brake bleeding

[Audia483]

I bleed all 4 brakes and the master cylinder yesterday and after putting 2L of brake fluid thru the system with a power bleeder I am still getting a soft pedal and air in the right rear wheel. I get my Ross Tech Vag-com today and all I can figure is that I got air in the ABS pump that will have to be bled thru the software. ABS light did come on. Does anyone know of anything else. System was opened to replace the master cylinder

[canadianA4B7]

I think I went through 4 bottles to completely bleed it all. The trans has a line on it too fed from the master (if manual) otherwise use the old pop bottle bleeder rather then power bleeder. I've never used one but heard there not the easiest units to use. I'd say your short on fluid still

[Audia483]

I think I went through 4 bottles to completely bleed it all. The trans has a line on it too fed from the master (if manual) otherwise use the old pop bottle bleeder rather then power bleeder. I've never used one but heard there not the easiest units to use. I'd say your short on fluid still

I have a cvt transmission. The master cylinder feeds directly into the abs pump. Ill be on my way to the store to buy more brake fluid and i thought 2 litres was overkill

[canadianA4B7]

I think the master holds 2 litres itself, then the full length of the line plus whatever is needed in the caliper. I have 18Z fronts so I know I use a bit more.

How low is the jug under the hood? And I always suggest 2 man brake bleeding.

[Audia483]

I think the master holds 2 litres itself, then the full length of the line plus whatever is needed in the caliper. I have 18Z fronts so I know I use a bit more.

How low is the jug under the hood? And I always suggest 2 man brake bleeding.

Reservoir is full and remained full during the bleed process. Res probably holds 1/3 liter


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[canadianA4B7]

Strange. I would re bleed and see how it is. If no leaks then it's usually just air pockets somewhere.

[Axis]

I think the master holds 2 litres itself, then the full length of the line plus whatever is needed in the caliper. I have 18Z fronts so I know I use a bit more.

How low is the jug under the hood? And I always suggest 2 man brake bleeding.

With this it can be done perfectly, alone:


Brake bleeder

Catch bottle

That system is a must for Brembo's.

[Theiceman]

I made my own with a garden sprayer for 8 bucks from the hardware store.

[Ray1031]

I made my own with a garden sprayer for 8 bucks from the hardware store.

Pictures?


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[Axis]

I made my own with a garden sprayer for 8 bucks from the hardware store.

I've seen the DIY's but I'm a lazy mofo. There's also cheaper versions, I just linked the one with the aluminium cap since the plastic version tends to leak and needs plumber teflon to work properly.

Pictures?


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[Audia483]

With this it can be done perfectly, alone:


Brake bleeder

Catch bottle

That system is a must for Brembo's.

I have the one made my motive


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[Brillo]

You might have air in the ABS unit. First, be sure your master cylinder is good and not the source of the soft pedal you are feeling. If you are still getting air in the right rear and cannot bleed it out you may have an ABS problem although this is pretty rare in my experience, and never with an Audi (so I have no direct Audi ABS brake experience). If the Audi system is like most other braking systems, during most braking situations the ABS is electrically active but not hydraulically active. When it becomes hydraulically active a pump, responding to the control unit which is detecting a difference in deceleration between the wheels, opens and closes valves depriving the wheel that is locking up (decelerating the quickest) of pressure so that it assumes the same angular velocity as the other wheels. This is very interactive and happens quickly, maybe 10 times per second.
Not to get too technical but if the valve to the right rear is stuck open that might provide a source of air into that line and result in a spongy brake pedal.
One suggestion that may work is to take the car out and force the ABS to function multiple times. Do this by driving so that the right side of the car is on grass or gravel and the left on solid roadway. At speeds well above 10 mph engage in very heavy braking forcing the right side ABS valves to activate. Do this multiple times. This may unstick the valve(s) if this is the problem. It may not work but is worth a try. After you do this braking exercise, bleed the right rear to see if you can now get all the air out of this line. Bleed them the old fashion way (with two people) so you can be sure the power bleeder is not sucking air into the system through a stuck valve.
If you find that the source of you problem is the ABS unit and can't fix it you might be stuck replacing it. Possibly a good thing to buy from a reputable used parts dealer as these typically do not go bad.
I hope this is helpful to you and good luck. Very frustrating I know. Brillo

[Brillo]

I forgot to mention that what I believe the Ross Tech Vag-com allows you to do is to activate the valves in the ABS unit independently while you bleed them. This can be very helpful. I do not know if it will tell you if you have a stuck or leaky valve. Someone else chime in here.

[Theiceman]

That the exact sprayer I used. My guage wasn't as neat thought


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[canadianA4B7]

Pop bottle and 1/4" hose. Still can be done alone. Old habhits will die hard.

[Okedokey]

Check you've tightened all the bleed valves properly.

[GTFORZA]

It may be different on your car, but I know if you have the rear calipers off on a B5 there is a special procedure to remove air from them. It involves tilting them or something, but if I'm not mistaken that's only if you are starting from scratch with dry calipers. I think it has to do with bleeder position.

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[Audia483]

So I have removed all of air from the lines after bleeding 4 times but the pedal still sinks its just alot slower and now the brake lights stay on unless i disconnect the battery

[Brillo]

Is your brake pedal just spongy or does it eventually sink to the floor if you keep pressure on it?

[Audia483]

Is your brake pedal just spongy or does it eventually sink to the floor if you keep pressure on it?

I don't take it to the floor at risk of damaging the new master cylinder. It's a very slow sink now. It has me wondering if the calipers are bad on stuck or something. I have now leaking brake fluid though


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[Charles.waite]

Did you get the correct master cylinder?

