I had an issue some years ago with vibration at certain speeds with the EH Ute below. I built the car in 1986 & it had a 327/TH350/9" driveline at the time. Generally, the vibration occurred when just coming off acceleration. After a lot of investigation, it turned out that it was an issue with the engine & diff pinion alignment. I addressed the problem about 5 years ago when fitting a TH700 transmission.
As with many box upgrades, lifting the box until it touches the floor, then mounting it 10mm lower seems to work. Made more sense than cutting out the floor right? Not so as I found out.
In basic terms, at ride height, the angle of the engine crank & the diff pinion shaft should be the same. i.e. parallel.
Uni joints, when rotated at any angle other than in a straight line, actually have a stop/start type of motion, they are not constant velocity joints. When running a driveshaft with 2 unis, this stop/start motion is cancelled out by having the input & the output angle the same.
Then there is an angular 'range' that unis will work within. It is something in the range of minimum 0.5 & up to 6.0 degrees.
Google this info for heaps of sites that can explain this far better than I can

My problem was actually 2 fold:
My box was too low at the rear & my diff was too low at the front.
In fitting the TH700 & cutting out the tunnel completely, I managed to get the rear of the box up in the range of 50-60 mm from memory.
As I had lowered the rear springs to almost flat, (yeah I know, not the best situation), I also fitted wedges to lift the front of the diff about 1.5 - 2 degrees. I believe that XW & XY's may have used this from factory to solve the same problem?
Now, the car has no driveline vibration to worry about.

Now, I know that you didn't mention anything about vibrations, but if you are chewing out unis at that rate, it may be time to have a close look at your driveline geometry, particularly if your box was fitted without trans tunnel mods. A protractor can be bought from Bunnings to measure the angles you have as in the image attached.



Was the tailshaft shortened & balanced by a professional machine shop making sure the length is suitable & the unis are 'in phase'? By that I mean the weld yokes are both on the same plane & not at 90 degrees to each other.

P.S. Have you considered fitting a tailshaft loop at the front of the shaft?

Edited by user Friday, 13 January 2012 9:25:01 PM(UTC)  | Reason: Not specified