Match front shock absorbers to the struts on your car
Performance Gain:
Better handling and performance
Complementary Modification:
Installation of a camber bar, replacement of ball joints, and tie rod ends
This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
Check out some other sample projects from the book:
One of the most popular projects to perform is the replacement of the front and rear shocks on the 911. It is usually recommended that you replace both the front and the rear at the same time, as they take roughly similar abuse over their lifetime, and the fronts or rears are not likely to be more or less worn than the other ones. As a rule, the shocks should always be replaced in pairs.
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 almost no oscillation up and down. If the car bounces up and down, then you probably need new shocks. Different driving patterns may also affect the life of shock absorbers. Cars that are raced or often driven on windy roads may need to have their shocks replaced more often than street cars.
The first step in replacing your shocks is to determine what type of front strut you have in your car. The front strut is the part of the front suspension that pivots on the ball joint that the brakes, wheels and tires are mounted to. Certain types of shocks will only fit certain types of 911 front struts. If your 911 car has Bilstein struts, then you must replace them with new Bilstein shocks. If you car has Koni struts, then likewise, you must use Koni shock inserts as replacements. You cannot use another shock, as it will not fit inside your 911s front strut.
The easiest and most basic method of determining which front strut you have is to take a look at the color of the strut. Green struts are almost always Bilstein struts, red is almost always Koni, black is Boge, and yellow struts can be either Bilstein or Koni. One sure method of checking for Bilstein struts is to look for the roll pin that is installed at the bottom of the shock (see photo). The Bilstein inserts are installed up side down as compared to the typical method of mounting the cylinder on the bottom. The shock extension therefore must be constrained in the bottom of the strut. The roll pin accomplishes this by securing the insert in the strut. If your strut has this roll pin installed in the bottom of the strut, then it is a Bilstein strut.
When you order your new front shocks, make sure that you order replacements that will match your strut type. If you wish to change to a different type or manufacturer of shocks, and you have Koni or Bilstein struts, then you will have to change out your inserts, which is not exactly a simple job. The Boge inserts can accept shock absorber inserts from a variety of manufacturers. When you order rear shocks, it doesnt matter which brand you order: they should all fit your 911.
Before you begin, jack up the front of the car and remove the road wheels from both sides. Now might be a good time to inspect your tie rod ends, brake discs, and pads.
The first step in removing your front shocks is to remove the large nut that holds the insert to the top of the car. If you have Bilstein struts, I recommend that you remove the small roll pin from the bottom of the strut prior to removing the large nut. This will keep the shock secured in place while you hammer or drill out the roll pin. Open the trunk and you will see the large nut located in the center of the shock tower mount. For pictures of this nut, see Pelican Technical Article: Installing a Camber Strut Brace, Installing a Camber Strut Brace. After you remove the nut off the top of the strut, you should be able to take the entire strut and pull it out from under the fender well. You will need to push down on the shock in order to gain enough clearance to do this.
After the strut has cleared the fender, remove the dust shield from the top of the shock. The insert should now pull out of the strut. Check the rubber o-ring at the top of the insert for damage, and replace it if necessary. Make sure that you dont let the shock hang from the rubber brake line. Doing so will almost certainly damage your brake lines.
Installation of the new shocks is easy. Simply place the new insert into the strut and reattach it to the shock towers with the large nut. For Boge, Koni, and other shocks, simply insert the shock in the strut and reattach it. If you have Bilstein inserts, install the roll pin in the lower part of the strut. A very important part of the installation is assuring that the roll pin is installed correctly. The roll pin must be installed with the groove facing away from the center of the insert. If the roll pin is installed backwards, or at some angle in-between, then the vibration of the shock will cause the roll pin to break after repeated motions up and down. Make sure that you install the roll pin as shown in the photos that accompany this project.
The rear shocks are much simpler. They are basically a bolt-in replacement. You can install any type of shock (Boge, Bilstein, Koni, etc.) on the rear suspension without any consideration of what the car originally shipped with. Before you begin the replacement of the rear shocks, jack up the rear of the car. You dont need to remove the rear wheels.
To remove the rear shock, place a jack under the rear trailing arm and lift it up slightly. The shocks support the weight of the trailing arm when the car is suspended in air, so you need to remove this tension from the shock prior to removal. Inside the engine compartment, all the way towards the front is the mount for the rear shocks. Remove this large nut while keeping the top tab of the shock from turning. Underneath the car, simply remove the large bolt that mounts the rear shock to the trailing arm.
Install the new shock by inserting it up into the car, and then replacing the rear trailing arm bolt. Back inside the engine compartment, reinstall the retaining nut on the top of the shock.
Figure 1
The top set of shocks are Bilstein front shocks, original equipment on some 911s. It is important to make sure that you match the front suspension struts to the type of shocks that you purchase. The lower two shocks are Boge rear shocks, and were also original equipment on the 911s. Unlike the front, the rear shocks do not have to be matched to the original shocks sold with the car.
The front strut pulls away after the top fastening nut is removed. At this point, the dust shield can be removed, and the shock insert can be removed. For the Bilstein inserts, make sure that you remove the roll pin that is installed at the bottom of the strut. For all other shock types (Koni, Boge, etc.) the shock should simply lift out of the strut. These are Bilstein struts, most easily determined by their green color. Koni inserts are usually red, Boge inserts are typically black, and yellow inserts can be either Bilstein or Koni. All the struts should be appropriately labeled by their manufacturer as well.
The roll pin that holds in the Bilstein shock must be installed properly, or it will break under normal driving conditions. The roll pin must be installed with the slit facing away from the center of the shock. If not, the shock will flex the roll pin, and over time this will cause the metal to yield and break.
The rear shocks are much easier to replace than the front one. Support the rear trailing arm, and then unbolt the rear shock mount located in the back of the engine compartment, towards the front of the car (shown by arrow). Make sure that you keep the top of the shock from turning as you remove the retaining nut.
Down below, the shock is simply bolted into the rear trailing arm. With the trailing arm supported by a jack, unbolt and pull out the shock from the chassis. The installation of the new shock is quite a straightforward, bolt-in process.
Comments: Try an impact wrench. Also on the rears you can stabilize the tab with vice grips and loosen the nut.
April 22, 2012
JordanSC
Comments: Wayne, do you have any tips or recommended tools for keeping the top 'tab' of the shock from turning? I've been struggling for a little while now with that piece. Thanks, Jordan.
April 18, 2012
Check out some other sample projects from the book:
