Urgent: Brakes Not Bleeding

[gilber33]

Backstory:

When I got my A4 a few months it needed new brakes. Installed new calipers, pads, rotors, and SS lines. The pedal feel was never great and the new pads never bedded properly and caused very poor braking. In an attempt to cure that, I flushed the system with OEM fluid using my motive power bleeder. Brakes were still poor.

Fast forward:

Installed front brakes from an S4 with SS lines to replace the bad pads and rotors. I went to bleed the system and no matter how many times I did each caliper I had air in the lines, always about the same amount. I would get about 5 seconds of bubbles, then it would flow. I did each caliper about 8-10 times. I tried with my motive bleeder, I gravity bled, and I had my wife press the pedal while I bled. All with the same results of having air in the lines.

Tonight I had a friend come over with his nicer motive bleeder (it sealed better at the reservoir) and we tried bleeding. Again, did each caliper about 3 times and each time I had air in the lines. The pedal feel was better, but not still not there.

We tried a combination of power bleeding and pedal. After doing this the pedal got worse, almost dead. The fluid reservoir got low during this, but did NOT empty.

In between bleedings tonight I closed up the reservoir and started the car to feel the pedal (with the car off the pedal is rock solid and doesn't have any motion). Then I noticed after we shut the car off there was a hissing sound coming from the master cylinder area somewhere that lasted maybe 30 seconds.



Cliff notes:

Doesn't matter how many times or in what fashion I bleed the brakes, they always have air in the lines. After 10-15 rounds of bleeding the calipers, the pedal is dead. In between bleedings I started the car to get a feel for the pedal and after I shut the car off, I am getting an hissing sound from somewhere near the master cylinder.

Any help would be appreciated.

[jacobsen]

Sounds like an air leak at the master then, you also need to cycle the abs pump to clean it out.

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[Spike00513]

In my experience, if you think the reservoir got low, then that means it got empty and filled the system with PITA air.
A tool is only as good as the person using it, and this mistake taught me to use it differently.
Now, I prep it in a way that at all times, the fluid intake is maxed above the reservoir, and even built up in the plastic Motive tubing that I hang from the opened hood top with a bungee cord.

And to keep it from magically pulling in air from anywhere, I also take it slow. Which is frustrating because I take more time, rather than just a quick 10min job.
I think diag said he can open the bleeder screw a whole two full turns for max fast fluid flow and that this helps get air out. But I always ran into problems trying. So as I said above, I go slow/little. On top of that, if I went a lot, it would try seeping out the sides of the screw threads too. Putting some anti-size seems to have helped. I think there's a rubberized product specifically for this on the market but I never tried it. I only put anti-sieze on that and the line connections as per a volvo or benz forum tip on old corroded cars, to protect it.
Plus, the bleeder screw seems to be made of a soft metal, and get stuck over time, so hopefully it helps with that. Next time I service it, I don't wanna strip anything.
I might've used the wrong wrench too, which only adds to that. Imagine using a 6pt socket tight on a 6pt bolt, versus a 12pt loose socket on it.

Might've even used 4L that time, to fix my mistake.
Otherwise during regular routine bleeding I might use 1, 1.5, or 2L.

Unfortunately I can't offer much beyond that, because I don't even know how the brake master cylinder works. Maybe someone else will chime in. Wonder if anything is leaking.

[5ktq]

did you let air into the mc ever? maybe air in the ABS pump, need vag com and a quart of brake fluid to bleed it.

id imagine hissing is the seals between mc and reservoir,

[gilber33]

Sounds like an air leak at the master then, you also need to cycle the abs pump to clean it out.

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The system appears to have a leak. It's pulling air in every time I bleed it. And maybe numerous bleeding attempts put it over the edge.

[gilber33]

did you let air into the mc ever? maybe air in the ABS pump, need vag com and a quart of brake fluid to bleed it.

id imagine hissing is the seals between mc and reservoir,

Not that I know of. Like I said, it got low, but it wasn't empty.

I have a the hex can cable clone from ebay on the way that if I need to I can bleed the abs with.

Kind of sounds like a new MC might be needed here.

[DarkoNova]

Yeah, sounds like the master got air in it or there's a leak somewhere. Do you have any signs of brake fluid leaking anywhere?

Does the reservoir stay topped off if you leave it overnight or does it drop at all?

Honestly, I've heard you need to cycle the abs pump when bleeding the brakes for basically every car that has abs, but I've never actually done it. I seriously doubt that's your issue.

[gilber33]

Yeah, sounds like the master got air in it or there's a leak somewhere. Do you have any signs of brake fluid leaking anywhere?

Does the reservoir stay topped off if you leave it overnight or does it drop at all?

Honestly, I've heard you need to cycle the abs pump when bleeding the brakes for basically every car that has abs, but I've never actually done it. I seriously doubt that's your issue.

No signs of brake fluid leaking anywhere. If I had gotten air into the master, any idea what would be causing the hissing sound after the car is turned off?

Fluid level does not drop in the reservoir.

[5ktq]

I didn't realize the car was running. Hiss is probably you losing vacuum in the booster. That's not going to be directly related ( it's servo assist related but not air in lines related).

You can look for vac leaks around there, that suction jet pump, the extra reservoir, checkvalves.. all that can leak vac. The booster itself too, but I think less likely.

I'd bet on the SJP though.

I've always done my pump bleeding with the car off? *shrug*

[jacobsen]

Yes bleeding is done with the car off. A word of advice is that if you are bleeding the brakes by using the brake pedal if you push down too far say any more than halfway or two-thirds of the way you will be pushing the rubber seals Beyond there working life. They normally don't travel that far back and when you do that you basically destroyed those seals and can cause a massive air leak. That's why it's best to use a power bleeder so you never run into that circumstance as well as the other added benefits. But if you hear a hissing sound that is very much a Telltale sign of a vacuum leak. The suction jet pump is known to crack and break and so there is an upgraded part number now from when these cars were new. Definitely inspect all the vacuum lines because a vacuum leak will cause very poor brake performance.

