My daily car recently developed a front end shake under light braking. It was pretty slight initially be gradually got worse, to the point where sometimes I’d have to either back off the brakes or apply them harder to try and ease the shaking. Apparently this is a fairly common problem, although I’ve never personally experienced it before.
While researching the problem I learned that in most cases such a shake is cause by one of two problems, or even a combination of the two.
- Glazing or “hot spots” on the disc rotors, which are seen as alternating shiny and dull patches.
- Distorted disc rotors.
Figuring on taking the easy (and cheaper) option first I removed the rotors and sanded the surfaces on both sides to get rid of any glazing. At the same time I also sanded the pads to get rid of any glazing on them. Sadly, this didn’t have any real effect.
I don’t have a ready way to attach a dial indicator to measure runout of the rotors but carefully holding the edge of a stick so that it only just touched the rotor while it was turning it was clear that there was indeed some runout, even if it did appear pretty slight.
As the rotors only have about 30,000 km on them it was very premature to replace them. Nevertheless, due to the hours I work it was not going to be easy to be able to take the rotors to a brake shop for machining. Clearly another option was required.
By pure chance I then learned about on-site brake machining services. A bit of Googling and phoning and I had an appointment to have the rotors machined at a time and place that suited my. Best of all, this convenience would only cost me $20 more than if I took the rotors to a brake shop for machining. Of course, never having seen this type of work carried out before I was curious about the procedure.
As agreed with the technician who would carry out the work, I had the car on axle stands with the wheels removed by the time he arrived (it’s cheaper that way). The tech arrived and proceeded to attach an adaptor over the rotor on one side of the car, attached with the wheel nuts. The machine itself was next slid onto the spigot protruding from the adaptor.
It took a minute or two to ensure the cutters for both surfaces of the rotor were each just contacting the rotor face before it was ready to go. Now, with the machine’s electric motor rotating the front axle, the cutters were fed back and forth across the rotor faces, taken only as much of a cut as was required to true them up. Another very light finishing cut and that first rotor was done. The same steps were followed for the other rotor and the job was finished. Total time was about 30 to 40 minutes.
So, what was the result? Silky smooth braking with absolutely no hint of a shake or a shudder. The total cost of the job was $70. A brake shop had quoted $50 if I took the rotors to them. The convenience was worth far more than the $20 difference.
Incidentally, I have in he past had rotors machined in a shop and had to have them redone because they had not been properly mounted n the lathe, resulting in runout. This problem is eliminated by machining them while attached to the axle of the car.
In case you’re wondering how the rotors got warped in the first place, this most likely occurred when driving through a puddle of water after having used the brakes. The rotors would have been hot from the braking. The sudden cooling by the water could easily warp them. Cast iron doesn’t warp easily but the soft grades used to make rotors these days are more prone to it than the harder grades used in days gone by.
