BMW E30 Gas Tank Replacement

Preparation for removal of the gas tank

Do the work in a spot where you could leave the car for a day or so, in case you need to make a parts run (or two). You should try to get a spot out of the rain and sun.

If you have less than 1/4 tank of gas, you will have less gas to mess with. If your tank is leaking on top (as mine did) then you will not be filling it over half full anyway.

Loosen the right rear wheel. Put the car up on jack stands, getting it as high as is reasonable given your jack and your jack stands. Remove the right rear wheel. Removal of the wheel makes it easier to move around under the car and also exposes the fuel filler pipe.

Remove the Exhaust

Start with the exhaust system. Remove it. All of it, including the front pipe/catalytic converter. If your muffler or cat needs replacing, this is the time to do it.

Remove the Driveshaft

Next, you have to remove the driveshaft. This is not as easy as it would appear. You have to remove the rear reinforcement bar (attached by 6 bolts, located just behind the transmission), the exhaust heat shield (6 bolts), and the gas tank heat shield (4 bolts). Refer to your E30 Service Manual, chapter 8.

You can now see the entire driveshaft, which is in two parts. The front part is attached to the transmission output flange through the guibo (flexible coupling), and the rear part is connected to the differential (final drive). These two parts are connected with a splined shaft, which allows the driveshaft to get shorter and longer. Just forward of the splined shaft is the center bearing, and just ahead of the center bearing is a universal joint.

The driveshaft is carefully balanced at the factory, and you must get it connected back in the same rotational position. Before you go further, mark the position of the driveshaft at the front and rear with paint. I used my ex-wife's red fingernail polish. Marking driveshaft/final drive position is easy, just pick one of the four bolts and mark the driveshaft side and the final drive side.

Marking the transmission end is slightly more complex. On my car, a cylinder called the vibration damper is attached to the transmission output flange. The vibration damper encircles the guibo. Mark the driveshaft (not the guibo) and the vibration damper (or the transmission output flange).

Remove the four self locking nuts on the differential and then remove the three locking nuts which connect the guibo to the transmission output flange. I found that putting the transmission in first gear was essential while removing the nuts. Put the transmission in neutral to rotate the driveshaft into position.

The driveshaft center bearing is held in with two bolts. When you remove the center bearing, the driveshaft will droop in the middle. Don't let the driveshaft rest on the line which connects the two halves of the gas tank.

I couldn't get the driveshaft out, so I called our local Technical Service Advisor, Jim Albright at Mighty Motors in Cambridge, for some help. He told me that you have to "horse" the front part of the driveshaft out of there. He told me that I had to be sure to put the transmission in neutral and rotate the driveshaft while pulling down on it. He also said I should consider prying the guibo away from the vibration damper. It finally came free.

Be careful while removing the driveshaft: it is heavy and you don't want to stress the universal joint. Don't let the driveshaft separate at the splined coupling.

Don't worry; the hard part is now completed. The rest of the job is straightforward.

Remove the Tank

You can now get busy with removal of the tank. Get a 5 gallon gas can and position it near the right side of the car. If you look carefully you will see a small drain plug at the bottom right of the tank, which you may remove with an allen wrench. I shouldn't have to say this, but gas is very dangerous stuff, so be very vary careful. Wear eye protection. You probably know enough to keep your face away from the drain plug as you remove it, particularly if you are outside on a windy day.

Drain all of the gas into the gas can. Replace the plug, because some of the gas will remain in the tank and you don't want it sloshing out later.

Removal of all of the connections on top of the tank is the next step. Remove your rear seat and the access cover over the pump and level sensor. Disconnect the electrical connections for the level sensor and pump, and secure them up out of the way. Disconnect the fuel supply line, the fuel return line, and the evaporative emissions line. You will probably have to cut off the crimp on style hose clamps.

The tank is attached at five points: center front, left front, left rear, right rear, and right front. Getting at the two rear connections is easy if you use a 1/4 inch drive socket. The other three can be reached with an 8 inch 3/8" drive socket. Don't try to remove the two brackets which held on the two rear bolts for the heat shield.

After you get the tank loose, you will need to support it while you remove the other two connections to the tank. I used a plastic milk crate.

At the right rear the filler tube is connected to the tank with a large diameter rubber hose. Since I removed the right rear wheel earlier, it was easy to disconnect the hose on the fuel filler side. On the left front is another small hose connected with a hose clamp, remove that clamp and pull the hose off.

The tank should now be free, so pull it out and set it next to the new tank.

