The Ford Barn

DNLs1930 · 02-10-2026, 09:55 AM

Is the stock OEM 1950 master cylinder reservoir "pressurized" during brake application or pedal return?

A little history on the issue and reason for the question.

I had a soft pedal and checked the reservoir (once I got the cap off which I believe has been on the car 75 years too) which was low; no apparent leaks. This is the second time for a soft pedal in the last two years. The cap and gasket were very dirty.

What I think was happening is a little fluid was escaping from the master cylinder cap each brake actuation and the residual was moving around under the car as it was driven. No static leaks other than oil that probably had some brake fluid in it looking back...

I applied the brakes a few times; I had a soft pedal due to low fluid and after adding fluid the pedal firmed up nicely.

My question is: Is the master cylinder reservoir pressurized? Because while I was applying the brakes with the cap off fluid would "squirt up" an inch or so in the reservoir which makes me think the cap is holding pressure but probably not much but enough to make the cap leak if the seal is bad.

Pretty sure the cap and seal are decades old. I cleaned the threads out they were very dirty and cleaned the gasket area which was caked with gunk. I reinstalled the gasket and added an o ring to seal it which seemed to work very well.

I will bleed the brakes just to make sure there is no air in the system and change out the fluid.

THANKS IN ADVANCE for any thoughts on this.

02-10-2026, 09:55 AM	#1
DNLs1930 Senior Member Join Date: May 2019 Location: Fort Worth side of DFW Posts: 194	1950 Ford Custom Brake Master Cylinder Is the stock OEM 1950 master cylinder reservoir "pressurized" during brake application or pedal return? A little history on the issue and reason for the question. I had a soft pedal and checked the reservoir (once I got the cap off which I believe has been on the car 75 years too) which was low; no apparent leaks. This is the second time for a soft pedal in the last two years. The cap and gasket were very dirty. What I think was happening is a little fluid was escaping from the master cylinder cap each brake actuation and the residual was moving around under the car as it was driven. No static leaks other than oil that probably had some brake fluid in it looking back... I applied the brakes a few times; I had a soft pedal due to low fluid and after adding fluid the pedal firmed up nicely. My question is: Is the master cylinder reservoir pressurized? Because while I was applying the brakes with the cap off fluid would "squirt up" an inch or so in the reservoir which makes me think the cap is holding pressure but probably not much but enough to make the cap leak if the seal is bad. Pretty sure the cap and seal are decades old. I cleaned the threads out they were very dirty and cleaned the gasket area which was caked with gunk. I reinstalled the gasket and added an o ring to seal it which seemed to work very well. I will bleed the brakes just to make sure there is no air in the system and change out the fluid. THANKS IN ADVANCE for any thoughts on this.