How hot is normal for front brakes?

[first-things-first]

Hi

I have standard ATE brakes on my diesel ZT auto.

I noticed recently after a good few hundred mile trip that there was quite some heat coming off the brakes. Licking my finger I touched the disk. It sizzled and the heat was quite fierce.

After letting them cool down, the first drive afterwards meant that the brakes were spongy on first application, but then fine afterwards.

Next day after making a short trip (around 4 miles) I checked the disks and again my spittle sizzled on the disk. I hadn't braked exceptionally hard.

Therefore only conclusion is that brakes were binding or calipers not moving freely.

So, I stripped them, cleaned them of dust build up, used degreaser, copper slipped pads (already had some which I cleaned off before re-applying). I also cleaned up the slider pins which were dry but had a bit of caked on brake dust. Then I used silicone grease to lubricate before re-fitting and torqueing back up.

Now, my brakes feel smoother and a little less grabby when coming to a stop. They were never bad before and had plenty of stopping power.

A short journey and check brakes - much better - very warm to the touch with a wet finger, but not roasting, sizzling hot.

On a longer journey today I noticed the brakes were quite sizzling hot again when I came home (spittle sizzled on disk) - not as bad as before, though.

Thanks for reading this far. :}

Is this normal heat? I noticed before on the long run that I had a grumbling type noise after some time. This is what alerted me to the issue. Bearings seem fine to me and not rough.

Back brakes are fine.

Cheers

Andrew

[T-Cut]

Brakes convert kinetic energy into heat. That's how the collossal energy dissipation of a braking vehicle is managed. This makes the discs hot - very hot. And you don't have to be travelling very fast and then stop, to get them untouchable.

The higher the speed, the more energy has to be converted into heat. A rally car for example can get the discs cherry red, so they glow in the dark.

TC

[first-things-first]

Thanks T-Cut for piece of mind.

I suppose you notice these more as the cars are quite heavy and therefore more punishing on the front brakes.

A binding brake will cause more unwanted friction (when not braking) and therefore heat.