The CV axle shaft seal is a rubber or metal seal that is located where a vehicle’s CV axle meets the transmission, differential, or transfer case. It prevents fluid from leaking out of the transmission or differential housing as the CV axle rotates when the vehicle is in motion. In some vehicles, the axle shaft seal also helps to keep the axle shaft in proper alignment with the transmission.
CV axle shaft seals are usually located along the surface where the CV axle enters the transmission for front-wheel-drive (FWD) vehicles, or at the differential for rear-wheel-drive (RWD) vehicles. They serve a simple yet important purpose, and when they fail, they can cause problems for the vehicle that will need to be serviced. Usually, when the CV axle shaft seals fail, the vehicle will produce a few symptoms that can notify the driver that there may be a problem.
1. Signs of leakage around the seal
One of the first signs that a CV axle shaft may need to be replaced is the presence of leaks. As the seal begins to wear, it may begin to leak slowly and cover the area immediately around the seal with a thin layer of gear oil or transmission fluid. A small or minor leak will leave a thin layer, while a larger leak will leave a noticeably greater amount.
2. Puddles of fluid
One of the most common and most noticeable signs of a problem with one of the vehicle’s axle shaft seals is a puddle of fluid. When the axle shaft seal fails, gear oil or transmission fluid may leak from the transmission or differential. Depending on the location of the seal and the severity of the leak, a bad seal may sometimes cause the differential or transmission fluid to leak out entirely. A leaky seal should be addressed as soon as possible, as a transmission or differential low on fluid because of a leak can quickly become damaged by overheating.
3. Axle shaft pops out
Another symptom of a potential problem with the CV axle shaft seal is the axle constantly popping out. In some vehicles, the axle shaft seal not only seals the transmission and axle mating surfaces, but it also acts as support for the CV axle. If the seal becomes damaged in any way, it may not only begin to leak, but it may also no longer be able to support the axle correctly and may pop out or come loose as a result. A shaft that has come loose would require the shaft to be correctly installed before the vehicle can drive again.
Because the CV axle shaft seals are what keep the fluid in the transmission and differential, fluid may begin to leak when they fail, which will put the transmission or differential in danger of overheating and becoming damaged. For this reason, if you notice that your CV axle seal is leaking or suspect that it may need to be replaced, have a professional technician, such as one from YourMechanic, determine what the correct course of action may be. They will be able to replace the CV axle shaft seal for you if needed or make any other repairs as necessary.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Axle Shaft Seal and was authored by Ed Ruelas.