[Andrew4375]

I have recently been working on getting my front breaks working again. Everything is good, I got new pads and caliper but after I got fluid through the lines and bleed the breaks, I then squeezed the lever just to find that when I let it go (the lever) the fluid travels back up into the master cylinder. Not sure if I have a line or lines that are leaking and air is getting it or what but thought someone could help me out.

 

[DD23]

Which 450 is it please ?

 

[WintrSol]

The fluid going back into the MC is normal - if it stays in the caliper, it won't release. Any fluid that doesn't return to the MC is replaced by that in the reservoir; both volumes should be minimal, though.

If, however, you mean with the bleeder open, that is also normal, as when you release the lever the MC has to refill, and first gets it from the line. You have to close the bleeder before releasing the lever; preferably before the lever stops moving.

Usual warning: don't let brake fluid get on anything it shouldn't, as it will soften paint and discolor polished metals, including chrome. I keep a spray bottle of clean water handy, in case something gets splashed.

 

[PoiPio]

It goes something like this....

Look down inside the master and notice a large hole and a small hole.
Large hole takes a lot of fluid to push the caliper piston, load up the pad against the disc, then release it. The built up pressure is released and spouts out the hole and fills the master back up with the same level of fluid. No loss, nor can it be added to change what you already poured in.

The small hole is more like the atmospheric hole for release or neutral flow fore and aft when pressurized. When the pad wears, these holes naturally compensate to fill the lines and lowers the level in the master. You add fluid as the pads wear, but have to remember the excess will flow over the master if you retract the pads for another set.

You can tell the pro videos when the arm pump goes numb at the lever like you were filling a bucket of water from a well pump. It's the same principal so if done right, the bleed nipple is opened and closed just one time. The amateur opens and closes at every lever pull, it just hammers that caliper taper, this side of pulling the threads out, to the point of almost leaking down the road.

 

[Andrew4375]

It was weird but after I while I just decided to try a new piston and seal so and that fixed the problem right away