Front brake disks - should they get hot?

I think the most likely cause of binding brakes is that the disk (or rotor as you say stateside) assembly is not floating properly laterally on its sliders. I have had this problem with my Prius when it was still under warranty and the dealer fixed it without charge under the warranty.

It is very easy to fix, just a matter of freeing up and lubricating properly. If they do not slide, one side of the pads can be pressed against the disks even when the brakes are not in use and so the brakes never properly release.

Get your dealer to jack up the car and demonstrate to you that the wheels spin freely. That way there can be no argument from them if they do not the brakes are binding. Tests when the dealer is absent on mountains etc. may not cut it with the dealer, esp if the dealer is not as honest as you might wish.

 

Umm ... whether it's called the disk or the rotor, that round thing ought not be floating laterally at all. The caliper, yes. (Do you guys also call it caliper there?)

Yes, the slide pins are the easiest test to conduct, because all you need do is loosen two small bolts, flip the caliper upward, and make sure the pins slide easily in and out. This is worth doing, say, every tire rotation, because usually you will find that the grease has begun to solidify, and simply working the pins in and out a few times will get them moving freely again. While the caliper is flipped up, you also have an excellent view to measure your remaining pad thickness, and see the condition of both faces of the disk (or rotor).* And carefully inspect the rubber boot around the piston; any nicks or tears will have allowed corrosion to begin around the piston, which also needs to move freely.

Now, if you have checked the slide pins and you find you still have heated rotors after a no-braking drag test, you may face the slightly more involved job of a caliper rebuild. The rebuild kit is not expensive, even going genuine Toyota from the dealer, and it contains the parts needed for two calipers and even a little wodge of the proper grease.

I've found the "does wheel spin freely" test, especially in front, to be not very useful in identifying moderate brake drag. Severe drag, yes, you'll be able to tell if the wheel is very difficult to turn by hand and the friction sound is especially loud. But otherwise, well, the front wheels never feel terribly free-spinning, just because of resistance within the transaxle, and it is normal for disk brake pads to be in light contact with the disk (or rotor) even when released, so a light friction sound is never entirely absent. The test for rotor heating in a real drive is more effective in showing that you really have any drag problem resolved.

Now, the difficulty of communicating such results to a dealer may be a real thing, and is one of the points in favor of biting the bullet and learning to DIY brakes.

-Chap

* If the rotor faces, especially the inboard face, have begun the 'rust encroaches from inner and outer edges' pattern, and it is not very deep or well advanced, this is a fine time to slip the rotors off and spend some quality time with a piece of 150 grit wetordry sandpaper. Do mark the position of rotor on hub before slipping it off; putting it back on in a different position can lead to a very measurable increase in runout.

 

Yes, by saying "the disk (or rotor as you say stateside) assembly", I did mean the caliper. Sorry that wasn't clear.

Couldn't swear to it, but suspect that if both front wheels are raised off the ground, they should be free to rotate and the transaxle will cause the other wheel to rotate rather than offer much resistance.

 

That is what happens, but you've still got the drag of several seals and the differential, and the mass of the other wheel. It's a noticeable difference compared to the rears, which you pretty much can just spin to get a sense of how free they are. You can make a very rough judgement of the fronts that way, but a bit of driving and temperature check will tell you more.

-Chap