Anyone with some technical expertise **cough Daniel B. Martin cough** Some help would be appreciated. My Brake pedal seems to go soft sometimes...let me ellaborate. When the car sits for a long time (ie. over night) I can press the brake pedal nearly to the floor board without any resistance whatsoever. After pumping the pedal a bunch of times, there is a noticeable change in the pedal firmness. After driving for a while the pedal will become very hard and as driving time increases, brake pedal travel becomes more (more than what can be accounted for by brake fade). What I would like to know is, does this appear to be a master cylinder gone bad, or a power booster? oh ya, there is no loss of brake fluid.

Sorry for this being so long, but I know that Daniel doesn't appreciate vague posts.

 

Thank you for the detailed report of symptoms. It is better to have too much information than too little.

The brake pedal "feel" you experienced points at a bad brake master cylinder. The pistons have nitrile rubber seals which wear with use. In addition, those seals lose some flexibility at the low temperatures which prevail at this time of year. The same problems affect the hydraulic clutch actuators in 5-speed Maximas.

An external leak would result in a steady drop in the brake fluid reservoir level. The lost fluid might drip onto the ground or collect inside the brake booster. The principal sign of an internal leak is a failure to perform. The driver steps on the brake pedal and the master cylinder pistons move through the fluid instead of forcing it downstream to the brake calipers.

Your symptoms point to an internal leak in the brake master cylinder. The remedy is to rebuild or replace the unit and bleed the brake system afterward.

The principal symptom of a bad brake booster is a loss of power assist. That is not among the symptoms you observed.

 

much appreciate it