Braker master cylinder or pump?

[liveandletdie]

It seems the brakes can't hold pressure at the moment.

I have checked all of the brakes and they are functional/no air bubbles.

Lines seem good, no leaks.

I have narrowed it down to either the brake booster or the master cylinder.

How can I find out which it is that is not functioning?

Obviously I'd rather not get both....but if that is the only option that that's what I'll do...

Tried to bleed the master cylinder but seems to conitunally not get pressure.

Should I replace the booster first? and then replace the master cylinder afterward if that doesn't work?

 

[YZ250Rider23]

Well... what do you mean by "not getting pressure"?
Is the pedal hard? Like if the engine isn't running and you push the brakes? (if yes than it's a booster or vacuum issue)
Is the pedal super soft and just squishing right to the floor? (if yes then it's a fluid leak)

Check your rear wheel cylinders.... those things leak like it's going out of style. Once the drums are off if you see no fluid, roll the dust cover off the edge of the cylinder and see if it's dry in there. It should be. This is really common (if the shoes are saturated in fluid they must be replaced). Then check to see that your rear brakes are adjusted. Now to the front brakes. Check to see that the caliper slides are not frozen, the pads are in good shape, and the rotors are also in good shape.

Now, after looking at all that, and then inspecting every inch of line for leaks (also look at the rubber hoses for anything unusual, like bulges), then take off the bolts and look for leaks at the back side of the master cylinder, around the piston.

Everything I've mentioned here can cause the issue of no fluid pressure... Good luck!

 

[Bryan22]

I just replaced a master on my 92 ranger. it didn't leak anywhere but the pedal just went to the floor like i lost a wheel cylinder. Turned out to be the master, no warning or signs of an external leak at all.