emptied reservoir while bleeding brakes

I dun goofed guys. Was bleeding brakes, son in the car pumping the pedal, me at the nipple draining the fluid. All was going fine, until it wasn't. I waited too long to check the reservoir level and it emptied. No more fluid was coming out the nipple, and the pedal went soft. So I refilled the reservoir and pressurized to 10 psi and pushed a lot of fluid through. I thought I had it beat, but nope. Softish pedal and low brake fluid error even though the reservoir is filled to the brim. Interestingly - I never saw any air come through the line even though I pushed a couple hundred ml through. So - what now - keep pumping fluid through until things clear up ? I know that air can get into the ABS pump and that's not good - but what to do about it? Thanks - away for teh weekend but back Monday to start again - I have another litre of fluid on the way from amazon.

Try bleeding the master cylinder first and then out to your calipers.

Buy a Motive brake bleeder and push more fluid through. No need to do anything else.

Quotes source post: 19587711

That has been my thought for quite a while but I've recently seen some reports that recommend "bench bleeding" a new master cylinder. I think I would at least operate the pedal a few times to fully purge the master cylinder in this case. Then do the usual bleed at the wheels.

That can and will work eventually, but..... By "pushing" fluid under pressure u will force all the air through the abs controller to the caliper very quickly. I do full system refreshes every year by myself in less then a hour. its worth the $100 tool and u can get the caps for other cars.

Quotes source post: 19587825

Do you actuate your ABS controller during your flushes? Should he do that also since he has air in the system here?

Quotes source post: 19587829

I dont and there is no need to when pressure bleading. U may have to do it with the traditional pedal push method. The issue is the amount of fluid that u can push in one stroke as opposed to just forcing the fluid through the system as a continuios stream.

Thanks all; I have a pressure setup. I use my shop compressor dialed to 10 psi and quick-connect the line to a reservoir cap with a brass barb epoxied through it. Works great. I used it yesterday to push through 1.5 litres of cheap DOT4 fluid. I also stroked the pedal while pressure flushing. The low reservoir warning is gone, but I'm still not thrilled with the firmness of the pedal. It's ok - but not rock hard. I suspect there may be air in the nooks and crannies of the cylinder bores. The pads are kinda low so there's a lot of volume in the calipers. My plan is to compress the pads completely with the bleed valve open, thereby pushing the fluid, and any air bubbles, out. Then I will push through another litre or more of fluid, this time using better quality DOT4. Away for the weekend - will report back.

If it is only softish, then it sounds like it is safe to drive on the public road. In that case find a stretch of gravel road and after having looked behind you to ensure that no-one is behind you, push the brake pedal as hard as you can and do full-4-wheel ABS activated stop. Do that a couple of times. It is the easiest way without means of activating the ABS pump and solenoids (piwis and the like).

Quotes source post: 19588355

Will probably try that... If i can find a gravel area... One question though. If there is air in the ABS pump, and i manage to activate the pump while driving, where does that air go? Does it burp back up into the reservoir? Cheers

No it pushes down the line. I would just reblead under pressure and check it again. I use 20-25psi on the motive tool

Quotes source post: 19588420

Aha.. Thanks for that. 1. Wheels on. 2. Lock em up on gravel a few times. 3. Wheels off 4. Pressure bleed

Should work or just pressure bleed again and check if the wheels r already off.

Quotes source posts: 19588420, 19588429

If the air is stuck in the ABS unit, which it probably is after having pumped 1l of fluid through and still having a soft(ish) pedal, then it will we pumped back into the MC together with the fluid by the ABS pump. You then get rid of it by normal bleeding. It is actually this pumping back which you feel through the pedal kicking back towards you during ABS braking. (The valve connects the caliper to the inlet side of the pump, which then pumps fluid into the MC. The hard/non-moving pedal is closing the ABS valve to one or more wheels and the sinking pedal is opening the valve and fluid being pushed by the driver into the caliper) If the air is past the ABS unit in a line to the caliper, then it can only be bled off through the bleed nipples on the caliper and ABS activated braking will not help. Steps 1-4 are the way to go. And check your mirror before ABS'ing! Good luck.

Update... 1) put the wheels on and headed to the big gravel parking lot at the sports field down the road. 2) the low fluid and PSM off warnings lit up on the way - despite fluid being topped up. 3) pedal felt not bad.. 4) Did about ten ABS stops in the gravel, pedal pushed back every time, ABS clearly kicking in. Did a few in reverse as well... 5) drove home without touching the brakes even once. 6) pressure bled about 250 ml fluid through the back caliper.. Just one bleed screw - through the spokes of the wheel. 7) went for a test ride - no lights, good pedal, solid hard panic stops on pavement - good enough... 8) Next day (today) pressure pushed one litre of pentosin DOT 4 through all eight bleed screws. I sucked the cheap fluid out of the reservoir first using a syringe. 9) Test ride - the hardest pedal I have ever felt. ROCK solid braking, couldn't be more happy. Funny thing - never once did I see any air bubbles coming out of the bleed screws while pressure bleeding. Weird. All is well - thanks for the guidance lads.

Quotes source post: 19593434

I recently replaced the soft brake lines on my 996. Pressure bled a bunch of fluid through every bleeder. I only saw bubbles from one of them -- and it was a LOT of bubbles. Very strange.

Quotes source post: 19593434

If the air bubbles are pumped back all the way into the MC and you then let go of the brake pedal the air can/will bleed off into the reservoir. Glad to hear the abs braking worked as intended

FWIW, you would not believe how small an air bubble in a caliper will result in a mushy pedal. Need to drive a bit, bleed. Repeat. Some say banging lightly on the caliper may release some air bubbles, YMMV. And don’t forget to do the clutch cylinders while you are in there! Also, if having someone pump the brake pedal, do not let them push all the way down; pushing all the way may result in the rubber diaphragm being pushed into a corroded area at the back of the brake cylinder, causing it to be abraded.

I read that water liquid is 775 times more dense than air, so it doesn�t surprise me that even tiny air bubbles can cause a soft pedal.