When I was but a tot, the adults used to say that driving through a big puddle could get your brakes wet, and it was best to dry them out by pressing gently on the brake pedal for a while while continuing to drive.
I went through a couple of pretty good puddles the other day, and want to know, if this bit of automotive wisdom is still operational?
There are road signs saying ‘Now Test Your Brakes’ after fords in the UK, so I guess there’s something in it.
Back in the days of drum brakes, driving through a puddle would cause the brakes drums to fill with water. If you stepped on the brakes either while in the puddle or right there after, the brake shoes would press outward against water instead of the brake drum. The co-efficent of friction of water is very close to zero point zilch. In other words you had little to no brakes until the water had a chance to work its way out of the drum. This could take several seconds. This was the reason for the press on the pedal while driving advice. It really did make a difference.
Now a days cars have disc brakes (at least on the front, if not all four wheels) Disc brakes do not tend to trap water like drums did, and therefore the advice is not as necessary. On cars with rear drums, the rear drums will still fill with water, and the advice is therefore still valid, but the fronts (discs) do a majority of the braking.
I will also note that brakes work best when at operating temp, the friction of the pads can and will change with temp. Going through a puddle may cool the pads and rotors to the point that it is like using cold brakes, so a light touch on the pedal may help from that point of view also.
Bottom line, if you have drum brakes Yup it is valid advice
if you have disc / drum combo yes to the extent that the drums need to dry out.
All disc A lite touch on the pedal, won’t hurt and will help keep the pads at operating temp.
Water will stay inside drum brakes and will need to be removed by braking; disc brakes dry fairly quickly. Almost all modern cars use disc front brakes, and rear brakes provide less than 30% of a cars braking force. It’s still a good idea, but it isn’t as important as it used to be.
The advice applies to drum brakes, which were virtually universal on American cars until the 70’s. Nowadays, all cars have disc brakes in front (which does most of the braking), and many have disc brakes in the rear as well. Disc brakes wipe themselves off and there is no need (nor point) to try to dry them. If your car has rear drum brakes and you went through a sizeable puddle, it may help a bit to try drying them, but in most cases I doubt there’s any real difference.