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Screwed up brake flush


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Today was the first time I've flushed the brakes on my 2004 986S. I got a new bottle of new fluid (ATE Super Blue to make it easy), picked up a loaner vacuum bleeder from the local auto parts store, and went to it.

I didn't realize there were two compartments in the fluid reservoir, and accidentally bled both rear lines completely dry. I refilled with new fluid and bled all 4 wheels until new fluid came out, but the brake pedal is going straight to the floor and I'm hearing a whooshing sound from the master cylinder (probably all that fluid rushing to compress the air.)

I had my son pump the brake pedal while I held the pressure bleeder, and both rear brakes are looking bubble free, but my pedal still goes to the floor. Help! What do I do now?

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If I remember correctly there are 3 chambers in the reservoir. 2 for the brakes and 1 for the clutch.

If you drain the reservoir way below the min level for a brake flush, then you have introduced air into the brake system.

You need to get the air out. Try to clear the air out the old fashioned way by filling the reservoir, pump the pedal, open the bleeder.

Because there are 4 calipers you will need about 3 liters of brake fluid to bring the pedal back to normal. Start with the RR since that is the longest line, then go around to the other calipers.

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Today was the first time I've flushed the brakes on my 2004 986S. I got a new bottle of new fluid (ATE Super Blue to make it easy), picked up a loaner vacuum bleeder from the local auto parts store, and went to it.

I didn't realize there were two compartments in the fluid reservoir, and accidentally bled both rear lines completely dry. I refilled with new fluid and bled all 4 wheels until new fluid came out, but the brake pedal is going straight to the floor and I'm hearing a whooshing sound from the master cylinder (probably all that fluid rushing to compress the air.)

I had my son pump the brake pedal while I held the pressure bleeder, and both rear brakes are looking bubble free, but my pedal still goes to the floor. Help! What do I do now?

I'd say keep bleeding them. I don't know how many times I've thought I had all the air out and then learned - nope. All the way to the floor.

I prefer the old fashioned way for bleeding - put your son on the car, have him pump three times, and then hold until you tell him to let up - while he is holding, open the bleeder valve; close before he lets up. (I have a 12-year-old daughter that is very good at this from lots of practice if you need a rental :D )

Start with passenger rear, then driver rear, then passenger front and then driver front. Keep doing it. If there is air around the master cylinder, it has to make it's way out. It can take a while, but you will eventually get it.

Only caveat which I am unsure of, is the role the clutch fluid plays. I always flush that too at the same time, so I am unsure if you need to bleed it as a result of letting the rears run dry - I don't think so, but maybe someone can confirm.

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I think you might need to do a combination of things suggested above.

First, buy/rent a pressure bleeder. A lot of us use the Motive pressure bleeder; I'm very happy with mine--used it on all my cars. Also, since you've already filled with ATE blue, I would go back to ATE 200 (regular color). You'll need at least two liters, and I agree with TP that you'll probably need three.

Use a turkey baster to get as much of the existing fluid out of the reservoir as possible. Then top off the reservoir with new fluid and fill the pressure bleeder with at least two liters of new fluid. Connect the pressure bleeder to the reservoir and pressurize per its instructions (i.e. do not exceed 20 psi, check for leaks, etc.)

Note to others: If you haven't run the master cylinder dry, you don't need to do this particular procedure. Starting at the right rear caliper:

- Connect a drain tube to each of the fittings on the caliper. Drain into a suitable container (I use a gallon jug).

- Open the outer bleeder valve. When the fluid runs clean/new and bubble-free, close it.

- Open the inner valve.

- When the fluid runs clean/new and bubble-free, open the outer valve. Now both valves are open and fluid is flowing.

- Move to the driver's seat.

- Fully depress the brake pedal three times. Each time: hold the pedal to the floor for 2-3 seconds before slowly releasing it.

- After the third cycle, return to the caliper.

- Close the inner bleeder valve.

- Let the outer valve bleed for a while until you are absolutely sure the fluid is clean/fresh without bubbles, then close it.

- Open the inner valve again and make sure the fluid flows clean and bubble-free from there, too, before re-tightening it.

Check the fluid level in the pressure bleeder. Re-fill and/or re-pressurize as necessary.

Repeat the same procedure at the left rear. Then the right front, and finally the left front. You'll use a lot of fluid on the right rear, then less and less as you move through the other calipers. Don't re-use any fluid.

After the brakes, I would bleed out the old fluid from the clutch circuit, too. Not too easy on jack stands, let me tell you, but it can be done with patience. I used Loren's DIY instructions for 996.

