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How much brake fluid is needed?

All 4 calipers are being replaced with new. Wondering how much brake fluid will be needed to entirely flush and fill the system.

Has anyone used a Schwaben pressure bleeder? Opinions on that unit?
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Old 06-06-2019, 03:48 AM
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1 liter is ok to fill the entire system.
Use ate typ 200 dot 4.
If you are running restered calipers replace (or drain some) after 2/3 months because it can contain zync residues from the replating process
Old 06-06-2019, 04:12 AM
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Quote:
Originally Posted by fizeus View Post
1 liter is ok to fill the entire system.
Use ate typ 200 dot 4.
If you are running restered calipers replace (or drain some) after 2/3 months because it can contain zync residues from the replating process
Thanks Fiz. Interesting note on zinc residue. Here, all calipers are new. ATE brand.

.
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Old 06-06-2019, 04:51 AM
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Quote:
Originally Posted by fizeus View Post
1 liter is ok to fill the entire system.
Use ate typ 200 dot 4.
If you are running restered calipers replace (or drain some) after 2/3 months because it can contain zync residues from the replating process
I use about a liter to flush my brakes. For a new system I would get 2 liters of inexpensive DOT 4 to fill and get the bubbles out and then a few months later flush with ATE.

If you will running the car aggressively immediately, I would use ATE only.
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Old 06-06-2019, 07:33 AM
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The system holds about a liter, I buy 2 so it don't run out part way though the flush. ATE 200 is a good high performance fluid for the money, maybe overkill for street but it's reasonably priced. I've used the Motive bleeder for years with good results.
Old 06-06-2019, 08:01 AM
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And don't forget to pinch off the reservoir overflow hose! I told myself not to forget and damned if I didn't get to bleed my brakes twice after hearing my power bleeder spitting brake fluid all over the front of the garage floor!
Old 06-06-2019, 09:45 AM
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All input is much appreciated guys. TY!
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Old 06-06-2019, 11:23 AM
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The motive bleeder works great. I don't put the fluid in the bleeder, just use it to pump to about 10psi before opening the bleeders. Just make sure you check fluid level in reservoir after each caliper. Start with the right rear then left rear, right front, left front, Then go around again until you have no bubbles in line.
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Old 06-06-2019, 11:28 AM
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Originally Posted by RSTarga View Post
The motive bleeder works great. I don't put the fluid in the bleeder, just use it to pump to about 10psi before opening the bleeders. Just make sure you check fluid level in reservoir after each caliper. Start with the right rear then left rear, right front, left front, Then go around again until you have no bubbles in line.
This is how I do it. One man show. No speed bleeders.
Old 06-06-2019, 01:51 PM
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Perhaps I am an idiot (well okay....we know I'm an idiot) but I am surprised the system contains a liter of BF. I would have thought less.

I very recently (two months ago) refilled my system after installing a new MC and rebuilding the calipers. Here is my advice: If your system is not empty....if you somehow capped the brake lines to prevent BF escape, I suggest you do this. Install the calipers and put BF in the reservoir. Put a little hose between the RR caliper bleed valve and a jar, and open that bleed valve. It will not take long for BF to come out. Do this at the LR, then RF, then LF. Chances are good your brakes are bled and ready to go. If not, then using an assistant just barely 'burp' the calipers. Air in the system (on these cars) is not likely to be in the MC.

I am no expert, but in my experience the brakes on these cars are extremely easy to bleed. Those Germans.....
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Old 06-06-2019, 05:23 PM
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I've used the Motive bleeder with and without fluid as well as a compressor powered Mity Vac. After rebuilding the front brake calipers and replacing the flex hoses two weeks ago, I decided to give gravity bleed a try. Worked very well, although it was slower than the alternatives. Try a gravity bleed if you have a bit of time... very easy and effective. No equipment required.
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Old 06-06-2019, 05:35 PM
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I notice Bentley suggests a more complex method and yet, I stick by my recommendation. You can also tap the calipers with a hammer to ensure there are no bubbles stuck to the inside of the caliper, however. This is not rocket surgery.

I have used more complex equipment and procedures but I do not use them anymore on this car. You will know when you are finished. The pedal is TIGHT. No sponginess at ALL.

One more thing: The square-sided O-rings on which the caliper pistons ride are flexible, and they can draw the piston back after braking. This causes some irritating pedal travel. If you remove the pins and clips and find any brake pads which you can move with your fingers, then you have this problem. You likely do have this problem. To address this, I remove the brake pads one by one then tap the brake pedal an inch or so. Sometimes, I then have to tap the brake pad back into position with a hammer. Problem solved. Again, your pedal should be TIGHT. These cars have wonderful brakes.
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Old 06-06-2019, 05:46 PM
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I am not finding a spec on the BF capacity. Again, I have used fancy (both positive and negative pressure) systems on these cars and I would guess the actual capacity to be not much more than a small bottle of BF. Using the gravity method (with caliper burping using an assistant or a vacuum setup), I'd be very surprised if more than 16 oz is needed. I may be wrong, but I would be very surprised.
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Old 06-06-2019, 06:07 PM
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Quote:
Originally Posted by Superman View Post
I am not finding a spec on the BF capacity. Again, I have used fancy (both positive and negative pressure) systems on these cars and I would guess the actual capacity to be not much more than a small bottle of BF. Using the gravity method (with caliper burping using an assistant or a vacuum setup), I'd be very surprised if more than 16 oz is needed. I may be wrong, but I would be very surprised.
I know to flush my system, I use about 1 liter. Back when ATE blue was available, it took about 3/4 liter to get a complete color change in all 4 calipers. Now I just pull about 160 ml from each one.

