Transmission Problems on a Porsche 928
A 1987 Porsche 928 is an esteemed classic car, designed to go the distance. However, like any vehicle it may eventually experience transmission problems that compromise its longevity.
Most problems can be quickly remedied by professional technicians. Regular services (like transmission fluid and coolant changes every 60,000 miles or four years) will keep your 928 running smoothly and help ensure its long term health.
Inadequate Fluid Levels
Porsche 928s use an ATF (automatic transmission fluid) fluid to lubricate their automatic transmission, which should be changed per manual to maintain optimal transmission performance and reduce wear-and-tear damage. When low on fluid levels, it can affect transmission operation as well as cause other vehicle-related problems.
Fill your transmission system with ATF and tighten up its drain plug; these products can be found at most auto parts stores.
One of the most frequent transmission problems is a defective modulator. A vacuum modulator provides feedback from your engine about when and how hard or quickly to shift your car, with more vacuum resulting in smoother shifting action and quicker shifting times. When these regulators malfunction they may leak automatic transmission fluid directly into your intake tract, leading to smokey engine conditions.
To test a vacuum modulator, shut the motor off and remove the blue/black vacuum check valve on the front of your vehicle. Use a Mity-Vac or similar vacuum pump to test for free flow in both directions of your hose using free flow indicator rods; if no free flow exists either direction then your modulator needs replacing immediately. To install the new modulator, you will require a mirror and bright light that allows for clear viewing inside of the intake manifold. Additionally, someone must assist you with taking out and installing the old modulator before installing a new one. A modulator can be fairly inexpensive; you just need to purchase it from your local Porsche dealer. They typically come in kits that include adapters for connecting it to your vehicle. Also be sure to replace the o-ring on your new modulator to ensure proper sealing; these parts should come included or can be found at most automotive stores with part number 003-095-023 available from most sources. Vacuum modulators can be found located under your car as small black boxes.
Fluid Leaks
No matter the fluid type used, any leaks must be taken seriously. Not only could leaking transmissions reduce vehicle efficiency significantly but can be very expensive to repair. If any signs of leakage, including burning smells emanating from underneath your car, become apparent it is crucial that they receive immediate medical attention.
The Porsche 928 was its inaugural front-engine, water-cooled V8 car produced since its introduction into production 18 years prior. Production continued without major design alterations for 18 years without major performance updates due to limited development funds due to an ongoing management crisis and diminished cash reserves.
Notable upgrades were to the engine and transmission. A 4.5 L engine originally displaces at 240 horsepower in Europe while 219 horses (177kW, 222-PS) can now be produced due to a higher 10.0:1 compression ratio used on North American models. Furthermore, transmission was upgraded as well with torque tubes strengthened and single plate clutch replaced on S4 models.
Attaining maximum power was made possible through a larger-diameter brake disc and more efficient ABS system featuring variable-speed electric fans instead of an engine-driven unit. Also new were larger fuel tanks, upgraded interior finishes and materials, and an electric heater which shut off automatically during high speed driving to reduce drag.
1990 model year saw two major advancements that would further solidify the 928’s reputation as an enthusiast car: standard dual air bags were clearly noticeable; an innovation from recently deceased 959, however, included an adaptive variable-ratio limited slip differential capable of locking between 0-100 percent according to wheel speed sensors – this helped compensate for variations in traction loss, brake and steering loads, road conditions etc. Additionally a digital trip computer and an RDK tire pressure monitoring system were added.
Vacuum Modulator
The transmission shifts automatically with input from the engine and is controlled by a vacuum modulator valve, a canister-shaped device with diaphragms and calibrated springs that measure load. As more load is sensed by this spring-loaded diaphragm valve, its pressure rises as does its force to push against transmission fluid causing it to shift automatically.
This valve works in an automatic and gradual fashion to open and close communication between inlet port (41) and outlet port (42), altering hydraulic fluid pressure on transmission clutches. As soon as a car decelerates, its throttle opens allowing vacuum pressure to exert itself by gradually closing communication between inlet port (41) and outlet port (42) thus decreasing hydraulic pressure on transmission clutches.
In 1990, the 928 saw several upgrades including a new rear spoiler and more compact alternator. A lower final drive ratio made the car better suited to street driving while an integrated battery box and relocation of exhaust manifolds reduced weight considerably.
Significant innovations included the installation of a variable-ratio limited slip differential that operated like a multidisc hydraulic clutch but utilized electronic controls linked to wheel speed sensors for its lockup rate adjustment from 0%-100% depending on sensor input; its aim was to match engine torque with traction demands.
Variable-ratio diffs present one major obstacle: their actuator can become malfunctioning. This could lead to loss of control at high speeds and result in accidents or engine failure, and possibly cause overheated brakes which overheat and eventually burn out – however fortunately replacement actuators can easily be purchased and fitted onto vehicles.
Solenoid
Solenoid controls the amount of fluid fed to clutches during each shift cycle, so if one fails it could result in too little fluid getting to them and cause a spongy engine feel as clutches don’t engage correctly with each other. This issue is among the most commonly experienced transmission issues on a Porsche 928 and will often result in smoke coming out from under the car as well as power reduction and sudden speed drops.
An automobile with proper maintenance should last 150,000 miles on its solenoid, and can easily be changed out if its fluid levels become low or oil leaks out. However, it should be remembered that solenoids can fail without warning at any time and the symptoms mimic low transmission fluid levels – with clutch not engaging and engine stalling potentially becoming hazardous hazards.
Your 1994 porsche 928 GTSS transmission connects your engine’s output directly to a driveshaft that turns the wheels, so any issues with its performance could render your car nearly undriveable and make regular preventative maintenance an essential requirement for longevity. For optimal performance and optimal longevity of transmission systems in cars such as this one it is recommended that regular preventative maintenance services be conducted regularly to maintain them properly.
If you are considering purchasing a used Porsche 928, ensure it comes complete with a detailed service history. These vehicles don’t come cheap so spending your money on one that needs extensive repairs or has been involved in an accident would only end up costing more in repairs later. Furthermore, an extensive inspection should take place prior to making a decision so that you know exactly what awaits you when buying.
The Porsche 928 marked an important entry into the market when it first debuted and remains highly-rated as an exclusive sports car today. Intended to appeal to a wider market than its predecessor, it successfully managed to pull in enthusiasts who would otherwise remain faithful to other manufacturers’ offerings. Over its 17 year production run, there were several updates to its engine and gearbox; including adding multi-link rear axle for reduced understeer.