brake master cylinder

[ron55]

As I pulled the caps off my master cylindr I heard a slight psssst. Is this pressure or vacuum. I never had a master cylinder with any kind of + or - pressure. This was over a week after driving.

[ron55]

As I pulled the caps off my master cylindr I heard a slight psssst. Is this pressure or vacuum. I never had a master cylinder with any kind of + or - pressure. This was over a week after driving.

[knebrdr]

Administrators please forgive me!
Where are all the professionals? Ron 55 has a valid question and no one seems to want to help. Oh thats right, there is no potential sale.
Randy

[Petro]

I have never heard anything similar when I have checked my brake fluid.

Don

[M&EM]

There has been a mention of master cylinder hissing sound with cap removal and several comments in a previous thread on this forum.
Do a search in FIND with words like: master cylinder pressure and cap

[George Z]

I have had a small pressure release from one master cylinder cap while removing. The reason for removal was I thought I had a brake dragging while on a trip and I was checking everything for a cause.

[CoastieSCPO]

Master Chief;

I'm not an expert, but a pssst sound means the possibility of air, and to my way of thinking, air is not good in the brake system. Also, it would be doubtful that a vacuum would make a sound. Like I said, not an expert, but just a thought.

Bob

[knebrdr]

Ron,
The brake fluid cap should be vented. If so the vent is probably blocked. Try replacing it.
Randy

[speed racer]

The master cyl. is not vented directly to the outside air. It has a rubber seal between the fluid and the air. As the fluid level goes down the seal goes down with it. Sometimes if it hasn't pulled down far enough to unfold the seal you could get a sound like that when removing the cap. It just means it was sealed good after all air and humidity are enemys of brake fluid.