Factory Five Technical Alert
Shock Absorber and Coil Spring Report
Updated July 9, 2007
About a year ago we received reports from customers regarding breakage of the Bilstein brand shock absorbers included with their Factory Five Racing kits. At that time we conducted an investigation and concluded, based on the evidence at hand, that there were two factors that had caused the small number of failures of Bilstein shock absorbers.
The first cause was attributed to incorrect assembly by customers whereby the shock bodies were mounted in a way that could cause bind in the travel of the shock. We also found that there were coil springs that were made by the coil-spring manufacturer to have too many coils on them, causing them to not have sufficient travel.
Affected customers were sent an inspection and assembly procedure, along with small parts suggested by the shock absorber manufacturer to be added to help prevent any possible occurrence of shock breakage. These parts included a spacer washer and zip ties to secure the coil-spring hats to the springs. We also replaced many springs that contained “too many coils”.
Our initial technical bulletin sent to you about a year ago incorrectly listed some cases where these springs were acceptable to use. From the data we now have, we have concluded that these “additional coil” springs cannot be used in any application. Click here to view the bulletin with the procedure to check your shocks and springs.
Following the mailing and corrective action of a year ago, reports of breakage were significantly reduced, but not eliminated. After receiving additional reports recently, the team here at Factory Five Racing renewed this investigation.
Recently, a team of six mechanical engineers was assigned the task of understanding all the facts relating to shock absorber breakage and determining the corrective action needed with the only priority that of our customers safety and without regard to cost..
After an exhaustive investigation of each and every incident, examination of returned products, and analysis of contributing factors such as procedure, the variety of aftermarket parts used and their combinations, our team was able to reach some definitive conclusions. These conclusions are attached along with our action plan.
Please read the attached report. If there is anything you do not understand, please call us immediately. Do not drive your car until it has been inspected and the parts and assembly have been verified to be correct.
If your car is running the Bilstein Shocks you need to check your springs to ensure that they are not causing damage to the shock shaft. We did not receive these springs all at once, the shipments were mixed in from the manufacturer, so the date of purchase does not guarantee that you have the correct springs. The pieces in question are any front and any independent rear suspension springs, the solid rear axle coil-overs did not use these spring rates and we have had no reported failures on those units.
If you suspect you springs to fall under these guidelines we need to get them back to the factory to inspect and, in cases where they are defective, replace them. Also when looking over the returned shocks we noticed a high amount of wear and some galling on the threaded rod end on a good number of shocks, this may also be contributing extra loading on the shaft and we have included instructions on greasing these ends to make sure that they are able to rotate freely.
Checking for high coil count springs:
First check the outer diameter of the spring, if the spring measures 3 inches or smaller then you need to count the coils, if the springs are larger bore (generally 3-1/4 to 3-1/2 inches) then they are not from the batch in question. Generally these larger springs were only given with Challenge cars. If you have the smaller springs then you need to count the number of coils. Use the picture below as a reference of where and how to count. If you are using 450lb or 500lb springs and you have 12 or more coils, the springs can not be used.
Spring shown with 12.5 coils
Checking for improper spring machining:
Some of these coil springs from the same time period also have not been fully machined at the seat and have a high point where the spring contacts the hat. If your springs appear to have the correct number of coils but are not machined flat on the ends they could still put a load on the shock shaft that it is not designed to take. Inspect your spring ends based on the picture below and if they are not machined enough they can not be used.
Correct spring on left, Under-surfaced spring on right
Rod end lubrication:
In several of these instances we have seen galling of the screwed on rod end that could lead to increased friction or bind and put a side load on the shock shaft. These ends need to rotate freely and should be lubricated with a thin layer of chassis grease (or white lithium grease) to ensure that they do not bind up. While you are in the process of applying the grease take the time to check for any signs of interference between the shock and control arm. Any interference between the shock body or spring hat and the control arm can also cause overloading of the shock shaft. If there is evidence of this on the shock body or spring hat follow the procedure below for contacting us.
What to do if you have the springs in question:
If you have either high coil count springs or a large step at either end of your springs they will need to be replaced. Call Factory Five immediately at (508) 291-3443 and one of our engineers will guide you through the replacement process. Do not continue driving the car as the shocks can break suddenly and without warning.