Land Rover Repair: Transmission rumble, main bearing, parabolics

Question
Hi,
I have a 1982 Series 3. Last week, I replaced the rusty leaf springs with new parabolics, but this has caused a rumble in the transmission on the overrun.

At first, I thought the new springs could be slightly higher and might be causing already worn prop UJs to make noise as they are at a different angle. I replaced these and the noise was still the same...

Then, I replaced the rear diff and bearings because there was a lot of play in the gears. However, the noise is still there.

What do you think is causing the noise? All I can guess is the transfer box main bearing. Its driving me mad, any advice would be great.

Many thanks for your time,
Tim

Answer
There is a good change that the rumble results from a change in the angle of the pinion flanges on the axles.  The pinion flanges should be parallel to the transfer case drive flanges, within 2 degrees

That's often a problem when we modify suspension.  You may need shims to adjust angle, or some other modification