It’s common practice to bleed all four brake lines after opening any one brake line. However, if the brake line you open is an independent brake line, then no, you don’t have to bleed all 4 brakes. The type of brake fluids you can mix and the types you must never mix.
Moreover, do you need to bleed all brakes?
No you don’t need to bleed all four as long as you don’t let the reserve run dry. I would suggest in investing in some speed bleeders they make bleeding them cake. The rears really don’t get that hot so bleeding them is not as important as the fronts.
Furthermore, what happens if I don’t bleed my brakes? A quick brake refresher: brakes are hydraulic. But if air gets into the brake lines, either from an improper bleed or from a leak, then the force from the pedals compresses the air and not the fluid. That means the energy from your foot isn’t getting to the brakes like it should be.
Considering this, can you bleed all 4 brakes at once?
You sure can bleed all 4 at the same time. Just use the “gravity” method. That’s where you simply open all the bleeders at once and allow the fluid to run through by itself, keeping a sharp eye on the reservoir so it doesn’t run dry.
Why are my brakes not bleeding?
Brakes might not bleed for several reasons, commonly the brake bleeder screws can be rusted stuck, then you have to apply heat, very carefully, or an impact wrench, or drill them out, or just buy a new caliper.