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Good morning all,

I recently completed a front and rear differential gear swap on my '83 CJ.  This included new carriers with a Spartan Locker up front and an Eaton TruTrac in an AMC20 in back.  I went with 4.10 gears, and had the U-joints replaced at a truck driveline shop on both driveshafts at the same time. 

Now that every thing is reassembled, I'm noticing a rattle or buzz coming from the transfer case shifter about 40 MPH or above. I would describe it as sounding like a bunch of nuts and bolts being shaken in a metal can. It seems most noticeable on acceleration or steady speed.  It is absent or significantly reduced under coast or engine braking conditions.   I haven't had it that fast in 4WD, so I can only confirm it happens in 2HI.  I've heard of various internal issues, as well as possible driveshaft phase concerns as possible causes.

I DID have the driveshaft out, but I DIDN'T pull it apart.  I can't say for sure that it went back in the same way (could be rotated 90-270 degrees), but the two halves are aligned the same as they were before.

I'm not noticing any other symptoms of driveline vibrations, but it's a CJ, so it kind of vibrates all the time.  Any idea how to isolate the problem?  I'm planning to twin stick the Dana 300, and I'd like to eliminate this rattle first so I'm not chasing a problem with multiple possible sources.

I ordered a Dana 300 isolator bushing.  That should be an easy fix, but I don't really expect that is the issue, as there was no problem before the gear swap and driveshaft U-joint replacement.

Any thoughts would be appreciated.

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Hi, 60Bubba!  Good to see you're still improving your Jeep CJ...Trust you're getting good use from the CJ-7.

First off, the 4.10 gears have increased your driveshaft speed substantially at given road speeds.  So, we could start with looking at a driveshaft issue.  Since you've ruled out the "out-of-phase" (misaligned splines in the coupler) possibility, I would check the driveshaft angles at each yoke flange.  You're apt to find an error at the rear driveshaft.

Note: A quick way to determine whether the front driveline is involved would be removal of the front driveshaft and driving the Jeep in 2WD high range without the front driveshaft in place.  (Remove U-bolts and hardware at the front shaft before driving.)  See whether the vibration persists.

This could be due to a mild lift kit without correction of the driveline angles (rear axle pinion angle must match/cancel the transfer case rear output yoke and joint angle).  There is also the possibility of a transmission/transfer case mount issue or misalignment of the transmission/transfer case mount, which would create a compound angle issue on the rear driveshaft.  If you need tips on measuring the joint angles, I can provide details...

Presuming your model has the transmission torque arm and mount(s), and this should be considered as well.  If you need parts illustrations, I can provide.

In any case, the problem likely existed before and was masked by the tall axle gearing.  The front driveline is seldom at fault, but I would check those joint angles as well...Also check the driveshaft coupler splines for wear by pressing against the driveshaft laterally at each coupler to determine whether there is play in the splines.

Of course, check the transfer case shifter for looseness and lack of tension at the pivot mechanism...

Moses

Edited by Moses Ludel

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I get similar chatter between acceleration and deceleration.  Dana 300.  In that sweet spot it does it.  jyst noisy.  Not sure its a problem.

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