im gettign that pulsating hum and my rear end shakes like no other

 

Bender where do you live? Maybe someone is close by you and they can help take a look. At least you know when the rear driveshaft was removed the vibe went away. You know where to focus your efforts.
Do you have a true driveline shop in your area? Maybe it's time to take it there?

 

All my jeeps have a little hummmm. MY 2000's humm went away after i got the rear drums replaced..

 

Well there is your answer. 2 different shafts and the only time the vibs went away was when there was no shaft on.

Sometimes parts in a junk yard are there for a reason.
It will probably be worth the money to have the shaft professionaly balanced.
I've found that most big rig shops are set up to balance shafts. They make their own shafts all the time and believe me if you've every driven a big rig the last thing you want swinging away at 60MPH is a drive shaft that has failed because of it being out of balance. It will help if you can check out the employee parking lot and look for a lifted rig. Then you've got a built in friend who will take care of you.

 

True. But what are the chances we have 2 bad rear drive shafts?

I live in central PA, not too many driveline shops around. I will get it to another mechanic for a 2nd opinion.

 

Actually quite good. There is a small weight spot welded to the tube from the factory for balance that will fall off from rust all the time. And having once worked in a bone yard those guys running the monster frontend loaders are not the most gentle when moving the carcases around. How hard do you think it would be to knock one of those weights off, or bend the shaft just the smallest amount.
Or for that matter the shop that replaces the joint may not have it precisely in the right spot, or they themselves bent it by accident.
There are only so many parts that affect the transfer of power to the wheels and WAY too many variables that affect balance of those components.
I know all the guys asking the same question today (Strange) would like it to be a cheap $2.00 fix but sometimes it's just not so.
Sometimes you have to go over the same thing 3 or 4 times before you go AHA thats whats messing me up.
It's also why I prefer to continue to work on my vehicle. I care about it more than someone I pay to do the work will. Here in Canada we have a huge nation wide chain we call Crappy Tire. They just keep throwing new parts at a problem until it goes away and then charge the customer for all those UNEEDED parts!

 

Rotate the current rear driveshaft 180 degrees and try it.

 

I can't believe no one has suggested this. My jeep hums too, from the rear end. It doesn't do it(or I don't notice it) in 4wd.

And I am pretty sure it is the rear pinion or center bearing.

I would love to get it fixed.

 

I think the big detail is that the vibs are only at 30 mph and 65+...

Anyone hear/suggest of "road force" balancing?

 

Not sure. What is it?
I remember from about 100 years ago (Actually 40) that we used to balance the wheels and tires ON the vehicle by spinning them up with an electric motor to 100MPH and the apparatus that we had attached to the wheel would tell us how much of a weight and where to place on the wheel. That way the whole rotating assembly was balanced.

 

Road force is supposed to check for out-of-roundness and things most balancers don't pick up. Because my tires are new and have been balanced (normal balance machine) about 3 times, I don't really think its the tires.

I could have gotten a bad tire, I need to personally pull the rear DS and drive it.

Are there ball joints in the front and rear that would make vibs are 30 & 65+? If so, how do you check them.

 

i thought it was my rear end or something found out yesterday that i bought crappy tires off CL and they are out of round, they said to many flat spots. so looking on CL for new ones. then my shake will be gone

 

did you check the fluid level and condition of your diffs? also, not to insult you in any way, did when you balanced your tires one of the three times did you get an alignment as well?

my 01 has also developed somewhat of a hum, i'm assuming it's my tires because i have not had them balanced in a little while. also, your exhaust might just be making excessive noise or moving around.

 

That's exactly what mine does, at 42.5mph and then around 60mph...otherwise there is usually nothing.

I have always been under the impression that it is the center bearing.

 

deleted....didnt realize there was a second page. (facepalm)