bmw 2002

Front Swaybar Replacement

May 26, 2008

     I wrote up a whole post about my teardown and refurb of the front suspension.  I left out, however, one crucial part of the front suspension, the part that comes off first and goes back on last:  the swaybar.

     Also called the "anti-roll bar" — which is a far more descriptive name — the swaybar counters body roll when a car is turning.  So if you've ever ridden is some barge of a car and feel the whole thing roll to one side through a turn, swaybars minimize that feeling.  They do so by essentially connecting the left wheel to the right wheel (front and rear separately).  When turning, the body rolls outward, pushing down on the outside wheel and pulling up on the inside wheel.  The swaybar counters those forces, keeping the car's body flat and it's weight more evenly distributed between left and right tires.

     In addition to keeping the car level in turns (for that cool "sliding through corners" sports car look), swaybar stiffness changes how much a car over- or understeers when cornering.  When turning, the inner wheels have less weight on them, so they lose grip.  That weight is thrown to the outside wheel, but one tire can only grip so much.  By keeping the car flat, both outer and inner tires can grip the road better.  And by changing how much grip the front wheels have vs. the rear wheels, over- and understeer can be adjusted.

     So, I'm all about making Webby a fun car to tear ass in.  In that vein, I decided to upgrade her swaybars to something much stiffer and sportier.  I called up Ireland Engineering and ordered a new set of swaybars, front and rear.  They're a lot thicker and shorter than the stock bars, so they're much stiffer.  Furthermore, all the bushings are urethane rather than rubber, so, again, stiffer feel when cornering.  Here's my teardown of the stock front swaybar and rebuild with Ireland's fat one.  It was a relatively painless install.

This is the passenger's side stock swaybar linkage.  The rubber bushings are showing wear and the bar itself is not terribly stiff (see its wobbly bend as it heads away from the camera?).

front swaybar linkage old

Here's the stock swaybar's linkage on the driver's side.  Notice the angle between the linkage connecting the swaybar to the control arm and the bolt underneath.  There shouldn't be an angle:  it's bent.

front swaybar linkage old

If it wasn't clear in the previous picture, here the bent linkage is obvious.  This part should be perfectly straight.  I only hope that this isn't evidence of a front-end collision in Webby's past.

front swaybar linkage old bent

These bushings might as well be sponges.  They can't provide much stiffness under load.

bad bushings

This was the packing paper protecting the new swaybar during shipment.  Any parts that arrive wrapped in this simply must be good.

super bubble

The new swaybar (bottom) stands in stark contrast to the stock one.  It's much thicker and considerably shorter.  Both give it greater strength/stiffness.  If you can imagine taking the bar and pushing downwards on one end while pulling upwards on the other end, that's pretty much what happens to a swaybar when a car's cornering.  The new bar on the bottom won't bend nearly as much, keeping the car nice and flat in the turns.  Yeeha!

old vs. new swaybar

Here's the bar completely installed.  It hangs low, so 2002's with air-conditioning probably won't have any clearance issues with the A/C compressor.  

front swaybar installed

The bar comes with two large mounting blocks made of Aluminum that bolt to the frame.  The bar's end link has two holes for the metal ball joint to attach.  By choosing one hole or the other, you can effectively adjust the length of the swaybar, thus adjusting its stiffness.  Here I've chosen to mount the linkage to the hole closer to the front of the car, making the swaybar shorter and stiffer.  There is very little clearance between the bar and the tension rod (the black bar here).  So little in fact that I jacked up the suspension to see if they would hit.  They just kiss each other, then everything's OK.  I think it'll work out alright.

front swaybar linkage new

     When I got this swaybar, I also ordered Ireland Engineering's rear swaybar.  It's big and fat just like this one;  they make a nice set.  I'll install it later, after the car's up and running for a while.  In the meantime, I'll have a very stiff front end and a really flexible rear.