Page 2 of 2 FirstFirst 12
Results 11 to 19 of 19

Thread: Brake issue

  1. #11
    Verified VCDS User
    Join Date
    Dec 2017
    Location
    Italy
    Posts
    2
    Post Thanks / Like
    Hi everybody from italy. I'm a satisfied VCDS owner, I'm not a professionist, I'm a mechanical and engine lover. I was reading all this forum looking for informations about VCDS bleed procedure, the legendary procedure, I found this thread, interesting. Old, but interesting.
    Must say that people should write if the problem is fixed at the end, not only wait for answers and then disappear. So we can't know if solutions were right.
    Anyway, I spent my last 2 years talking to VW official technicians, seeing officials VW instructions (in VW garages, not Bentley or others instructions), then reading thousands of web pages about people bleeding VW with VCDS in various absolutely wrong ways.

    Now I talk about VW cars equipped with MK60 ABS unit, only ABS no ESP.
    Must say that VW instructions ask to use a pressure bleeder at least 2 bar / 29 PSI, no other way to bleed. So procedures like the old "press and release pedal with 2 people" or like "vacuum bleed" (which works only at absolute atmospherical pressure) or home made/cheap "pressure bleed" which works at a too low pressure become completely inappropriate.
    I'm surprised that VW instructions do not say anything about OBD bleed procedure and all VW technicians confirm that they never had to bleed any new/drained MK60 ABS unit in their career. The only way to bleed them is to pressure bleed, pressure must not be less than 2 bar / 29 PSI to get air out of ABS unit.
    They say that OBD bleed procedure is requested only for MK60/EC1 ESP (and late versions) equipped cars due to very narrow conduits of the ESP unit.
    I can confirm that I was able to bleed a drained ABS unit without VCDS, just using a 2,5 bar bleeder. I test drove the car and it braked correctly, then I tried also a VCDS bleed and the brakes were exactly the same. No differences.

    Now I talk about our VCDS.
    It has 2 advanced ABS-Brakes functions that are normally used:
    03 - Output test
    04 - Basic settings
    What I report reading web pages is that people uses "03 - Output test" to bleed brakes! Crazy! Fool! This function is just to verify functionality of ABS valves, to check if brake is applied or not for every single wheel with brake pedal pressed or not. It's a long procedure and requests 2 people, one on board to press or release pedal, other off the car (which is lifted) to manually check if wheels are free or braked, just following detailed instructions on VCDS screen. No bleeder screw has to be opened during this test!
    I read about people who says that were able to get air out of the ABS unit using the "Output test" and they believe to have done a good job. Ok, let's them be happy.

    The only bleed procedure can be found in "04 - basic settings", selecting "group 1". It has four steps which are repeated in loop until user decides to stop. There is any massage to confirm that procedure is ended.

    1) Starting procedure makes appear message "Press brake pedal and hold". You press pedal like a normal stop and istantly it drops near to the floor because ABS valves are opened and fluid goes into expansion chambers. Please keep pressing pedal like a normal stop, dont' let it. After few seconds we can hear ABS pump activated for a few seconds, fluid is pumped from ABS unit to the master cilynder, so pedal is pushed back with force, you can feel your foot pushed back. Please don't be scared, keep pressing pedal like a normal stop while it's moved back and it's very important you let pedal come back, don't try to keep it down to the floor, it must come back to the normal brake position.

    2) Second step appears automatically. "Release brake pedal and open FL/FR bleed screws". Easy. Let the pedal, get off from the vehicle and open both front bleed screws. it's clear that there is no reason to open bleed screws if brake system is not under pressure.
    This operation must obviously be done while a pressure bleeder is connected.

    3) Third step appears only after confirm previous step. "Wait 10 seconds", ABS pump is automatically activated for 10 seconds. Brake fluid is moved from ABS unit to the master cylinder. (Must say that some people on the web believe that this pump activation is to pump fluid out of calipers, this is not true, fluid is pushed out by pressure bleeder, while ABS pump moves fluid from ABS unit to master cylinder).

