Never changed the brake fluid in my GS4 and not sure if previous owner ever changed it. I know the master cylinder is very expensive, can changing the fluid that’s possibly never been changed cause any problems? Am I better off leaving it alone? I do remember changing the brake fluid in my GS430 I used to have and the master cylinder did fail on that car a year or two later. I’m sure that’s a coincidence but now I’m curious…

 

Fresh fluid won't be the reason the brake master cylinder fails. If it does, it is just a coincidence. Fresh fluid will have no water or dirt in it, which is a good thing for any brake system. These master cylinders that are 20+ years old with 200k+ miles are all on borrowed time....

 

Not to mention fresh brake fluid is a lot safer when it comes to multiple hard stops, old brake fluid has a lower boiling temperature because of the water and the brake pedal might feel spongy. You really don't realize how good new brake fluid feels until you try it, my GS completely changed when I flushed the old stuff out. There was actually a degree to safety when braking

 

yea it is kinda mushy but I’m used to it and since I have new rotors and pads all around it’s manageable. Made me want to change it now.