[click to enlarge]
popular project among BMW 3 Series owners is replacing the front and rear
shocks. Replace both the front and the rear at the same time, as they take
roughly similar abuse over their lifetimes, so neither is likely to be more
or less worn than the other. The shocks should always be replaced in pairs
(left and right together, see Project 61).
I recommend that you replace your shocks every 50,000
miles or so, or if they start to show signs of fading or wearing out. If you
push down on a corner of the car, it should spring back with little
oscillation up and down. If the car bounces up and down, you probably need
new shocks. Different driving patterns may also affect the life of shock
absorbers. Cars that are raced or often driven on winding roads may need
their shocks replaced more often. It is also important to remember that, if
you install performance springs that lower the car from its stock level, you
will need to have the car realigned. Changing the height of the suspension
also changes the values of the alignment settings.
The replacement process is somewhat similar for E30 and
E36 cars with one glaring exception: E30 cars have a replaceable front shock
(called a “strut insert”), whereas E36s require you to replace a more
complex integrated shock absorber/strut assembly. Although the E36 design
requires the replacement of a more complex part, its replacement procedure
is actually easier.
Begin the process for both E30 and E36 cars by jacking
up the car and removing both front road wheels (see Project 1). E36 owners
should read the following E30 section and then the subsequent E36 section,
as there are elements of the strut disassembly process that are not
specifically mentioned in the E36 section below.
With the car
elevated (see Project 1) and the wheels removed, start with one strut, and
remove the brake caliper (see Project 57). Unplug any brake sensors
connected to the caliper, and disconnect the caliper from the strut. Use
rope or wire to tie the brake caliper aside so it doesn’t hang by its
rubber hose. With the brake calipers secured out of the way, disconnect
the tie rods from the struts (see Project 59). It is difficult to
disconnect tie rod ends from struts without damaging the rubber boot that
protects the tie rod. Consider replacing the tie rod ends at the same time
if you think you might damage the boot.
With the tie rod disconnected, you should be able to
rotate the strut quite easily. Now, disconnect the sway bar drop link from
the control arm (see Project 59). This allows you to drop the strut
downward to its lowest point, so that you can pull it out from the car
after you remove the shock insert and spring.
Next, install the spring compressor onto the spring and
compress it until it no longer is tight in the strut assembly. While
compressing the spring, be sure yo wear safety goggles. These springs are
under a lot of pressure, and the spring compressor could suddenly slip
off. Place the two halves of the compressor on exactly opposite sides of
the spring. You may use two ratcheting wrenches (I prefer the ones
manufactured by GearWrench) on each side of the compressor to ensure even
and equal compression. Failure to maintain even compression when
compressing the springs can make the compressor slip off.
With the spring compression removed from the strut
assembly and the springs loose on their perches, now move to the engine
compartment. Pry off the small black cap in the center of the strut mount,
and remove the center nut attached to the top of the shock. This, of
course, is easier said than done. If you have an impact wrench, simply zap
this nut off. The reassembly process requires an impact wrench, so if you
don’t have one, now is a great time to buy one. I recommend electric
impact wrenches that function without an air compressor is required (see
Tools of the Trade in the front of this book).
If you don’t have an impact wrench at this time, remove
the nut by latching onto the top of the shock rod in the wheelwell with
some carefully placed locking pliers, in between the springs. This is not
the best method for removal, and if that top nut is on really tight, it
may not be possible to remove it this way. If that’s the case, disconnect
the entire strut from the car by disconnecting the lower ball joint (see
Project 59). Once the strut is out of the car, you have a few more options
for removal, including taking the entire strut over to someone who has an
With the top nut removed, place your floor jack
underneath the bottom of the strut to relieve some of the pressure from
the weight of the strut assembly. Next, disconnect the three nuts that
hold the top shock mount to the chassis, and lower the strut. Reach up
inside the wheelwell and remove the top strut mount, the upper spring
retaining plate, and the old rubber gasket.
Now you’re ready to remove the shock insert. Remove the
dust cover from the insert and you will see a threaded collar that secures
the insert to the strut housing. Lubricate this collar a bit with WD-40 or
similar penetrant, as you don’t want to damage the threads of the strut.
