Brake fluid in reservoir

[Howard]

Does the volume of fluid in the reservoir increase if the brake pedal is pressed while the reservoir cap is loose or removed? i.e. is the reservoir a pressure vessel?

 

[NutBucket]

No, it does not.

 

[JulesMaximus]

No, the only thing that would increase the level in the reservoir is compressing the pistons in the calipers.

 

[herm0016]

the level may go down slightly as you pump fluid into the calipers/wheel cylinders. it is not a pressure vessel. it is just a reservoir, same as any hydraulic system.

 

[5150MyU]

WTF Howard you give good advice on here-any modern brake system is appying alot of pressure when you step on the brakes-that would blow that pressure vessel right out of the car.
As for volume of course it will deminish a small amount as you are using it to activate your brakes.

I believe what you are thinking about is the normal blow back that you can experience while pumping/depressing the pedal with the cap off.

GOOD conversation nun the less.

 

[5150MyU]

OK

 

[Raizinman]

Depending on the vehicle.

On many older vehicles as the brakes wear, the fluid in the master cylinder goes down and causes a vacuum in the reservoir. This is why you sometimes will remove an older style master cylinder lid and the rubber seal has been pulled down into the reservoir. Yes on some master cylinders the seal is air tight and secure enough to cause a reverse pressure (vacuum) inside the master cylinder. Having an air tight seal at the top of the master cylinder is one way to combat any moisture from getting into the master cylinder.

 

[SpatiallyAware]

While the reservoir doesn't hold pressure, I have definitely seen the brake fluid level rise just a bit when the level is pulled on a motorcycle. I haven't really paid much attention with a car since it's rarely that full with the brake being applied.

 

[skyking]

The reservoir is a useful gauge for determining front brake wear. If you have a car for many years and many brake changes, you can look at the fluid level and extrapolate front pad wear. Make a mental mark on the side of it and check the brakes for condition when the fluid reaches that level. You will be surprised at how accurate this method is.

 

[manimal]

The reservoir is a useful gauge for determining front brake wear. If you have a car for many years and many brake changes, you can look at the fluid level and extrapolate front pad wear. Make a mental mark on the side of it and check the brakes for condition when the fluid reaches that level. You will be surprised at how accurate this method is.

pro-tip!