phase or something. That pictures does not show me a double cardan but a slip joint. It would be higher up though by the transfer case.

[inline 6]

double cardan shafts?

[kingjason]

double cardan shafts?

This