Transplant Tank Components

Some hardware must be transplanted from your old tank to your new tank. Remove the two brackets which are the rear mounting points for the gas tank heat shield, marking them as left and right. Removal of the brackets will allow you to remove the fuel tank connection pipe which allows gas to pass between the two lower portions of the tank.

Carefully remove both compression nuts, because the pipe is easily bent. Mount the connection pipe on the new tank. Don;t over tighten the compression nuts.

Mount the heat shield brackets on the new tank. Using a new hose clamp, move the filler pipe hose from the old tank to the new tank.

Remove the fuel gauge sending unit by carefully removing the four small nuts on the top of the fuel pump. Carefully withdraw the sending unit and set it aside.

Twist the fuel pump counterclockwise about 1/8 turn to loosen it. Don't turn the fuel pump by the pipes attached to the top of it! Turn it by placing a couple of screwdrivers on the lugs on the outside of the pump. Carefully lift out the fuel pump. You will have to twist it because the bottom is flat and wider than the opening on top of the tank. Carefully clean the strainer/filter, but only if it appears to be clogged.

Clean the O-ring which is between the fuel pump and the tank. Lubricate the O-ring with a bit of fuel, place it on top of the new tank, and carefully install the fuel pump. Turn the fuel pump about 1/8 turn by pushing on the lugs with a pair of your lifetime guarantee screwdrivers.

Replace the fuel gauge sending unit, and replace the four small washers and nuts. Do not over tighten the nuts or you will be buying another fuel pump.

My tank had a spongy rubber block glued to the tank just to the rear of the fuel pump hole. This spongy thing was to keep the electrical connections away from the tank. It looks like it is there just to stop the wires from vibrating on the tank. Move the spongy thing to the new tank. My sponge was gooey enough to stick on the new tank without a problem.

The tank is now ready to put back into the car.

Install the Tank

Position the tank up under the car and connect the long medium diameter hose to the output of the fuel pump. Use a hunk of duct tape applied to the tank about halfway down the length of the hose to keep the hose down in the channel that runs along the top of the tank. If you don't do this, you may pinch the tube and the tank will not seat properly.

Attach the hose on the left side of the tank using a new hose clamp. Squish the filler tube hose back into position hear the filler tube.

Loosely attach the tank to the body at the five attachment points.

Return to the inside of the car, and attach the three hoses with new hose clamps. Plug in the electrical connections for the pump and sender unit.

Connect the filler tube to the filler hose with a new hose clamp.

Make sure nothing is pinched and tighten all five tank attachment points. Fill the tank from your gas can.

Test the system for leaks before you put in the driveshaft!

If you have been careful and used new hose clamps, you should have no leaks at all.

Install the Driveshaft

I noticed that my 13 year old guibo was cracked in two places. It was the perfect time to replace the guibo, since it was out of the car already. The replacement guibo was $43 (with the club discount). Yeah, I'll spend $43 now to avoid replacing this thing later.

The guibo is held on with three of the self locking 17mm nuts, and it was easy to remove. There are arrows on the outside of the guibo which point towards the transmission output flange (3 nuts) or towards the driveshaft (3 more nuts).

Installing the driveshaft is easier than removing it. But it still isn't all that easy.

Insert the rear portion of the driveshaft first, making sure to line up your mark on the differential. You are supposed to coat the center pin on the transmission with molybendum disufide grease, but mine looked plenty greasy so I left it alone.

Line up your mark on the vibration damper (or output flange) and start working the guibo onto the transmission flange bolts. You will have to "horse" the driveshaft onto the transmission center bearing, particularly if your car is equipped with the notorious vibration damper.

Once you have the driveshaft in place, loosely install the two center bearing bolts. Tighten the final drive nuts and then the transmission flange nuts by placing the transmission into first gear. Use neutral to allow you to spin the driveshaft to line up each bolt.

The last thing to do is to tighten the center support bearing bolts. Try to get the bearing centered inside the driveshaft tunnel and perpendicular to the driveshaft. On my car, it was pretty clear where the bolts used to be so I just positioned the bearing using the old bolt marks.

Install the Exhaust

Installing the exhaust is always a bit of fun. See the E30 Catalytic Converter Replacement article for instructions on installing the cat and front pipe. Installing the rear pipe is straightforward. You will probably end up replacing some exhaust hardware.

After the exhaust is installed, get in the car and start it up. Immediately get under the car and check for gas leaks, then check for leaks in the exhaust system. If everything is OK, reinstall the right rear wheel and lower the car to the ground.