The transmission system on the Porsche Boxster Series consists of a six-speed manual gearbox with a dual mass flywheel to reduce engine noise. The transmission can operate either in full automatic or via driver-commanded gear changes. When problems arise within the Boxster’s transmission system, the problem can stem from several possible causes. Remedies will target the parts relevant to the occurring symptoms.
Problems of the Transmission Fluid
If you have trouble shifting your Porsche Boxster, check your transmission fluid levels. Keeping the transmission and integrated differential lubricated plays a pivotal role in preventing wear on the rings and sliders involved in shifting smoothly. The transmission fluid will also help abate temperature increases in the transmission. A general rule of thumb for transmission for Boxsters calls for a fluid change every 30,000 miles or every two years, depending on use. You must jack up all four corners of the vehicle. Changing your transmission fluid will involve changing both your automatic transmission fluid and the differential transmission fluid, which uses the same oil as a manual transmission. (The transmission fluid is specially designated for the Boxster; do not mix or match it with other types of transmission fluid.) Transmission gear oil with the specification SAE 75W90 should work as a lubricant for the differential of a Boxster.
Problem of the Mounts
One of the more common transmission problems you will face with a Porsche Boxster involves the wearing down of the rubber on the transmission mounts that separate the drivetrain from the rest of the chassis. As the mounts become older and more brittle, they will not be able to hold the drivetrain securely during shifting. Telltale signs that you need to replace these mounts include cracks in the mounts (regardless of the number of miles on the car), as well as leaking from the mounts, as your Boxster has a hydraulic system. Replacement Porsche Boxster mounts are expensive at about $250, but they do include a triangular bracket. To secure your drivetrain completely, replace the front motor mounts at the same time you replace the transmission mounts.
Problems of the Differential
Several Porsche Boxster transmission problems may originate from the differential — part of the transmission in what is together called the transaxle. Leaking from the driveshaft could likely stem from differential seals that have deteriorated. When replacing these seals, also check the differential’s carrier bearings to find out whether you must replace them as well. If you experience high-pitched whining or grinding noises that replacing the wheel bearings or CV joints does not alleviate, the sounds may stem from worn carrier bearings. Replace these preferably when the transmission is out of the car — during a clutch or engine job, for example — as it will facilitate these tasks.
Problems of the Suspension
If the suspension system is creating problems for your Boxster’s transmission, some common items to replace involve the Constant Velocity joints, boots and axle that connect the wheels to the transmission. These components take the brunt of abuse and tend to wear down after 100,000 miles. You will know you have a suspension problem when you hear clunking sounds coming from the rear axle while driving. You have the option of replacing either the inner CV joints or the entire axle system. The new axle will include the outer CV joint as well as inner joint, along with the boots or coverings that protect these joints. If you are only replacing the inner joints, lubricate them thoroughly.
Problems of the Clutch
If the hydraulic clutch engagement system in your Porsche Boxster fails, you may experience the following symptoms: leaking the slave or master cylinder, a spongy feeling to the clutch pedal and grinding during gear shifting. Start with checking or replacing the slave cylinder, then do the same for the master cylinder an bleed the brakes. If the clutch problem is more serious, you may have to replace the entire clutch assembly. Warning signs of clutch assembly failure include spongy pedals, excessive free play, grinding or changing noises when you press the pedal and slippage of the clutch when you do not depress the pedal. City driving will tend to produce these problems more often than highway driving and may call for clutch replacement at 30,000 miles.