Harmonic thingy?

It changes the harmonic frequency of the axle, and stops it wobbling around in normal driving conditions. You could knock it off it you tried, but there should be a cable there to catch it if it falls. If you lost it altogether, you might get a bit of steering wobble, but it wouldn't be the end of the world.

Can't for the life of me remember what it's called though...

David

...mass damper.

"That thingy is a "Anti vibration" device to take out any inbalance vibrations caused by the prop shaft. As the vehicle is permanent 4wd LR felt that it would assist in keeping everything running smoothly. Think of it as a harmonic balancer for your front diff. To add to this, the mass & dynamics of the attached bits and pieces are such that they tend to oscillate around a lot during normal. The mass damper, for that is what it is called, alters the oscillation frequency so it's not so much of a problem. There's also a piece of wire attached, so that if the mass damper falls off, it stops short of going through the windscreen of the vehicle behind. They were also fitted on some 1993 Classic RRs." All completely plagiarized, but amazing how intelligent you can sound using a bit of Google.....

Guy

Thanks chaps, very good replies, nice and easy to understand for my poor brain. Does the range rover classic axle vibrate less and does not need one? Thanks again Fred

It's like pushing a kid on a swing. There's a natural frequency for the axle, or the swing, and little pushes at that frequency will build up. You can get the same effect on some sorts of rough road (and watch the movie "The Wages of Fear" for a demonstration). The harmonic damper changes the natural frequency of the axle to one which isn't likely to match something else, either on the vehicle or in the road.

You can see the same sort of idea on some bridges -- weights on suspension cables on the Humber Bridge, for instance.