Have a 1999 Dodge Ram 1500 with the 5.9 engine. 4wd pickup.

all of a sudden it’s started to make a loud rumble noise right at 60-65mph and 1800-1900rmps kind of at that top gear when it gets in the lower rpm’s. It sounds like the noise/shake is coming from directly under the cab. Now I can be driving and if it starts to make that sound and I either give it more gas or let off the gas a bit the sound stops and goes away. It always makes the sound at about those same points. Checked the tranny oil, it’s a bit low and needs to be changed. Could the problem just be low fluid and maybe a dirty filter? The tranny has about 70k miles on it and engine is at 150k. (Note: the noise/growl is a decent amount louder in 4wd) (put pickup up on blocks to run it and see if it would make the noise while running on blocks, but never makes any sounds. Runs smooth as can be then.)

 

Might want to check the u joints.

 

Well.....despite the fact that it seems to be under the cab I'd first suspect the rear axle or rear d/s u-joints. Check rear fluid level and give the pinion a shake in N with parking brake set and wheels chocked.

I find it unlikely the transmission is doing this. Also the transmission has nothing to do with 4wd, although neither do my suggestions above, really.

It could be transfer case. Check fluid level and also shake the rear d/s at rear of t-case. Perhaps your OEM snap ring went south (known problem)

The noise may just seem louder in 4hi due to the additional harmonics of the chain, front d/s, and front axles spinning

 

I’ve checked all the rear end out. No bad bearings or u joints that I can tell. Rear dif is full as well. Where is the snap ring you mentioned? I also had the front end all apart to fix the 4wd actuator and put in a few passenger side stub axle as the one was worn out from the 4wd not engaging properly. All the things in the front dif and bearings looked to be fine then

 

I'm not saying this is the problem, and if it was I'd think you'd likely get bad noises at all speeds as it allows the rear output to float fore/aft in the t-case

 

Opened up tranny and replaced filter and oil. Everything looked good in there, oil was pretty dirty and kinda low but that’s all good to go now. Still making the noise. Any other tips or things I need to check out? Should I pop the back dif open and look at stuff in there?

 

I'm having this same issue in a sense. The floorboard vibrates at speeds of 65+ pretty bad. I always assumed it was my knobby tires but after having two transfer cases destroy the rear housing half I'm suspecting rear driveshaft balance and/or u-joints. It will be worth checking yours as well as a few have suggested already. Best to catch it early.

 

How do I check if that’s the problem? Never heard about the driveline being out of balance. How do I fix it?

 

If you wanna check d/s balance you'll need to take it to a driveline shop that can chuck it up and spin it.

It's unlikely unless a weight came off. You might carefully inspect the entire length of the tube for anything that looks like remnants of tack welds

 

awesome I’ll check that as well. Thanks for the advise!