turbobrick240
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My guess is a weak master cylinder.
Poor Mk6 Golf brakes
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turbobrick240
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Not necessarily. Master cylinder could be leaking internally. Or rear calipers might be marginal.
OK, I have found the report of previous inspection for this car, when the brakes were OK.
It shows that front pushed 2.9 kN and rear was 1.8 kN. Same as my old Mk5 with lots of miles. (However, this car's brake pedal felt never that solid as my old Mk5's used to be. But it seems they push equal force at the calipers, strange). It also shows that parking brake pushed 1.3 kN.
A colleague suggested to see if the parking brake on now was tighter than the foot brake at the rear - that would show me if I had problems with hydraulic unit of rear brake calipers/pads/rotos. Also, he said that slightly wrapped rotors might cause poor performance.
I will try to pass the inspection as is. In either way, if it passes or fails, then the next thing I am going to try is to run the VCDS adaptation for 'hydraulic valves' and 'disconnecting valves' per Ross Tech's guide. I haven't ran this after I replaced the ABS module as I didn't have the fault described in the wiki.
If that does not help, I am probably going to install my original/old master cylinder back. My God, what a messy and ugly job!
It shows that front pushed 2.9 kN and rear was 1.8 kN. Same as my old Mk5 with lots of miles. (However, this car's brake pedal felt never that solid as my old Mk5's used to be. But it seems they push equal force at the calipers, strange). It also shows that parking brake pushed 1.3 kN.
A colleague suggested to see if the parking brake on now was tighter than the foot brake at the rear - that would show me if I had problems with hydraulic unit of rear brake calipers/pads/rotos. Also, he said that slightly wrapped rotors might cause poor performance.
I will try to pass the inspection as is. In either way, if it passes or fails, then the next thing I am going to try is to run the VCDS adaptation for 'hydraulic valves' and 'disconnecting valves' per Ross Tech's guide. I haven't ran this after I replaced the ABS module as I didn't have the fault described in the wiki.
If that does not help, I am probably going to install my original/old master cylinder back. My God, what a messy and ugly job!
I came accross a member in this forum who owns a Mk5 Jetta. He was doing a brake bleeding and let the reservoir go dry. This introduced lots of air into the system to a point that there were absolutely no brakes.
He bled multiple times using power bleeder (low pressure, ~15 PSI) and cycled the VCDS procedure multiple times. Brakes are back but pedal can be easily pushed to floor and the brake power ir reduced too. The case is exactly the same as mine.
I wonder how these systems should be brought back to operational level. It seems that there must be some tricks to bleed properly as doing this in "the right way" does not seem to work 100%
He bled multiple times using power bleeder (low pressure, ~15 PSI) and cycled the VCDS procedure multiple times. Brakes are back but pedal can be easily pushed to floor and the brake power ir reduced too. The case is exactly the same as mine.
I wonder how these systems should be brought back to operational level.
It seems that there must be some tricks to bleed properly as doing this in "the right way" does not seem to work 100%
Now the last thing left is to try to pressure bleed the system with pressures of a bit higher than 2 bar (30 psi).
I have had a chat with a tech at VW dealership. He said that doing the above is the way which VW procedures say to do the bleeding. I expressed my fear of blowing up the brake reservoir or clutch line when going such a high pressure. He confirmed that such things have happened in his career - this happens when the old plastic gets brittle and especially on cold days. Reservoir might blow up but clutch line should be OK.
I have a non-professional pressure bleeder rated to 20 PSI max. What I am going to do is probably I will exceed its rating to ~30 PSI and see if the bleeder itself doesn't blow up. If not, then I'm going to try to bleed the system (for the last time) at that pressure.
Question: has anyone pressure-bled the brake system on Mk5/Mk6 cars with ~2 bar? Did the reservoir survive?
I have had a chat with a tech at VW dealership. He said that doing the above is the way which VW procedures say to do the bleeding. I expressed my fear of blowing up the brake reservoir or clutch line when going such a high pressure. He confirmed that such things have happened in his career - this happens when the old plastic gets brittle and especially on cold days. Reservoir might blow up but clutch line should be OK.
