Ok, first I have to fess up......I think I might not have gotten the driveshaft parts mated back up correctly when I replaced the u-joints. I marked them with a welders chalk stick, but by the time I went to put them back together, the *^#^ chalk had mostly worn off.

I thought that I put everything back together correctly, but now the vibrations that I was getting at about 50 mph is starting at around 40 mph. Is there any way to figure out how they are supposed to go back together?

While on the topic of u-joints, how are the front driveshaft (output from AWD transfer case) supposed to come out? I tried to press them out, but they didn't clear the yoke enough to remove the caps. I ended up cutting the old one out.

When I put the front one back together, one half was a bit tight. Could that be the cause of the increased vibrations?

By the way, how do the rest of you get the front shaft out of the vehicle without removing the transfer case?

 

I dont have my service manual handy, but it seems to me that they tell you to strike the ears of the driveshaft with a hammer after the new u joints are pressed in. I think that its to make sure the joint is properly seated into the shaft. I guess when you are pressing the new joint into the shaft there is a possibility that the one of the ears could get flexed out of position??

 

what were the condition of the old removed bearings, any heat damaged? heat damage can warp and misalign the yokes

any dings/dents in either driveline from hitting something?

are all the new u-joint bearing cups seated out against the lock rings?

Chilton's has a great section on Aero specific driveline and u-joint servicing, bearing replacement and shade tree balancing.

 

To remove the front driveshaft, you have to put a jack under the transmission cross member (on the driver's side), take the tension off the crossmember, remove the large retaining bolt and then jack up the crossmember a few inches to allow the splined end to be removed from the transfer case. The front end of the shaft obvously must be moved as far forward as possible to accomplish this.

If the shaft was vibrating before removing the original joints, you may have lost a balancing weight off the shaft or the shaft itself is bent. Most larger towns have a drivetrain repair shop that can rebalance the entire shaft assembly-might have to ask around at the parts stores or machine shop to find out.

 

There are two reasons for rapping the ears after you intall new U joints.

First, when we press in the new cups, we don't usually stop at the right spot and almost always press them in too far, thus the inner face of the cups are rubbing on the U joint's cross. As a result, after the retaining rings are installed, we must rap the assembly in such a way that the cups are pushed back outward against the retaining rings.

Second, the cups almost always come in a little crooked when we press them in, and rapping around the ears will relieve the stress and hopefully straighten them out.

I have had vibrations like yours when I'm not careful with the new U joints. After assembly, they should move freely. You shouldn't feel any binding as you move them back and forth. If you do, you will get vibrations.

 

I'm getting back under the van right now and checking to make sure everything is OK. I have a couple of replacement joints in hand, so if I messed one up, I can replace it while the driveshaft is off the van.

There werent' any dings/dents or missing weights, but I'm not sure I put things back together exactly as they came apart. If a part was turned 180 degrees, would that cause vibrations as well?

 

yep, they are dynamically spun balanced as a whole unit across rpm range at factory with computer placement of balancing weights.

somewhat like spin balancing a tire/wheel unit or even more advanced on vehicle wheel balancing where tire/wheel/brake unit/axle is spun.