Does brake fluid circulate?

[trixman]

Here's a question If you are good about sucking out and filling the MS reservoir three or four times, say during OCIs

Would that eventually renew all the fluid?

Another words, does the fluid circulate between the slave cylinders and the master cylinder ?

 

[Hootbro]

I am gonna say no. Brake systems are not a constant pressure and return systems as with let's say a power steering or automatic transmission fluid. Brake systems are a pressure only with very little of the fluid at a caliper or brake cylinder migrating back into the reservoir. The only way to have clean fluid is to bleed the complete system with fresh fluid. What you wish to do will accomplish nothing.

Hootbro

 

[1040 WreckerMan]

There isn't much circulation, however the new fluid would pull moisture from the wheel ends. By just changing the the fluid is master cylinder reservoir you will keep the moisture content quite low. This method doesn't do much for oxidation and contaminants though.

 

[MN Driver]

No it wouldn't. In fact I tested this by emptying out 3/4 of the resevoir of brake fluid and after about 500 miles of driving I could clearly see the line of new and old fluid in the resevoir. I noticed this on another thread recently where we had people who were saying that instead of doing a fluid replacement through the bleeders they were just swapping the resevoir which in my opinion is a waste of time and it really doesn't accomplish anything at the actual wheel cylinder end.

You need to think about the system. It's little more than some straight tubes that go one way when the brake pedal is pressed and travels the other way when the brake pedal is released. The fluid goes back and forth only a finite distance and I don't see any way that the fluid would ever end up working it's way back to the resevior to get exchanged with what is that far upstream.

It seems to me that as far as fluid replacement goes, replace it all or don't bother opening the system up. I generally leave it alone between brake jobs unless I am specifically going to be replacing all of the fluid through the wheel cylinder bleeders.

 

[Shannow]

As previously mentioned, diffusion will eventually distribute the water present throughout the system so that it's of equal concentration.

That's all it will do. Gunk will stay where it is.

 

[Kestas]

This myth should be easy to prove or bust. Since some people alternate between blue and yellow brake fluid, just keep swapping the fluid in the master cylinder with blue fluid. After 2-3 years, do a brake bleed and see what color comes out. If it takes a long time for blue to come out then the myth is busted. Make sure to post back if you do this.

 

[mechtech2]

Yes. There is a lot of movement.
Some more than others, and an ABS system isn't certain.
At the shop we have performed and recommended turkey baster type flushes for people with economic restrictions. It usually helps or fixes some problems, and is certainly good maintainance.
My latest experience was a Chevy work truck. We had the owner suck out his master cyl and clean it, then refill with fresh fluid every couple of days. It would get black rapidly, then started to clear up, and his rear brakes started working properly again.
Of course bleeding the system is faster and better. But we have to deal with people with no money and broken off rusted bleeders.
I turkey baster my personal vehicles as a regular maintainance procedure
-quick and clean for PS and brakes.

 

[oilboy123]

Turkey baster every three months. Kinda rolls off the tongue.

I like that idea.

 

[wander2039]

I wouldn't say it circulates but it does seem absorb the junk in the oil fluid. I had some problems on bleeding our Escape so it took a couple days and the fluid in resiovor was darker than the day before when I worked on it. I used Valvoline's Synpower so maybe different brands absorb faster than others?

 

[trixman]

Wow! Never thought there would be such a variation of opinion.
"No, there isn't much circulation."
"Yes, there is a lot of movement."


Mechtech2 makes the most sense to me.

I have done the turkey baster suck and fill, but not consistently because of naysayers.

Think I will follow through more often during OCIs.

Certainly does not take long.

 

[bar1]

2. that MN Driver.
There isn't circulation, but there is a little movement.
If it's enough to mix old and new fluid is not proved.
I would follow what many car mfg. recommend, a full bleed every 2 years.

 

[alreadygone]

Once it's in the wheel cyl or caliper, it aint going to back out! Only way to make any difference is to flush it out the bleeder.

Bob

 

[Whitewolf]

I don't think that the answer to this is easy. I would think that it depends not only on the system design but also on the amount and severity of brake application.

 

[stojakovic]

It does circulate - only in a rather slow manner. I have added new fluid and some dirty stuff coming out after 2 weeks, and I replace new fluid in the reservior and this process repeated again each 2 weeks. After about 6 month I did not see any more dirty stuff coming out - may be stuck at some palce - but the fluid did circulate a little bit.

This is on a 97 Mitsubishi Galant.

 

[Ken2]

Originally Posted By: Kestas
This myth should be easy to prove or bust. Since some people alternate between blue and yellow brake fluid, just keep swapping the fluid in the master cylinder with blue fluid. After 2-3 years, do a brake bleed and see what color comes out. If it takes a long time for blue to come out then the myth is busted. Make sure to post back if you do this.
Flushing the brake fluid does not remove all of it, especially when the ABS unit isn't flushed using it's special procedure. The blue dye is so pervasive that the fluid will remain some shade of blue long after the blue fluid was used for the last time.

 

[hooligan24]

I would say, if you get the brakes hot enough, the fluid will move and mixed based on expansion and contraction of the fluid during heating and cooling cycles. I am a firm believer in adding speed bleeders to all my vehicles shortly after aquiring them. I bleed the system by myself in less than 5 minutes, once every other summer.

 

[tig1]

Yes it does, but slowly. I've been doing the turkey baster method for years.

 

[mechtech2]

It is true that 'circulate' is not proper terminology.
But there sure is movement.
It is a fluid with widely varying temperatures and actual physical movement of mechanical parts..

 

[Torino]

Originally Posted By: alreadygone
Once it's in the wheel cyl or caliper, it aint going to back out! Only way to make any difference is to flush it out the bleeder.

Bob
Now, now, are you advocating common sense? With the authorities monitoring emails thats a RISKY routine. John--Las Vegas

 

[wings&wheels]

From what I understand about brakes and every car I've done brake work on, aside from the ABS pump, the only significant movement is between the reservoir and master cylinder and between the wheel cylinders and master cylinder a vehicle w/ conventional drum brakes. With discs, unless the pistons are somehow pushed back (warped rotors, very loose wheel bearings, flex in the wheel spindles and hard cornering...a TR6 will do this) very little fluid moves around.

a little bit of fluid will be pushed into the reservoir at the very beginning of the m/c piston stroke before the 'tip valves' (valves that allow the reservoir to replenish the system) close and fluid will flow back to the bore when the piston returns to to the rear and the valves open again. On a drum brake car, a fair amount of fluid is pushed back when the return springs retract the shoes and compress the cylinders.

What is interesting is that on one of my (rear drum) cars, the reservoir will be fuller if I stopped the car wile reversing vs. going forward...only reason I can think of is the wheel clyinder (one piston) slides in a slot and is pushed into a different position by the shoes when the car is rolling backwards...???