So some of you are aware that I got the dreaded fuel tank rattle and being a perfectionist I don't do rattles or squeaks so this is why I have written this thread.

So I'm working on a 1998 Z3M with 60,000 Miles on the clock. Its been very well looked after through its life.

A little about me, I'm 26 and left school 10 years ago starting an Engineering Apprenticeship. 10 Years on now working in the Nuclear industry on fusion research and with a wealth of knowledge i would say I'm quite confident to tackle any task big or small.

After doing some research I found very little about this problem, only that it led to a replacement tank. So i hope this thread helps anyone who thinks they may have the same problem. I can confirm it is the fuel tank that rattles, or to be more precise the vapour catcher unit on the top (I'm assuming that's its purpose?). The way to find this out is to get yourself a rubber mallet and tap the bottom of the tank on the passenger side. (The less fuel in the tank the better) If it rattles or sounds like something rattling on the top (Metallic in sound) you've found it!

It could also be the tank straps losing their rubber vibration pads but that is more obvious when laying under the car and a simple fix that can be done without having to drop the rear axle.

So this lead me to look into how I was going to tackle this little dilemma. First things first I got the car up in the air and started taking notes on what was in the way of getting this tank out. The first being the rear axle (this doubles as the diff carrier too) and the list went on in fact everything has come off!

Apologies on the order of pictures they were taken when i had my phone handy.

Step 1: I jacked the rear up off the swing arms and put axle stands on the lift points located in front of the rear wheels also worth noting a brick in front of both front wheels. Once in the air I removed both wheels too and although I didn't remove both arch liners now, this would be a good point to do so!

Step 2: Once you are happy the car is safe and not wobbly slide yourself under and start looking around making mental notes of the order you going to do things. Next is the exhaust pipes, The z3m has a twin exit exhaust system so both sides need removing. Whilst i was under there, its worth noting i had a custom exhaust set-up so the rubber mounts had very large hooks stopping it falling off. It was far easier removing the whole mount from the bottom of the car. If my memory serves me well its a single 13mm nut and bolt. Also at the rear there is two brackets behind the bumper on each exhaust, i noticed when i removed this each bracket had two washers under each bracket. In the photo you can see the exhaust mounts. I have also included a photo with the exhausts removed showing how the car is sat on the stands.

Exhaust n mounts.jpg Exhuast removed.jpg

Step 3: The next steps are in the order i chose to do them. You can tackle them in any order as they all need disconnecting at some point. Firstly I disconnected the prop shaft, these bolts are easily accessible. A little trick i found was remove the two nuts, with the handbrake applied to stop the prop shaft being able to spin, then release it and spin the shaft by hand then re apply the hand brake and remove the two other nuts. Also note that the bolts are fixed to the end of the prop shaft and will not come out. See photo.

Diff Bolts Removed.jpg

Step 4: I removed the bolts holding the anti roll bar on. This is a single nut both ends just behind the diff itself. When i released the nuts there was a little bit of tension but nothing to take your fingers off. You can also see the mounting point for the exhaust bracket to the right.
Anti roll bar and exhaust mount.jpg

Step 5: The next step was the tricky one. The handbrake cable needed to be detached from the car. I looked at both ways of doing this, so first i removed the disc and looked at the assembly and the pin that held the cable needed to be pressed out. I immediately went back into the car and lifted the handbrake gator. There are two cables attached to the handle (one for each hub) these are adjusted with a 10mm nut and an 8mm locking nut. Remove all four nuts and you can pull the cables through from beneath, they are a little tough to pull out as they are a very snug fit. Once out I left them to sit on the axle.You shouldn't have any trouble pushing them through as they come out right behind the handle. See photo (apologies this was after I removed the tank)
Handbrake Location.jpg

