Looks like I got alot on my plate at the moment as the symptoms slowly increase. Cannot get my Disco in to be looked at until January 23rd so in the mean time Im hoping to narrow down the possibilities.

Newest symptom Ive experiencing is a constant straight line noise while driving at 70MPH. When I step on the gas and push the speed up to 70 the noise gets slightly louder, when I release the gas the noise gets softer. As mentioned before sometimes it difficult to get my truck up to 70MPH. Difficult to determine where exactly the noise is coming from, my guess somewhere related to either the drive shafts, diffs, transfer case or the transmission. The noise does not sound like grinding gears, there is not any distinctive vibrations or thumping noises. Its just a straight consistent noise that gets slightly louder as you press harder on the gas peddle and only starts at around 70 MPH. My former D1 had a bad rear driveshaft and I know first hand what it sounds like. Very loud clunking noises and very noticeable vibrations. That is not what Im hearing.

Front driveshaft was replaced with a Proshaft driveshaft and I greased it before I installed it. Rear driveshaft re rebuilt and greased. New rotoflex and new hardware on both shafts. Transmission fluid and filter just changed and transfer case fluid topped off. Old fluid that came out of tranny was a nice red color and I do not have any problems shifting through gears. Every once in awhile I hear a clunk when I let off the gas while driving at town speeds but not often. Tires are newer all season highway tires, recently balanced and just had an alignment.

How can I test the diffs front and rear, as well as the transfer case and tranny? Could it be the engine making the noise?

 

I would doubt your driveability issues are related to the driveline, but you can check the differential fluids for signs of metal. You can also check them after a drive to see if they are getting hot. For the transfer case, without being able to drain it you will have a tough time confirming if it has any problems. Driveshaft issues won't slow you down but they will make the truck shake while driving. Problems with the transmission would probably show as a fault or an overheat. Is it shifting ok? You can check the fluid color pretty easily to see if there is any evidence of any breakdown of the clutches.


Your transfer case isn't locked, is it? That would make the truck feel weird in sharp turns on pavement.


You can also check out the hubs. If the rear hubs are going bad there will be gear oil leaking out onto the brakes. You can check out the fronts by jacking up the truck and trying to rock the wheel back and forth with your hands.

 

Did you try knew O2's or look into the speed sensor on the tranny?

What do you mean by straight line noise?

 

As mentioned above I just changed the transmission fluid and filter. Only a very small build up in the pan. I was very impressed especially with how red the fluid was. My Transfer case is in high and the Diff if not engaged. By straight line noise I mean that its a very constant humming, there are no gaps between the noises. Its nothing like " thug, thug or bom, bom". Just a consistent very noticeable humming like noise that gets louder as you reach 70mph. The minute I let off the gas the noise nearly goes away.

 

Do you think it could be your tires? Maybe you didn't notice it before.

 

Mounts might also be worn.

 

No sure if my situation applies to yours...

I changed the fluids in the transmission, transfer case and diffs when I first bought the Disco. Also new front prop shaft, rotoflex, shock absorbers and steering damper. Steering linkages were not worn. New tires and alignment.

I noticed a very slight whirring noise when increasing speed. Everything was bolted up tightly and fluids were all topped up. It was not any sort of driveline vibration. I chalked it up to gear lash from the differentials.

 

I was going to say that. Check to see if there is anything making contact anywhere. Check the tranny mount and the engine mounts to see if they are excessively worn, check the exhaust, check the heat shields, just look around everywhere.

 

Not likely the new to me tires. The first day driving with the new tires my vehicle was out of alignment and even then I did not notice any noises at excess speeds. I have since gotten the truck aligned and maintain proper PSI in the tires. Did not notice the noise until about a week ago. I always pay attention to what my vehicle is trying to tell me so I would have noticed it right away. I commonly drive at 70mph and have been doing so since I purchased my truck.

Tonight I dare conclude that the loud humming noise I hear between 66-70mph is NOT the engine. When I ride up the steep long hill to my place I can hear the engine blaring away and I can tell how it sounds and where it is located..... that being in the engine bay. But when Im on the highway driving along at 66-70mph it sounds very different, louder and sounds like its coming from beneath the vehicle, rather than up front in the engine bay. I also noted that the sound is NOT effected by the RPM's. Sound seems to follow the speed of the vehicle. Had I not already serviced the prop shafts I would assume they were the source but as I said I already serviced/replaced them. I also just had my vehicle inspected like a month ago and everything passed so id like to think that my suspension parts up front are good? Plus the tie rods are all new. Steering damper is new. Shocks and springs are new.

I dont hear any clunking noises, no metal grinding noises, no thumps and no seriouse vibrations. The humming creates a minor vibration, but to be expected as sound waves do make vibrations. But its not the kind of vibrations common when a steering damper or prop shaft fails.

I have noticed one other new noise but I only hear it often during "takeoff" from a complete stop, where sudden pressure is applied to the gas pedal. Sounds like something metal hiting something and it lasts for about 1.5 seconds. Cannot always replicate it though, tried to today but no luck. Again this noise sounds like its coming from beneath the vehicle. I briefly inspected the rotors and they feel pretty smooth. Though if it were the brakes then I could hear them grinding metal and it would be constant especially at low speeds. Not the case right now so I dont think its the brakes.

Is there a diagram that shows the locations of all the mounts you guys speak of? Im not at all familer with them. This weekend I will feel around and see if I can find anything that is lose. I wish there was a way for me to lift the vehicle up safely so that I can have a friend accelerate the gas pedal to 70mph, that way I could get under the truck and pin point exactly where the noise is coming from.

I hope my truck can make it until the end of the month. Im worried.

 

On a D1, the TC will have a slight "whine" at higher speeds.

I don't notice it as much on the better-insulated D2 though.