I have a non-professional pressure bleeder rated to 20 PSI max. What I am going to do is probably I will exceed its rating to ~30 PSI and see if the bleeder itself doesn't blow up. If not, then I'm going to try to bleed the system (for the last time) at that pressure.
Question: has anyone pressure-bled the brake system on Mk5/Mk6 cars with ~2 bar? Did the reservoir survive?
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turbobrick240
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Why not try using the master cylinder hydraulics to pressure bleed. You could generate the higher pressures in the components designed for it. The prospect of a reservoir exploding , showering the car in brake fuid doesn't seem very appealing.
turbobrick240
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I was just referring to the old tried and true technique of having a helper pump and hold the brake pedal while you open one bleeder at a time. Doesn't produce a large volume of flow, but does produce very high pressures to dislodge air pockets and obstructions. Just keep the reservoir topped off.
Yep, this was done at least 4 times all around. No improvement.
Anyway, I took a risk and did the high pressure bleed in the backyard.
Did something explode? No. Did I spill the fluid? Yes, exactly 500 ml into engine compartment. The seal on the reservoir was not tight and once I connected it to a tyre with pressure of 2 bar, it instantly pumped the whole 500 ml around. I was topping up the bottle then and my hands started shaking and I spilled even more in the headlight area.
Everything else went fine. I bled ~400 ml per each caliper.
Did it help the brakes or pedal feel? No, not a bit. Time wasted. Don't try this at home.
Anyway, I took a risk and did the high pressure bleed in the backyard.
Did something explode? No. Did I spill the fluid? Yes, exactly 500 ml into engine compartment. The seal on the reservoir was not tight and once I connected it to a tyre with pressure of 2 bar, it instantly pumped the whole 500 ml around. I was topping up the bottle then and my hands started shaking and I spilled even more in the headlight area.
Everything else went fine. I bled ~400 ml per each caliper.
Did it help the brakes or pedal feel? No, not a bit. Time wasted. Don't try this at home.
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mu3098
Veteran Member
check out the tech note '103. Handbrake Calipers - Occasional spongy pedal' at http://brakeparts.co.uk/#!/technote
It seems to indicate it is possible that air can get trapped in the piston area of some handbrake calipers. It recommends unbolting the caliper and rotating it piston down to get the air out. It might be worth a try.
It seems to indicate it is possible that air can get trapped in the piston area of some handbrake calipers. It recommends unbolting the caliper and rotating it piston down to get the air out. It might be worth a try.
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Replacing master cylinder on Mk5/Mk6 guide
So I feel I have enough experience to wire a howto on proper replacing of the master cylinder.
Let's assume you find out your MC is bad. You find either a used-good one or buy a brand new. In case of brand new one, don't bother swapping the reservoir from old MC to new one - get a net reservoir too.
Disassembly:
Remove air box, air intake plumbing from the filter to turbo. Disconnect alternator wire from the fuse box, remove the battery and the battery tray. Yes, all of this is required.
Use a large syringe to suck out as much of old fluid from the reservoir as possible. Don't try to remove the strain inside it - I think it's impossible to do it without damaging/breaking it. Unscrew the lines from the MC to ABS pump (2 of them) but don't remove them yet. Before doing this, you might want to find a catch can to catch the dripping fluid. While the fluid is dripping, go to the ABS pump, remove the platic shield to gain access. This will be required later.
Remove the lines from MC once they are finished dripping.
Unbolt and remove the MC (with the reservoir). You might need to exhaust the vacuum of the booster so don't hurry.
Reassembly:
Bolt on the new MC altogether with the reservoir attached. The seal between the MC and the booster should be renewed but worst case scenario you could reuse the old one.
Bleeding:
Connect master cylinder bleeding nipples (could be found in MC bench bleeding kit in local car parts store). Connect clear tubes. Point them back to reservoir. Don't go deeply, midway inside the reservoir ir OK. Keep the tubes as short as possible. Fill the reservoir with brake fluid. Be sure the pipes are fully submerged. Don't fill it to the max mark as you will have the fluid spilled in later step. When filled, let the reservoir rest for 15-20 minutes. If you are a smoker, go and smoke a cigarette at this point, if not then have _some_ beer but not much.
