The CV joint boot on the front left of the E53 BMW X5 is notorious for premature failure - quite often it is found to have failed whilst the other 3 corners are near pristine! When the boot tears, grease inside the joint can escape allowing dirt and grit in. When this happens, failure of the joint is just a matter of time. Before total failure, the giveaways will be clunks over bumps, or possibly a constant clicking sound when moving, particularly when turning. If you catch the boot failure early enough then it's possible just to replace the boot itself, but as you'll see below the labor process to replace just the boot is virtually the same as replacing the entire shaft. If you have any doubt that grit may have got into the joint then a full shaft replacement may be a better idea than just a new boot.
Most BMWs use a 36mm axle nut
-The hub nut is highly torqued (420NM) and of course the hub and shaft rotates so I like to make sure this nut is broken free with the car still on the ground so the weight of the car counteracts the rotational movement. If you don't have an airgun then a large breaker bar and socket will be absolutely fine. Most BMWs use a 36mm axle nut, but in this case I found a 41mm nut - so I suspect a previous owner already had an aftermarket shaft fitted due to previous failure.
-With the nut loosened go ahead and jack the car in the corner required, remove the wheel and support the car with a jack-stand.
-Remove the brake caliper and then support it via some bungee cords, or just sit it on another jack-stand so the pipe is not stressed. You don't need to disassemble the caliper so this is just a simple removal of (2) 17mm bolts.
-Remove the brake disc/rotor.
-Remove the lower (lateral) control arm at the bolt side - we'll just leave the ball joint side attached to the hub assembly.
-Fully remove the axle nut.
I have heard of others removing the forward control arm, and also removing the bolts that hold the shock absorber to the hub assembly - I don't see a need for this - I easily had enough room to pivot the hub to remove the shaft with those points still in place. (and it's less work!)
The shaft is held in place by a circlip
Next the splined shaft needs removed from the hub. If you are just replacing the boot then you may need to use a puller to gently ease the two apart. If you are replacing the entire shaft then no harm in just giving a few sharp hammer knocks to the center of the shaft and it will just pop out. Be careful not to damage the threads while hammering, it may help to finger-thread the axle nut on a bit to protect them. You can now replace the rubber boot or if removing the entire shaft you just need to pry the far side out of the differential. The shaft is just held in place by a circular clip at that end and it's one of those cases where it may pry free almost immediately, or you may be prying and hammering for some time to free it up. If it does give you problems then you may need to remove the metal undertray to get better access - if you do this note the sway bar bolts through this panel, so there will be tension on the rearward 4 bolts.
The car may need an alignment
With the old shaft removed, use a wire brush to clean up any rust on the hub splines, then apply some lubricant so the new shaft will go in easily, I used some engine oil. Then simply push the new shaft into place, re-attach the brake disc and caliper and rebolt the lower control arm. Remember this arm needs the bushing preloaded, so don't apply final torque until the car weight is back on the arm. Likewise you'll need the car on the ground to get the full torque on the axle nut which then, by convention, you can crush the top of the nut to safely lock it. The car may need an alignment performed after the lower control arm removal, but otherwise job done!