Step 6: Its time to remove the brake callipers and bottom shock bolt. First undo both 5mm allen bolts under the plastic caps at the rear of the caliper and it should pull off, once off i hung this from the shock with a cable tie to reduce the strain on the brake cable. Next you will need to use your jack; pump the jack to take the weight of the arm ready for when you undo the 19mm nut (I think its 19mm) the jack will stop the arm dropping the damaging the bush. Also once the bolt is out the shock will expand to its relaxed length with a little thud which may make you jump. Now lower the arm gently so it hangs freely. Also worth noting that because you have removed the anti roll bar previously, the arm will hang lower allowing the spring to fall out. Remove the spring and both cups. You will also see i removed the speed sensor and hung it over the shock this is a 6mm allen bolt then it pulls out (once removed place some tissue in the hole keeping the dirt out). The sensors are attached to the arm, all these attachments push one way to un-clip and then tuck them out of the way. see photo.

Step 7: I removed the nut on the diff and took the weight with the jack. Note i have the jack on the diff casing as this is the most central point to balance the whole axle. Once it took the weight you will see the diff lift slightly allowing the bolt to be moved by hand, leave it there for now untill you're ready to drop. see photo.


Step 8: You are almost at the point of lowering the whole axle, Next you will be tackling the big bush nut. But first this is the point where i found a lot of corrosion. First cover both 6mm allen bolts in WD40 try to keep this out of the head (personal experience) then spray the big nut too and leave to soak for an hour. At this point i was around 4 hours in so a good point to get fed and watered while they soaked. A man cannot focus on an empty stomach. See photo

Bush and 6mm.jpg
once soaked:
WD40 Soak.jpg

Step 8.1 (After snacks) With the jack in place and taking the weight remove the two 6mm allen key bolts. You will need some serious arm power to move these so i hope you've eaten your weetabix! I ended up using a breaker bar with a 3/4 inch attachment then finished off with the ratchet. Also please, please make sure that the socket has located fully into the bolt, give it a few gentle taps with a mallet you don't want any rounded bolts as its a very tricky spot. Once out you will notice the plate will wobble, that's because the jack is taking the weight of the axle. Now get your breaker bar out with a big socket (21mm I think) and take those nuts to within a couple of threads aka hand tight.

Step 9: The next step is the point of no return you have now committed to the drop. You wont be able to do this on your own (unless you have a jig that bmw use) you will need one person either side.This is another good time to make sure you have nothing in the way when it comes to lowering. And at this point i did spot a breather pipe from the fuel tank that ran through the passenger arm. I was hesitant to remove this encase petrol ran everywhere but nothing came out (bucket to hand). Its worth the jack being at an angle where you can release the handle so you don't have to let go of the arms.

Step 10: This turned out to be very tricky, once we started lowering the whole axle together, the prop shaft that runs into the diff carrier tunnel with fixed bolts left very little room to wiggle free. Luckily the universal prop shaft joint was facing down allowing the shaft to tilt and touch the top of the exhaust pipe connections, this still didn't give us enough room. From this we had two options 1) remove the rest of the exhaust and prop shaft or 2) get jiggy with the axle. Because our hands were full we chose getting jiggy, what we ended up doing was lowering as far as we could go approx 3-4 inch which was very close to being out. We then tapped down the passenger side bush untill it was off the long bolt, we then pushed the axle into the car arch and raised it allowing the other end to be tapped down and repeated on the other side. Once we were off the long bolts the whole axle had to come back to allow the prop shaft clearance to come out. Then we lowered gently to the floor. See photo
Axle Down.jpg

Step 11: At this point it was time to call it a day (5pm Boss finishes work) so from starting at 11am I was quite happy to get this up on the bench and tackle the fuel tank the following day. Good opportunity to annotate the picture. See photo
Day 1.jpg

Day 1 summary: Now that the axle is up on the bench i will strip and clean every component. You can see on the top of the axle i had a little start and rubbing it down. I also made a list of all the parts i need to order. Although all the bushes are in good condition it would be silly not to change them all.Note i have chosen power flex. The list is as follows:

Main bush x2 at £39.14
Arm Bushes x4 at £27.53
Diff Bush £28.98
Drop link arms £18.84
Anti roll bar bush £17.95

Total: 116.99

All of these prices were off the power flex website. Also I thought it would be handy to purchase a bush removal tool from ebay at £34 - Note that this tool is not required to fit the new bushes, no tool needed :)

Information on the fuel tank to follow later.