After the break, assistant will be required to observe the bench bleeding process. Get into the car, depress the brake pedal fully to the floor. Go very slowly and gently. When down, hold it there for about 20 seconds then slowly release. Fill the fluid to the MAX mark. Repeat the full travel pumping at least 3 times. After that, vary the pedal travel. Let your assistant observe the air bubbles in the plumbing. Repeat until no signs of air is visible.
Use a stick or a special tool to _slighly_ depress the brake pedal (~5 cm is sufficient) and block it. This will close the MC and prevent the fluid fromescaping.
Remove the tubes from the reservoir first. Starting from the line closest to firewall, remove the bleed nipple and quickly reconnect the original pipe. Then the same for 2nd one. Tighten the nuts.
At the ABS pump side, undo those two lines coming from MC. Connect long clear tubes to them (doesn't need to be a tight seal) and point them to a catch jar under the car or somewhere else. Remove the brake block. Connect power bleeder to reservoir and make *minimum* pressure. Observe the clear pipes at ABS pump side for air/fluid. Once air has stopped comming from both pipes, quickly reconnect them one by one (starting from the closest to firewall) back to ABS pump. This will make a mess due to fluid slowly pouring out of them because of the minimal pressure from the power bleeder but will ensure minimal amount of air is introduced to ABS pump.
Subsequent bleeding:
Open both fron caliper bleed nipples. Set the power bleeder to something like 10-15 PSI. Practice has shown that higher pressure does not give any result. Bleed simultaneously while air stops comming out. I think somewhere ~2 liters of fluid should be poured out in total.
After this, close the bleed nipples and bleed the system in the conventional manner, each caliper one by one: FL, FR, RL, RR. Let no less than 300 ml fluid of each caliper. Front ones will go faster, rear ones are the slow ones but be patient.
After this has been done, I'd suggest to cycle the ABS pump using 'Basic Settings' at least 3 times. Keep an eye on brake reservoir, NEVER EVER let it go dry! Refill it to MAX mark each time the pump cycles and bleeds. Better safe than sorry here, trust me.
At this point, brake performance should be acceptable.
NOTES:
Brake fluid can be reused if you use a clean jar to catch it. In this case, you will only need 2 liters of fluid maximum to perform these repeated bleeds. You cycle the same fluid over and over. But make sure it is not contaminated with anything (sand, dirt, rust particles, etc).
You want very minimal amount of air to be introduced into ABS module. It is really difficult to get rid of air inside it. A member in this forum had a leak and that ran his reservoir dry on Mk5 Jetta. After that the brake pedal never feels the same even after bleeding the system multipe times (ABS pump cycling).
Hope at least one person will find the above useful.
So I feel I have enough experience to wire a howto on proper replacing of the master cylinder.
Let's assume you find out your MC is bad. You find either a used-good one or buy a brand new. In case of brand new one, don't bother swapping the reservoir from old MC to new one - get a net reservoir too.
Disassembly:
Remove air box, air intake plumbing from the filter to turbo. Disconnect alternator wire from the fuse box, remove the battery and the battery tray. Yes, all of this is required.
Use a large syringe to suck out as much of old fluid from the reservoir as possible. Don't try to remove the strain inside it - I think it's impossible to do it without damaging/breaking it. Unscrew the lines from the MC to ABS pump (2 of them) but don't remove them yet. Before doing this, you might want to find a catch can to catch the dripping fluid. While the fluid is dripping, go to the ABS pump, remove the platic shield to gain access. This will be required later.
Remove the lines from MC once they are finished dripping.
Unbolt and remove the MC (with the reservoir). You might need to exhaust the vacuum of the booster so don't hurry.
Reassembly:
Bolt on the new MC altogether with the reservoir attached. The seal between the MC and the booster should be renewed but worst case scenario you could reuse the old one.
