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Discussion Starter · #1 ·
Dakota guys:

I have a '92 Dak Club Cab with the 2-piece drive shaft. a 46RH at one end, and a stock 3.55 rear gear at the other. NO MODS TO SUSPENSION. its stock height. and stock wheels/tires.

Ever since my 46RH tranny was replaced i get a vibration at 70 to 90 MPH. the vibration matches wheel speed. i can feel it when i put my hand on the cab floor near the "hump" or drive shaft tunnel. and i can also hear it faintly. put truck in neutral while at highway speed and the vibration is still there. as truck slows down, the tone of the vibration gets lower and lower. ( its like a faint drone sound ) so i know it driveline or rear gear.

other work done at the same time as tranny was the u-joints. all of them.

i took the truck back to the shop and the checked driveshaft angles. they found that the driveshaft angles were about 3 degrees off and they corrected it by inserting some spacers between tranny mount and frame. now the drive shaft angles are within 1 degree
of perfect. they also looked for any weights on the driveshafts that may have gotten lost. they are all there. looked for dents. no dents in shaft.

but the vibration is still there. so, what can it be? rear gear backlash -or- that drive shaft center support bearing?

when you push up and down on the driveshaft near the center support bearing should it be able to move? or should it be pretty well fixed in one location within the bearing?

p.s. the driveshafts, rear gear and axles are all original from manufacturer.

-dan
 

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I'd say that center support bearing is bad. This may be the reason why your driveline angle was wrong.

I don't understand why they would add shims to the transmission mount. In a two piece driveshaft design, the "front" shaft doesn't move. It supposed to stay stationary....it's the rear shaft that travels with the suspension. I bet they added shims to compensate for a bad center bearing....you may have to remove these shims once you replace the center bearing. Besides adding shims to the trans. mount affects the angle at which the engine sits as well, which could cause undue stress on the motor mounts amongst other components.

The only way I've ever heard of adjusting the driveshaft angle is to shim the rear axle, which raises or lowers the rear diff.
 

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Discussion Starter · #3 ·
do you know if the shaft is supposed to move up/down in that center support bearing when you push/pull on the driveshaft? or is it supposed to be fixed pretty solid in one location within the bearing?
 

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2-piece

The center bearing should not move. If you have not modifyed anything you should not need any shims.I would pull the shafts and bearing.Check the splined shaft for side play. Side play will give you vibration. It should slide in and out with out binding.
 

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Get rid of the 2 piece drive shaft, and have a full length one made. It is much better.
 

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Discussion Starter · #6 ·
thanks!
 

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Discussion Starter · #7 ·
injmopar:

forgive the next stupid question, but.........

how do i check the splined shaft for side play?

-dan
 

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driveshaft

Well the only ones I have seen were chev4x4 front shafts that were so bad that it was easy to see. But I would check to see how much the shafts are separated when it in the truck.Then when you lay it on the floor pull it apart the same as it was in the truck.Now you can kneel on the front shaft and pull up and down on the splined shaft to see if it has side play.Now you will know if the bearing or the splines are moving.Pull the two apart and check the splines for wear pattern.
 
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