I have an 88’ GTA with 4 wheel discs and noticed that when you press the middle of the master cylinder reservoir cap I can hear air escaping or coming in, almost like its pushing air out?

The brakes work great, firm pedal and are not leaking anywhere including around the master cylinder. I even double checked that the cap gasket was on and seated correct.

The only thing I can think is the cap gasket may be worn out???

I just find it odd that it makes that noise. Also I really hate that design, the cap that the later cars have is much better.

 

I looked at it further tonight, the air noise is coming only from the back of the plastic cap pointing to the firewall. There is no noise in the front.

 

Did some more with it and tried a different MC cap I had lying around and a new gasket. Still the sound persists so I went with the new gasket and old cap.

At this point I will assume it’s normal as brakes work great etc.

 

that doesnt "sound" right. pardon the pun. if air get out, air get in. air has moisture, not good for brake fluid or brake lines. last I checked, they had exact replacement gaskets at rockauto and elsewhere.

 

I replaced the gasket, no change. Also swapped the plastic cap with another I had and no change. It’s odd but no fluid leaks and brake performance is good too.

 

ya man, I dunno. I'll try to check mine if I think of it. maybe you can put your hand back there and see if you can determine where it comes from. or push down on cap and see if noise goes away.

someone around here mentioned about DOT2 brake fluid in a post, they had a 90 or newer. I wanted to tell them there cap should say DOT3 on it, but cant find the post.

 

My 88’ says DOT 3, I just bled the brakes a few weeks back and refilled with 3.