Brakes - initial bite variability

[Tom M]

I installed new rotors and pads on my 2011 CS just over a year ago and also flushed the brake fluid. At that time I switched to ceramic pads to help reduce the dust and knew they wouldn't have as much bite (or dust) as the stock pads and I was OK with that. Over the course of the year the brake pedal became a bit softer but they would bite firmly once in a while.

 

Last weekend I flushed the brakes again and the softness is gone but they do still seem to have more boost at times. I've checked the vacuum pump at the secondary port and it's got plenty with no leak down after the engine is turned off. I don't think it's anything major as no codes are being thrown so I'd tend to rule out a faulty brake booster.

 

The other possibility seems to be a faulty check valve but I can't find any information or part numbers for a replacement if that's indeed what the problem is.

 

Looking for any additional ideas or the check valve p/n.

 

[scanner-1]

Is it possible it's just the PSM in combination with driving style (and differing thresholds based on sport/normal)?

The brakes on my 2011 CTT are noticeably different depending on how I drive--there was that ONE time I drove nice and easy in normal mode on the way to church, haha!

 

from the manual pg 190:

 

Examples of PSM control operations 

– Brake system prefilling: 
The brake system is prepared for possible subsequent emergency braking if the accelerator pedal is released suddenly 
and quickly. The brake system is prefilled and the brake pads are already applied gently to the brake disks. 

 

 

[Tom M]

No real change in driving going on so I don't think that's it.

 

It'll happen, for example, when I'm just starting out after backing out of a parking space or shortly thereafter. It's happened on an off ramp while just coasting to slow down and then using the brakes with no other cars around. It's also happened on the highway just flowing with traffic and needing to slow a bit due to traffic slowing a reasonable distance ahead.

 

Try as I might I have not been able to reproduce at will nor can I correlate it with any specific activity.