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.
The 911 suspension uses both front and rear torsion bars to spring the weight of the car. While many normal cars use coil springs, the 911 suspension uses the torsional stiffness of the metal bars in order to provide the necessary spring. Like traditional coil springs, as the cars age the torsion bars have a tendency to become weak, or even snap and break. The replacement procedure for the front bars is quite easy, and can be carried out by the home mechanic.
The front torsion bars are mounted parallel to the direction that the car travels, and spring the a-arm using an adjustable stop that is mounted on the end of the bar (see Pelican Technical Article: Lowering the 911). To remove the front torsion bars, begin by jacking up the front of the car and removing the front wheels. Remove the bottom belly pan cover that protects the steering rack and fuel pump. Do not support the car using the front torsion bar covers, as you will have to remove these in order to access the torsion bars. Instead support the car from the bottom of the car, near the seams of the sheet metal. Also place an emergency floor jack underneath the cross member, near the torsion bar adjusting screw after you
Now, unscrew and remove the torsion bar adjustment screw (see Pelican Technical Article: Lowering the 911). The torsion bar adjusting lever that the screws mate with should be able to be pried off of the end of the torsion bar. If you cannot remove the adjusting lever because it is still under pressure from the weight of the a-arm, place the jack underneath the a-arm and lift it up slightly. When the pressure is relieved, and the adjusting lever is free, it should pull off relatively easily. Remove the foam gasket that is behind the adjusting lever.
At this point, you should be able to see the torsion bar sticking out of the a-arm. Try to remove the torsion bar by pulling on it. If necessary, use a cloth rag and a pair of vise grips to get a better grip on the bar. Make sure that you don't damage the splines on the end, or scratch the paint on the bar. Twist and wiggle the bar back and forth. If it will not come out, then you need to tap it out from the opposite end. If your torsion bar is broken, then you will have to tap out the other half from the opposite end anyways.
To tap the torsion bar out, move to the very front of the car and remove the front cover bracket from the front of the a-arm. On later cars, this cover is integrated into the mount, so you may have to remove the a-arm mount. Check again to make sure that you did not place the jack stand that supports the front of the car under this a-arm. Once this bracket is removed, you should be able to see the small dust cap on the end of the a-arm. To remove this dust cap, drill a small hole into the center, and then use a punch to pull it out. You can also bang out the bar from the other end, knocking the plug out in the process. After the dust cap is removed, tap out the torsion bar with an appropriate punch. Make sure that you do not damage the torsion bar splines as you tap it out.
After you tap the bar out, you should reinstall the front dust cap and reattach the a-arm to the chassis. It's a wise idea to weld up the small hole in the dust cap, or fill it with a little bit of epoxy or silicone. If the cap has become damaged, then it will be necessary to replace it with a new one. On the older cars, it is common that the splines will be dry and rusted. You may also find damage to the female splines, necessitating replacement of the A-arm or adjuster.
When you have the bar removed, inspect it for any corrosion or damage to the bar or the end splines. If such damage exists, then the bar should be replaced.
Reinstallation is straightforward. Simply reinstall the bar after liberally coating it with some white lithium grease. The bars are pre-stressed from the manufacturer, so don't mix up the left and right sides. The bars are marked L and R on their ends.
When fitting the torsion bar back into the car, make sure that the suspension a-arm is hanging as far downwards as possible. Insert the bar into the a-arm, and install a new foam seal over the torsion bar if the old one was worn. Now, place the adjustment lever back onto the end of the torsion bar. Make sure that you leave as little clearance as possible between the adjusting arm and the inside top of the cross member. Thread the adjustment screw into the adjustment lever, and then follow the adjustment guidelines explained in Pelican Technical Article: Lowering the 911.
Whereas the front torsion bars are mounted along the length of the 911, the rear bars run across the width of the car. The bars provide the spring for the suspension of the rear trailing arms. A large spring radius arm, or spring plate, connects the end of the torsion bar to the trailing arm, and provides adjustment for ride height, and balance from left to right.
The first step in removal of the rear torsion bars is to jack up and remove the rear road wheels. Do not place jack stands underneath the torsion bar covers, as you will need to remove these. Instead, support the car from underneath the engine and the transmission, taking care not to place the jack stands in any location that may cause damage to the engine case. You can also place the jack stands under the torsion bar tube that runs the width of the car.
Now, place the jack under the rear trailing arms and raise them up slightly, so that the shock absorber is compressed about an inch or so from its maximum travel. Make sure that you don't jack up the shock absorber too much, as this will tend to raise the car off of the jack stands. Remove the lower bolt from the shock and let it hang there next to the trailing arm. Now, remove the four bolts that hold on the torsion bar cover and the spacers that go underneath it. Use two large screwdrivers to pry off the cover.
Unfortunately, the removal of the torsion bar requires that you remove the radius arm as well - particularly if you want to save your original suspension bushings. You will need to remove the rear caliper and brake disc in order to access the bolts that hold on the radius arm. See Project 47 for more details on this procedure. You will also need to remove the small torsion bar access cover on the outside skin of the car. This cover is painted the same color as the car, and on early cars may require the removal of some rocker trim below the door.
