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Tuesday, September 02, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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Doug's BMW E36
DIY Sway / Stabilizer Bar Service

(Image: 2006 BMW ETK E36 Front Swaybar Parts Screenshot)
Sway bar end links and bushings are easy to replace and
can substantially improve the quality of your driving experience.

Introduction

Like all modern vehicles, a BMW is equipped with suspension components called stabilizer bars, also referred to as sway bars. There are two stabilizer bars on the vehicle, one for each “axle” (front and rear). They are designed to redistribute the weight of the vehicle in turns and can have far reaching effects on the vehicle's handling properties. My sport-package equipped 328is, for example, has slightly larger stabilizer bars on the front and rear of the vehicle to complement the factory lowering springs by reducing body roll.

Stabilizer bars accomplish their goal in part by tying the left and right wheels of a particular axle together. The physical connection at the end of each stabilizer bar is made through what is known as an “end link”. The end link can take many forms, but on the E36 BMW the front end links consist of a metal-sleeved rubber bushing on one end and a ball joint on the other, while the rear end links are simpler – a metal-sleeved rubber bushing on one end and a plain rubber bushing on the other.

The ball joint on the front end links allows the flexibility required as the suspension geometry changes throughout its range of motion. The system is, after all, trying to tie something that resists motion (the bar, fixed to the frame rails) to something constantly in motion (the lower control arms...or strut in the case of the M3). Over time, the ball joints in these links can loosen up, the ball joint rubber boot can crack and release grease (or allow water in), and the rubber bushings on all the end links can crack and lose elasticity that helps reduce noise and vibration transmitted to the body.

The effects of old bushings and end links are most notably felt in the front end of the vehicle. When the front end links loosen up, they tend to cause a momentary shimmy or shake in the wheel and possibly an accompanying clunk as the vehicle traverses bumps during turns. When the rear bushings and endlinks are shot the rear tends to wander a bit more, particularly at speed in a straight line. This can contribute to a false diagnosis that something is wrong with the front end as the driver has to continually correct the car's trajectory with steering as the rear of the car wags like a dog's tail.

Make no mistake: servicing the sway bars can be an effective and inexpensive way to eliminate general sloppiness in the suspension.

Notes

Prerequisites

Front Sway Bar Service Procedures

To “service” a front sway bar, you replace the end links that tie the bar to the suspension, and the bushings that hold the sway bar securely to the frame of the vehicle. We'll start by replacing the end-links.

End Link Service

To remove the end links:

  1. Jack up the front of the vehicle and put it on jack stands. If you don't know how to properly jack a BMW, STOP RIGHT HERE and educate yourself on correct jacking procedures before you kill yourself. And re-read my site disclaimer while you're at it.
  2. Remove both wheels, mark them using tape or some other method as left and right and set them aside out of the way. Marking the wheels is particularly important if your vehicle is equipped with directional tires.
  3. Start on either side and orient yourself to the task at hand. Look just behind and to the rear of the hub, rotor and kingpin assembly. You will see one end of the stabilizer bar connected to the lower control arm (the flat curved metal component with large holes in it).
  4. Remove the ball joint back nut. Use the special thin 16mm wrench to hold the ball joint backnut steady and a 16mm socket or combination wrench to remove the associated nut. You may find it helpful to use a smaller breaker bar or long-handled ratchet to remove this nut, as it's torqued to 59Nm (44 ft*lbs).
  5. Remove the ball joint from the mounting flange. Using 13mm combination wrenches and/or a socket, remove the bolt that ties the lower bushing of the end link to the U-shaped mounting flange (which is in turn mounted to the control arm), then remove the end link and set it aside. This bolt is torqued a bit less than the ball joint nut, but it may still be tight.
  6. Remove the mounting flange. While not strictly necessary to replace the U-shaped mounting flange, I did for aesthetics and basic sanity (since I have heard of these failing, particularly on cars equipped with larger aftermarket stabilizer bars and lowered suspensions). To remove the mounting flange from the lower control arm I found I needed to use a combination wrench wedged between the “ears” of the flange to prevent it from rotating while I removed the lower 13mm bolt.

To install the new end links:

  1. Install the new mounting flange. Torque the nut (under the control arm) to 42Nm (31 ft*lbs). The concave surface of the control arm will serve to prevent the flange from rotating when it's near the final torque, but you may again need to use a combination wrench wedged between its “ears” to prevent it from rotating initially.
  2. Flex the ball joint. Grab the new end link, break the ball joint free and then return it to near the center position. The joint tends to stick since it is tight to begin with, but also because it hasn't moved since it was manufactured. You'll need this joint to move slightly to align it with the bar and it's easier to break it free while the part is in your hand rather than on the car.
  3. Loosely mount the end link in the flange. Hold the end link in position in the mounting flange and then the bolt that connects the lower bushing of the end link to the flange. Spin the nut on loosely but don't tighten it down yet. This is just for initial fitting. We'll tighten everything down shortly.
  4. Torque the ball joint back nut to 59Nm (44 ft*lbs) . Using the thin wrench to hold the ball joint back nut, torque the ball joint nut to 59Nm (44 ft*lbs). Make sure that the flats on the back nut are parallel to the strut (near vertical). While the Bentley glosses over this important point, the BMW TIS emphasizes the importance of this step, so I will too. Warning: The torque spec for non-M cars specified in the Bentley manual is incorrect according to the TIS. Follow the 59Nm recommendation for all E36 models.
  5. Torque the end link to the mounting flange to 30Nm (22ft*lbs). You will note that the new flange “ears” are slightly Y shaped, but they will pull in as you reach the final torque. This is, incidentally, one of the advantages of using the new part. It's easier to install the end-link with the extra play in the flange. Warning: The TIS does not provide a torque specification for this connection, nor does the Bentley from what I can ascertain. This is a reasonable guess on my part given the size of the bolt and the fact that it uses a self-locking nut. Note that I originally estimated this torque to be 42Nm (31ft*lbs) but have reduced it based on reader feedback and further research.
  6. Wash, rinse, repeat. The end link is installed. Repeat the process on the other side.

Bushing Service

When I went to find the proper bushings for my vehicle, both realoem.com and the current BMW ETK software showed different options for the sport suspension, but only for the rear bar. The only bushing for the front bar was 24.0 mm. It turns out that BMW imprints each bushing with a inner diameter and a partial part number. While I was under the car for other reasons I found that my bushings were 25.5 mm, so the ETK information was wrong.

To make a long story short, I took the partial part number to my dealer's parts guy and he came up with a number for the 25.5 mm bushings. I ordered those and installed them without difficulty. I point this out simply to demonstrate that the ETK is not infallible and there are what I choose to call “phantom” parts on these cars, which is to say that they are available if entered into ETK manually, but are not shown in the graphical parts diagrams. This is also a lesson to verify you have the right parts before you start work, or you may wind up doing things twice.

Note that you need not replace the bushing brackets unless they have been damaged in some way (and if they have been, you have bigger problems and probably should be taking the car to a professional for evaluation). Based on the gauge of the steel, I imagine the studs would rip out of the frame before the bracket itself would bend. Of course, if you want to buy a new part for painting or other cosmetic enhancement ahead of time, this would be the time to do that.

To remove the old bushings:

  1. Mark the location of the bushings on the sway bar. Optionally, using a fine tipped permanent marker, mark the location on the sway bar where the bushings sit. This will be used as an aid during installation of the new bushings and to let you know if the bar has shifted to either side as you reinstall it.
  2. Loosen each of the four nuts (two on each side) that hold the bushing brackets in place so that they're still grabbing a few threads. Then hold the bar up with one hand while you remove the nuts with the other. This prevents the bar from falling down, though there's little chance of that happening because the brackets tend to stay where they are unless you hang on the bar at this point.
  3. If the brackets don't come down on their own, motivate them. Use a screwdriver wedged between the frame and the bushing to pull the bracket down on each side. Remember to hold the bar with one hand while you pry with the other, as the bar weighs about as much as you'd expect a 3/4” bar of steel to weigh and it may drop down suddenly. Keep your head out from under the bar to make sure it doesn't put a nice dent in your skull. Set the brackets aside somewhere safe.
  4. Remove the bushings from the bar. I pulled the bar down about 1/2” and rotated the bushings 180 degrees (so the split was facing upward) and then leveraged gravity to pull them off the bar (pulling down is easier than pushing up). You may also be able to slide the bushings one way or the other and pull them off that way. It's easy, really.

To install the new bushings:

  1. Install the new bushings on the bar (split facing downward, of course) and align them with the marks you made on the bar. If using the OE rubber bushings, make sure they are applied to the bar DRY. Do NOT apply any grease to them or they will swell and make noise. Grease only belongs on aftermarket poly bushings.
  2. Clean the inside of the metal bushing brackets in a parts washer or just rub it with some brake cleaner and a scotch-brite pad. Let it dry.
  3. Optionally apply some Spray 9 to the inside of the bracket to serve as a temporary installation lubricant. The new bushings are slightly oversized relative to the brackets and will be a tight fit. Note that I did not use any lubricant and I was able to get them up far enough to get the nuts started. Whatever you do, do NOT use grease of any kind for this application.
  4. Install the cleaned bracket over the new bushing and push it and the bar assembly up until you can get the two nuts started. Torque the nuts to 22 ft*lbs.

This completes the procedure to service the front sway bar. Before you do any additional work, make sure you've torqued everything to spec on the front bar and then jack the car down and go for a test drive. I think you'll find your steering a lot tighter and smoother over bumps.