    4) Fourth step appears automatically. "Press brake pedal 10 times then close bleed screws". Another clue that this operation must be done with a pressure bleeder. In other cases, air will be sucked back every time the pedal is released. 10 pedal pressions just help old fluid (which is already pressurized) to be pushed out of the calipers in less time. They are not counted from VCDS in anyway, they are not counted from ABS unit, 10 pressions are a theorical number of pressions to help fluid to be pushed out. I believe that they are not really necessary, we can let the pressure bleeder does its work until new fluid comes out whitout touching brake pedal.

    Now if we press "continue" button, VCDS goes back to the first step and repeats the 4 steps in loop. So there is no message which confirms that procedure is complete. We have to decide when to stop it. When we are sure that only new brake fluid is coming out with no air we can stop at the step 4, we close bleed screws and select "Done, go back" then "Close controller, go back" buttons on VCDS, ABS unit status will return normal and we can disconnect VCDS and pressure bleeder.

    Some final considerations:

    Why VW technicians use only pressure bleeder to bleed ABS units while an ABS unit bleed procedure is possible?
    Many people goes crazy using wrong ways to bleed, they keep to get a spongy brake pedal, then they buy VCDS to perform ABS unit bleed but in many cases they don't fix the problem. That's because of the bleeding method, not of the VCDS.
    I can suggest:
    - Forgot old bleeding method "press and release pedal with 2 people". If there's any air bubble in the ABS unit, it will come back up into unit every time you release pedal, also if bleeder screw is closed. Fluid movement must be costant to take air out.
    - Forgot vacuum bleeders, they are not serious, not only for low pressure but also because some air is ever sucked from bleed screws (Venturi effect), we cant' be sure if fluid is really coming out without air and an old bleeding method (press and release with 2 people) is anyway needed at the end.
    - Cheap pressure bleeders make too low pressure, about 10/15 PSI, too far from 29 PSI requested from VW. So maybe that they are not able to push air bubbles out of ABS unit. In this case (and only in this case) I must believe that VCDS bleed function can help, especiallly in the step when it asks to press pedal 10 times. Maybe that this will help old fluid and air bubbles to get out of the ABS unit. I suggest to press and release the pedal very very slow to let time to cheap pressure bleeder to mantain pressure. If pedal is released too fast may be that air is sucked back into calipers.
    - Pressure bleeders at least 2 bar / 29 PSI are professional and very expensive and normally are designed to contain several liters of brake fluid. I have mine, I'm lucky to have found a used one. Consider what is cheap for you. Take your car to a VW garage to do a good brakes job for next 2 years or spend a lot of time and money to do bad job on youself and get a dangerous car?

    I'm happy to discuss about with anyone.

    Regards and happy new year.
    Last edited by AleZava; 12-31-2017 at 12:55 PM. Reason: grammatical errors

  2. Likes Uwe, Mr. M, vodonnell, toniodiaz, NZDubNurd, Eric liked this post
  3. #12
    Verified VCDS User
    Join Date
    Jan 2017
    Location
    Ireland
    Posts
    18
    Post Thanks / Like
    I have a 09 audi a6 with abs and eps used the pressure method as described in the vw literature to change break fluid no problems and straight forward would recommend it, are your calibers in good condition, no rust on the pistons to impede their operation, basics need to be right first.

  4. Likes Uwe, Jack@European_Parts liked this post
  5. #13
    NostraJackAss Jack@European_Parts's Avatar
    Join Date
    Jan 2014
    Location
    1001 State Route 17K Montgomery New York 12549
    Posts
    16,095
    Post Thanks / Like
    Hi everybody from italy. I'm a satisfied VCDS owner, I'm not a professionist, I'm a mechanical and engine lover. I was reading all this forum looking for informations about VCDS bleed procedure, the legendary procedure, I found this thread, interesting. Old, but interesting.
    Must say that people should write if the problem is fixed at the end, not only wait for answers and then disappear. So we can't know if solutions were right.
    Anyway, I spent my last 2 years talking to VW official technicians, seeing officials VW instructions (in VW garages, not Bentley or others instructions), then reading thousands of web pages about people bleeding VW with VCDS in various absolutely wrong ways.

