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Old 08-11-2006, 03:13 PM
Hotswimmer Hotswimmer is offline
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Location: Irvine, CA
 
Join Date: Mar 2006
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Mein Auto: '98 BMW 540iA
DIY Article - How to Replace the Thrust Arms on your E39 540i - 56k No!

HOW TO REPLACE THE THRUST ARMS ON YOUR E39 540I BMW

(1997-2003 5-SERIES V-8 CARS)


Most drivers of higher-mileage E39 BMW's have probably experienced the infamous shimmy that occurs in the front suspension at speeds between 50 and 60 MPH. The shimmy is often very pronounced when braking through the same speed range as well, giving the false impression of an out-of-round brake rotor. Assuming that your tires are properly balanced and aligned, and your lug nuts are properly tightened, the likeliest cause of this problem is worn out thrust arm bushings. Removing the thrust arms and installing new ones, or simply replacing the bushings once the thrust arms have been removed from the vehicle is a job that is well within the capabilities of a reasonably experienced shade-tree mechanic.

Whether you want to replace the entire arms or just the bushings is up to you, and the decision pretty much comes down to cost. The amount of work is about the same. The entire thrust arm assembly costs about $100 per side for OEM quality Lemforder units, whereas the bushings alone can be replaced for about $40. If you replace the whole arm, you're also getting a new ball joint on the front end, which probably isn't a bad idea on a higher mileage car. My feeling is, if you can't afford to drop $200 for a pair of new thrust arms, you really can't afford to be driving this car, especially in an era of $3.50 per gallon gasoline.

This is an illustrated do-it-yourself (DIY) write-up showing how to change the thrust arms on an E39 540i (model years 1997-2003). The subject car is a 1998 540iA. The job is conceptually the same on the 6-cylinder cars, but the front suspension and steering are somewhat different, so the pictures may not be an exact match. The procedure I followed is the one outlined in the Bentley manual. The driver's side of the car is shown in my pictures, but the passenger's side is identical.

This write-up is provided as a courtesy to other E39 enthusiasts, but your use of the information herein is entirely at your own risk. I assume no responsibility in the event of injury or adverse outcome resulting from the use of this information. Above all, BE SAFE and don't get in over your head. The labor for this task is only a few hundred dollars at a good, independent BMW mechanic's shop. It isn't worth life, limb or damage to your vehicle if you don't have the experience necessary to competently perform this procedure.

Suggested Tools and Supplies

-Floor jack
-2 jack stands
-4 blocks or car ramps
-Breaker bar with 4-inch extension, or tire wrench
-17mm socket for removing lug bolts
-13mm deep socket for removing sway bar bracket nuts
-16mm and 18mm socket and combination wrenches for loosening pinch nut and bolt on strut collar
-22mm combination wrench for removing ball joint nut
-21mm socket and combination wrenches for removing thrust arm bolt and nut
-Torque wrench
-Large screwdriver, chisel, or other strong, flat-bladed tool for prying open pinch collar on strut
-Various lengths of extensions, universal joints, etc. for your socket wrench are helpful
-Ball joint removal tool (highly recommended)
-Permanent marker pen or paint to scribe reference line on strut tube
-Rags
-Denatured alcohol or lacquer thinner

Procedure

1) Make sure the car has a full tank of gas before you start (this is important later you will need the weight of the fuel in the vehicle). Have the key in the ignition and unlock the steering wheel so you can turn the steering array as needed when you are working.

After loosening your lug bolts with the 17mm socket and breaker bar, get the car up on jacks. The front jack point for the E39 540i is shown in image #1 you want the jack on those four big dented-out triangle sections which all point to that hole in the middle. I strongly suggest padding your floor jack and jack stands with a folded rag to avoid tearing up your car. You do not need to remove the splash shield from the bottom of the vehicle.



Images 2 and 3 show the car up on jacks from the front and side. I keep the floor jack under the front jack point as an added measure of safety. Chock the rear wheels for safety.





2) Lower the front sway bar you need to do this to get room to reach the bolt that holds the bushing side of the thrust arm to the frame. The sway bar is held to the frame by two, large gold-colored brackets one on each side of the car. You can see it in image #4 on the left side of the picture.



Remove the two nuts from the studs using a 13mm socket wrench, and pull off the brackets. The sway bar will only drop an inch or two, but that's all you need. You don't even need to remove the rubber bushings that are under the brackets you can see one of these bushings in image #5.



The large bolt you will eventually remove to drop the bushing side of the thrust arm from the frame can be seen above and to the left of the rubber bushing on the sway bar in image #5.

3) Image #6 shows the bottom of the strut tube and the steering knuckle. At the bottom of the strut tube you can see two large nuts. The rear nut is the one that fastens the ball joint side of the thrust arm to the steering knuckle. The bottom of the strut tube is so close to those nuts that you can't get a wrench or ball joint puller on them. This necessitates lowering the steering knuckle.



In order to lower the steering knuckle (slide it down the strut tube), it will be necessary to loosen the pinch bolt in image #7 (also seen from the bolt end near the top of image #6). I used a 16mm wrench on the bolt and an 18mm wrench on the nut to do this. PRIOR TO LOOSENING IT, clean the area where the strut tube comes out the bottom of the pinch collar, and using paint or permanent marker, draw a line exactly where the strut comes out of the collar so you can properly reposition it later.



After you have loosened the pinch bolt (there is no need to remove it entirely), stick a large, heavyweight screwdriver, a large chisel or some other prying tool right in that slot where you see the middle of the pinch bolt in image #7, and pry the collar open a small amount. You can also stick a small chisel in the slot and then use a wrench to turn the chisel and pry the collar apart this very closely simulates the special tool BMW dealer mechanics uses for this task. Either way, it will take a bit of force.