Bleeding:
Connect master cylinder bleeding nipples (could be found in MC bench bleeding kit in local car parts store). Connect clear tubes. Point them back to reservoir. Don't go deeply, midway inside the reservoir ir OK. Keep the tubes as short as possible. Fill the reservoir with brake fluid. Be sure the pipes are fully submerged. Don't fill it to the max mark as you will have the fluid spilled in later step. When filled, let the reservoir rest for 15-20 minutes. If you are a smoker, go and smoke a cigarette at this point, if not then have _some_ beer but not much.
After the break, assistant will be required to observe the bench bleeding process. Get into the car, depress the brake pedal fully to the floor. Go very slowly and gently. When down, hold it there for about 20 seconds then slowly release. Fill the fluid to the MAX mark. Repeat the full travel pumping at least 3 times. After that, vary the pedal travel. Let your assistant observe the air bubbles in the plumbing. Repeat until no signs of air is visible.
Use a stick or a special tool to _slighly_ depress the brake pedal (~5 cm is sufficient) and block it. This will close the MC and prevent the fluid fromescaping.
Remove the tubes from the reservoir first. Starting from the line closest to firewall, remove the bleed nipple and quickly reconnect the original pipe. Then the same for 2nd one. Tighten the nuts.
At the ABS pump side, undo those two lines coming from MC. Connect long clear tubes to them (doesn't need to be a tight seal) and point them to a catch jar under the car or somewhere else. Remove the brake block. Connect power bleeder to reservoir and make *minimum* pressure. Observe the clear pipes at ABS pump side for air/fluid. Once air has stopped comming from both pipes, quickly reconnect them one by one (starting from the closest to firewall) back to ABS pump. This will make a mess due to fluid slowly pouring out of them because of the minimal pressure from the power bleeder but will ensure minimal amount of air is introduced to ABS pump.
Subsequent bleeding:
Open both fron caliper bleed nipples. Set the power bleeder to something like 10-15 PSI. Practice has shown that higher pressure does not give any result. Bleed simultaneously while air stops comming out. I think somewhere ~2 liters of fluid should be poured out in total.
After this, close the bleed nipples and bleed the system in the conventional manner, each caliper one by one: FL, FR, RL, RR. Let no less than 300 ml fluid of each caliper. Front ones will go faster, rear ones are the slow ones but be patient.
After this has been done, I'd suggest to cycle the ABS pump using 'Basic Settings' at least 3 times. Keep an eye on brake reservoir, NEVER EVER let it go dry! Refill it to MAX mark each time the pump cycles and bleeds. Better safe than sorry here, trust me.
At this point, brake performance should be acceptable.
NOTES:
Brake fluid can be reused if you use a clean jar to catch it. In this case, you will only need 2 liters of fluid maximum to perform these repeated bleeds. You cycle the same fluid over and over. But make sure it is not contaminated with anything (sand, dirt, rust particles, etc).
You want very minimal amount of air to be introduced into ABS module. It is really difficult to get rid of air inside it. A member in this forum had a leak and that ran his reservoir dry on Mk5 Jetta. After that the brake pedal never feels the same even after bleeding the system multipe times (ABS pump cycling).
Hope at least one person will find the above useful.
One year later and I am still not satisfied with my brake performance.
The pedal goes down to the floor, way too low than it should have. It does behave like that with both, engine running (brake booster active) and the very first depress of the pedal with the engine shut off (brake booster inactive but still has got vacuum).
I cannot pump the pedal to acceptable performance (like if you have air in the system, you can compress it by quickly pumping the pedal and after that, while still holding the pedal, you have acceptable pedal travel). It pumps up slightly but slowly it is sinking on its own if I maintain firm pressure on it. Holding the pedal pumped with my left leg and with the right leg pressing on the throttle increases the speed of pedal sinkdown.
There is no air in the system. Bled the classic way, VCDS way and power bleeder way. More than 8 liters of fluid has been pushed. Confirmed there is no air at least in the calipers (if loosen the bleed screw with clear tube attached upwards, the gravity starts pushing fluid without any bubbles).
The braking is even between sides.
Any ideas? Suggestions? Should I try the "hydraulic valves adjustment" and "hydraulic disconnecting valves adjustment" adaptations with VCDS? What else on the earth I can try to get acceptable pedal feel? Comments appreciated.