    Now I talk about VW cars equipped with MK60 ABS unit, only ABS no ESP.
    Must say that VW instructions ask to use a pressure bleeder at least 2 bar / 29 PSI, no other way to bleed. So procedures like the old "press and release pedal with 2 people" or like "vacuum bleed" (which works only at absolute atmospherical pressure) or home made/cheap "pressure bleed" which works at a too low pressure become completely inappropriate.
    I'm surprised that VW instructions do not say anything about OBD bleed procedure and all VW technicians confirm that they never had to bleed any new/drained MK60 ABS unit in their career. The only way to bleed them is to pressure bleed, pressure must not be less than 2 bar / 29 PSI to get air out of ABS unit.
    They say that OBD bleed procedure is requested only for MK60/EC1 ESP (and late versions) equipped cars due to very narrow conduits of the ESP unit.
    I can confirm that I was able to bleed a drained ABS unit without VCDS, just using a 2,5 bar bleeder. I test drove the car and it braked correctly, then I tried also a VCDS bleed and the brakes were exactly the same. No differences.

    Now I talk about our VCDS.
    It has 2 advanced ABS-Brakes functions that are normally used:
    03 - Output test
    04 - Basic settings
    What I report reading web pages is that people uses "03 - Output test" to bleed brakes! Crazy! Fool! This function is just to verify functionality of ABS valves, to check if brake is applied or not for every single wheel with brake pedal pressed or not. It's a long procedure and requests 2 people, one on board to press or release pedal, other off the car (which is lifted) to manually check if wheels are free or braked, just following detailed instructions on VCDS screen. No bleeder screw has to be opened during this test!
    I read about people who says that were able to get air out of the ABS unit using the "Output test" and they believe to have done a good job. Ok, let's them be happy.

    The only bleed procedure can be found in "04 - basic settings", selecting "group 1". It has four steps which are repeated in loop until user decides to stop. There is any massage to confirm that procedure is ended.

    1) Starting procedure makes appear message "Press brake pedal and hold". You press pedal like a normal stop and istantly it drops near to the floor because ABS valves are opened and fluid goes into expansion chambers. Please keep pressing pedal like a normal stop, dont' let it. After few seconds we can hear ABS pump activated for a few seconds, fluid is pumped from ABS unit to the master cilynder, so pedal is pushed back with force, you can feel your foot pushed back. Please don't be scared, keep pressing pedal like a normal stop while it's moved back and it's very important you let pedal come back, don't try to keep it down to the floor, it must come back to the normal brake position.

    2) Second step appears automatically. "Release brake pedal and open FL/FR bleed screws". Easy. Let the pedal, get off from the vehicle and open both front bleed screws. it's clear that there is no reason to open bleed screws if brake system is not under pressure.
    This operation must obviously be done while a pressure bleeder is connected.

    3) Third step appears only after confirm previous step. "Wait 10 seconds", ABS pump is automatically activated for 10 seconds. Brake fluid is moved from ABS unit to the master cylinder. (Must say that some people on the web believe that this pump activation is to pump fluid out of calipers, this is not true, fluid is pushed out by pressure bleeder, while ABS pump moves fluid from ABS unit to master cylinder).

    4) Fourth step appears automatically. "Press brake pedal 10 times then close bleed screws". Another clue that this operation must be done with a pressure bleeder. In other cases, air will be sucked back every time the pedal is released. 10 pedal pressions just help old fluid (which is already pressurized) to be pushed out of the calipers in less time. They are not counted from VCDS in anyway, they are not counted from ABS unit, 10 pressions are a theorical number of pressions to help fluid to be pushed out. I believe that they are not really necessary, we can let the pressure bleeder does its work until new fluid comes out whitout touching brake pedal.

