Brake Pedal Pulsate

Brake Pedal Pulsates

With the car stopped and the break pedal applied, I feel a slight tap or short vibration on the break pedal at very even intervals.
It seems to happen about every 4 to 5 seconds.
I just had a full inspection done at my local dealer and the car received a clean bill of health.
This included a brake fluid flush.
I was wondering if anyone in the group has felt this and/or knows the cause.

PMB, I think your wild-assed guess is on to something.
I have a new symptom now that literally sounds related to your hypothesis.
After starting a very warm engine (and only on a very warm engine) I now frequently hear something that sounds like a hydraulic system releasing pressure.
It's a short burst that is quite loud.
I have witnessed the sound startle some people close by in the parking lot.
Its rather embarrassing I must say.
My vibrating brake pedal concerned me, but now this sound has me outright worried! My braking power is seems to be good.
As I mentioned, the car passed a full inspection by my reputable dealer.
However I cant help not to imagine the terrible scenario of losing all braking power when pulling up to a red light at a busy intersection.
Will the failure of the hydraulic system result in a total loss of brake power?
Should I take it back to my dealer and ask them to focus in on the hydraulic system?
Any thoughts (including wild-assed guesses) are appreciated.

Brad Hedlund

That is the pressure control valves opening and closing on your hydraulic system brake booster.
It is normal, but if you find that when you stomp on the brake hard and you get great resistance followed by a sinking of the brake pedal after a second or two then you may want to check your hydraulic pressure accumulator (bomb).
The pressure regulator valves themselves get old and need replaced too.

JustaGuyInOKC

I had a similar problem, it turned out to be the pressure accumulator (also known as the pressure bomb).
The problem most likely is in the hydraulic system rather than the brakes.
Remember that the hydraulic powers the brake booster, steering boost and ASC.
There is also a pressure valve in the hydraulic system that can get "sticky" with age and cause a similar sound.
Have your mechanic check the hydraulics rather than the brakes, due a complete pressure test and check for leaks.

Stan Conston

Could this be an accumulator problem?

Bertsmith

That slight bump you feel is the pressure regulator cycling.
Depending on who you consult, it's either normal or an indication of impending failure of either the regulator or hydraulic accumulator.
If the accumulator eventually fails, you'll receive a brake warning light flash when you first apply the brakes.
You'll notice a momentary loss of braking power, and then it'll grab - very disconcerting.

If it gets more pronounced, I'd have the dealer perform a hydraulic system pressure test.
Reason: If you replace the accumulator and the problem resides in the regulator, you'll destroy the accumulator in short order.

Fling, Mark F.

Sounds a bit like the ABS is coming into operation.
If the problem always happens, you could temporarily remove the ABS fuse from the under hood fuse box to see if it goes away.
The dealer should be able to diagnose such a fault with ease if it can be readily reproduced.

Richard Chapman