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[gilber33]

Bleeding was always done with the car off. I should have been a little more clear with that. In between bleedings I closed up the reservoir and started the car to see how the pedal felt. With the car off the pedal is rock solid and I don't have any motion of it.

This hissing was coming from the brake booster area after the car was shut off. It was coming from the booster area ONLY after the car was shut off. It was not coming from the engine bay. I do not have any vac leaks. Running -21 in/hg at idle. I went through the entire vac system when I got the car.

[5ktq]

Yeah I don't know about that, I can't see anything hydraulic and not being used hissing for 30 seconds, vac near the booster leaking makes more sense.

If you shut it down the pedal should stay soft (= has assist) until you use it once or twice, or wait a very long time (as the booster will be full of vac and save it, unless it's leaking).

If you shut the car off and 30s later the pedal is rock hard... you got a vacuum leak. it can be miniscule, not effect idle, but the booster will still empty with a tiny leak. In this case the leak would be after the SJP (checkvalve on a normal car). so SJP, the other checvalve, that elbow, hose to the booster, grommet where the hose enters the booster, or the booster itself.

If you're dedicated you can put a tee and gauge between booster and the car, it shouldn't go flat right away when you shut the car off.




buuut anyway, none of that will hurt your pedal feel unless the car is off, unless the leak is huge.



If there were a leak in the hydraulics it would suck air when you let off the brake, and piss brake fluid when you press on it.. so is it wet anywhere? If the seals inside the MC are worn they'll let fluid past (so system pressure will be weak) but shouldn't let air in, unless it's the end seal (which again, would let brake fluid out.. into / onto the booster), so even with a dead MC pressure bleeding would get the air out, I would think. (brakes still wouldn't work great, but there wouldn't be air in the system)

[gilber33]

I agree. I don't think the hissing sound is related to the hydraulic system. I feel like I have two separate issues going on right now.

There was brake fluid on the booster but I assumed it was from excess brake fluid while bleeding. My bleeder does not seal at the reservoir tight and let's fluid leak out. But I'll look again.

The hissing sound has to be vac related. I'll try spraying soapy water around the booster when I shut it off next time.

[gilber33]

Well, started the car and then shut it off and it took less than 30 seconds for the pedal to be completely hard again. So it appears the booster is at least bad. Sprayed down the whole thing and did not see where it was leaning from, so it's gotta be the the seal from the master. Going to replace both the master and booster.

Is there a special process to bench bleed the master before it goes in the car or can I install the assembly and then use vcds to bleed the system?

[5ktq]

maybe try listening for the hiss with a stethoscope first, see if you can locate the leak.


Or you could try hooking a vacuum gun directly to the booster, pump it up to -20 and see if it leaks down / is hissing

[gilber33]

maybe try listening for the hiss with a stethoscope first, see if you can locate the leak.


Or you could try hooking a vacuum gun directly to the booster, pump it up to -20 and see if it leaks down / is hissing

Is that barb on the side of the vac line where it connects to the brake booster used for that?

[gunde]

are you sure the calipers are installed correctly. left caliper on the left side and vice versa?
the bleed screw has to be higher than the caliper piston.

[gilber33]

are you sure the calipers are installed correctly. left caliper on the left side and vice versa?
the bleed screw as to be higher than the caliper piston.

Yes, they are on the correct sides. I had air in lines from all four corners, not just the front.

[jacobsen]

are you sure the calipers are installed correctly. left caliper on the left side and vice versa?
the bleed screw as to be higher than the caliper piston.

I did that once haha

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[coffeysm]

I've bled the brakes on a few different cars and honestly this A4 I have was the worst. I ended up having my mechanic fix it for me, because no matter what I did with my Motive bleeder the pedal was always spongy. I don't even crack the bleeders anymore when I change the pads, I just open the MC cap and allow the fluid back up the system. Not worth the headache...

Hissing sound could be a vacuum leak at the booster either internal or external. I had a nasty vacuum leak in my G35 that was due to an o-ring between the firewall and brake booster. Other issue is maybe the diaphram ruptured inside, but a hissing whooshing noise is normal when you press the pedal, if that's what you are hearing. Sounds like one of those things you use to give air to a fire.

[gilber33]

The hissing sound was present once turning the car off after it running for a bit. Since the pedal is completely stiff less than 30 seconds after shutting the car off, I assume the hissing sound is the vacuum leaking out of the booster.


I'm picking up a beater daily Toyota today to have for times like this. My wife is at home with our baby so I had to take her car to get to work. Which is definitely not ideal.

[jacobsen]

It's good to keep fresh fluid and flush once a year. It helps protect the seals. Also don't bleed the brakes by using the brake pedal itself. Only if you don't have a bleeder and you have to do it that way, only push down a little bit on the pedal or you'll wear out the Seals because you're pushing them too far. I have a schwaben power bleeder and I really think the thing is neat. I had some trouble bleeding my brakes initially when I first went to the big brake setup. I drove like that for a couple months. I knew there had to be air in there... So I put the car back up in the air and did it again with the power bleeder and that solved it. The first time I did it without a power bleeder having someone pump the brake pedal, and clutch pedal. It goes in order clutch first, driver front passenger front driver rear passenger rear. Priming the power bleeder line and ensuring that you're not pushing air is a good idea. You can simply hold it up high so the fluid flows down tap on the line. you should cycle the ABS pump to get the old stuff out and then the air that might be in there. This is actually a really important step. Otherwise you can stop fast a bunch of times on a dirt road or on ice but then you have to put the car in the air again.

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