A little warning, this is a pretty long post but I needed to type detailed info, sorry guys.

Well, to start out I have a 98 5.9 QC 4x4 sport with 140,000 on it. I bought the truck for an amazing price knowing I had a loud noise comming from the rear end. Changed diff. fluid and the noise quieted a little bit but not much at all. At slow speeds its like a continuous hum/howl that is in sinc with the rotation of the wheels(like pulsating). High speeds its just howling like crazy, loud as hell, but when I let off the gas it quiets a ton(almost goes away for a short period of time). Coming to a stop you hear the pulsating hum/growl. I jacked the back end up one day and just engaged it in Drive to see if it was tires or something stupid...it was loud outside the truck, passenger side rear wheel has a little wobble in it, but the noise seems to be generally comming from the pumpkin. The gears looked good to me when i pulled the cover, so my first guess would be bearings...hub or gear bearings???

The other night I took it off road a lil bit with some buddies. After I got done, I now have a grinding but I can seem to figure out the exact time at which it happens. I know it def. happens on an off ramp that wraps me all the way around a big circle and when I accelerate at the yeild sign up hill. I can barely feel it in my feet, but it almost sounds like a droaning exhaust in the cab.

Sorry bout the length of this post but this is the last thing...My little wheelin' trip led me to some other questions. In 4 low, I push the shifter all the way towards the front of the truck and she slips right in nice. Arent you supposed to have high rpms in 4L. Like just crawling around, I always thought you would have high torque but also high RPMS?? But my main concern is 4H. At a stop, from 2H, I put the tranny in Neutral and I pull the shifter all the way down, and it just doesnt feel like it drops in like 4L and 2H. Like it only goes halfway. Even using muscle doesnt get it in(I didnt use to much dont worry). The light comes and I do belive it engages, but it slips out shortly after I start driving.

Again guys I'm terribly sorry for the elongated post, but I had to get it all out...I'm really hopin for some insight, I do not believe this is a driveway job, but I still would like more insight before I drop it off at my mechanic. Thanks a TON guys! I appreciate the help I'm sure you guys will supply me.

 

that sucks. sounds like the bearings and the seals in the axle got water in them. when you drained it did the fluid look like a gray soupy color? th T case sounds like it could just be a linkage problem.

 

I drained both diffs a week ago today. The fluid was not water logged, it was normal, just a little used...however it was quite low. I did a hell of a job cleaning up both covers and the seal on diff itself. Did a sweet RTV seal job, and precise tourqe job...filled them up with fresh fluid, and the sound went down a little(i'm guessing due to the fluid level being low). Then last night I went wheeln' and now I have the reg noise, plus a deeper bass kinda grinding nose during acceleration. I noticed on the way home tonight that i can be coasting at like 30 and just tap the gas and the deep bass noise comes on then let off and it goes away. this can be repeated over and over just tap and let off.

 

i would bring it to a shop and have them look at it before something happens. like your rear locking as your doing 65.

 

it goes in the shop tomorrow(monday)

 

Sounds like bearings to me!

For the t-case I'd say linkage too. It probably moved a little bit and now it doesn't engage right. She can be a bitch to get into 4L though sometimes, thats normal. Last night I had to pull Jeep with 32's and a lift out of a snow bank that he drove up. I tried to 2H and just broke the back tires loose. 4H sucked too, didn't even move the tires with the pedal to the floor Threw her into 4L again after she kicked me out of it and I barely even touched the gas and that jeep flew out of the snow