Last winter while driving in slush I first noticed a delay before the brakes engaged as if the rotors had ice on them. This winter on my 04 CS the phenomenon has become more noticeable. Today on a wet, foggy day at 4C, or about 43 degrees F, I had a hard time keeping the brakes ready for a quick stop. On the highway, a one-second delay before the brakes heat up enough to engage and slow the vehicle simply won't do. It seemed too warm for mist to freeze on the rotors.

The rotors at the time were clear of corrosion and smooth, without cut-outs. I'd assume about half of pad depth remains.

When dry (or warm?) the brakes work very well, without evidence of excessive wear. ABS is fine.

Suggestions?

 

It's probably wet pads. Some pads are worse about this than others. The brakes aren't heating up - the pads are scraping the water layer off the rotor. Slush is even worse - especially if it's combined with salt used on the road to clear snow off. The salt or brine solution gets on the rotor and creates a very nice lubricant keeping the brakes from working effectively until it's scraped off. Some newer cars use the ABS system to move the pads so they just touch the rotors, scrape off the water, then release - repeatedly - when the wipers are on - in order to eliminate or lessen the problem. You can try doing that yourself if you see a stop coming up.

 

 

When was the last brake fluid flush and with what DOT #

 

Brake pads too - higher performance brake pads might not work as well in very cold conditions if they have not heated up - rare, but even my old Miata's Porterfield RS4's were basically useless on cold mornings upon first application. If you have OE brakepads - ignore this. I do like rotors with small slots (Stoptech, EBC Ultima) on my SUV's, mainly to clear bits of gravel off the brake pads and preventing scouring\squealing when driving off-tarmac and crossing streams\deep mud. I like to think the slots help vacate water from between the rotors and pads too.

 

-Is there any change in pedal feel? Do the callipers “feel” like they are engaging but not performing, or does it feel as though there is a delay between pressing the pedal and the callipers engaging? Sounds to me like a master/slave cylinder or other hydraulic issue because of the change in performance based on temperature.

Interesting question. When the "icing" condition is in effect, the pedal feels the same as normal, but only with considerable pressure does braking occur. With increased pedal force they take effect exponentially, as if ice has to burn off to expose lining to metal.

On today's 100 mile drive over dry pavement and a 24 degree F temperature, the brakes worked perfectly.

-I replaced the brake fluid last fall with the appropriate stuff. I don't recall which # at this time, but I remember having to use some of my son's supply rather than what I had bought because of the DOT #.

-The pads came on the car when I purchased Ruby. They are non-ceramic, apparently of uniformly good quality, and about five years of age. Where we drive, one doesn't use brakes much. Years ago my mechanic did the first brake work on my 95 4Runner at 221,000 km.

Rod