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FCP Euro Service Kits

FCP Euro Kits

A while back I had to replace a lower (lateral) control arm on my E31 850Ci.  Whilst it's not a very complex job, I feel you can never have enough pictures for reference, so let's take a look at it.

The lower arm is sometimes called the lateral arm as it faces along the width of the car rather than to the front like the upper/thrust arm.  The 'bushing end' in this example was clearly destroyed and the ball joint end had a torn boot though the joint itself still seemed to be fine.  This arm is made from aluminum alloy rather than steel and the E31 (first available 1989) was one of the earliest applications of this.  The alloy is much lighter than steel and contributes to a lighter unsprung weight on the car.  The E31 specific trick is that the 'bushing end' is actually not a bushing at all - but a spherical bearing - really a ball joint that can rotate within certain degrees of freedom.  I've heard of some M5 owners replacing their lower arms with E31 versions for improved handling.

cWhen replacing the arm you'll see the primary problem is the bottom of the strut covers the nut at the ball joint end.  The official E31 service manual suggests the correct procedure is to remove the strut from the top to gain access.  In actual fact you can remove the 3 bolts at the bottom of the assembly and push the part down so you have enough clearance for the nut.  Then you just need the specialist ball-joint removal tool and a regular socket and wrench at the other end.  Don't let anyone suggest you can remove the ball joint with a few sharp hammer impacts!  That may work fine on smaller joints but I've always found these ones to be very heavy duty and require quite some force with the specialist tool.

You may have heard about having to tighten control arm bushings with the car on the ground (or the suspension loaded via jacking it up to the appropriate level).  With a spherical bearing you do not have to do that - because it freely rotates.  So you can re-attach the arm completely with the car on a stand or lift without having to worry about a final torque with the car on the ground.

31121138477After changing this arm the alignment of the car should be checked.

 

 

 

 

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Written by :
Bryan McPhail

Bryan is a longtime BMW enthusiast in Florida.


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