Gravity bleed is ok if you want to wait. I use the motive bleeder with good results on all my cars.
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Old 06-06-2019, 06:53 PM
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Yo' KinkyKarl, do you have an air compressor and simple air gun at home (seems like you would, being the mad scientist DIY guy that you are )? If so, then you already have a pressure bleeder that works perfectly.

Attach a suitable sized hose to the tip (just the ) of the air gun, and then attach the other end of the hose to the vent nipple () on the master cylinder res. Set your pressure regulator to 15-17 PSI and then control the on/off air supply with the gun (I use a strip of Velcro to hold the trigger down as I move about the car - a rubber band works well, too). Open the caliper bleed valve(s) in the order you desire (one at a time since you are not supplying additional fluid with this simple method), start the air, and then watch the fluid and air bubbles start cascading out. Turn of air when fluid reaches your panic level in the res, close bleed valve(s), fill res, and then repeat with the next caliper. Since you are installing new calipers, you will have to pump () the brake pedal some during the process (bleeders closed and air supply turned off) in order to set the pistons in position. Obviously, the cap is on the res when you are supplying air pressure (I forgot to mention that earlier) - good to have a rag wrapped around the cap area incase some fluid dribbles out () if the air pressure is a little high.

The process is quick, easy, one-man, and works perfectly on all brake systems that have a traditional style master res (including many aircraft) . . . systems that vent the res through the cap need a hose barb added to a donor cap, but that is easy to do, as well, and not an issue with 911s.

PS - you can use lower air pressure if you want to (8-10psi); works okay, but is much slower and doesn't seem to do quite as good a job of firing trapped air out of the system as 15-17 (at least not as quickly). The plus side is that there is more room for operator error with lower psi, as the res does not empty as quickly - maybe wise to experiment with lower pressure first. That is also why using an air gun works so well - you can shut the air supply of instantly, if you need to.

Last edited by Rawknees'Turbo; 06-06-2019 at 10:27 PM..
Old 06-06-2019, 09:48 PM
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+1 on about a liter of brake fluid to fill the system. Gravity bleeding will minimize BF waste. If not careful, a pressure bleeder can ruin a Castrol SRF brake fluid budget.

Old 06-06-2019, 11:52 PM
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Quote:
Originally Posted by Rawknees'Turbo View Post
Yo' KinkyKarl, do you have an air compressor and simple air gun at home (seems like you would, being the mad scientist DIY guy that you are )? If so, then you already have a pressure bleeder that works perfectly.

Attach a suitable sized hose to the tip (just the ) of the air gun, and then attach the other end of the hose to the vent nipple () on the master cylinder res. Set your pressure regulator to 15-17 PSI and then control the on/off air supply with the gun (I use a strip of Velcro to hold the trigger down as I move about the car - a rubber band works well, too). Open the caliper bleed valve(s) in the order you desire (one at a time since you are not supplying additional fluid with this simple method), start the air, and then watch the fluid and air bubbles start cascading out. Turn of air when fluid reaches your panic level in the res, close bleed valve(s), fill res, and then repeat with the next caliper. Since you are installing new calipers, you will have to pump () the brake pedal some during the process (bleeders closed and air supply turned off) in order to set the pistons in position. Obviously, the cap is on the res when you are supplying air pressure (I forgot to mention that earlier) - good to have a rag wrapped around the cap area incase some fluid dribbles out () if the air pressure is a little high.

The process is quick, easy, one-man, and works perfectly on all brake systems that have a traditional style master res (including many aircraft) . . . systems that vent the res through the cap need a hose barb added to a donor cap, but that is easy to do, as well, and not an issue with 911s.

PS - you can use lower air pressure if you want to (8-10psi); works okay, but is much slower and doesn't seem to do quite as good a job of firing trapped air out of the system as 15-17 (at least not as quickly). The plus side is that there is more room for operator error with lower psi, as the res does not empty as quickly - maybe wise to experiment with lower pressure first. That is also why using an air gun works so well - you can shut the air supply of instantly, if you need to.

I like the idea of using the gun to switch pressure on/off. I normally use a 20oz CO2 for pressure which works until the burst cap goes in the regulator with a loud hiss 😅. I believe the recommended factory procedure calls for 1 bar or 14psi.

I normally go through appx 750ml of fluid but think if you were really judiscious, you could bleed a system with 500ml with no room for error.

Nice job Knees weaving in tips and drips into your post.
Old 06-07-2019, 04:14 AM
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