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Vibration between 30 and 40mph?

Vkbikes

NAXJA Forum User
Location
Portland Oregon
So I have a vibration that i've been chasing but i'm a little st a loss. Seemed to happen after I got new wheels and tires.

Starts at about 30, goes away at about 40.

Can feel it in the brakes as I slow through that speed range. Not in the steering, it's an audible low growl, almost sounds like tread slap. Totally speed dependent.


235/75R15 on Cragar 15x8 4in BS. Recently balanced so I dont think that's it.

Doesnt change with road surface, so it's not tread slap.

New unit bearings, U joints, and rotors on front didnt make a difference.

Removed front driveshaft, still there.

Rear u joints are fairly new.

Any suggestions? I'm wondering if it's the rear DS or if I have failing carrier or pinion bearings.
 
Shift the transfer case to 4hi, remove the rear driveshaft, and go for a drive under the same conditions.


Seemed to happen after I got new wheels and tires.

I would suspect the tires as the root cause, possibly some kind of harmonics from the tread design. Do the rims spin true ?
 
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Shift the transfer case to 4hi, remove the rear driveshaft, and go for a drive under the same conditions.

I would suspect the tires as the root cause, possibly some kind of harmonics from the tread design. Do the rims spin true ?

As far as I know they do, they were dynamicly balanced without much drama. I would think if it was the tread it would be road surface dependent though?

I will rebuild the front drive shaft then I will try driving without the rear.
 
Before pulling the rear driveshaft, what year? 95 and earlier (and possibly some 96 models) can't do this without capping off somehow the tcase output to prevent dumping all the fluid out...
 
Checked my tire pressures today, set them all to 30psi and went for a drive. The growl sets in hard at 20mph, I can feel it in the accelerator pedal, but not really the steering wheel. It then goes away 25 to 30, then comes back 30 to 40 as more of a low audible growl.
 
Rebuilt the rear driveshaft with Dana SPL 14
310 Joints. It definitely lessened the vibration portion. There's still a heavy vibration right at 20mph but it immediately goes away once you're above or below. The roar is still audible at higher speeds however it is also lessened.

The only thing I can think of is that the smaller backspacong is putting more pressure on the wheel bearings in the rear-end and that's what's causing the vibrations. If so I'm planning on an 8.8 swap soon so I'm just going to let it ride.
 
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