I was advised to have the driveshaft (propeller shaft) balanced after putting new U-joints, which is scheduled to happen this week.

 

There's a new vibration last few weeks that may or not have to do with the U-joints.

 

No vibration previously, and the driveshaft hasn't been altered or dropped, so balancing seems unnecessary to me. But maybe I'm wrong.

Balancing wouldn't hurt, but if the vibration wasn't there before you changed the U-joints, something is out of alignment since the change.

Did you check the clearance in the U-joints? There are Snap rings available from 2.00 to 2.06mm to get the clearance within specs. If the clearance is excessive then the propeller shaft be of center and vibrate.

 

TWhen I did the u-joints they were delivered with standard 2.00mm snap rings. After fitting them I put the yoke in the bench vice and tapped the other side with a rubber mallot to get all the cups out against the snap rings. Measured the movement with a dial indicator and divided that by two. They ended up at 2.04mm on both ends of the propeller shaft and the diff flange. The transmission yoke needed 2.06mm IIRC.

It doesn't sound like much, but it could be enough to cause the vibration.

Edited July 28, 20159 yr by EuroDat

What year Z, and what speed do you notice the vibration.  The early ones had a shaft vibration at speeds over 55.  the old joints might have dappened the vibration.  The speeds the vibrations start and sometimes stop give clues to the issue at hand. 

Cheap u-joints and or excess clearance can affect the balance. If you installed quality u-joints, the problem is probably lateral movement as described by EuroDat in #2. In my experience, driveline vibrations have occured at higher speeds, 80 mph + and the front joint has been the cause. With the car on stands, grab the front of the shaft and try to move it horiz. and vert while watching the u-joint. There should be NO visible movement other than rotational. I've not encountered a balance problem with OEM or a quality brand. Spicer has been my choice and was recommended by our local primo drive line shop.

73 Z. Vibration is noticeable after 35 mph and gets worse with more speed. I'm staying off the freeway until it's fixed. Sounds like a tire going flat at 50 mph plus. Got the wheels rebalanced; tire shop said they were balanced ok anyway; made no difference. 

The new U-joints haven't been installed yet. A few weeks ago I had a shop put new front wheel bearings. Supposedly they also installed new lower control arm bushings and greased the rear wheel bearings. This was after I reported various noises that started after they installed new front pads and turned one rotor. The noises just got worse after they worked on it again, and the vibration started soon after.

 

A different shop is doing the new work.

I'd be real suspicious of any shop claiming to have greased the rear wheel bearings. Given the effort required to get there to do that, unless they charged you for 2-3 hours for that item, they didn't do it at all. I see you've already had your BS detector tripped and went to a different shop. Very wise.

Have you checked the condition of the mount for the diff? Mine was all torn up from the diff being moved up and down due to rotation from the driveshaft. i would double check that. 

Yeah, diff mount shot, ordered a new one.

Are these replaceable? Don't see snap rings. Thought they were up to 1975.

Yep, They are servicable per Aug 75 type. The snap rings are on the inside and hard to see. If it was the non-servicable type you would be able to see the spurs pushed in on the outside to hold the cups in place.

 

OK, picture worth 1000 words. But the new Moog U-joints I bought have the snap rings on the outside. Will the still work?

External clip u-joints typically have the groove for the clip machined in to the yoke.  The Nissan type, internal, have a flat machined in to the yoke fro the clip to sit on, but the groove is on the u-joint bearing cup.  So they're not interchangeable.  Stole a picture from the ZStore below.

 

I'm with zKars, I think that your first shop may have sent you off on a wild goose chase.  May also have screwed something up.  Probably started here - 

 

"This was after I reported various noises that started after they installed new front pads and turned one rotor. The noises just got worse after they worked on it again, and the vibration started soon after."