OEM Wing Hydraulics
IF the wing is lower on one side,
OR there is hydraulic fluid on the rams or engine lid gasket,
OR the “Failure Spoiler Control” warning is displayed:
THE FACTORY HYDRAULIC MECHANISM IS FAILING.
“NO MORE HYDRAULICS!”
The hydraulic wing lift system can never be fixed permanently.
Factory Wing Mechanism Background
The water cooled Turbo’s rear wing is not a cosmetic part, it is a functional part. For the first time, the Turbo lineup employed a 2-piece spoiler wing assembly built into the rear deck lid. This is the same system as utilized in the Carrera GT supercar. The upper wing is an inverted airfoil. The same principle that lifts an airplane up is used to push the back end of the Turbo down. Down-force climbs as the car reaches top speed, down-force pressure on the rear axle builds up to 20 Lbf [90 N].
The 996 Turbo coupe’s inverted wing extends 2.4″ [60 mm] once the vehicle reaches 74 MPH [120 km/h]. As the cabriolet top creates additional air turbulence at the rear deck lid, the wing was extended even higher to 3.2″ [80 mm] in order to create the same down force as the coupe. The wing retracts flush onto the deck lid spoiler once the vehicle slows to 37 MPH [60 km/h]. The 5th generation 996 Turbo has a minimal lift at the front axle with a cAF = 0.02 and very slight rear axle down-force of cAR = -0.01.
For the 6th generation 997 Turbo, the 2-piece spoiler wing extends 1.4″ [35 mm] for the coupe or 2.6″ [65 mm] for the cabriolet. The 997 Turbo’s wing area increased by 23% over the 996 Turbo wing, with a down force of 61 Lbf [273 N] at 194 MPH [310 km/h]. The water-cooled Turbos took rear down force to a whole new level!
The inverted airfoil design by Porsche® is covered by patents for an extended wing and the attachment device:
However, the “permanently sealed” hydraulic system to raise and lower the wing was designed and supplied to Porsche® by an outside firm near Nuremberg, Germany starting in 1999. It is likely that Porsche® drafted a specification for the Turbo’s wing extension requirements – then searched for a nearby firm to provide it.
The question is why did Porsche® choose such a complex, yet inherently faulty design – perhaps there was time pressure to get something working adequately enough, in order to launch the 5th generation water cooled Turbo for display in 1999. This was the first time such an electro-hydraulic mechanism was used by Porsche®. The 964, 993, 996 and 997 Carrera retractable wings all utilize complex electro-mechanical actuation devices. Only the Carrera GT, 996 Turbo and 997 Turbo have the electro-hydraulic mechanism.
Carrera GT – Factory Hydraulic Wing Lift Mechanism at Rennkit
(before conversion to the all-electric eRam system)
How Does the Hydraulic Wing System Work?
All too often Turbo owners experience a broken or malfunctioning wing or leaks under the engine lid from the rams or the motor module.
Operation: The heart of the system consists of an electro-hydraulic drive module with 12v electric motor and jack screw along with two separately driven plungers or syringes. The electric motor spins a jack screw in one direction or the other, which pushes or pulls two plungers via a threaded plastic block. The two plungers force Pentosin fluid through hoses into two spring tensioned hydraulic cylinders (rams) connected to the wing. Only the right side ram has a set of “extended” and “retracted” microswitches. The switches send a signal back to the instrument cluster ECU (computer controller) to turn off the 12v drive motor. The computer tracks the time it takes for the wing to deploy. If it takes too long – a SPOILER FAILURE warning alarm is displayed at the dash. The SPOILER FAILURE warning is also activated if only the right side ram never extends fully or retracts fully. The left side is not monitored in the Turbo – it is monitored in the Carrera GT. Upon failure, the only protection to keep the motor from burning up is a thermister overheat fuse near the motor commutator. Strangely, discrete electrical failure protection is missing, as one fuse in the panel is for the entire back lid electrical; hydraulic system, light, e-latch, etc.
Why Does the 996 / 997 Turbo Hydraulic Wing System Fail?
There are several root cause failures identified. All are likely now, given the age of these vehicles. The entire mechanism sits directly over the hot engine. The entire hydraulic system gets very hot when the car is shut down, baking and accelerating deterioration of all components. Of course part of the system is exposed to the elements with the wing up. We are finding a lot of dirt and moisture inside the ram cylinder cavities.
- Starting with the motorized plunger device, a black plastic plunger block is often broken, usually due to wear, age, heat or malfunction of a limit switch and motor over-run:
2. The white plastic end piece for the plunger cylinder is often broken, usually due to wear, age, heat or malfunction of a limit switch and motor over-run:
3. There are several potentially leaky seals and multiple o-rings in the plunger system itself – it has been found that the O-rings can flat spot – causing leakage of the corrosive Pentosin PS fluid (this happened to me):
4. The 12v motor can overheat and self-destruct due to dirt, heat, wear, age or limit switch failure (this happened to me):
5. Each hydraulic plunger connects to a high tension spring loaded hydraulic ram via high pressure tubing and banjo fittings. The tubing and banjo fittings are notorious for leaking – loosening up with heat cycling over time (this happened to me):
6. Outer cylinder seals are very delicate, and can become brittle, crack and loose their pliability due to dirt, age, wear, sunlight, heat and other environmental factors. The seal is no longer maintained, allowing moisture and dirt into the inner cylinder area wetting the brass plunger cylinder and high tension steel spring, causing deterioration, rust and failure.
