thanks!
Now I know what is involved - if anybody needs some help doing a diff change - count me out!!!! lol
I get back with MPG difference - if any in the coming weeks.

Well they're in and what a difference :D
Took a few days on and off but got there in the end.
A few points to note when changing diffs.
>Drain oil out first!!!
>Rear diff is easy by youself if you have a high lift trolley jack. - the two half shafts simply unbolt from diff and bend out of the way ...

I took the plunge and sought a pair of 3.64 diff froma 4.4 petrol X5. They arrived today and hope to have them fitted in a day or so. wish me luck!!
I'll soon have a working albeit redundant 3.91 front diff and rear diff in bits if anybody needs them?
The rear diff casing is intact along with pinion ...

After much head scratching I have decided to replace both front and rear diffs to a taller ratio - mainly because after speaking to various BMW breakers - the 3.91 diff are very weak and will at some point break.
So do I go for 3.73 or 3.64 ratio. I will be towing a twin axle caravan in the future ...

The one pictured looks as though its exploded ??
Believe it or not the car was driving before i took it apart. - it had a judder - almost misfire like above 40mph - esp under load - but free wheeling in neutral - even at 70 - smooth as butter.

Currently no - but I ve only had her for a year and travelled 6k miles in it with same mid quality tyres. In hindsight probably been busted for quite some time as car always had a bit judder above 60 which dissappeared as car warmed up, which then eventually became permanent - hence investigation.

Ive rang a dozen or so "bmw" breakers - and they are like hens teeth. Only option is to get a front and rear lower/higher ratio and swap both.
Thinking along the lines of getting a 3.73 or 4.1 diff and swapping my ring gear over??? to keep the same ratio?? probs not that easy!

So pulled the diff out this morning and stripped down to find root cause.
Guess Im now searchinf the breakers for a very rare 3.91 ration diff.

Hi folks - been around lurking for years - and only do I feel the need to ask a question to all those in the know.
My vehicle is a X5 E53 3.0d ( 2006) but the question is related to rear diffs on the whole.
Im getting a weird vibration / throbbing /juddering at any speed although the faster - the ...

Hi - recently registered to this forum after viewing many helpfull posts and articles from here.

Im Alistair - 48yrs maint tech in motor maufacturing company, and home mechanic / tight wad. (I tend to try to repair rather than replace.)
My current daily driver is a 2006 e53 X5 3.0d sport - high ...