Brake fluid flushing and Brake work
 

If the brake pads and rotors are changed, is it necessary to flush out the brake fluid as well? The reason I ask is that my dealer changed the front pads and rotors about a year ago and on the detailed invoice do not mention anything about changing the brake fluid. And if I flush out the brake fluid myself NOW, would it have to be flushed out again if I need to change my brake pads soon, say in 3 months for example? I guess what I'm really asking is if the fluid is in a closed system and does changing pads or rotors contaminate that system in any way that requires it to be changed when this type of brake work is done?

You do not need to change the brake fluid as long as you do not open the bleeder screw. Pushing the piston back will simply displace the fluid behind the piston back to the reservoir. Just as long as the brake fluid is be changed at least every 2 years.

If the brake system were really closed then you wouldn't have to flush it ever.

You don't have to flush your brake system because you replace the pads or rotors. It's conventient to do so when you bleed the brakes which you should probably do after any brake work.

If you get a pressure bleeder then flushing isn't more work than bleeding. Plus you eliminate the risk of accelerating wear on the master cylinder seals that comes from bottoming the pedal while bleeding. Or use a suction bleeder if you don't have ASR.

Maybe you can get the same security by not pressing the pedal all the way to the floor.

Sixto
91 300SE
87 300SDL
83 300SD

Both replies or accurate, but I would like to add something. It is money well spent to flush the brake fluid annually. If you don't you eventually have hydraulic problems. If you keep it flushed, you will most likely only replace friction items (pads and rotors) for the life of the vehicle.

If you fail to flush the brakes, moisture collects in the fluid causing corrosion.

Have a great day,

Minor addition:

Braking systems are not closed to the atmosphere.
The reservoir cap is vented, and rubber hoses are somewhat permeable.

Some folks do advocate opening the bleeders when the caliper pistons are retracted for a pad change. The idea is that this prevents the dirty fluid in the calipers from being forced back through the master cylinder. The fluid within a calipers tends to be the most contaminated, since they are at the lowest point in the system.