The pedal goes down to the floor, way too low than it should have. It does behave like that with both, engine running (brake booster active) and the very first depress of the pedal with the engine shut off (brake booster inactive but still has got vacuum).
I cannot pump the pedal to acceptable performance (like if you have air in the system, you can compress it by quickly pumping the pedal and after that, while still holding the pedal, you have acceptable pedal travel). It pumps up slightly but slowly it is sinking on its own if I maintain firm pressure on it. Holding the pedal pumped with my left leg and with the right leg pressing on the throttle increases the speed of pedal sinkdown.
There is no air in the system. Bled the classic way, VCDS way and power bleeder way. More than 8 liters of fluid has been pushed. Confirmed there is no air at least in the calipers (if loosen the bleed screw with clear tube attached upwards, the gravity starts pushing fluid without any bubbles).
The braking is even between sides.
Any ideas? Suggestions? Should I try the "hydraulic valves adjustment" and "hydraulic disconnecting valves adjustment" adaptations with VCDS? What else on the earth I can try to get acceptable pedal feel? Comments appreciated.
So okay. Looks like nobody is reading this thread any longer. I will continue my monologue.
After trying the brakes in a few Mk5's and Mk6's, I came to a conclusion that my brake pedal is too spongy. This behaviour started after replacing my original master cylinder with a used one with unknwon miles from an unknown car.
As my original master cylinder was not faulty (turns out if was ABS pump fault), I think I will replace the MC again, back to my old one!
At the same time I will be replacing my front brake pads and rotors. The rotors got slightly wrapped because of all that braking issue (I suspect they overheated).
This is my plan on how to replace/bleed:
1. Lock the brake pedal with a special locking tool to close the master cylinder (prevent fluid from puring out when lines will be disconnected)
2. Use a large syringe to extract all the brake fluid out of the reservoir
3. Disconnect the two lines from MC, one by one, and cap them with a cap ASAP to prevent fluid loss from the lines as much as possible.
4. Remove MC, remove brake pedal locking tool.
5. Install another MC, attach the bench bleeder kit with clear lines pointing back to the reservoir, fill with fresh Ate SL.6 fluid.
6. "Bench bleed" the MC on the car to get all the trapped air out of the cylinder
7. Lock the brake pedal with locking tool again.
8. Disconnect the clear lines and reconnect the brake system lines back to MC as fast as possible
9. *NOT SURE* Should I fully tighten the lines at this moment or make them slighlty loose in order to allow for air to escape? What about brake lockdown tool?
10. Remove from wheels, remove calipers and use the brake tool to squeeze them. I hope this will to the function of backflush what will push all the air back to MC or through the gaps between partially tightened lines and MC.
11. Replace brakes rotors, pads, assemble everything back, check and do a test drive.
Guys, what do you think about my plan? Does it sound right? What about step #9? What would you suggest?
Thanks!
After trying the brakes in a few Mk5's and Mk6's, I came to a conclusion that my brake pedal is too spongy. This behaviour started after replacing my original master cylinder with a used one with unknwon miles from an unknown car.
As my original master cylinder was not faulty (turns out if was ABS pump fault), I think I will replace the MC again, back to my old one!
At the same time I will be replacing my front brake pads and rotors. The rotors got slightly wrapped because of all that braking issue (I suspect they overheated).
This is my plan on how to replace/bleed:
1. Lock the brake pedal with a special locking tool to close the master cylinder (prevent fluid from puring out when lines will be disconnected)
2. Use a large syringe to extract all the brake fluid out of the reservoir
3. Disconnect the two lines from MC, one by one, and cap them with a cap ASAP to prevent fluid loss from the lines as much as possible.
4. Remove MC, remove brake pedal locking tool.
5. Install another MC, attach the bench bleeder kit with clear lines pointing back to the reservoir, fill with fresh Ate SL.6 fluid.
6. "Bench bleed" the MC on the car to get all the trapped air out of the cylinder
7. Lock the brake pedal with locking tool again.
8. Disconnect the clear lines and reconnect the brake system lines back to MC as fast as possible
9. *NOT SURE* Should I fully tighten the lines at this moment or make them slighlty loose in order to allow for air to escape? What about brake lockdown tool?
