Could be a seized master cylinder or an ABS problem.

 

Sounds like either your brake servo vacuum pipe is leaking or the servo has failed. Can you hear any hissing under the bonnet when the engine is running or in the car when you apply the brakes?

With the engine off pump the brake pedal a few times and see if it gets harder, then hold your foot hard on the brake pedal and start the engine. If the servo is working the pedal will drop when you start the engine.

 

Servo seems fine (engine started, pedal dropped)

 

Thats the easy fix for a rock hard pedal out the window then. Devil may be right.

 

Sounds costly?

 

Unlikely to be a cheap fix if its the ABS. Haven't heard of this problem before with 300Cs, but I've read in the motoring press that some German marques are susceptible. The good news is that a UK firm has come up with a low cost fix for such problems, which doesn't involve a complete ABS replacement.

 

Now Sorted.

 

Well what was it then? You came on asking for advice and when you got it sorted didn't bother telling us what it was :twak:

 

How the h**l can I tell you when I don’t even know myself? I depressed the brake pedal on the Friday night as Lambournkoi suggested, I unscrewed the master cylinder cap to look at the fluid, By the time the mechanic took a look at it Sat morning & it was perfect, everything back to normal, Im as stunned as anyone. That good enough for you?

 

A ball got stuck under the brake pedal !!!!!

 

Had you driven it really hard on the brakes just before it happened?

 

No thats what I cant figure, its really baffling??

 

Hiya mikecc, just had the same problem as you with my Brake Pedal. Out of the blue brake pedal went hard and didn't brake properly. Then within half an hour later after driving in a car park my brakes returned to normal again. Did you ever find out what caused your Hard Brake Pedal issues ?
Regards Peter UK Chrysler 300 card 2008 model.

 

A bit worrying if the cause hasn't been identified. Presumably you've checked for carpet/trim snagging the pedal?

 

A bit worrying if the cause hasn't been identified. Presumably you've checked for carpet/trim snagging the pedal?

Yep thats what I said to the mechanic the fact that a fault hasnt been identified, means that it could come back again! Nothing under the pedal, carpet or otherwise, I have no Idea what the fault was or how it cleared?

I do have an assumtion but I would only be guessing

 

I don't think you'll get a response after 13 yrs!

 

I just saw an automotive TV show wherein they had the same issue and they diagnosed it as master cylinder failure. Sorry but that's all I know about the subject.