If you mean the car is stopped and it's shaking, that's due to an engine misfire, or a collapsed engine mount is allowing metal parts to touch each other and transmit normal engine vibration into the body. If the shaking occurs as you're slowing down with the brakes applied, and you feel it in the brake pedal or steering wheel, that's due to a warped brake rotor. Standard practice is to take a light cut with a brake lathe to true up the two front rotors. If the pads are worn to the point of replacement, machining the rotors is a part of that brake service.
For some time now brake rotors have been made very thin to save weight. Often that means they're too worn to be machined, and they have to be replaced. All manufacturers publish a minimum legal thickness their rotors can be machined to, (the "machine to" spec), and a slightly thinner minimum they can be allowed to wear to, (called the "discard" spec). As long as both rotors will still be above the machine-to spec after they've been machined and trued up, they can be reused.
The good news is today replacement rotors are uncommonly inexpensive compared to 30 years ago. Given the mechanic's time and the cost of consumables such as cutting bits, it can be less expensive to just start out with a pair of replacement rotors.
One thing to be aware of is with new rotors, they commonly warp the same way as your current rotors, but the shop that does the brake job will take care of that, again, with a light machining. When we make parts out of cast iron, we set them aside for 90 days to "age" before they get their final machining. Most new rotors today come from China. There's nothing wrong with their quality, but they don't let them age first. That cast them, machine them, pack them, and ship them, then they age on your car. Once they warp a little and are machined, you won't have the same problem again.
Here's a link to an article that explains it better:
https://www.2carpros.com/articles/symptoms-of-a-bad-brake-rotor
Thursday, September 25th, 2025 AT 4:10 PM
