admin Subaru fans used to appreciate these cars for their boxer engines, with a pleasant sound and a satisfying driving sensation, as well as for their symmetrical all-wheel drive. However, Subaru has used a CVT automatic transmission, one with a continuously variable ratio and no steps, for a long time on many models. This type of transmission was once considered for compact cars with less powerful engines, where drivers valued efficiency over excitement.
Subaru decided to install CVT transmissions even on the WRT STi, relaunched in January 2025, causing dissatisfaction among fans. The Germans do not appreciate this transmission either, not even on more compact models, with the Impreza’s sales figures being modest. Some fans also complain about the reduced performance of these boxes, and a mechanic in the US recently disassembled a CVT box (not the cord name TR580) to reveal its construction and show why they sometimes fail.
The gearbox came from a 2013 Subaru Outback, and after 11 years of operation, it experienced a “catastrophic” failure in 2024, as the mechanic describes it, rendering it irreparable.
Eric, the mechanic, says he is aware of the problems often discussed among owners: the first component to fail is the solenoid block because Subaru tells owners never to change the oil, unlike other brands. He says drivers should not follow Subaru’s advice and should change their oil at reasonable intervals. However, this box did not fail for this reason. The box has metal particles in the oil, makes terrible noises, and probably has a serious situation inside.
The box is unusually large for a CVT, but it was intended to be mated to Subaru’s larger engines. It also uses a relatively conventional torque converter, similar to a regular automatic transmission.
It all started with the dismantling of the converter, then the sound- and heat-insulation elements, and continued with the uncovering of the hydraulic block, which controls the box’s operation. The block and the surrounding area were in very good condition, with no visible problems. Disassembly of the gearbox’s outer body began with the rear, and there, the gears seemed intact at first glance.
Eric, the mechanic, then dismantled the gearbox’s oil pan, and here the first undeniable signs of major problems were seen. The gearbox contained not only shavings in the oil but also metal shavings and broken parts, which were collected by the magnet below. Upon closer inspection, the main chain of the box was also visible and in an unnatural position. After removing the next component, Eric had direct access to the transmission chain, which turned out to be broken. The mechanic says it’s the first time he’s seen such a massive chain break in a CVT transmission.
Next, the protective cover for the box’s active part was removed. It was covered with wear chips that appeared to have formed before the chain broke. But even after removing the cover, the source of the problems remained unclear. The mechanism intended to position the chain and change its active diameter via hydraulic pressure appeared to be in good condition. The oil pump in the box showed signs of wear and metal particles, but it seemed to be an effect rather than the primary cause of the problems in this box.
Further disassembly showed that essentially all the gears had good bearings and could be turned easily. And their condition seemed good, so the pieces of metal were from the chain, not these gears. However, inside one of the hourglass-shaped wheels, there were clear signs of chain erosion. These conical parts approach each other during operation, pressing the chain towards the outside of their diameters, and thus the transmission ratio changes continuously.
Next to it is another hourglass-shaped wheel that does the same thing, and the combination of possible diameters covers the entire range of possible ratios. All other internal components still seemed good, and the mechanic says they are built as solidly as possible and should have held up well over time with proper maintenance. The differential compartment, part of the same box, was also reached. The differential didn’t seem to have any obvious damage either.
So, the cause of the chain break remains an enigma, and the mechanic assumes it was more likely a sudden change in grip, such as skidding at high speeds on snow or ice, followed by the wheel suddenly reaching dry asphalt. Even though this box seems better built than those from Nissan or Mitsubishi, the mechanic says its failure rate remains higher than that of normal automatic boxes, and overall it would withstand less mechanical stress, as shown by the broken chain in this situation.
See everything in the video below.