Hope it works out for you.

--Brian

Edited by Q-Ship986
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Because there are 4 calipers you will need about 3 liters of brake fluid to bring the pedal back to normal. Start with the RR since that is the longest line, then go around to the other calipers.
Why so much fluid? I don't think I even removed a half liter of old fluid. Does it take that much to cycle the bubbles out? If so, is it OK to re-used the fluid I just bled out? I'm not trying to flush the brakes again, just get out any remaining air bubbles.

I have a tip, btw, so no clutch to bleed.

Starting at the right rear caliper:

- Connect a drain tube to each of the fittings on the caliper. Drain into a suitable container (I use a gallon jug).

- Open the outer bleeder valve. When the fluid runs clean/new and bubble-free, close it.

- Open the inner valve.

- When the fluid runs clean/new and bubble-free, open the outer valve. Now both valves are open and fluid is flowing.

- Move to the driver's seat.

- Fully depress the brake pedal three times. Each time: hold the pedal to the floor for 2-3 seconds before slowly releasing it.

- After the third cycle, return to the caliper.

- Close the inner bleeder valve.

- Let the outer valve bleed for a while until you are absolutely sure the fluid is clean/fresh without bubbles, then close it.

- Open the inner valve again and make sure the fluid flows clean and bubble-free from there, too, before re-tightening it.

LOL, I missed the inner bleeder valves. Fronts are full of old fluid, but if the rear inner calipers are full of air, that's probably the worst of my problems right there.

Edit: I bled both rear inner calipers with my son manning the brake (bunch of air came out both). We pumped the brakes 2 more times after the bubbles stopped, and gave a pump from the outer caliper, too. I then moved to the front... and the inner caliper bled blue? Not sure what's going on there as they *should* have been full of yellow fluid, but I stopped, cleaned up with brake cleaner and hosed everything down very well.

Brake pedal feels stiff now, and braking feels as good as ever, maybe even better, and no problem locking up the tires at low speeds (25-30mph). Am I done, or is there still danger? I at least feel safe driving to work on Monday, although I have an autocross next Sunday.

Edited by grover
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Well, after driving a bit, I think there's still a small amount of air trapped in the lines somewhere. It's not bad, but it's still a little squishy if I push hard enough. What's the best way to flush it out, would bleeding the lines a full cycle (EG, 5 or so brake pedal pumps) push it out? I'm quickly running out of fresh fluid, though, there's not much left of my 1L bottle of ATE Super Blue :(

Edited by grover
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You might be surprised how little air in the system will make the pedal feel soft. I would bleed again until it is firm. Make sure you do each wheel position, first the outer, then the inner bleeder valve. You probably don't need to do the pedal pumping routine anymore, and since you seem to have it most of the way, I doubt now that you'd need more than another liter to do it again (especially w/o needing to do a clutch circuit). Never re-use any fluid.

--Brian

Edited by Q-Ship986
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Today was the first time I've flushed the brakes on my 2004 986S. I got a new bottle of new fluid (ATE Super Blue to make it easy), picked up a loaner vacuum bleeder from the local auto parts store, and went to it.

I didn't realize there were two compartments in the fluid reservoir, and accidentally bled both rear lines completely dry. I refilled with new fluid and bled all 4 wheels until new fluid came out, but the brake pedal is going straight to the floor and I'm hearing a whooshing sound from the master cylinder (probably all that fluid rushing to compress the air.)

I had my son pump the brake pedal while I held the pressure bleeder, and both rear brakes are looking bubble free, but my pedal still goes to the floor. Help! What do I do now?

I saw that Durametric's version 6 (now in beta, see www.durametric.com) supports brake bleeding. This would allow you to get any air out of the ABS pump.

JP

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Today was the first time I've flushed the brakes on my 2004 986S. I got a new bottle of new fluid (ATE Super Blue to make it easy), picked up a loaner vacuum bleeder from the local auto parts store, and went to it.

I didn't realize there were two compartments in the fluid reservoir, and accidentally bled both rear lines completely dry. I refilled with new fluid and bled all 4 wheels until new fluid came out, but the brake pedal is going straight to the floor and I'm hearing a whooshing sound from the master cylinder (probably all that fluid rushing to compress the air.)

I had my son pump the brake pedal while I held the pressure bleeder, and both rear brakes are looking bubble free, but my pedal still goes to the floor. Help! What do I do now?

I saw that Durametric's version 6 (now in beta, see www.durametric.com) supports brake bleeding. This would allow you to get any air out of the ABS pump.

JP

Yes, I have not tried it yet on a car - but it should work fine.

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