7. The outer cylinders are easily damaged during prior repairs or by other means. This allows dirt and moisture to enter the inner cavity with every stroke. The inner cavity is where the narrow brass hydraulic cylinder and spring reside.
8. A high tension spring within each ram is designed to force the wing to lower, should there be a failure. But in reality – it may not accomplish this as one side may fail – but not the other. It is not simply 1 chance of failure, but 3, as the left ram circuit, the right ram circuit or both will fail. Often one side of the wing lowers, the other remains up! The actual piston and cylinder that raise and lower the wing are quite a bit SMALLER than the surrounding chrome outer cylinder, about the diameter of a pencil!
9. Whenever the wing is extended, the steel springs are compressed under great tension. This exacerbates failure and leakage at every joint and seal – since the entire hydraulic system (both rams, fittings, hoses and both motor plungers) experiences excessive hydraulic back pressure. The steel springs often break due to age fatigue or rust corrosion:
10. Each hydraulic ram has a non-rebuildable factory sealed brass inner cylinder and piston. The inner seals often end up leaking as they become flat spotted around the perimeter, brittle and lose compliance to the barrel with age. As shown below, this inner cylinder was cut apart, new seals installed, aligned, hardware store plumbing fittings installed, then all soldered back together. It is difficult not to bend or damage the soft brass tube – or to keep it round during cutting, heating and soldering. Ultimately the heat from soldering the assembly back together can damage new elastomer o-ring and support seals. Often rebuild services don’t bother cutting the plungers to renew the seals. Wonder how long this one with hardware store fittings will last?
11. Unfortunately, each hydraulic ram is actuated by a separate hydraulic circuit. If either circuit fails, the wing is crooked and inoperable. This is indicated by a cocked wing, warped engine lid seal or a wet cap on one of the hydraulic rams.
12. There is a set of two very tiny microswitches on the passenger side ram. They have very intricate and delicate inner workings that easily malfunction. These delicate little microswitches control operation and direction of the hydraulic motor and spoiler failure warning function. There is no fail safe, over-ride or pop off valve for the hydraulic circuit. The microswitches are the only signal to the ECU for switching off the hydraulic motor. They easily fail, and this in turn causes breakage, over pressurization, leaks or other problems. Oddly, the microswitches are only on ONE ram – begging the question, what prevents motor operation if the other circuit leaks and fails? These delicate little switches coupled with hydraulic fluid loss are a major reason for the dreaded SPOILER FAILURE warning:
Two More Causes that Accelerate OEM System Failure:
13. Heat: The hydraulic system sits directly above the engine in the hottest part of the car, which promotes accelerated aging and breakdown of all components. We are hearing that cars in hotter climates, once having failed, continue to fail regularly because of excessive heat. Test labs use the Arrhenius method for testing materials or systems to failure under high heat. Why? Because mechanical and electrical devices fail faster at higher temperatures! In effect, our 996 and 997 Turbos are conducting a high temperature experiment on the hydraulic system every time the car is driven!
14. Hydraulic Fluid Contamination: The primary contamination factor is from humidity. It may not be obvious, but water contamination from moisture in the air is picked up on the internal extended ram cavity and introduced into the Pentosin PS fluid through the seals. Water decomposes organic hydraulic fluids as well as seals and corrodes internal metal components. Water molecules can diffuse through hydraulic hoses and age seals. Contamination also comes from internal moving parts that wear. Microscopic metal particles wear the seals and adjacent metal surfaces. Being a closed system, (no dipstick, no reservoir, no drain plug) the fluid was never intended to be changed.
If you ever consider a “professional rebuild” of your hydraulic system: 1) insist they supply and wire up microswitches on BOTH rams, and 2) make sure they rebuild the ram plungers adding new o-ring and guide seals inside the permanently sealed brass cylinder units!
Don’t wait for failure – our eRam kit is easily the best value for maintaining wing operation:
A new factory replacement hydraulic system costs $2200 – $2400! Replacement by the dealer is $3000 or more ($4900 for the 997 Turbo!). The factory kit can be rebuilt or replaced, but the root cause problems will NEVER go away. It was a poor design from the beginning. THERE ARE FAR TOO MANY THINGS THAT CAN FAIL. Even “professionally rebuilding” the hydraulics can NEVER fix the design and potential problems.
Why risk corrosive Pentosin PS fluid leaks into your engine compartment or down the back bumper?
Rennkit eRam System:
Lighter / Faster / Higher / Simpler / Robust / Maintenance Free / Better Downforce
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