Why does the Subaru 5AT transmission fail?

[McJoy]

There are three main reasons for Subaru 5AT transmission failures. Aging or damaged oil seals: Transmission oil leakage issues are primarily found in half-shaft leaks, front oil seal leaks, and front differential leaks. Chain and pressure cylinder wear: CVT transmissions are prone to chain and pressure cylinder failures after the vehicle has traveled a certain mileage. Subaru Forester transmissions may exhibit abnormal noises, slipping, shaking, slow acceleration, and even severe consequences like inability to move. Clutch failure: Clutch wear occurs under normal operating conditions. However, when the transmission experiences high internal temperatures, the clutch plates inside the clutch can overheat and burn out, leading to issues such as slipping, shaking, gear disengagement, and failure to accelerate when pressing the accelerator.

[VonSilas]

I've driven several Subarus, and their 5AT transmission failures are indeed a headache. The most common issues occur with the valve body and solenoids - these small components controlling hydraulic pressure are particularly prone to sticking or wearing out. Especially after 70,000-80,000 kilometers, you can always feel jerking during gear shifts, and sometimes sudden freewheeling occurs. The torque converter's lock-up clutch is another trouble spot, with older vehicles frequently experiencing reduced power transmission efficiency. Electronic control module failures are even more troublesome, as sensor false alarms directly cause shifting logic confusion. The worst case I've seen was burnt clutch plates, mostly caused by owners not changing transmission fluid for five or six years. I recommend fluid testing every 40,000 kilometers, and immediately checking the hydraulic system if shifting becomes rough.

[OAyla]

The issues with the Subaru 5AT are primarily related to its structural characteristics. This transmission uses a planetary gear set, with the multi-plate clutch in the middle being the weak point. The friction plates are prone to fatigue and breakage under high temperatures, especially during frequent hard acceleration. The oil circuit design also has inherent risks—the valve body's oil passages are too narrow, making them susceptible to clogging with even minor sludge buildup, leading to unstable oil pressure during the 3rd to 4th gear shift. During one disassembly, it was found that worn bearing supports in older vehicles can cause excessive axial clearance, resulting in imprecise gear engagement. It's recommended to replace all seals before reaching 100,000 kilometers and to use manual mode in city driving to avoid repeated low-gear shifts. The solenoid valves have a high failure rate, which can be mitigated by directly installing additional heat sinks.

[EvaLynn]

Subaru 5AT failures are concentrated in several areas: valve body sticking causes delayed or jerky gear shifts, solenoid valve failures lead to incorrect gear switching, and oil pump wear results in insufficient oil pressure. Most issues appear after exceeding 100,000 kilometers, related to the factory's choice of sealing materials. Some batch owners report shift shocks during the first 15 minutes of cold starts in sub-zero temperatures - this is actually a torque converter lock-up mechanism issue. I've handled several cases where cleaning the valve plate provided temporary relief. Worn mechanical shafts produce metallic noises, most noticeable during deceleration. It's recommended to replace with upgraded pressure solenoid valves at 80,000 kilometers.