Getting back to your first post the conditions you describe also sound like a possible drive shaft U joint noise. If your going to a shop to fix the gears have them look at the drive shaft U joints. If their original they may be wearing out and making the noise.

 

Good thought! Thanks!

I just did a quick price check online, and it's about $30 bucks for the U-joint and a strap kit.

I think I'll toss that in there just for grins, and see what I get. Even if that does not get rid of the vibration, I'll want new u-joints if I replace the axle anyway....

It'll be two weekends before I can get to it, but I'll try that and report back.

 

Well, the job is fianlly done. Sort of.

The good news is, the rear u-joint was definitely bad, and I'm 98% sure that was the whole problem.

The bad news is that 2%. I have a new vibration that is entirely speed dependent. It does not get worse when under load, but increases with speed.

I'm thinking I managed to do something to make the driveshaft assembly unbalanced.

But what?

I'm not clear on how to make sure the rear u-joint goes back together centered. It's the kind that has two u-bolts to hold it in place. Could I have gotten that off-center?

 

Did you replace the front U-joint??

Did you turn the transmission yoke 180* to the drive shaft??

This alone would cause the drive shaft to be off OEM balance.

Did you replace the differential U-clamps with new ones??
Old U-clamps should never be re-used, as they become "stretched"

It's almost impossible to get the rear U-joint out of alignment with the differential yoke, as there are "nubs" on the yoke to center the U-joint.

 

Wow! Thanks for the very fast and very useful reply! I love this forum!


Oh, straps. I completely forgot about them!

Off to the store first thing in the morning!

As to getting it off 180*..... maybe. The new joints are greasable (yay!) after the new joints were back in, we found my grease gun had fallen apart. (Cheap Chinese junk, I guess.)

So I went off to town to get a new one, and left my two older sons to put the shaft back in. That was a mistake on two counts. They got it done, then we had to undo it to grease the front one. (Yes, I did get a new front joint.) Couldn't get to the zerk otherwise. That's when I found I had trouble getting the rear centered.

Of course, they had taken the van down off the jackstands, so I was doing the last part with not much clearance.

With some better room to work, and some new straps tomorrow, I'll take a more careful look at how things go together.

I hope that clears things up!

Then it will be on tot he IAC valve, and then the heater resistor.....

 

Success!

I got some new straps, and noticed that I had put the new rear joints in with one end riding on top of the nub that centers it. Got that corrected when I installed the new straps, and it's now smooth as silk. No more vibration, even under acceleration going up a steep grade.

I do get some just before the shift, but it's engine speed dependent, not vehicle speed, so it's not driveshaft or differential.


Thanks very much to all who contributed!