Complete Brake Flush question.

[supton]

Originally Posted by Or
Originally Posted by hallstevenson

I'm not sure that brake fluid circulates that much so I think you just have clean fluid mostly in the reservoir and not so much in the lines or more importantly, the calipers.



A lot of people are under that mis-perception. But it does.

Immediately, no. But over a period of use it will mix fully and become homogeneous. Brownian motion guarantees it.

It is an interesting thought, and I've wondered about it, but it's gotta be the slowest thing going, getting the fluid from the calipers back to the master cylinder. It may well be better than doing nothing, and if done frequently enough, so as to keep what is in the master cylinder very low in moisture (so as to cause the greatest gradient) maybe it'd be good enough--especially most don't change at all yet manage a decade plus on the system.

 

[Oro_O]

Originally Posted by supton

It is an interesting thought, and I've wondered about it, but it's gotta be the slowest thing going, getting the fluid from the calipers back to the master cylinder. It may well be better than doing nothing, and if done frequently enough, so as to keep what is in the master cylinder very low in moisture (so as to cause the greatest gradient) maybe it'd be good enough--especially most don't change at all yet manage a decade plus on the system.


It mixes pretty quickly with some driving. The MC acts like a "stirrer" and then simple physics does the rest mixing it fully. I was a bit surprised myself quickly it mixes fully.

Recent example:

I had not changed to fluid at all in my SUV for three or maybe a bit more yeas. It had turned green from the natural effect on the joints in the system, as well as whatever water was in the system. About two weeks ago, I did a drain/fill with the MC and drove that day about 50 miles mixed city/highway. It was green again in the reservoir, but less so. I was planning a second d/f soon-ish as I knew I needed new front pads.

Two days ago I went to change the front pads. I emptied the reservoir, then pulled the front brakes and compressed the pistons all the way flush (front only). Then I siphoned that out, too. I refilled the MC and let it sit over night. The next day I decided to see what the fluid in the REAR pistons looked like - they had not been opened in three to four years. I attached a clear plastic tube to them and cracked them - they immediately ran pure clear yellow/amber, no air or water visible, or green tint detectable.

So this works well and you don't need to really be manually bleeding. The only time I'll do that again is when a system is opened or for some reason I suspect air in the system.