Brake Rotors heating unevenly?

That doesn't sound right, way too hot. One question though: is this a US spec 2nd gen Prius? I thought they had drum brakes on the rear?

 

Probably very slightly, but not to this extent. If one brake is significantly hotter, then it is likely from friction caused by the brake not releasing. On rear brakes, this can be due to a parking brake not properly releasing.

Did you use the parking brake between the 10 mile normal drive and this event?

 

Have you informed you parents what you think of the quality of work of their preferred mechanic yet?

 

That's an awesome mechanic if they're willing to give a refund on the work...

And yes their would be a pulling if one brake wasn't sticking more than the other. And anyone who hasn't yet burned their finger touching a mechanically sound brake rotor that was recently used needs to learn that lesson ASAP. Whereas, if you had a sticking break pad or other damage and it was pulling and you touched that rotor for a 1/10 of a second it wouldn't be a simple 1st degree burn, it's be 2nd degree with oozing and swelling.

 

You typically won't feel a pull from a lightly dragging rear brake. You may feel a pull with a significantly dragging front brake, since this is on a steering tire.

If the brake is only dragging slightly, it can get quite hot without affecting mpg significantly. If the brakes were not so hot that they smoked or smelled bad, a disassembly when they are cool may not show any evidence of heating. If the brake gets really hot, it can heat the drum or rotor to such an extent that it discolors the metal, or can permanently damage the brake friction material, or melt the grease in the wheel hub, etc.

Edit - road car brakes are not designed for continuous heating. Brakes generate heat through friction, and the heat is dissipated to the atmosphere, typically at a much lower rate than generated. When you apply your brakes, they heat up quickly, then you release the brakes and the heat dissipates and the brakes cool off. If you ride your brakes down a long hill, for example, the heat is generated much more quickly than it can dissipate, and temperature builds up to a point where the brakes become ineffective or you boil the brake fluid away and lose your brakes. When you have a brake dragging, the amount of heating is proportional to the amount of drag and the speed of the car.

 

And that's why regenerative braking is so smart... Rather than dissipating that braking energy as heat, it stores it as electricity for future use.

 

Most drum brakes do have automatic slack adjusters, so that's not far fetched. When you install new drum brake shoes, you use a tool to manually adjust the slack to get it correct to start. If they overtightened it, it could cause drag.

One of the Gen 2 experts can confirm if that is the case on that model.

 

Yes, there's an adjuster in the rear drum brakes. It ought to be pretty familiar to just about any mechanic though; there are only about two designs for that type of adjuster, and they've both been around about forever.

 

Here's 2nd gen brake info, might shed some light on the auto adjuster, or whatever.