    Now if we press "continue" button, VCDS goes back to the first step and repeats the 4 steps in loop. So there is no message which confirms that procedure is complete. We have to decide when to stop it. When we are sure that only new brake fluid is coming out with no air we can stop at the step 4, we close bleed screws and select "Done, go back" then "Close controller, go back" buttons on VCDS, ABS unit status will return normal and we can disconnect VCDS and pressure bleeder.

    Some final considerations:

    Why VW technicians use only pressure bleeder to bleed ABS units while an ABS unit bleed procedure is possible?
    Many people goes crazy using wrong ways to bleed, they keep to get a spongy brake pedal, then they buy VCDS to perform ABS unit bleed but in many cases they don't fix the problem. That's because of the bleeding method, not of the VCDS.
    I can suggest:
    - Forgot old bleeding method "press and release pedal with 2 people". If there's any air bubble in the ABS unit, it will come back up into unit every time you release pedal, also if bleeder screw is closed. Fluid movement must be costant to take air out.
    - Forgot vacuum bleeders, they are not serious, not only for low pressure but also because some air is ever sucked from bleed screws (Venturi effect), we cant' be sure if fluid is really coming out without air and an old bleeding method (press and release with 2 people) is anyway needed at the end.
    - Cheap pressure bleeders make too low pressure, about 10/15 PSI, too far from 29 PSI requested from VW. So maybe that they are not able to push air bubbles out of ABS unit. In this case (and only in this case) I must believe that VCDS bleed function can help, especiallly in the step when it asks to press pedal 10 times. Maybe that this will help old fluid and air bubbles to get out of the ABS unit. I suggest to press and release the pedal very very slow to let time to cheap pressure bleeder to mantain pressure. If pedal is released too fast may be that air is sucked back into calipers.
    - Pressure bleeders at least 2 bar / 29 PSI are professional and very expensive and normally are designed to contain several liters of brake fluid. I have mine, I'm lucky to have found a used one. Consider what is cheap for you. Take your car to a VW garage to do a good brakes job for next 2 years or spend a lot of time and money to do bad job on youself and get a dangerous car?

    I'm happy to discuss about with anyone.

    Regards and happy new year.
    Nice post but a little inaccurate and long
    Standard brake bleeding for ABS while engine is running, or static gravity bleeds are also possible & in "all" systems, as is using the outputs or basic settings with multiple technicians depending on control units ability based on firmware/hardware.

    There is a reason the RTFB states otherwise & it is not to be substituted for a forum or a guide on NHTSA approved safety systems or possible enhancement's & which can be done with a scan tool & not for all possible controllers.

    http://forums.ross-tech.com/showthre...ll=1#post14197

    I reiterate Uwe's position here:
    http://forums.ross-tech.com/showthre...ll=1#post14191

    http://forums.ross-tech.com/showthre...uot-JPPSG-quot
    Last edited by Jack@European_Parts; 12-31-2017 at 11:20 PM.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
    Certified Master Trained NY/BAR/BAD 7076062/ASE/SAE/NASTF Legal Factory Authorized/Licensed GeKo/FaZit # 403738
    Specializing in Custom Services IE: "welding-fabrication" / EPA-SMOG Update or Pass-Thru-Programming / Data Transfer / Immobilizers & OEM Quality Parts
    Above Magic! No Written record, AUTO-SCAN or Appointment = NO HELP!
    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email or call facility for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

  6. #14
    Benevolent Dictator Uwe's Avatar
    Join Date
    Jan 2014
    Location
    Earth
    Posts
    23,788
    Post Thanks / Like
    Blog Entries
    1
    Jack -- please stop demanding Auto-Scans from people who aren't asking for help.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

