Fluid capacity of brake system

[Walt Fricke]

While flushing my brakes it occurred to me that I can easily measure how much fluid I have pulled out of each caliper. If I knew how much fluid was in the system, I could stop bleeding before I drained either side of the reservoir (I'm thinking about pre-1988 911s, with no clutch MC).

The reservoir holds X, and the two sides of the reservoir (for the front and for the rear) hold X-A and X-B (maybe they are of equal size) below the center divider.

Each line to the front calipers holds a certain amount. The common line to the rear holds a certain amount. The lines at the rear to each side are as close to equal as maybe not to matter, though the right side one is shorter by a bit.

And then the calipers themselves hold something. I'd be inclined to use "pistons fully retracted" (as in changing pads) as the spec, but knowing what it is with very thin pads would be useful.

And so does the MC.

That way, after the turkey baster (I have an alternative - a huge plastic syringe)has removed the old fluid from the reservoir, and you have poured in new, you can determine when you have flushed the left rear, then the right rear (much much less), then the two fronts (right maybe a little bit less). If this is less than what you put in, you are good and can top off the reservoir and call it good.

I have a spare reservoir, so when I have time (leaving on a trip soon)I can measure its capacity easily enough. Knowing the length and ID of the lines should allow calculating that. I can measure the ID of a line, but don't have a full set to measure. I've not fiddled with the calipers to figure out how much fluid is inside them, and don't have one handy. I do have a spare MC somewhere.

Anyone ever tried to figure this?

The 2.7 little white spec book says the brake fluid reservoir holds 0.2 Liters (200 ml). A typical can of fluid is 500ml. Plenty, but the trick is to avoid getting air from an empty reservoir into the lines.

[Porboynz]

Ambitious plan, I simply buy a different color each time and problem solved.

[ClickClickBoom]

Originally Posted by Porboynz

Ambitious plan, I simply buy a different color each time and problem solved.

DOT stopped different colored brake fluids. One color now.

“Please Note: As of late 2013 'Blue' tinted brake fluid is no longer DOT approved or legal for use or sale in the USA.
Sale of ATE Super Blue is discontinued but ATE Type 200 'Gold' color will thankfully continue to be available for all fans of Super Blue.
All orders will be fulfilled with Type 200 "Gold".”

[Walt Fricke]

Yup. I've wondered if some sort of dye could be put in the fluid without adverse consequences. A bit beyond my ken, though.

And I don't like to have the fluid get dark all by itself!

[patkeefe]

I did measure this once on my SC, when the calipers were rebuilt. I blew out the entire system, and measured what I put back in minus what I bled out.

The bad news is I don't remember the number. It was greater than 1 liter, and not as much as two liters, IIRC.

[T77911S]

just buy a power bleeder.

I resisted for years. even made my own back in the 90's with a shredder valve on an old reservoir cap. worked great on the 914.

also use to just gravity bleed.

when I rebuilt the 930 brakes I ended up getting the power bleeder and never looked back.

[sugarwood]

Originally Posted by Porboynz

Ambitious plan, I simply buy a different color each time and problem solved.

When is the last time you bought brake fluid?
In the last 5 years, I have never seen anything but clear.

[sugarwood]

When I last bled my brakes, I did 10 pumps in the rear, and 5 up front.
I didn't use much fluid at all. Maybe 1/4 of the liter.

[HarryD]

Back in the day, I alternated blue and gold for my 1973.5. I found that if I removed all the fluid from the reservoir and refilled it, I would use about 170 ml per caliper before the color change was 100% complete. Hence a 1 liter container is adequate. Given I could flush less in the fronts, 500 ml is minimum. For me, It is inexpensive enough to always use s liter.

[Walt Fricke]

T77 - I've used every known method of bleeding except filling through the bleeders, but that would have the same uncertainties unless you first completely drained the system (which, by filling "backward" might avoid the air pockets in the MC or maybe the odd caliper we all wish to avoid.

I used the Schraeder valve method (Upfixin article on it), and still have the stuff in my traveling tool chest (this is now a dedicated race car). I added a ball valve to my pump power bleeder (after reading a recent discussion of issues with that device), which is something I should have done to the front tire system - makes opening the reservoir for a look or refill a bit easier.

Gravity bleeding all four at the same time was the absolute best, but that was because the whole system was drained so I could cut off the front half of the car (firewall included) to have wreck damage repaired), so there was no question about how much was enough - the tubes rose above the reservoir level and did their job over night.

At the track, if needed, having someone depress the pedal half way on command is the most efficient system for getting rid of a few bubbles. It is when doing the annual or more flush/fluid change which leads to the potential to put some air into the MC.

The two color ATE was nice, although for an SC on the track its boiling temperature isn't as high as one might want. And it is NLA. Talk about silly rules, based on the least common denominator principle.

[911pcars]

With gravity bleeding, one liter of brake fluid is all it takes, but typical pedal up/down and pressurized bleeding methods will use more.

Sherwood

[dannobee]

The other fly in the ointment is that when you open your new can of brake fluid, it will immediately start absorbing moisture from the air, lowering its boiling point (hygroscopic). Better to use the whole can when bleeding.

Or buy a pressure bleeder.

Gravity does work good too. It just sometimes takes awhile.

[ClickClickBoom]

Been using these for 7-8 years.
Introduction - Speed Bleeders - Russell Performance Products
Flush and bleed annually. Takes more time to jack up and remove the wheels. Crack the valve, 6-8 pumps on the pedal, add fluid, rinse and repeat for the other 3. Bleeding brakes became routinely easy.

[Quicksilver]

BTW - The old ATE "Super Blue" fluid was never a DOT 4 fluid and it said so on the can. It did fulfill the DOT 4 temperature requirements and they had it clearly marked that it was for off road use only.

(I have a really old 'flat shaped' can that has a sliver and blue finish with a lot less writing on it. Not sure how it is labeled. I'll have to check it out.)

[Porboynz]

Last canister of ATE Super Blue, it was good enough for the race track.
Meets or exceeds DOT4 is OK here in New Zealand