When the collar is open sufficiently far, grab the brake caliper or rotor and slide the steering knuckle down on the strut tube by pulling downward it only needs to come down an inch to an inch and a half. Look at image #8 you can see the clean, shiny part of the strut tube that was exposed after I slid the steering knuckle down. You may need to jiggle the steering knuckle assembly a bit, but it is heavy and should slide down without too much trouble.



4) As you can see in image #8, there is now enough room to get a wrench on the ball joint nut. Remove the nut using a 22mm combination wrench.

Now, the hard part pressing the ball joint stud out of the steering knuckle. It is in there TIGHT. I would not do this job without a ball joint press of the type you see in image #9 and #10. I bought mine at ZDMAK Tools (www.zdmak.com) for $40, and it's a pretty decent unit. There are many sources, and you can pay less, or a whole lot more - up to $263 for the gods-honest BMW tool.

I have read posts from guys who say they've been able to remove the ball joint using a pickle fork, or by banging on the top of the stud. You're on your own if you decide to go that route. I rejected that option from the start. Space is just too limited, and you're talking about banging around on aluminum suspension components here.





HOWEVER YOU DO IT, DON'T DON'T DON'T DAMAGE THE BALL JOINT AND BALL JOINT STUD IF YOU'RE JUST GOING TO CHANGE OUT THE BUSHINGS AND WILL BE RE-USING THE OLD THRUST ARM AND BALL JOINT. If you're replacing the whole thrust arm, then this isn't an issue. The steering knuckle will look like image #11 when you finally get the ball joint stud out.



5) Now we're ready to remove the bushing side of the thrust arm from the frame. This is easy by comparison to the last step. Image #12 shows you what it looks like in place.



Image #13 shows the 21mm socket wrench on the bolt that goes through the center of the bushing and holds the thrust arm to the frame. You can also see the end of the bolt in Image #5. You may need to jiggle the steering back and forth a little bit to get the socket wrench on the bolt I did this just by grabbing the brake rotor and turning the steering a tad. There's not a lot of extra room to maneuver. You'll also need to have a 21mm combination wrench on the nut to keep it from slipping.



Once you have the nut off, pull the bolt out and you can drop the thrust arm. Again, you may need to jiggle the steering a bit this way or that to give yourself room to pull the bolt. Image #14 shows how the frame side looks with the thrust arm removed. Image #15 shows the old thrust arm with bushing, ball joint and retaining bolt and nut. At this point, you're halfway there on the driver's side, and the hardest part of the job is behind you.





If you're only replacing the thrust arm bushing and are re-using the old thrust arm and ball joint, this is where you will press the bad bushing out of the thrust arm and re-install the new one. I went with all new thrust arms, so I regret that I can't provide you with any counsel on this step. I understand it is possible to do this yourself, though it's a lot less trouble to simply take your old thrust arms to a mechanic's shop that has a hydraulic press and remove/replace your bushings that way.

6) Image #16 is a picture of the new Lemforder thrust arm. Leave the protective cap in place over the ball joint stud until the last minute when you are ready to push it into its hole on the steering knuckle. Wiggle the bushing side of the thrust arm into its place in the bracket on the frame of the car. Push the 21mm bolt back in and thread the nut back on. DO NOT TORQUE THE BOLT DOWN AT THIS TIME! Just put the nut on the bolt and hand-tighten it. Image #17 shows the new thrust arm in place on the bushing/frame side.





7) Remove the protective safety cap and insert the ball joint stud in its hole on the steering knuckle. Thread the 22mm nut onto the stud and tighten it. As you tighten the nut, it pulls the ball joint into its proper position there's nothing special you have to do here. See Image #18. Using your torque wrench, tighten the 22mm nut to 80Nm (59 ft-lb).



8) Reposition (raise) the steering knuckle on the strut and tighten the pinch bolt. Using your torque wrench, tighten the pinch bolt to 81Nm (60 ft-lb). Again, this took a 16mm wrench on the bolt and an 18mm wrench on the nut on my car.

9) REPEAT STEPS 3 THROUGH 8 ON THE PASSENGER'S SIDE OF YOUR CAR.

10) Use denatured alcohol or lacquer thinner to clean your brake rotors if you grabbed them with your hands at some point during the procedure. Put the wheels back on the car and torque down the lug bolts. The lug bolts are 17mm, and should be torqued to 120NM (89 ft-lb) plus or minus 10Nm (7 ft-lb).

10) NOW we're going to tighten the bushing bolts on the thrust arms. The car needs to be LEVEL and SITTING ON ITS TIRES up on blocks or ramps, about 8 inches off the ground in front AND back. The car needs to be at spec ride height before you torque down the bolts. In addition to a full tank of gas (remember this?), you need about 150 pounds in each front seat, 150 pounds in the middle of the back seat, and 45 pounds in the trunk. If you're really anal you can measure and adjust the ride height further following the procedure in the Bentley manual, but this gets you plenty close enough. NOW you can get under the car and torque down the bolts that hold the bushing side of the thrust arm to the frame. Torque these 21mm bolts to 110Nm (81 ft-lb).

11) Re-install the sway bar brackets, making sure that the little nub on the rubber bushing fits in the corresponding hole in each bracket (See Image #5). Torque the 13mm nuts to 24Nm (18 ft-lb).

12) Lower the car to the ground and enjoy your shimmy-free ride! Incidentally, it is not necessary to have an alignment done following this procedure.
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