Stock rubber brake lines, usually good for around 4 years, they are just average at best.
An upgrade a lot of riders do it to trade out for braided stainless brake lines at some point, increase brake pressure and durability…this is the point where brake fluid has no choice but to be serviced/ swapped out.
…but why should you?
Brake fluid is somewhat hygroscopic (tending to absorb moisture from the air) so a quick a full brake fluid flush NOT just a case of drain it out, clean and add new fluid!
You might at this point buy a rebuild kit and replace old rubber parts, as you are in there anyway and most are relatively cheap.
How do you know it needs doing?
- there might be more free play in your lever than you remember
- your bike has sat in a cold wet winter, and been absorbing without you realizing
- your braking doesn’t seem as strong as before
What else to do/check when you do this?
- take your brake pins out and lube them
- take your brake pads out and see that the wear is even, uneven wear most likely means a stuck piston, most likely corrosion…service it
How do I bleed and flush brake fluid?
I use a Snap-on vacuum bleeder that pulls with the required pressure to get all the bad stuff out. Then I clean and check the master cylinder and all components
I then run thru about an equivalent of a double what the system takes or until the fluid coming thru is crystal clear and no dirt fragments are showing in the liquid in the master cylinder
*** remember to do the back brake as well, and the same applies if you have a hydraulic clutch.
if you are more of a visual learner I added a video I found on the learning channel…aka YouTube