Sway Bar Upgrade Instructions
1997-2003 BMW 540i
2000-2003 BMW M5

by Dave Zeckhausen

The BMW 540i handling can be dramatically improved by upgrading the front and rear sway bars.  A cost-effective approach is to use factory M5 parts.  Depending on your 540i model, the existing front sway bar diameter is either 24.5mm or 25mm (Sport Automatic and 6-Speed Manual).  The rear sway bar diameter ranges from 13mm to 15mm depending on model year and options.  The M5 front and rear sway bars are 27mm and 16.5mm in diameter, respectively.  If you don't mind spending a bit more, Dinan offers 28mm front and 17mm rear sway bars.

Replacing the rear sway bar is simple and should take 30 minutes or less.  However, the front sway bar is located between the engine and subframe and is more challenging.  With two people, following the instructions below, it should be about a three hour job.  With one person, the time required more than doubles, since several operations benefit from two people working together.  Zeckhausen Racing does not recommend attempting this modification solo.  A professional mechanic, with a lift, should be able to complete the job in about three or four hours.

These instructions apply only to the 8-cylinder 540i.  While the M5 rear sway bar will bolt on to a 525i, 528i, or 530i, the front sway bar will not.  The front subframe on 6-cylinder models is a different design and will not accomodate the M5 sway bar.  For these models, you need an aftermarket solution for the front sway bar, such as Eibach or Dinan.  However, these 6-cylinder models will benefit from the addition of the M5 rear bar, if you are trying to reduce understeer.  The rear sway bar installation is trivial and probably the best $235 you can spend improving your car's handling.

Zeckhausen Racing does not sell the parts required for this modification.  We recommend Tischer BMW, since their pricing is outstanding and they are easy to order from on-line.  Prices shown below are subject to change without notice and were accurate as of April 27, 2017.

Parts required to upgrade 540i to M5 front sway bars:

Tools required:

Floor jack with a lifting height of at least 20".  More is better.  A professional lift is best.

One pair of QUALITY Jackstands

Air impact wrench is helpful.  Otherwise a medium to long 1/2" drive breaker bar.

Large Philips screwdriver

Metric combination wrenches including: 10, 15, 16, and 18mm

Ratchet handles (small, medium, large) with the following 6-point sockets: 8, 10, 13 (deep), 15, 16 (or 5/8"), 17, 18, and 21mm

Torque wrench with a range of at least 50 to 120 N-m (37 to 90 lb-ft)

Variety of socket extenders (short, medium, long)

Stubby wrenches: 15, 18, and 21mm

Small hammer

Dead-blow hammer with non marring face

Small and medium pry bars

Working on your car can be dangerous.  Even quality jack stands can collapse if not positioned properly. A floor jack can fail suddenly and without warning.  You can be seriously injured or even killed if you do not follow proper safety procedures.   Zeckhausen Racing assumes no liability expressed or implied for any injuries or damages suffered, as a result of following these instructions.

Front Sway Bar Upgrade Instructions:

1. Position the jack saddle in the center of the BMW cross member, directly behind the engine.  Be careful not to crush the aluminum strap holding the rear of the plastic belly pan.  It may be necessary to drive the car onto two pieces of wood or a ramp, to gain sufficient clearance for a floor jack to slide underneath, from the front of the car.

2. Place jack stands under the two plastic jacking blocks on the bottom of the rocker panel, just behind the front wheels.  Lower the car onto the stands.  The car may move several inches backwards as the jack is lowered, so be prepared to re-position the stands as you lower the car.

It is important to raise the front of the car as high as possible.  While the sway bar is being removed, all sorts of twists and turns are required to clear the subframe. If the car is too low, the end of the sway bar digs into the ground, restricting your ability to remove it.

3. Using a 17mm socket, remove the front wheels.  If you do not have an air wrench, have your assistant step on the brake pedal while you remove the wheel bolts.

4. Using a large Philips screwdriver, loosen the fasteners that hold the plastic belly pan under the engine.   Fasteners are 1/4 turn only and should not be removed from the panel.  Remove panel and set aside.

5. Using a 15mm socket and wrench, remove the bolt and nut holding the idler arm (passenger side) to the subframe.

Idler Arm

6. Remove three 15mm bolts and nuts holding the steering gear box (driver's side) to the subframe.  One vertical bolt and another horizontal bolt are easy to remove.  The forward most vertical bolt is a challenge, since the nut is on top of the steering box and is difficult to access.  This is where the stubby 15mm wrench comes in handy.  Work the wrench onto the nut, then loosen the bolt with your 15mm ratchet.  It can be done, but requires patience and small hands.  An assistant can see the nut from above and help guide the wrench.  Alternatively, if you have a 15mm socket and at least 18" of extensions, you can loosen this nut from above. 

Steering Gear Box

7. Just forward of the driver's side engine mount (within 2")  is an 8mm sheet metal screw that holds the power steering line bracket to the subframe.  Remove this screw.

8. Disconnect the ends of the sway bar, using a 16mm socket to loosen the nut and a 16mm wrench to prevent the stud from turning.  You may need to grind a 16mm wrench to make it thin enough to fit.

9. Remove two "C" brackets holding the sway bar to the subframe.  Use a 13mm deep well socket to remove the two nuts holding each bracket.  Pull off the two rubber sway bar bushings.

10. The threaded studs are easily damaged during the subsequent steps.  To prevent this, reinstall the nuts you removed in the previous step, to protect them.

11. If your BMW came with Xenon headlamps, you have auto-leveling sensors located on the right front and right rear suspension.  Before proceeding to the next step, you must disconnect the linkage connecting the front level sensor to the lower wishbone.  Using a 10mm wrench to keep the threaded stud from spinning, remove the nut with a 10mm socket.  Pull the linkage away from the sensor arm and reinstall nut a few turns, by hand, so it won't be misplaced.

