Following recent negative reports about Tesla Model S drive unit reliability, Tesla has increased the Model S drive unit warranty to match that of the battery pack. That means the 85 kWh Model S, the most popular model by far, now has an 8 year, infinite mile warranty on both the battery pack and drive unit. There is also no limit on the number of owners during the warranty period. Moreover, the warranty extension will apply retroactively to all Model S vehicles ever produced.
The drive unit is now covered under the same provisions as the existing battery warranty, so owners with an 85 kWh battery will benefit from eight years of coverage with no mileage restrictions, while 60 kWh owners have up to 125,000 miles.
The drive unit issue, described as a grinding or “milling” noise that increases over time, was picked up by Motor Trend Magazine who reported that they had to have a drive unit replaced in their Model S. The issue really hit the headlines when Edmunds reported they are on their 4th drive train.
Tesla had transmission issues with the Roadster. The two-speed transmission designed for the Roadster by Magna International proved not to be durable so in 2008 Tesla Motors selected BorgWarner for the production of a single-speed gearbox.
While the single speed BorgWarner fixed gear (8.27:1 ratio) transmission in the Roadster was reliable, anecdotal evidence suggests the BorgWarner eGearDrives supplied for the the Ford eTransit Connect has quite a high failure rate. The source of the current 9.73:1 gearbox in the Model S is not known but because the transmission housing is integrated with the AC Induction motor enclosure and without knowing which components have failed, it's too early to attribute blame for the design fault.
When you take into consideration how common transmission failures are within the automotive industry and how high performance the Tesla Model S is, it's not so surprising to find the powertrain needs some mechanical debugging. For example, Subaru have been making the Impreza WRX since 1992 yet after two decades in production this high performance model is still prone to transmission failure. The only sure way to avoid mechanical transmission issues / losses is to delete all gearing and differentials from the vehicle by using direct drive wheel motors.
The standard warranty for Tesla Model S is 4 year, 50,000 mile (80,000 km). In April last year Tesla announced an unlimited "no-fault" battery warranty. Elon Musk says that in hindsight, the infinite warranty should have been policy for the powertrain from the beginning of the Model S program. If they truly believe that electric motors are fundamentally more reliable than gasoline engines, with far fewer moving parts and no oily residue or combustion byproducts to gum up the works, then the warranty policy should reflect that.