10. Remove from wheels, remove calipers and use the brake tool to squeeze them. I hope this will to the function of backflush what will push all the air back to MC or through the gaps between partially tightened lines and MC.
11. Replace brakes rotors, pads, assemble everything back, check and do a test drive.
Guys, what do you think about my plan? Does it sound right? What about step #9? What would you suggest?
Thanks!
It might not seem like it but make no mistake there are folks still following this thread...
As for #9. I think that tightening the lines down would be best for a few reasons:
-more air will likely get pulled into the system if things aren't air tight.
-leaking brake fluid is very bat for paint
Do you have a vacuum bleeder or a pressure bleeder? I think the latter is best from all I've read on bleeding brakes in German cars.
Example:
https://youtu.be/1d8sKGaHUHU
***** that paint, I need brakesIt might not seem like it but make no mistake there are folks still following this thread...
As for #9. I think that tightening the lines down would be best for a few reasons:
-more air will likely get pulled into the system if things aren't air tight.
-leaking brake fluid is very bat for paint
Do you have a vacuum bleeder or a pressure bleeder? I think the latter is best from all I've read on bleeding brakes in German cars.
Example:
https://youtu.be/1d8sKGaHUHU
Seriously, paintwork is not an issue - I will be having brake cleaner and will clean any mess. I need to do it right.I think you did not quite understand what I was meaning. Once I install the MC (with reservoir) onto the car, I will connect bleeding kit with clear pipes to bench bleed it.
But look at this picture:
Do you see the two lines going from master cylinder almost straight vertically? No matter how quickly do I work and cap them, gravity will pull the fluid out of the pipes. Air will be at the bottom of them. At this moment, when reconnecting, I do not want the air to be pushed with the brake pedal (or power bleeder) through entire system (I believe it can get trapped in ABS unit or anywhere else).
What I want to do after reconencting the pipes is to remove the brake calipers and use the brake tool to push the pistons back - that will force the fluid (as well as air which has been introduced) to go BACK towards brake reservoir. Do you get the idea?
Now the dilema - should I leave partially lose nuts (air would escape through them but would not be introduced - liquid weights more than air)
OR
tighten all things to spec and push the fluid (as well as air) back straight to the reservoir throught the master cylinder taking the risk of having air trapped somewhere in the MC?
And yes, I do have a power bleeder.
Thanks for advice. Now the only thing I need is to deal with the mechanic and make an appointment He was really tired messing with the brakes on my car since a year ago...
Meanwhile I'll purchase the required parts - brake fluid, guide pins lube (will be doing pads/rotors at the same time), clear tubes so bench bleeding, etc.
He was really tired messing with the brakes on my car since a year ago...Meanwhile I'll purchase the required parts - brake fluid, guide pins lube (will be doing pads/rotors at the same time), clear tubes so bench bleeding, etc.
Another thing that I'd like to recommend is the Tyrolsport brake caliper bushings...
http://www.tyrolsport.com/brakes/tyrolsport-brake-caliper-stiffening-kit-for-vw/audi/
I installed them on my car a few months ago and they really helped the kill the stock spongy brake pedal feel. The only downside to them is that they should be cleaned and relubed at least once a year from what I've read from others that have this kit. Not really a big deal though since all that you'd need to do is take the caliper pin out, clean up both the pin and brass bushings, relube it with caliper grease then screw it back in. Not hard at all and could easily be done during a oil change.
http://www.tyrolsport.com/brakes/tyrolsport-brake-caliper-stiffening-kit-for-vw/audi/
I installed them on my car a few months ago and they really helped the kill the stock spongy brake pedal feel. The only downside to them is that they should be cleaned and relubed at least once a year from what I've read from others that have this kit. Not really a big deal though since all that you'd need to do is take the caliper pin out, clean up both the pin and brass bushings, relube it with caliper grease then screw it back in. Not hard at all and could easily be done during a oil change.
