Removing the fuel tank on the BMW Z3 requires dropping the rear subframe. I would strongly recommend refurbishing this along with the diff, and replacing all the bushes and maybe the tinware around the brakes when you do this. Maybe even recondition the rear shafts if you’re feeling so inclined.

Note: I can’t totally remember the order in which I did all this so please (even if I am speaking to my future self here) check some other sources before you do this.

Jack the car up and get it on axle stands, ideally with some extra support for safety. This can be tricky though as you need space to work. Some stacks of wood under the wheels while they’re on would be an option. But taking them off does give you more light and makes it a little less claustrophobic under there.

Remove the exhaust if you haven’t already

Take out the spare wheel and mounting frame.

You will need to disconnect the brake lines – there are flexi lines that run from the body to the subframe. Mine were crusty as hell on the first car and I ended up cutting them off as they just would not come undone. Try not to damage the mounting flanges on the subframe as I did.

Disconnect the handbrake lines. I’ll try to update this section after I’ve done it a second time, but I have a feeling this means removing the wheels and drums.

Disconnect the shocks from the top. This requires peeling back the carpet behind the seats from under the rubber strip.

Disconnect the anti-roll bar. It shouldn’t have much tension on it now.

Remove the springs. This shouldn’t need much compression now as they should be fully extended.

Disconnect the bottom of the shocks and remove these, carefully unclipping all the brake lines etc.

Now find the four hex or if you’re unlucky, allen-head bolts that hold the subframe mounting flanges to the body. These are on the inside of the back of the sills, pointing outwards. These took me days to get out the first time around. Eventually I had to drill them out – not fun.

Loosen but don’t undo the big nuts on the two vertical mounting pillars for the front of the subframe.

Undo the big bolt on the diff mount – don’t remove it yet

Support the subframe with a jack and a block of wood under the diff.

Now remove the big rear bolt and slowly lower the diff, bit by bit, while undoing the two nuts on the subframe pillars. If you have disconnected everything, it should drop out. Help to keep it steady would be very welcome.

Slide the subframe out and see what sort of a mess you’re dealing with.

Remove the straps that secure the fuel tank. Disconnect the various filters and ancillaries, and the filler neck. With a bit (a lot) of wiggling, it should come free.

Note that this doesn’t free up as much space as you might hope. I might move the back wall of the boot around a little to create space for a battery pack here at some point.