[Audia483]

Did you get the correct master cylinder?

Yes, verified before I ordered


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[Brillo]

I don't take it to the floor at risk of damaging the new master cylinder. It's a very slow sink now. It has me wondering if the calipers are bad on stuck or something. I have now leaking brake fluid though


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Well, where is the fluid leaking from?? If you have a new master cylinder and it's functioning properly and you still have a sinking brake pedal you may have a valve stuck open in your ABS unit, possibly the one to your right rear. Did you try the ABS test I suggested in post #12? You seem to have enough undiagnosed issues with your brake system that you might be better off taking it to a brake specialist. Brakes are pretty critical to the function of the car. You want to be confident that they are functioning properly. While I know you are concerned about them I don't feel like we are making much progress here, but it's your call.

[Okedokey]

You still have air in there. Trust me, it takes quite a bit to remove all the air, keep bleeding.

[Brillo]

You still have air in there. Trust me, it takes quite a bit to remove all the air, keep bleeding.

Okedokey Audia483 apparently had bled a half gallon of fluid through his system. If air was the problem his pedal would just be spongy, but he claims that the pedal is sinking which is usually indicative of a leak or problem with the ABS unit. That's why I specifically asked him about this (post #19) and he now admits to a leak but doesn't say where. It just sounds like his problems are greater than air alone.

[Okedokey]

Yeah fair enough, but when I replaced my booster and master, it did the same thing until I pressure bled and shit tonnes of air came out even though I bled over a gallon of fluid the traditional brake pedal way.

[Brillo]

Okedokey - I don't claim to know that much about the Audi braking system. I have only changed pads and bled new fluid through the brake lines. I was under the impression that the clutch uses the same brake fluid reservoir as the braking system. Is is possible that one system could adversely affect the other in some weird way?

[Okedokey]

Okedokey - I don't claim to know that much about the Audi braking system. I have only changed pads and bled new fluid through the brake lines. I was under the impression that the clutch uses the same brake fluid reservoir as the braking system. Is is possible that one system could adversely affect the other in some weird way?

Look I don't know mate, I would assume yes given it's the same system but I have a cvt. make sure you bleed in correct order as it's opposite to what you may think ie furtherest caliper to closest

[Audia483]

Well, where is the fluid leaking from?? If you have a new master cylinder and it's functioning properly and you still have a sinking brake pedal you may have a valve stuck open in your ABS unit, possibly the one to your right rear. Did you try the ABS test I suggested in post #12? You seem to have enough undiagnosed issues with your brake system that you might be better off taking it to a brake specialist. Brakes are pretty critical to the function of the car. You want to be confident that they are functioning properly. While I know you are concerned about them I don't feel like we are making much progress here, but it's your call.

I meant to write that I have no leaking brake fluid. I did run the output tests thru vag-com and ABS seems to be working properly. The only trouble code I had was for low voltage to the ABS unit which is explainable because the battery was bad and I replaced it with a new battery. Visual inspection shows i probably need new brake pads. i did read an article that mentioned internal leaks in the caliper could cause this issue also. This vehicle appears the have sat for almost a year before I got it. Decent amount of rust on the rotors and many things sticking on the car but on the positive the only codes vcds gave me were related to a bad battary

[Brillo]

Audia483 I have to admit that I have never heard of an internal leak in the caliper. Typically, there are only 3 places for leaks at the caliper. 1. at the brake line input port and onto the ground, 2. at the bleed screw and onto the ground, and 3. between the piston and cylinder, passed the rubber dust dover and onto the ground. If your car sat for a year perhaps your rubber brake lines have degraded and become compliant and 'spongy' feeling. They are easy to replace but you'll have to re-bleed the system again. Just want to be sure so I'll ask - you see no brake fluid on the ground beneath any of the braking system??

[Audia483]

Audia483 I have to admit that I have never heard of an internal leak in the caliper. Typically, there are only 3 places for leaks at the caliper. 1. at the brake line input port and onto the ground, 2. at the bleed screw and onto the ground, and 3. between the piston and cylinder, passed the rubber dust dover and onto the ground. If your car sat for a year perhaps your rubber brake lines have degraded and become compliant and 'spongy' feeling. They are easy to replace but you'll have to re-bleed the system again. Just want to be sure so I'll ask - you see no brake fluid on the ground beneath any of the braking system??

Nope, no brake fluid on the ground. I have plenty of brake fluid now so I may replace the lines and rebleed

[Okedokey]

Make sure there is no air leaking at the booster

[B7S3wannabi]

When you finish bleeding the system and you pump the brake pedal, does it firm up and stay up? Is it only when you move the vehicle that the pedal sinks? If so I am going to bet you either A, have a seized slide pin on one of the calipers, or B, you have a wheel bearing or warped rotor problem. Either one will cause the piston of that caliper to be pushed back in enough to give you that issue.

[Audia483]

When you finish bleeding the system and you pump the brake pedal, does it firm up and stay up? Is it only when you move the vehicle that the pedal sinks? If so I am going to bet you either A, have a seized slide pin on one of the calipers, or B, you have a wheel bearing or warped rotor problem. Either one will cause the piston of that caliper to be pushed back in enough to give you that issue.

When I pump the brake with the car off it firms up and stays firm. When I pump it with the car on it firms and then slowly sinks

[B7S3wannabi]

Could still be a seized slide pin. Pull the rear calipers off and check that the pins move freely.

[Okedokey]

When I pump the brake with the car off it firms up and stays firm. When I pump it with the car on it firms and then slowly sinks

Booster

[Benhurb4]

Also check for vacuum leak at the booster

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