[I've already asked on the jag-lovers forum, but nobody seemed able to answer]

My XJ8 3.2 is making an occasional knocking sound, noticeable in reverse or when cornering while engine braking. I suspect a knackered diff. (Though I welcome suggestions of other things that may be causing it, especially if they're cheaper and easier to solve.)

The X300 XJR has the same 3.27:1 ratio, is stronger and has LSD. Does it make sense for me to get hold of one of these (and how do you fit one with the different input shaft)?

 

You will have to change the end of the diff to a flange type, also the X300 diff is offset whilst the X308 is inline, not much about 25mm, most get over this using a 2 piece prop, to be honest I am unsure if the XJR has a split prop but I do know the XKR has. You will also have to change the front section of the subframe the diff passes through

If the XJ8 has a similar setup to the XK8 which I suspect it does your prop will be a larger diameter made from aluminium, the XKR is slimmer and steel, the problem with the aluminium prop due to its size/offset is it will rub on the tunnel, using the R counteracts this.