Fizzboy7

Has happened twice now. After car sits overnight, the brake pedal is hard as a rock when depressing it to start the car. Once the motor runs, all is fine. Also fine when driving. No leaks on the ground as far as I can see. Brakes are original with plenty of pad left according to the dealer at my last service (I'm at 40k miles). Is this something related to a brake boost leak or??? Not dealt in this area before and am out of warranty.

Thanks for any suggestions.

Zynthe

iTrader: (5)

Your brakes lost compression. Happened to me on my 1IS before. Do you step on the brakes after the engine is off? That could be one reason.

scott1256c

It has happened to me in the past. Not regularly. I don't think I'd get too concerned just yet. You say twice now. How far apart between? How many times would you have run the car in between without experiencing the hard brake pedal? It goes away when, as soon as the car starts, i.e. the pedal softens up before you even get it out of park? Or a few moment/seconds/minutes thereafter?

redspencer

iTrader: (1)

Hmmm....this is an interesting thread as I have the same issue. I noticed that my 2IS has been behaving this way on cold starts (time-wise not temperature-wise) for about a year now.

I used to be able to press the brake pedal all the way down before starting my car in the mornings but nowadays, the brake pedal has about a 1/2" play before coming to a complete stop and will remain that way until I start the engine up. The brake pedal and pressure behaves as expected throughout the rest of the drive.

So far I'm still alive and haven't crashed due to a brake system failure.

cquence

Going with what Zynthe has mentioned, loss of compression, once your engine is off, this cuts power assistance to the brake master cylinder; which leads to a stiffer or harder pedal feel.

"If the vacuum fails because the engine stops, for example the brakes still work because there is a normal mechanical link between the pedal and the master cylinder. But much more force must be exerted on the brake pedal to apply them."

More about master cylinders and power assistance can be found here:
http://www.howacarworks.com/basics/h...g-system-works

Another example is your steering. Modern cars have power steering. When your vehicle is on, it is easy to turn the steering wheel. When it is off, it is much harder. Same technology, just different purpose.

Hope this helps but if it is not the case, definitely have your master cylinder checked out for leaks and other points of failure.

Gville350

iTrader: (10)

Nobody has found the root cause of this "issue" and it is a known gremlin that does pop up and then just disappear as quickly as it came. My car has done this 3-4 times in 4 yrs. Does catch you by surprise, but it is not dangerous; no one has posted any ill effects of their cars braking after having experienced this "issue."

Fizzboy7

It happened again today. It's been very hot and humid here in L.A. and so far this latest batch has been during the heatwave. Has anyone else noticed the weather conditions when it happened to them?

I should also add, one of my original concerns was I wouldn't be able to start the car if the pedal can't be depressed. How much motion is required for the sensor to be triggered in order to start the car? It feels like I have barely moved it at all when this happens, yet the car thankfully starts.

600rr05

iTrader: (9)

its happened to me a few different times. not enough to make me want to take it in.

Bichon

Yes, for me it has only happened a couple times, always in snowy winter weather. I initially thought it might be related to excessive activation of the ABS system.

Not far. I've never had a problem starting the car due to a firm pedal.

Cdawg250

I noticed if you step on the breaks w/ the car off the breaks tend to get stiff..if that helps