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2003 Dodge Dakota 2wd 5 speed standard transmission. Stack rear end was an 8 1/4 with 3.55. Changed to a 9 1/4 with 3.92 from a 2002 Durango. Had to add shock mounts, and instead of the flat plate at the end of the drive shaft that bolts to the diff. It has the two caps that bolt the rear U-Joint to the diff yoke. Here is the issue, when barely pressing gas pedal or when pushing the clutch in, I hear a noise that sounds like it’s co from under the cab. No noise when accelerating or deceleration. Only when clutch is pushed in, or when barely applying gas. When installing the driveshaft to the new differential, I did have to slide the drive shaft toward the differential just a smudge. 1/4” or so. My best guess is that that small movement may have been just enough to introduce a rusted dirty spot into that mid span bearing looking thing. What do you guys think? What the hell is that mid span bearing looking thing?
 

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If you have a club cab or quad cab with the manual transmission (131 inch wheelbase), you have a two-piece drive shaft. Between the two pieces is the center bearing, sometimes called the carrier bearing. Where the rear drive shaft fits into this bearing is a slip joint, so moving the shaft aft 1/4" should not be an issue with maintaining proper drive connection.

It is possible I guess that the shaft being in a different position could cause some minor vibration/noise until it gets "seated" in the new position. If the noise doesn't go away, inspected the center bearing and drive shaft closely. The center bearing is mounted in rubber - check that the rubber is still in good condition, not cracked or deteriorating. Check all your universal joints, especially the center and rear joints. If the angle between the center bearing and the pinion of the differential changed, the universal joints may be exposed to different loads and develop some play.
 

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Thanx, I did a visual and looked at every U Joint while moving the drive shaft by hand, didn’t see any play or obvious signs of a bad one. Then again, these probably have never been changed. I think tomorrow, I’ll loosen the bolts for the carrier bearing and let it decide where it wants to be, then tighten back down. I’ll also check all U-Joints again. I’ll give it a few drives, (a week or so) and see if it eases off. If not, i’ll Start from the back and work my way forward changing U-joints. Going from the 3.55 to 3.92 is a much welcomed improvement. It has a 239 V6. So far I’ve done a P&P V8 Throttle Body, Hughes Plenum plate, cleaned up the intake casting and port matched to V8 TB. 1:7 Roller Rockers, P&P heads, accel coil and wires, CPS Mod, TPS Mod, superchips programmer, and upgrading to the 9 1/4 rear with 3.92 gears. Next trick will be Cam, Timing set, headers all in one go. Then either get a Dyno tune, or SCT programmer with custom tune. End game will be about 40-60 shot NOS
 

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Additional information- I noticed after a drive this morning that the first part of the driveshaft before the carrier bearing is hot to the touch. Much hotter than the second part(after the carrier bearing)
 

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Another thought- since I just changed out the diff. I was thinking along the line of that. It just dawned on me that this whole problem is acting like a bad throw out bearing. Do you think it may be a coincidence that the throw out bearing is bad? Maybe the extra torque applied due to the different gear ratio in the new diff maybe forced the bad throw out bearing to show itself?
 

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This is getting freaking frustrating!!! Improvements are, there is no longer a vibration just a noise. Sounds almost like really thick gears grinding only when pushing in the clutch pedal or just when I am giving it enough gas for the driveshaft to “free spin”. I have changed the throw out bearing, all U-Joints, driveshaft support bearing, slave cylinder. I have no Idea what it could be! Maybe the pinion bearing? Any insight? The noise has not changed.
 

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Woohoo!!! Figured it out!!!! Here was the issue. The 9.25 differential from the Durango is at a downward angle compared to the 8.25 from the Dakota. Since I wanted to lower it anyway, here is the path I chose to correct it. 1st I put the truck on jack stands. These jack stands were under the frame. I then got the jacks from the truck and from my wife’s Jeep and put them under the rear axle to simulate the load placed on the rear springs as the truck sits down on the ground. I loosened the U-Bolt nuts. I used a bottle jack to push the front of the differential up to the correct angle(slightly elevated and pointing directly at the Yoke from the output shaft of the transmission.I then measured the gap between the front of the spring perch on the axle and the spring and the back gap. Worked out to be 5 degrees. So after measuring the distance from the wheel well to the ground in the front and back, I determined I wanted to bring the back down about 2” inches. So, I started at the 2” mark on my 3” block and drew a line at 5 degrees. I cut it with my 4” grinder around the edge, and finished it center section with a sawzaw. Used that block as a templates for the second block. Made sure both were the same. (Cut the bottom of the block as waste not the top. Leave the dowel alone. Cut off the hole) redrilled the hole in the bottom of the block, installed with the high side forward. You will need new U-bolts as the factory U-bolts aren’t long enough. I just picked some up from autozone. Installed new U-bolts and bottom plate and Boom!!!!!! The pinion of the differential was pointing directly at the output shaft of the transmission. Then, as I looked up the driveline, I saw that the driveshaft support bearing had to come down. So, after measuring and thinking on it, I determined it had to come down an inch and a quarter.
 

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So I cut the tops off the rivets holding on the cross member with my 4” grinder and cut-off wheel. Used my air hammer to pop the rivets through(take out the bolts for the center support bearing, and support the drive shaft before removing the cross brace. I used a 6x6 and a series of smaller pieces of wood and held the drive shaft in the exact spot it needed to be) once the cross brace was out, I cut out about 1” out of where the driveshaft support bolt hole were. This will leave you with 2 small Stella strips at the bottom of the cross brace. This allows you to maintain the length and everything from the original center brace. So looking at it from the side of the brace, there is a notch out off the brace where the driveshaft support bearing mounts. I took a piece of 3/16” steel and welded it in that notch. I welded it all the way along both edges of the two strips we left. I picked up the brace, and it was supper wobbly, needed some supper from twisting as well as bowing. So I used two pieces of 3/4”x3/4” angle, as this allowed clearance for the driveshaft. Welded that all the way out. Was super solid and I couldn’t budge it even jumping up and down on it(I’m 230lbs). I then grabbed the part that I cut out with the bolt holes in it and used it as a template to mark for new holes. Drilled the holes. Reinstalled the cross member with 4 grade 8 bolts and bolted down the driveshaft support bearing. Now my driveline is in a straight line from the output shaft of the transmission to the pinion on the differential. Now the truck looks like it had a leveling kit, but with the back being dropped instead of the front being lifted. I think I may need a pair of drop shocks on the back, but it maintains factory parts up front. Now I have zero noise or vibration. Apparently the angle that the differential was sitting was not allowing it to properly lube the wheel bearings which is what the noise was, and the vibration was cause by the right angle of the U-joint close to the yoke. I’m only out for a cutting wheel, wear and tear on my sawzaw blade, gas and wire for my welder, and $90 for U-bolts and blocks.
 
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