New to me 2005 Ram 1500 5.7 Automatic 2WD Quad Cab 120K miles

So from a dead stop to 45 mph there is a squeak, squeak, squeak, sound from the rear of vehicle and then it either goes away or the wind drowns it out. The squeak changes based on speed from a slow squeak to a fast one based on speed. If you completely let off the throttle and coast the squeak goes away and the truck coasts very smoothly. I thought for sure the squeaking had to be a wheel bearing something like that but having zero noise and being super smooth off the throttle makes me think it has to do with the next issue...

From a dead stop the truck has only the squeak until 25 mph and then you start to feel a vibration under throttle. The vibration is relatively constant from 25 mph to 78 mph (fastest I have ever gone so far with this new to me truck). Between those speeds if you lightly let off the throttle (as though you are approaching traffic, but don't need to let off the gas entirely) the vibration worsens and is pretty bad (feels like you are diving over rumble strips on the side of the interstate), but if you get back on the throttle to either maintain speed or accelerate the vibration gets better BUT never goes away. However, if you are driving between 25 and 78 mph and completely get off the throttle the vibration is at its worst for 1 second and then it completely goes away and the truck coasts very smoothly. Go back under throttle and the vibration returns.

Now the next part is just a little observation but it is hard to do a complete test on this without a long strip of road with no one on it...
Non throttle coasting is always smooth except for the following situation. Slowly decelerating without any throttle down to 30 mph the vibration returns until you coast down to under 25 mph. I think I can feel the transmission shifting into second gear at this speed range and the vibration appears. If you are just driving between 25 and 30 mph no matter what you are doing with the throttle the vibration is there. I have not tried this under heavy acceleration from a stop, because I think you would still be in 1st gear at those speeds, so I don't know if the vibration changes when you let off the throttle.

The motor runs very good and the transmission shifts very smoothly so I didn't know if this is one of those dirty transmission fluid problems or if it is a faulty torque convertor or something else? Changing the fluid and filters will be a somewhat costly job so I didn't want to do it until I knew if a torque convertor was in my future. I don't want to waste the time and money on the fluid change just to change the fluid again

I hope I have explained this thoroughly enough but if you have any more question please ask and I will do my best to answer quickly.

Thanks,
Zac

 

I would suspect rear u-joint.

 

u-joint... possible rear spring bushings. as well.

easy test for any shop.

 

Wow that is good news! How can I check it? You think it is the rear universal joint that connects the driveshaft to the differential correct?

 

Well the good news goes bad The rear u-joint looks line and has no movement but the front u-joint has been bad for so long that it has worn out the driveshaft connection so I need a new driveshaft. Time to call around! Thanks for steering me in the right direction!

 

check out wrecking yards... or have you driveshaft rebuilt.

 

I found a power train shop that can weld on a new yoke, replace both joints and balance everything for $215 but it won't be ready until Monday evening.

Can someone please explain to me why this vibration would go away if you completely let off the throttle? When you are in gear the driveshaft is still spinning so wouldn't it still be out of balance causing the vibration?

 

No load on the driveshaft when your coasting.

 

Letting off the gas, unloads the worn joint.

 

no load. it tried to rebalance shaft.. a spinning object want to spin smoothly ... or break its self apart..

you got the smooth side.. of the choice..
I have seen the front u-joint fail and the driveshaft come thru the floor...

a TV show did this test.. and there's came thru the floor as well.