  7. #15
    Verified VCDS User
    Join Date
    Dec 2017
    Location
    Italy
    Posts
    2
    Post Thanks / Like
    I'm sure that if we let all bleed screws open, brake liquid will slowly get out due to gravity, so we can put new liquid into reservoir until we see new liquid outcoming from calipers.
    But air has less density than brake liquid, so I'm sure that a gravity bleed can't take away many air bubble, especially from ABS unit.
    Many little air bubbles remain adherent to surfaces due to molecular cohesion/surface tension, phenomenon that can be observed also in natural water inside plastic bottles.
    Brake liquid must be moved with a certain speed to catch all little air bubbles and drag them away.
    A gravity bleed is a poor method, maybe good to subsitute brake liquid but not for bleeding air.

  8. Likes vodonnell, Uwe liked this post
  9. #16
    Verified VCDS User
    Join Date
    Jul 2019
    Location
    Czech Republic
    Posts
    2
    Post Thanks / Like
    Quote Originally Posted by AleZava View Post
    Hi everybody from italy. I'm a satisfied VCDS owner, I'm not a professionist, I'm a mechanical and engine lover. I was reading all this forum looking for informations about VCDS bleed procedure, the legendary procedure, I found this thread, interesting. Old, but interesting.
    Must say that people should write if the problem is fixed at the end, not only wait for answers and then disappear. So we can't know if solutions were right.
    Anyway, I spent my last 2 years talking to VW official technicians, seeing officials VW instructions (in VW garages, not Bentley or others instructions), then reading thousands of web pages about people bleeding VW with VCDS in various absolutely wrong ways.

    Now I talk about VW cars equipped with MK60 ABS unit, only ABS no ESP.
    Must say that VW instructions ask to use a pressure bleeder at least 2 bar / 29 PSI, no other way to bleed. So procedures like the old "press and release pedal with 2 people" or like "vacuum bleed" (which works only at absolute atmospherical pressure) or home made/cheap "pressure bleed" which works at a too low pressure become completely inappropriate.
    I'm surprised that VW instructions do not say anything about OBD bleed procedure and all VW technicians confirm that they never had to bleed any new/drained MK60 ABS unit in their career. The only way to bleed them is to pressure bleed, pressure must not be less than 2 bar / 29 PSI to get air out of ABS unit.
    They say that OBD bleed procedure is requested only for MK60/EC1 ESP (and late versions) equipped cars due to very narrow conduits of the ESP unit.
    I can confirm that I was able to bleed a drained ABS unit without VCDS, just using a 2,5 bar bleeder. I test drove the car and it braked correctly, then I tried also a VCDS bleed and the brakes were exactly the same. No differences.

    Now I talk about our VCDS.
    It has 2 advanced ABS-Brakes functions that are normally used:
    03 - Output test
    04 - Basic settings
    What I report reading web pages is that people uses "03 - Output test" to bleed brakes! Crazy! Fool! This function is just to verify functionality of ABS valves, to check if brake is applied or not for every single wheel with brake pedal pressed or not. It's a long procedure and requests 2 people, one on board to press or release pedal, other off the car (which is lifted) to manually check if wheels are free or braked, just following detailed instructions on VCDS screen. No bleeder screw has to be opened during this test!
    I read about people who says that were able to get air out of the ABS unit using the "Output test" and they believe to have done a good job. Ok, let's them be happy.

    The only bleed procedure can be found in "04 - basic settings", selecting "group 1". It has four steps which are repeated in loop until user decides to stop. There is any massage to confirm that procedure is ended.

    1) Starting procedure makes appear message "Press brake pedal and hold". You press pedal like a normal stop and istantly it drops near to the floor because ABS valves are opened and fluid goes into expansion chambers. Please keep pressing pedal like a normal stop, dont' let it. After few seconds we can hear ABS pump activated for a few seconds, fluid is pumped from ABS unit to the master cilynder, so pedal is pushed back with force, you can feel your foot pushed back. Please don't be scared, keep pressing pedal like a normal stop while it's moved back and it's very important you let pedal come back, don't try to keep it down to the floor, it must come back to the normal brake position.