Rear Sway Bar Service Procedures

The procedure to service the rear sway bar is similar to the front in concept, but the application is quite different. Let's get started.

Remove the sway bar

  1. Jack up the rear of the car, put it on jack stands, and remove the rear wheels. This is required for clearance as there is no practical way to get access to the fasteners on the top of the control arm near the spring without doing so. Believe me. I tried.
  2. Lower the muffler. Unless you're using a lift and can manage to get the car 5+ feet into the air, you'll need to lower the muffler slightly to get the required clearance to remove the bar. If your muffler has twin exhaust pipes, look for the vacuum line going to the solenoid valve and disconnect it. Release the muffler by supporting it with one hand and using a 13mm socket and ratchet to remove the two nuts holding the pinch clamps on either side of the muffler. The muffler can be gently released and allowed to hang without fear of damaging anything, but it would be unwise to step on it or drive the vehicle in this condition.
  3. Remove the end link mounts from the upper control arm. Use either a short or deep 13mm socket along with a small ratchet to remove the nut that fastens each upper end link mount to the control arm. The nut is located just to the inside of the spring. The need for short and deep sockets will depend on the specific ratchet in use and the clearance present between the individual coils of the spring and the tool. On my car the deep socket worked well on the right side while the shallow socket worked best on the left.
  4. Remove the sway bar clamps from the subframe. Again using a small ratchet with 13 mm socket combined with a 13 mm box end wrench, remove the fasteners holding the sway bar bushing clamps to the subframe (central rectangular frame of the car holding the differential). Remove the clamps and pull the bushings off the bar to detach the bar from the car.
  5. Take note of how the bar is installed and then snake it out from under the car by pulling the right side down first, tilting the bar in the process.

Prepare for installation of new end links

Once the bar is freed from the car, take note of the angle at which the end links sit relative to both the bar and the upper mounting bracket. This is important and should be duplicated by the installation of the new end links as closely as possible. I set the bar on the ground, aligned a piece of paper with the "flat" buttom of the bar, and scribed a line where the end link shaft crossed the corner of the page, and then duplicated this for the opposite side as well. This preserved the angle of the end link relative to the sway bar. See the Rear Swaybar Highlights section for a picture.

As for the angle of the upper mounting bracket to the end link, I must admit that I guestimated this as there was no convenient way to measure it. I simply replaced one end link at a time and with the bar back on the garage floor sighted the old and new end links and adjusted the new bracket to the correct angle before applying the final torque to lock it down. And speaking of torque, the spec is 44 ft-lbs but I only managed to get 35 ft*lbs on it before I gave up. I think that's good enough.

Install the new end links

  1. Fit the end links to the bar. You can try to use a vise and a small socket as a drift as the TIS and my technician suggested, but I had no luck with that and wound up pressing the links on with my bare hands. Use some Spray 9 to lube the end of the bar and the interior of the end link bushing and then push and twist the end link onto the bar as far as possible. Before the lube dries, make sure that the end link is positioned at the proper angle. Use the measurements taken before as a guide.
  2. Wait for the lube to dry. With both end links installed, wait 15-30 minutes for the lube to dry. This will help bond the end link to the bar at the proper angle required for installation.

Reinstall the bar

  1. Position the mounting bushings on the bar at the proper locations and weave the bar back up under the car, taking care not to push the end links out of alignment just in case the lube hasn't fully dried.
  2. Fit the the end link bracket to the control arms and loosely install new metal self-locking nuts.
  3. Reinstall the clamps. Using a bit of Spray 9, spray the exterior of the mounting bushings and interior of the clamps and pull the bar up into place before pressing the clamps over the bushings and loosely installing the hardware.
  4. Check over the entire bar and make sure it is positioned correctly.
  5. Tighten the brackets to the control arm to 22nm (16 ft*lbs). Warning: I managed to strip one of these fasteners while I waited for my torque wrench to click, so all I can conclude is the actual required torque is far lower than the spec, so proceed carefully. Do this by feel only and stop when you feel resistance and/or when you judge the mount is seated with the underside of the control arm. You may be able to use the anti-rotation "barb" on the bracket as a gauge, as it will appear in a mating hole in the control arm and sit slightly above the surface of the control arm when properly installed.
  6. Torque the bushing mounts to 30 Nm (22 ft*lbs).

Finish Up

  1. Reinstall the wheels and torque the lugbolts to spec. You can use the parking brake to hold the wheels still while you torque, incidentally.
  2. Let the car down off the jackstands and go for a test drive, being careful to "re-learn" the car at the limit, since it may very well react slightly differently than you expect. It's amazing to me how much "quieter" the rear of the car was after this work.

Rear Sway bar Highlights