Honestly I don't think I really need them. The issue is hiding somewhere between the master cylinder, ABS pump and hydraylics/fluid. See this: http://forums.tdiclub.com/showpost.php?p=4685197&postcount=23
I had a momentary good experience after brake pad replacement and air removal from the system. This leads me to believe that my brake pads/calipers/rotors are OK and that my original MC which was on the car at that time was also powerful enough to create required hydraulic force. As well as brake booster.
Again, at this point the replacement MC and replacement ABS pump are on the hook. I've read somewhere on the net that ABS pump might be faulty - it might have an internal leak ( my God, what misfortune I'm dealing with )
I had a momentary good experience after brake pad replacement and air removal from the system. This leads me to believe that my brake pads/calipers/rotors are OK and that my original MC which was on the car at that time was also powerful enough to create required hydraulic force. As well as brake booster.
Again, at this point the replacement MC and replacement ABS pump are on the hook. I've read somewhere on the net that ABS pump might be faulty - it might have an internal leak ( my God, what misfortune I'm dealing with
)Yeah, I think you're on the right track.
I did a bit of research on this just because I don't recall ever seeing spongy brakes quite to the extreme as what you have. Seems that most point to a bad MC, but VWs can be quite difficult to properly bleed correctly.
From what I've read it seems that 3 liters is the amount of brake fluid that is needed to fully bleed the brakes. But I'm sure that you have put through more than that...
Anyway I'm still rooting for you and hope that you find the root cause of this maddening issue.
I did a bit of research on this just because I don't recall ever seeing spongy brakes quite to the extreme as what you have. Seems that most point to a bad MC, but VWs can be quite difficult to properly bleed correctly.
From what I've read it seems that 3 liters is the amount of brake fluid that is needed to fully bleed the brakes. But I'm sure that you have put through more than that...
Anyway I'm still rooting for you and hope that you find the root cause of this maddening issue.
I swear, I will spend no less than 30 minutes bench bleeding the MC. I'll use syringe to bench bleed it at first ( https://www.youtube.com/watch?v=USdtwqju4GY ), then will put it into vice and continue bleeding it by pushing the rod back and forth with clear lines pointing back to the reservoir ( https://youtu.be/4oi3Y6HMCbc?t=361 ). After that, I will remove it and try to shake/wiggle it at different angles to get any trapped air out.
BTW, did you know interesting facts about our VW brake fluid reservoirs? Firstly, it has got a separate "pocket" for clutch line. Even if you drain all the fluid out of the reservoir to the last drop, the clutch line will have its fluid in a separate pocket.
Also, there seems to be a separate "pocket" for overflow. It is located in the front/left side if you look at it from the front of the engine. You can easily fill it in by overfilling the reservoir past the MAX mark (or by using power bleeder) but you will never be able to remove that fluid, unless you remove the strain and use syinge with attached tube to extract fluid particulary from that pocket.
BTW, did you know interesting facts about our VW brake fluid reservoirs? Firstly, it has got a separate "pocket" for clutch line. Even if you drain all the fluid out of the reservoir to the last drop, the clutch line will have its fluid in a separate pocket.
Also, there seems to be a separate "pocket" for overflow. It is located in the front/left side if you look at it from the front of the engine. You can easily fill it in by overfilling the reservoir past the MAX mark (or by using power bleeder) but you will never be able to remove that fluid, unless you remove the strain and use syinge with attached tube to extract fluid particulary from that pocket.
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I have talked to a few mechanics at the workshop which will be assisting me (scheduled my visit to the shop for 14th of January).
They suggested the following troubleshooting sequence:
1. Unscrew all pipes going to wheels from ABS pump and install blocking plugs.
1.1. After that, try starting the car, let it idle and check if the pedal still goes to floor. This eliminates all the wheels and related plumbing from the game. If the pedal still goes to the floor, then it is either brake boster, master cylinder or ABS pump internal failure.
2. Unscrew the plumbing from master cylinder and install blocking plugs into the ports.
2.1. Start the car, check pedal feel. If it does feel OK, then the ABS pump is faulty. If it still sinks down, then it is either brake booster or master cylinder.
3. Replace master cylinder (with my original one).
3.1. If it feels OK, then assemble everything back and do the system bleeding. If it still sinks down, then seek for replacement brake booster.
Does this sound reasonable? Any comments/suggestions/etc?