I hope everyone is still with me. Day 2

Day 2 step 1
: Clean up all the mess and relocate all your tools you have used- this is generally a stock check. At this point i also put nuts and bolts in separate tubs depending what part they were associated with. This will help you a lot in the long run as I'm only doing this on evenings and weekends.

The next photo shows the bottom of the fuel tank. Note the very rusty straps. I could also see here that the pads had been replaced in the past. Also in the background you can see the very long axle bolts pointing downwards and you can see the end of the prop shaft. And behind that the next part to tackle. The passenger side strap has another small tank inside once you remove this strap it hangs on two fuel return lines which pull off (note only a couple of drips and separate to the main tank). I'm not entirely sure on its purpose but the lines come from the vapour tank and feed back to the main tank (just putting two and two together)
tank strap.jpg
Bush bolt.jpg
Day2 tank..jpg

Day 2 Step 2: The next job is to lower the fuel tank. To make this job easier i ran the fuel in the tank as low as i dared so it was not heavy to lift. Before lowering, the fuel sender connector needed to be unplugged. This is located behind the drivers seat under the carpet. Once the carpet is up you will need a Phillips screwdriver to remove the sender cover plate. Once off, slide the clip off of the connector and pull free. Next open the fuel cap and remove the tank lid (I'm not sure if this would cause a clearance issue but i removed it anyway) That's everything from the top covered now back under the car, passenger side you will find two main fuel lines to disconnect, again very little fuel leaked out. Drivers side, up by the fuel sender you will see an earth strap which only took a Phillips to remove. That's everything disconnected now all that is holding the tank up is the two rusty straps and a bolt. You will need another person to help remove the tank - one either end. Next remove the main bolt which is located centrally, slacken off the straps, these straps are held on with one bolt and a hook at the other end. Once these are off you will need to lower towards the passenger side then down at an 45* angle towards the rear because of the prop shaft being in the way. This was very fiddly too with lots of "to me, to you" jokes between me and my dad. See photos
One Fuel tank
Fuel Tank.jpg

If you are still with me, I bet your wondering what caused the rattling? Lots of people i spoke to just said it was knackered and needed a new one. So me being me, i had to find out what was causing this mysterious rattle! Nothing obvious showed itself so i began tapping things only to find the small tank on the top of the main fuel tank had a horrendous rattle inside. I disconnected the small pipe and began attempting to remove the white fitting to see inside. I quickly discovered that this fitting was bonded and could not be removed. Now knowing i would need a replacement tank, my curiosity got the better of me, I had to see inside!!!

So obviously only using hand tools (Small flat head screwdriver and rubber mallet) I begun breaking the seal around the fitting which took some time and ended we me using a Stanley blade.Some of you may be wondering if the small tank comes off, but its plastic welded to the main tank. Once out i was shocked at what i found. See photos.

tank hole.jpg fitting.jpg fitting2.jpg

So if you hadn't guessed it.... to the best of my knowledge, that looks like a form of a non return valve that's failed.
It's a very heavy ball too which sits in a cup, and judging by the wear marks on the top of the cradle something did hold it in place but has since perished. So every time i went over a bump this thing was rattling and echoing inside that tank.

I was lucky today to win another fuel tank for £45 delivered. I'm now waiting for all the parts to arrive ready for re-assembly. But in the mean time i will strip down and clean all components, source new straps & bolts etc.

I have plenty more photos if anyone needs them for reference.

I hope some of you guys find this useful. Feel free to drop me an email if anyone needs any help.