My '96 has had a vibration since i've had it. I have put u joints in the rear driveshaft, and I jacked up each rear whell seperatly to see if it is a tire, but it always does it. I recently saw a thread about the dual mass flywheel causing this. Mine is an auto, could this be the problem?

 

Nope, Not an issue with a dual mass flywheel on an auto. You have a flex plate (some people mistakenly call it a flywheel) instead. Is your truck a 4x4? Have you checked the front drive shaft u-joints? Does it vibrate at all speeds or does it seem to get worse at one speed? Can you feel it in the steering wheel? Does it feel like it comes from the front or the rear? Give us some more information and I am sure of the "experts" on here (of which I am not) will be able to help you out.

 

Yes my front u joints are fine. It is from the rear, I jacked up each of the rear wheels and put the truck in gear, vibrates no matter which side was turning. It is only a slight vibration and hasn't gotten any worse in 10,000 miles. I was thinking the driveshaft might be out of balance. The little weight was rusty and pushed off the shaft on one side so I pushed it back and put a spot of weld to hold it on.

 

Sounds like a likely candidate to me! Take the drive shaft to a shop and have them check it. They should be able to balance it if needed. FWIW, if it is the drive shaft the vibration would be a lot faster than if it is a tire or something. Does it feel like a quick vibration like that to you?

 

Yes it's fast, that's why I changed the u joints, that's what it felt like.

 

I take it this is a one piece driveshaft? Fill out your signature so the folks here know what you have.

 

I would have that drive shaft balanced if it were me. FWIW it might be cheap to find a used one at a junk yard.

 

Not so fast there on the driveshaft. Do a couple simple things first.

1, take the driveshaft off the rear end and take the rear tires and brake drums off. Turn the yoke by hand and see if it's gritty feeling at all. too tight, too loose, any runout at all. Go grab the rear hubs and turn them check for the same thing. Might be a good idea to readjust the bearings too. Back them off a couple turns and readjust. You need a special socket for this and a torque wrench.

Now pull the driveshaft out of the transfer case and clean and lube the splines with that special grease someone already posted about. That stuff works great. GM also has the same thing. I forget the entire part number but it starts 12345. Seriously.

Check for any play in the carrier bearing.

It's super uncommon for a driveshaft to lose it's balance. Unless it's bent and you should be able to see that.

Is it lifted or lowered? If so then you'r pinion angles are trashed and the back axle will need to be shimmed to fix it.

Does it only do it at a certain speed? Or is it a certain RPM? That would be really nice to know.

Is it high pitched like an electric drill sortof or low pitch like a growl? That would also be really nice to know. It would tell me the difference between carrier bearings or pinion bearing. If it does it more when you turn to one side or the other then it is likely a hub bearing. If it starts about 45 mph and is constant all the way up then u joint or possibly driveshaft balance. or carrier bearing.
please try to get me some more info and I can probably tell you where it's coming from. This is what Ford and GM sent me to school for and to teach for a while.

The most common cause of this on 4x4's is one or both hubs locked and the driver doesn't know it. Even if you think they are unlocked you need to verify. It often sounds and feels like the back end is doing it.

 

Ok RRanch it is a low grumble, start to feel it about 40 and continues all the way through. I have checked the carrier, it has no play, and replaced all three u joints. I jacked up the truck and let it run, so it is definately in the rear driveline. I will try the splines on the front end of the shaft. The main reason I am thinking it's a balance issue is the little weight on the driveshaft was loose on one side because the spot weld rusted. It isn't a bad vibration but just always there.

 

That sounds like carrier bearings. Maybe outer axle bearings but more likely carrier. 40-45 mph and low grumble are classic symptoms for them.
you have to pull the carrier to look at them. It's not that hard. Just keep the shims where they belong.