Spongy Brakes only when cold

[firstq]

Guys, I think I may a vacuum leak that only manifests when the car is cold. In the morning when I start the car, the brake pedal is heavy and the brake is sluggish - for quiet some time until the temp gauge comes to the middle. Once the car has warmed up enough, the brake pedal smooths out (light force results in excellent braking, what you would normally expect) and I experience much crisp braking (short stops - does not grag any longer).

If it were to be anything else than the vacuum, it would affect it both cold and hot, right?

Also, it really makes no difference if the car was warmed while parked or the car warmed up while driving on the road. Important to note that the symptoms does not change even after using the brake for some time - only when the overall engine temp rises to a certain level that the braking and brake pedal feel changes.

Any pointers?

Thanks

[PalmerWMD]

you dont have performance pads do you?

Fred...

[DAEDALUS]

When stopped in park or neutral, do the RPMs change at all when you press the brake pedal all the way down?

[firstq]

Fred - the pads are OEM.

Daed - I have not observed this behavior, I will keep an eye on it when I drive it next time - I do not recall noticing an RPM change when pressning the brake pedal while in parking (I always try to observe in the morning how the brakes are doing, I would think that if RPM were to change, I would have noticed it by now).

Thanks

[Q45tech]

Master cylinder seals can sometimes cause such sympthoms .....examine everything for leaks, and observe rubber brake lines for swelling [temperature related] on a lift.

Obviously the brake fluid should be changed [totally flushed] to make sure no moisture is present as weird things can happen near 32F...........just like 212F when the water would boil.

[natsoundup]

I had a similar problem last year..... I had all of the fluid exchanged and the system bled.....including the ABS unit.... no problems now.....

They said lots of air in the system.

[firstq]

Okay, I guess the brake fluid flush is in the order - including from the ABS lines.

Anything special to watch out for when doing this DIY to make sure air is not trapped in the system? I have done this a couple of times and would like to make sure I do it right.

Thanks

[Q451990]

These will be your best friends! This way you can open a valve, put a tube into a container, and pump them yourself w/o having to have someone else open and close the bleeder valve. I have never actually disconnected the master cylinder to ABS Actuator lines for the bleeding, but Q45Tech has mentioned that air sometimes hides there. I guess you'd just bleed them into a rag?

Heath

[Chally]

Just make sure any brake fluid is washed of with plenty of water IMMEDIATELY!

If the bleeding don't work, make sure the vacuum one-way-valve to the booster isn't full of crud.