You can use the special BMW tool designed to fit this collar, but I found
it just as easy to use a plumber’s wrench or a set of channel locks, to
loosen it. Once the collar is loose, pull the shock up through the top
inside the engine compartment. It’s normal for the older-style hydraulic
shocks to be submerged in oil, so be prepared that oil will leak and drip
everywhere as you pull the shock out. Have paper towels handy.
With the shock removed, lift the old spring off of the
bottom spring perch. Swing the strut out and look down the tube with a
flashlight. If the old shock inserts were conventional hydraulic shock
absorbers, there should be oil in the bottom of strut. The oil is used as
a lubricant and also aids in heat dissipation. If you are going to use new
hydraulic shock absorbers, siphon out the old oil and replace it with
about 1 quart of new oil. You can use regular motor oil for this. If you
are using replacement gas shock inserts (like the Bilstein units), siphon
out the old oil in the strut and install the new shock inserts dry.
If you reuse the old springs, simply place them back
onto the top of the lower spring perches. If you replace your springs with
new ones, move the springs to your workbench and slowly release the spring
compressor on your old springs. Compress the new springs in a similar
manner. The E30 shown in this project was upgraded to Eibach performance
springs, which created a stiffer suspension and lowered the car about 1.8
inches in the front and 1.5 inches in the rear.
Install the compressed spring assembly back onto the
lower spring perch. Install the new shock absorber through the top of the
engine compartment, and tighten the collar to the strut. Reinstall the
dust boot/rubber bumper assembly over the shock to protect it from road
debris and grime. The Bilstein sport shocks installed on this car have the
boot and stopper already integrated into the assembly.
Reinstall the upper spring plate and spring pad, and
verify the plate is nestled correctly against the top of the spring.
Inspect the upper strut mount carefully. This part is manufactured out of
rubber and has an integrated ball bearing inside. It will wear over time,
so replace it if it looks old, or if it hasn’t been replaced previously.
Reinstall the upper strut mount on top of the spring plate, and zap it on
with an impact wrench. Unfortunately, the impact wrench is pretty much
required here—do not use pliers on the shaft of the new shock inserts.
Once the shock rod nut is affixed, have an assistant
raise the strut assembly with the floor jack while you guide the upper
strut mount into place. Reattach the three nuts. Now, carefully release
the tension on the spring compressors and the spring should seat between
the upper and lower perches. Reattach the sway bar drop links, tie rod
ends (Project 59), and brake caliper (Project 57). Plug in any sensor
connectors you may have disconnected, and route the wires and hoses back
through the tabs in the strut.
With the car elevated (see Project 1) and the two front road wheels
removed, start with one strut and disconnect the brake sensors and brake
hose from the strut. They are wedged into a mounting tab in the strut and
held in place with rubber grommets. Slide the grommets out of the tabs;
this may require some gentle nudging with a screwdriver. Then, remove the
upper mounting bolt for the strut. Hold the nut on the other side of this
bolt with a crescent wrench. Remove the two lower bolts as well. Place
your floor jack underneath the bottom ball joint and lift up on the strut
about 1/8 inch to support the weight of the strut when you disconnect the
top from the chassis.
Moving to the engine compartment, remove the three
small nuts that hold the upper shock mount to the chassis shock towers. At
this point, the strut should be free to be removed from the car. Lower the
floor jack and press down slightly on the control arm, and pull the strut
out and away from the car. Don’t let the steering arm assembly hang. Tie
it up with rope and wire, as you don’t want to damage the outer ball joint
or rubber brake hose.
Take your strut assembly over to your workbench.
Compress the spring using the procedure discussed in the above E30
section. Remove the top nut from the shock, also using the procedure
discussed in the E30 section. Again, it is very difficult to remove this
nut without an impact wrench. Move your spring to the new strut and
reassemble, using all of the hardware from the old strut. As with the E30,
inspect the top shock mount to see if it needs replacement. Zap in the new
top mount with the impact wrench and reinstall the entire assembly into
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