Hey CF,

I have a 98' 4.0 with D30, NP231 and C8.25 to start off. I have been getting this crazy humming coming from underneath my TC shifter. I have already replaced the TC with a new one. That didn't fix it. I pulled the front drive shaft this morning, and boom, no more humming. So, what could it be? Should I try rebuilding the drive shaft, buy a new one, or could it be something else?

 

U-joints?

 

Maybe it needs to be balanced

 

Rebuilding it will cost about $90 for the three joints and the center ball, if you do it yourself. Takes about a hour. ALOT cheaper than a new one. If you get one from a jy chances are it may need a rebuilt too. If there is a clean spot, it probably lot a weight & would need to be re balananced.

 

No clean spots. The weight is actually still on the DS.

 

Do the u joints feel loose?

 

What are/were the symptoms of your humming? I have a similar sound/vibration coming from, what I think is, either a bad pinion bearing or front driveshaft u-joints. I only get the humming on deceleration and I'm trying to pinpoint the source. Cheers!

 

My sound/vibration starts at about 25mph and increases in noise as I accelerate. The sound/vibration continues whether I'm on the gas, coasting or even put the transmission in neutral.

 

They don't feel loose, but the front portion of the DS where it slides in and out is not as tight as I think it should be. Plus, its not really holding grease.

 

Sounds like a loose slip joint on the front driveshaft. I would check the double cardan joint to see if that's OK and possibly grease that too. There's a ball and socket there to keep things straight and might cause the vibration. In mine, it took me a long time to figure out that ball socket had grenaded, having to hold the transfer case flange and try to move the shaft to see any movement. I had to lift the front axle to able to turn the driveshaft to find the problem and see that the joint had failed.

https://goo.gl/photos/nDjicNDrqJcBAizq7

https://goo.gl/photos/hDJmq1MKyoMKAzueA

I bought a rebuilt shaft last month and I am happy that it works now.

 

Its gotta be your centering bearing (ball and socket) in the double cardon joint or something with the pinion alignment or bearing or nut.... is your D30 an open or do you have a lunchbox locker or limited slip installed?

 

I'm pretty sure the D30 is open. It's completely stock at this point. I think I may try a remanufactured drive shaft.