The rear suspension bushing is molded into the radius arm itself, and the two together are considered a single part by the factory. You can cut or burn away the older bushing, but then you will have to replace it with a newer bushing. The replacement bushings are a different style than the original ones: they are not molded into the radius arm, but instead wrap around the inner torsion bar cover. Whereas the original bushings twist as the car moves up and down, the replacement bushings don't - they rotate instead. This means that the replacement bushings have a tendency to squeak. Needless to say, I recommend that you remove the entire radius arm and save your original bushings.
Before you remove any of the bolts that hold the radius arm to the trailing arm, lower the trailing arm until the tension from the torsion bar exerted on the radius arm decreases. There should be a point to where radius arm can be lowered, where the torsion bar will not exert any force on it. At this point, all of the spring will be taken out of the torsion bar so that there is no tension at all on the trailing arm/radius arm assembly. You may have to use trial and error, and raise and lower the rear trailing arm a few times to find the right height where there will be no tension from the torsion bar. It's important to relieve any tension on the radius arm before you disconnect the bolts that attach it to the trailing arm. Otherwise, the radius arm may spring back violently when you remove the last bolt that attaches it to the trailing arm.
On the older cars, there are four bolts that attach the radius arm to the trailing arm. Two of these are the camber and toe adjustments and the other two attach the radius arm firmly to the trailing arm. On the later style cars with the right height adjustment screws (see Pelican Technical Article: Lowering the 911), you will need to remove the large adjustment bolt and the locking bolt as well. When there is no more tension on the radius arm, and all the bolts have been removed, you should be able to pry off the radius arm with two large screwdrivers.
Pull out the old torsion bar, being careful not to scratch the protective paint. Make sure that you mark the location of the torsion bar with respect to the radius arm, if you are planning on reinstalling it in the car again, and would like to keep the car at the same ride height. The paint plays an important role, as it prevents rust and scratches in the bar. If the bar is allowed to rust, or is scratched, then this will create a stress concentration in the bar that will decrease its strength.
If the torsion bar has broken, then the other half of the bar will be trapped in the center tube. To remove the broken half, simply remove the torsion bar on the other side of the car, and poke a long rod through the tunnel. The broken bar end should be able to be pushed out of the tunnel.
If you are planning on reusing the torsion bar, then carefully inspect it once you have it out of the car. Repaint any damaged paint with primer. The bar should be replaced if there are any splines on the ends that are damaged. Check the bar for rust and corrosion: you should replace it if you find either.
Reinstallation is straightforward. Make sure that you place the correct bar in the correct side of the car. Although the left side will fit the right side, the bars are pres-stressed from the factory to be installed on a specific side of the car. The bars are marked L or R on the ends of them, corresponding to the left and right side of the car.
Coat the bar and the splines with some lithium grease and reinstall into the car. The bar should be appropriately adjusted according to the procedures detailed in Pelican Technical Article: Lowering the 911. Make sure that you have the bar balanced against the opposite side to make sure that the car sits level. You should also have your suspension alignment realigned and adjusted after you replace your torsion bars.
This is the view after removing the torsion bar adjustment screw, the adjustment lever, and the foam seal. Sometimes it will be easy at this point to pull the torsion bar out of the a-arm. Make sure that you don't damage the splines as you pull the bar out. Also note that in the background, you can see the jack stand supporting the weight of the car underneath the cross member, not the a-arm. It's not safe to disconnect the a-arm mounting point while the car's weight is supported on it.
This photo shows the front of the a-arm when the cover/bracket are removed. The small arrow points to the dust cover that is pressed into the end of the torsion bar. This cover is about the same size as a quarter, and is made out of thin sheet metal. The plug is pressed into the end of the torsion bar cover, and needs to have a hole drilled in the center of it in order to gain enough leverage to pull it out. Be careful not to damage the torsion bar when you are drilling the hole.
In this photo, the trailing arm has been lowered to the point where the radius arm bolts can be removed, and the arm can be pried off with the help of a few large screwdrivers. This is the point where the torsion bar is no longer twisted in either direction. You can find this point by raising or lowering the rear trailing arm with the jack. Make sure that you find this point, as the radius arm will spring off of the trailing arm quite powerfully if there is still tension from the torsion bar. The yellow arrows indicate the four torsion bar cover screws (one hidden from view). The red arrows show were the rear of the radius arm mounts to the trailing arm. The two green arrows indicate the camber and toe adjustment bolts that also must be removed.
With the radius arm removed, the torsion bar can be pulled out of the torsion bar tube. Make sure that you remove the small outer access cover on the car before you try to remove the bar from the tube. You may have to remove some of the lower rocker trim on the early cars in order to remove the access cover.
This is what the radius arm looks like removed from the car. The arm has a vulcanized rubber bushing that is molded into the metal piece. The inner torsion bar cover (what you place the jack stands on) is pressed into the inside of the round bushing. Replacement bushings like the one shown in this picture are not as good as the original ones, and should only be installed if the original bushing is deteriorated.