I have a situation that I'd love to have the membership lend their expertise in troubleshooting to. I own a 2008 Dodge RAM 2500HD SXT 4x4 (6.7L Cummins engine) w/ manual trans.

I have noticed a vibrating feeling coming from the truck, the vibrations are like what you would feel if you were driving down an asphalt road with overly aggressive off-road tires. The tires that I'm presently running on the truck are BF Goodrich All Terrain T/As. The tires are 1" larger than the stock tires that came with the truck. These tires are far from being what would be termed as "aggresively treaded".

This vibration is NOT felt in the truck when it is sitting still and there are not abnormal noises heard from the engine compartment or drivetrain area. The vibration becomes noticeable (pronounced) when approaching 50 mph and continues through to around 65 mph, increasing in frequency as the speed increases. When you let off of the gas pedal, the vibrations vastly less pronounced then when accelerating through the previously mentioned speed range.

I jacked the front end of the truck up so that both front tires were off the ground and spun the front wheels. No abnormal sounds came from the wheels and the wheels did not have any abnormal travel in them, in other words, the front wheel bearings are NOT the source of this vibration. While she was up on the jack stands, I crawled underneath and looked at the drivetrain and steering linkages. Nothing seemed amiss there....no shiny spots on any of the linkages and I could not detect anything wrong with the universals on the shafts.

I don't know....maybe I'm just getting old and more sensitive to my surroundings and didn't notice this when I first got the tires. Whaddya think?. It's fine if you want to tell me to "Lighten up, Francis!" (Remember the movie, Stripes?)

 

I know you had a look at them already, but it sure sounds to me like a bad u-joint on the rear shaft. The AAM joints the factory uses are sealed poorly and tend to cause these problems. I like to replace them with Spicer non-greasable joints.

There are two failure modes: a joint can become loose from having the needles rust away, or can seize internally and stay tight, but not be able to articulate.

To check for looseness, you need to leave the truck in neutral so the drivetrain isn't loading the joints. Set the emergency brake firmly and chock the wheels for safety, then climb underneath and try to rotate the shaft in opposing directions on either side of each joint. Hopefully some looseness will show up.

A seized joint can be harder to diagnose because you won't necessarily feel any looseness. If you're lucky, you can see the telltale rusty powder oozing out between the cap and cross of a seized joint. If it's not that obvious, you may need to remove the shaft from the truck and flex each joint through its range of travel to feel for resistance or binding.

 

I would first pull the front drive shaft go out and drive truck to see if vibration is gone. Usually you will feel the vibration in your seat if it is from rear driveshaft. No pun intended.

 

Torque, don't you think that I'd be feeling this vibration anytime that the truck was going down the road and not just through the speed range that I talked about?

How long do the Spicer non-greasable joints tend to last? I'm used to the good old fashioned joints with grease fittings on them.

I'll crawl underneath again and check them again. I'll take the shafts off just to make sure that they move through their complete range of motion just to make sure that they're not seized.

Thanks for the input, take care, and stay outta trouble.

 

Big Iron, you and Torque seem to think alike and I'm gonna troubleshoot that route and see what happens. Thanks.

 

U-joint vibrations can be kinda funny that way. A loose rear joint can act a bit differently than a front or center joint on a rear shaft, and a seized joint can act differently as well. The key symptom you describe is that you feel the vibration under load, then it goes away on decel. That's pretty classic u-joint there, although an out of balance shaft can show the same symptoms. Being as how the AAM joints on the 3rd gens are so problematic, it's a good place to start.

I recommend the Spicer non-greasable joints because they pretty much last forever. Really never saw a problem with them on the second gen trucks as a Dodge technician in the old days, maybe one or two on miled-out tow trucks. Mine are all original on my 96, except the axle joints which I've changed.

The problem with the greasable joints is that the seals aren't nearly as positive. They are designed to allow old grease to exit the seal as fresh grease is pumped in. These seals seem to allow lots of moisture and gunk to enter the joint and cause problems.

Just my opinion here, but it works for me. Good luck finding your vibration.

 

Hey Torque Fan and Big Iron, it turned out to be the universal on the rear drive shaft. The universal that connects to the rear axle flange. I guess the first time that I fooled around with it I didn't move it the right way. Sure enough, it was sliding sideways about 3/16ths of an inch. Went to Parts America and put in the replacement and the truck is running smoothly now. Thanks.

 

You're welcome! Glad you found it.