Xenon headlamp auto-leveling sensor

Two aluminum control arms are connected to the bottom of the subframe.  The forward arm is called a "wishbone" and the rear arm is called a "traction strut."  Both must be disconnected from the subframe and pushed out of the way.

Wishbone

Traction Strut

12. The wishbone is held in place by a 16mm bolt with an 18mm nut.  Remove the nut and bolt.  Pay attention to the orientation of the bolt as you remove it.  The threads face the front of the car for some models and the back of the car for others.  A Sharpie pen is useful to label the bolt so you don't forget which way to put it back.

13. The traction strut is held in place by a 21mm bolt and nut.  You will need to rotate the sway bar to gain access to the head of the bolt.  Remove nut and bolt using 21mm socket and 21mm stubby wrench.  Once nut is removed, it may be necessary to use a socket extender to push the bolt through the traction strut end before you can remove it.  Pay attention to the orientation of the bolt.  The threads face the rear of the car.

14. Remove the left and right heat shield from the rear of the sub frame.  They are held in place with 8mm self tapping screws.  Move them off the floor so you don't accidentally damage them.  They are fragile.

15. After you remove the heat shields, a collection of wires, protected by black flex tubing, and a bracket with sharp edges will be left dangling.  These should be pulled off the back edge of the subframe, leaving them hanging at least 8" down.  It's helpful to temporarily secure these out of the way.

16. Remove the 13mm nuts holding the engine mounts to the sub frame.  There are two nuts per mount.

17. Place a piece of wood on the saddle of your jack to spread the force across a wider area and to gain more height.  Place jack under flat part of engine oil pan and lift until engine mounts clear subframe.  Be careful mounts don't catch on subframe, as they might tear.  A prybar is helpful to coax mounts and subframe apart.

18. Remove six 18mm bolts holding subframe to chassis.  The front four bolts are easily accessed.  The rear two bolts are hidden beneath plastic panels that must be pulled back to gain access.  Several 8mm sheet metal screws and two Phillips plastic fasteners must be removed to gain access to rear subframe bolts.  Once bolts are removed, the subframe will not fall on you, but it will drop several inches.  Protect your face!  (Optional: Leave the center two bolts installed, but only engaged a few turns.  This makes it easier to align the subframe, when reinstalling, and limits how far the subframe will drop.)

19. Work the sway bar out, on the passenger side, by rotating and pushing until it can be slipped completely free. This will take some time and it's when you will be thankful you raised the car as high as possible.  Your assistant may need to move the steering wheel, for the sway bar to clear everything.

20. Work the new sway bar into place.  This is easier if you start from the driver's side.

21. Push the subframe back up and insert front four bolts first, turning by hand to ensure they aren't cross-threaded.  Do not pinch power steering fluid line between subframe and chassis. 

22. Tighten front four subframe bolts first, before inserting two rear bolts.  Torque to 57 lb-ft (77 N-m).

23. Reinstall plastic rivets and Phillips screws, as well as 8mm sheet metal screws holding plastic fender liners and rocker covers in place.

24. Have assistant lower engine back down, making sure engine mount bolts are aligned with holes in subframe.  A short pry bar may be used to align engine with mounts, as it is lowered.

25. Install four 13mm nuts under engine mounts and tighten to 18 lb-ft (24 N-m).

26. Reattach traction strut to subframe mounts.  It is easier to line up and insert bolt if your assistant turns the steering wheel.  Remember, the threaded end of the bolt faces rear of car.  Attach nut to bolt finger-tight but DO NOT TORQUE at this time.  The traction strut and wishbone hardware must be torqued with car at resting height, otherwise bushings will tear apart in a few thousand miles.

27. Reattach wishbone to subframe mount.  Insert bolt, threads facing forward, and tighten nut finger-tight only.

28. Install new rubber bushings on sway bar and press U-shaped bracket into place, making sure bump on bushing is aligned with hole on bracket.  Install and tighten 13mm nuts (two per side) on bracket.  If using factory rubber bushings, do not apply grease.

29. Rotate sway bar so you can reattach end links.  Use 16mm wrench to keep threaded end link stud from rotating and use 16mm socket to tighten nut and hold sway bar end in place.

30. Reattach steering box with three 15mm bolts and nuts.  It will be just as hard to install the nut on the vertical bolt, in front, as it was to remove in step 6.  Be patient and use stubby 15mm wrench to hold nut in place, after you have threaded bolt into it.  Alternatively, use 15mm socket and 18" of extension to reinstall nut from above.  Use magnetic socket or two-sided tape to hold nut into socket, while you lower it past the power steering hoses.

31. Reattach power steering line bracket with 8mm sheet metal screw.

32. Reattach idler arm with 15mm bolt and nut.

33. Install two heat shields, using 8mm sheet metal screws.

34. If your car has Xenon headlights, reconnect sensor linkage you disconnected in Step 11.

35. Hold plastic panel under engine and tighten all metal screws 1/4 turn to fasten.

36. Place floor jack under driver's side shock absorber and raise suspension until car just begins to lift off jack stand.

37. Tighten driver's side wishbone chassis bolt to 58 lb-ft (79 N-m) and traction strut chassis bolt to 81 lb-ft (110 N-m).  Tightening must be done while suspension is compressed.  If suspension is dangling while bolts are tightened, the bushings will be destroyed within a few thousand miles.

38. Repeat previous two steps for passenger side.

39. Reinstall front wheels and torque wheel bolts to 88 lb-ft (120 N-m).

40. Lower car to ground.  You are done!  Crack open a beer and celebrate.