    2) Second step appears automatically. "Release brake pedal and open FL/FR bleed screws". Easy. Let the pedal, get off from the vehicle and open both front bleed screws. it's clear that there is no reason to open bleed screws if brake system is not under pressure.
    This operation must obviously be done while a pressure bleeder is connected.

    3) Third step appears only after confirm previous step. "Wait 10 seconds", ABS pump is automatically activated for 10 seconds. Brake fluid is moved from ABS unit to the master cylinder. (Must say that some people on the web believe that this pump activation is to pump fluid out of calipers, this is not true, fluid is pushed out by pressure bleeder, while ABS pump moves fluid from ABS unit to master cylinder).

    4) Fourth step appears automatically. "Press brake pedal 10 times then close bleed screws". Another clue that this operation must be done with a pressure bleeder. In other cases, air will be sucked back every time the pedal is released. 10 pedal pressions just help old fluid (which is already pressurized) to be pushed out of the calipers in less time. They are not counted from VCDS in anyway, they are not counted from ABS unit, 10 pressions are a theorical number of pressions to help fluid to be pushed out. I believe that they are not really necessary, we can let the pressure bleeder does its work until new fluid comes out whitout touching brake pedal.

    Now if we press "continue" button, VCDS goes back to the first step and repeats the 4 steps in loop. So there is no message which confirms that procedure is complete. We have to decide when to stop it. When we are sure that only new brake fluid is coming out with no air we can stop at the step 4, we close bleed screws and select "Done, go back" then "Close controller, go back" buttons on VCDS, ABS unit status will return normal and we can disconnect VCDS and pressure bleeder.

    Some final considerations:

    Why VW technicians use only pressure bleeder to bleed ABS units while an ABS unit bleed procedure is possible?
    Many people goes crazy using wrong ways to bleed, they keep to get a spongy brake pedal, then they buy VCDS to perform ABS unit bleed but in many cases they don't fix the problem. That's because of the bleeding method, not of the VCDS.
    I can suggest:
    - Forgot old bleeding method "press and release pedal with 2 people". If there's any air bubble in the ABS unit, it will come back up into unit every time you release pedal, also if bleeder screw is closed. Fluid movement must be costant to take air out.
    - Forgot vacuum bleeders, they are not serious, not only for low pressure but also because some air is ever sucked from bleed screws (Venturi effect), we cant' be sure if fluid is really coming out without air and an old bleeding method (press and release with 2 people) is anyway needed at the end.
    - Cheap pressure bleeders make too low pressure, about 10/15 PSI, too far from 29 PSI requested from VW. So maybe that they are not able to push air bubbles out of ABS unit. In this case (and only in this case) I must believe that VCDS bleed function can help, especiallly in the step when it asks to press pedal 10 times. Maybe that this will help old fluid and air bubbles to get out of the ABS unit. I suggest to press and release the pedal very very slow to let time to cheap pressure bleeder to mantain pressure. If pedal is released too fast may be that air is sucked back into calipers.
    - Pressure bleeders at least 2 bar / 29 PSI are professional and very expensive and normally are designed to contain several liters of brake fluid. I have mine, I'm lucky to have found a used one. Consider what is cheap for you. Take your car to a VW garage to do a good brakes job for next 2 years or spend a lot of time and money to do bad job on youself and get a dangerous car?

    I'm happy to discuss about with anyone.

    Regards and happy new year.
    Nice post! One thing. If you open FL and FR ABS pump actually pumps fluid out of calipers, not back to master cylinder. Tested today. How did you find it is pumping back to master cylinder? I am very interested. It would make sense..

  10. #17
    NostraJackAss Jack@European_Parts's Avatar
    Join Date
    Jan 2014
    Location
    1001 State Route 17K Montgomery New York 12549
    Posts
    16,095
    Post Thanks / Like
    It doesn't and it won't if you don't do it wrong!