They suggested the following troubleshooting sequence:
1. Unscrew all pipes going to wheels from ABS pump and install blocking plugs.
1.1. After that, try starting the car, let it idle and check if the pedal still goes to floor. This eliminates all the wheels and related plumbing from the game. If the pedal still goes to the floor, then it is either brake boster, master cylinder or ABS pump internal failure.
2. Unscrew the plumbing from master cylinder and install blocking plugs into the ports.
2.1. Start the car, check pedal feel. If it does feel OK, then the ABS pump is faulty. If it still sinks down, then it is either brake booster or master cylinder.
3. Replace master cylinder (with my original one).
3.1. If it feels OK, then assemble everything back and do the system bleeding. If it still sinks down, then seek for replacement brake booster.
Does this sound reasonable? Any comments/suggestions/etc?
Hello.
So today I have spent the entire day at the workshop. This is what we did:
1. Removed all "wheels" plumbing from ABS pump and blocked the ports with manufactured block-offs.
2. Started the vehicle - Pedal feels very solid, absolutely NO pedal travel.
3. Removed the block off plugs for rear wheels and attached rear wheels. Did dome manual bleeding "pump and hold". 3 times per each rear wheel.
4. Started the car, pedal still feels solid. A bit softer than with all 4 corners disconencted but is it still 100% perfect!
5. Removed the block-off plug and connected front right wheel.
6. Started the car. Pedal feels soft, it is possible to squeeze ir under pressure.
7. Removed the front right caliper. Inserted a piece of hard metal brick between the caliper and the caliper piston.
8. Started the car, pedal still squeezes.
9. Replaced the caliper with another one, known-good. Beld the manual way.
10. Started the car with metal brick inside the new caliper - still sinks down.
At this point we decided to replace the master cylinder to my original one, as we thought that one of its circuits might be bad. The master cyliner was belnch-bled, no air got trappen in it.
11. After replacement, (front left wheel port still plugged at ABS unit), we bled the manual way (engine and ignition off) at least 5 times. Then we bled with engine running, 5 times. The pedal still is soft, even worse than it was before.
12. Attached front left wheel with hopes that air is trapped somewhere in ABS and it needs the 4th wheel to bleed.
13. Bled all the wheel again. Pedal still goes almost to the floor.
At this point the working day is over and I don't know what to do next.....
Any ideas, suggestions, etc?
Would appreciate quick response, as tomorrow morning I will be going to the workshop again and we need to do something further. No one has got any ideas
So today I have spent the entire day at the workshop. This is what we did:
1. Removed all "wheels" plumbing from ABS pump and blocked the ports with manufactured block-offs.
2. Started the vehicle - Pedal feels very solid, absolutely NO pedal travel.
3. Removed the block off plugs for rear wheels and attached rear wheels. Did dome manual bleeding "pump and hold". 3 times per each rear wheel.
4. Started the car, pedal still feels solid. A bit softer than with all 4 corners disconencted but is it still 100% perfect!
5. Removed the block-off plug and connected front right wheel.
6. Started the car. Pedal feels soft, it is possible to squeeze ir under pressure.
7. Removed the front right caliper. Inserted a piece of hard metal brick between the caliper and the caliper piston.
8. Started the car, pedal still squeezes.
9. Replaced the caliper with another one, known-good. Beld the manual way.
10. Started the car with metal brick inside the new caliper - still sinks down.
At this point we decided to replace the master cylinder to my original one, as we thought that one of its circuits might be bad. The master cyliner was belnch-bled, no air got trappen in it.
11. After replacement, (front left wheel port still plugged at ABS unit), we bled the manual way (engine and ignition off) at least 5 times. Then we bled with engine running, 5 times. The pedal still is soft, even worse than it was before.
12. Attached front left wheel with hopes that air is trapped somewhere in ABS and it needs the 4th wheel to bleed.
13. Bled all the wheel again. Pedal still goes almost to the floor.
At this point the working day is over and I don't know what to do next.....
Any ideas, suggestions, etc?
Would appreciate quick response, as tomorrow morning I will be going to the workshop again and we need to do something further. No one has got any ideas