Last month we had a new customer bring in his 2005 Subaru Legacy GT Limited because he was hearing a rotational noise while driving.
During our test-drive, we heard a noise from the left rear wheel bearing. After putting the car on the lift, we verified that the noise was indeed coming from that bearing. We also found that two of the lug studs were broken on the left rear wheel hub and one was broken on the right rear wheel hub.
After telling the customer what we found, he told me this was not the first time he had work done to the left rear wheel bearing assembly. He sent me the records from work done by the other repair shop, which I found amazing.
In August 2011 at 77,377 miles, the other shop replaced the left rear wheel bearing assembly. Approximately one week and 500 miles later, the customer felt a vibration and discovered that three of the five lug nuts of the left rear wheel were loose. That shop replaced the lug nuts and checked the lug studs the next month. Nearly a year later at 89,918 miles, the car had a brake job that included replacing the front and rear brake pads and resurfacing the rotors. Later that August, after another 828 miles, the left rear lug nuts came loose again. The shop checked the left rear lug nuts and studs, and retorqued the lug nuts.
In September 2015 at 105,783 miles, the car went in for its timing belt, and the shop found that one of the lug studs was broken on the left rear wheel. All of the lug nuts and lug studs on the left rear wheel bearing assembly were replaced.
The car got to me in March of this year, and that’s when we found the worn left rear wheel bearing assembly and the two broken lug studs.
Diagnosing the problem
After reading through the customer’s records, I tried to figure out what in the heck was going on. While we were taking the left rear wheel off, one more lug stud broke. When we looked closely at the lug stud, we saw rust in the fracture line. Once the wheel and the brake rotor were off, I had a pretty good idea of what was going on. There was a large amount of rust and corrosion on the hub surface, on the front and back of the brake rotor and on the back of the wheel where it mounts to the brake rotor. When a wheel goes through a puddle, it picks up water and dirt on the inside of the wheel. When the wheel is spinning, centrifugal force sprays water and dirt all over the wheel, some of which may get stuck in the wheel, brake rotor and hub.
I came to the conclusion that the dirt and rust trapped among the hub face, rotor and wheel were causing a pressure differential in the lug studs. Every time the wheel made a rotation, it would push and pull on each lug stud differently, eventually fatiguing the stud and breaking it.
We spent a good amount of time cleaning the back of the wheels and the brake rotors. The wheel bearing assembly comes with a new hub, so we did not have to clean it. After cleaning the brake rotors, there was still a large amount of pitting due to rust. I told the customer that unless we replace the rotors, it’s likely the problem will arise again. I also wanted to replace the wheels, but it was cost prohibitive.
After performing all the cleaning, replacing the left rear hub assembly and one of the right rear lug studs, installing new rear lug nuts and replacing the rear brake rotors with pads, we torqued the lug nuts. We asked the customer to come back after 500 miles so that we could check the lug nut torque, and all was fine.
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