    The only reason something like the OP stated happens is when someone pumps or releases a pedal with a bleeder open.

    It's called fluid mechanics and why when you compress a caliper piston why fluid reverse flows inverse & through the lines, a bias & ABS manifold/pump
    too and back to the fluid tank.

    PASCAL WTF was he thinking writing laws right?

    https://en.m.wikipedia.org/wiki/Pascal%27s_law

    Using the ABS pump to bleed brakes is a mistake! Unless it is called for specifically by the RTFB!


    Fun stuff to read while dropping anchor.

    http://www.vaglinks.com/vaglinks_com...on_Control.pdf

    http://www.volkspage.net/technik/ssp/ssp/SSP_204.pdf
    Last edited by Jack@European_Parts; 07-07-2019 at 07:03 PM.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
    Certified Master Trained NY/BAR/BAD 7076062/ASE/SAE/NASTF Legal Factory Authorized/Licensed GeKo/FaZit # 403738
    Specializing in Custom Services IE: "welding-fabrication" / EPA-SMOG Update or Pass-Thru-Programming / Data Transfer / Immobilizers & OEM Quality Parts
    Above Magic! No Written record, AUTO-SCAN or Appointment = NO HELP!
    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email or call facility for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

  11. #18
    Verified VCDS User
    Join Date
    Jul 2019
    Location
    Czech Republic
    Posts
    2
    Post Thanks / Like
    Sorry man it was done according to instructions and it came out through caliper bleed screws How did you do it that is came back to master cylinder?

  12. #19
    Verified VCDS User NZDubNurd's Avatar
    Join Date
    Nov 2014
    Location
    New Zealand
    Posts
    997
    Post Thanks / Like
    Quote Originally Posted by ivantichy View Post
    Nice post! One thing. If you open FL and FR ABS pump actually pumps fluid out of calipers, not back to master cylinder. Tested today. How did you find it is pumping back to master cylinder? I am very interested. It would make sense..
    I believe he's correct (and you too!), but it's just not 100% clear what he means:

    Based on my limited understanding/experience:

    He didn't say it doesn't come out the bleeders while the pump is activated - he's saying that two processes are happening simultaneously: the pump is actually circulating fluid internally through the ABS block (pump valves) and the pressure-bleeder is feeding the fluid out the callipers - two different processes, but at the same time. So there is fluid coming out the bleeders, but the pump isn't doing it. The pump is doing a different process; pumping air out of the pressure release circuit and valves.

    This actually makes complete sense, as it would eject the air out of the pump/valve system, as the fluid moves through, taking the air bubbles with it. That return path is only normally opened when the ABS require reduced pressure at the calliper, so would not be bled during a standard bleeding procedure as those particular valves are normally closed - the circuit needs to be opened, but also the pump needs to circulate fluid through it, to eject the air from the entire release circuit, including the pump, pressure accumulator and the return into the internal system inlet.

    Jack already linked to the SSP regarding the hydraulic layout: http://www.vaglinks.com/vaglinks_com...on_Control.pdf

    You can see one of each front calliper will bleed each side of the system, as the brakes are diagonally split.

    Process 1: Non-aerated (fresh) fluid is moving down from the master and direct through the block to the callipers and out.

    Process 2: The pump circulates aerated fluid from within it's own circuit, into the ABS inlet (internally) and it mixes with the fresh fluid from Process 1. Process 1 then "washes" the air bubbles out through the callipers. The cycles are repeated more than once, to ensure all air is ejected from the system, as a certain amount of internal recirculation could happen.

    The MK60 doesn't use an external charge pump, like some other systems, so requires this internal "flush" to empty that circuit of air. Systems with an external charge pump and return line to the Master cylinder reservoir can do this same process, without requiring internal flow through the path the the callipers.
    Allan
    The R32ran Thread
    How to post a full Auto-Scan
    "Duct tape can't fix stupid, but it can muffle the sound"

  13. Likes Uwe, Jack@European_Parts liked this post

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •