I had a chance to execute the 3.15 rear end swap, I will be making a separate thread on this but will add some cliff notes here. For those who have done diff swaps, the change from 3.64 to 3.15 doesn't offer any surprises. Install was straight forward. The downside is acceleration from a dig isn't as dramatic but normal daily driving benefits from the gearing as the X5 has a lot of torque and has no issue moving itself along. The real benefit of this comes at highway speeds, I did some stretches at 60-65mph and it was returning ~35mpg which is what the 3.64 mustered. 65-80mph is where the 3.64 would fall apart and MPGs would drop down to the low-mid 20s, with the 3.15 at 70mph the X5 was still returning 35mpg. I still need to do some testing at higher highway speeds, 80+mph, but the X5 is definitely not as affected by the added speed. I will be swapping in the front diff to complete the gearing conversion and recommend this mod to others who value highway MPG and a less dramatic driving experience overall.

I was able to get a drive from San Diego up to Orange County, just under a 200 mile round trip, mainly flat with some rolling hills. On the drive up I was able to get 32.2mpg and this included 10 miles of urban driving to a shop. On the way home I got 35.1mpg highway only. Unfortunately I wasn't able to hand calculate the figures, this is based off cluster read-out and mine is usually 0-1mpg optimistic so take it for what it's worth.




Big Ass Wrench


If you recall I was playing around with running the shorter rear-air struts with the taller (2" taller) upper strut mounts from a non-air X5 and the goal was to get proper strut actuation while lowered. the air strut with the air mount was too compressed and the air strut with the non-air mount was too extended so I made some 1/2" and 3/4" spacers out of plastic cutting boards which are used to space the taller non-air mount down bring the strut into normal operating range.

To accommodate the spacers I needed to replace the OEM M10 studs with longer versions, after some research I found that ATVs run M10 wheels studs and with all the crazy modding that is going on in that industry, some companies make extended wheel studs to accommodate spacers. I found some that gave me an extra ~20mm of usable thread length.

Old studs out


Extended studs


Building spacers


I made 2 sets of 1/2" and a pair of 3/4" so I can space the mounts as needed between 1/2-1"


What's interesting is how little stanchion travel BMW allows before the bump stops come into play on the rear struts. There are 3 OEM bump stop options: short, medium, and long with the short being sport, long being for 3rd row, and medium for X5s spec's in the middle.
Looking at the meidum bump stop install you can see there is only about 10mm of travel before the bump stop is activated, this is why most X5s ride so poorly when lowered, most are riding on the bump stops, literally.


Here is the medium BS in the back and the sport (short) bump stop installed.


Here is a sport trimmed.


I installed the medium bump stop and paired with a 1/2" spacer which positions the strut in an acceptable operating range but closer to the "extended" side of the spectrum as opposed to "compressed." I know I am still mis-matching the dampening characteristics of the strut with squished air bags but this is a step in the right direction, more testing to do.


I got around to installing the switch for my QTP exhaust valve. I ditched the huge/ugly/hard-to-operate switch QTP supplies for a sleeker momentary switch I bought off eBay, I wanted a more OEM look and easier operation. The goal was to mount the switch in an easy to access location that was also a bit out of sight, and I wanted to mount the switch into a panel or piece of trim that could be easily replaced if I wanted to revert back to stock. Very happy with how everything came together.



With the dark theme of the X5 the taillights and their bright red bothered me a bit so I got some Lamin-X smoked film. This is the lightest they make and offers the "dark-cherry" look I was going for. I also used some knifeless tape to cut the film so that it was only on the red and the white/clear sections have no film.

As a lighting nerd this is a step in the wrong direction in terms of illumination and safety so I had to offset that. I upgraded the rear turn signal and brake light bulbs to Diode Dynamics LED bulbs, I also coded the light module to do a double hazard flash. The bulbs are significantly brighter and combined with the instant-on flash of LEDs the turn signal more effective now than it was in the OEM configuration, even with the tint.