Soft brake pedal with car running - Firm when its off

[A4SoftWalker]

Recently used the motive power bleeder and my reservoir bled dry when I turned my head away for a few seconds - pumping air into the system.

(never using that pos again)

I was able to bleed the system properly using a $20 (on sale yesterday) hand pump VACUUM bleeder from Harbor Freight and a friend.

Was able to get pressure with a firm and slightly falling pedal with the car bled clear with a combination of old school brake pump and hand vacuum pump methods.

Started car same problem with the car stuttering upon brake application and pedal headed to the floor but I back off b4 reaching the floor.

What's giving me this problem?

Doing a forum search revealed that:

1>>>People use a rubber mallet to tap the master cylinder and ABS systems to release pockets of air.

2>>>Master cylinder needs to be bled from somewhere along the firewall.

3>>>???

4>>>???


How did u fix yours?

I think I'm on the right path but any ideas or help appreciated.


PS:::
Also I think I might be in bigger trouble cause the motive crappola made my system spring a leak when I pumped it to btw 12 an 14 psi. maybe something else blew out??? Not sure where the leak was coming from.

[me4tmfw]

did u do all 4 corners starting with the rear right then rear left etc... i just use a lil tube and a empty water bottle hahah takes me like 30mins max less if i had some sort of car lift :/

[Undisputed]

It'll take some time for it to firm up anyway. I'd re-bleed it and then give it a couple of days of use to firm back up. I had the same problems when I installed my BBK. The pedal went almost to the floor for it to stop. After 3 days or so, it was firm. Never had a problem since.

[A4SoftWalker]

Good tips all but I bled the system only at the front with the Motive.

Started the traditional rear to front pass rear, driver rear, pass front, driver front

Then I looked in the Bentley CD and it states to go the opposite way.

Well I bled both the old school way and vacuum pump twice.

Pedal got much firmer with the engine off

but

with the engine started the pedal goes straight to the floor with ZERO resistance.

Toooo scary to drive in traffic only brakes I have are hand/parking brake or to shut off the motor.

[MikeWire]

PS:::
Also I think I might be in bigger trouble cause the motive crappola made my system spring a leak when I pumped it to btw 12 an 14 psi. maybe something else blew out??? Not sure where the leak was coming from.

Eh, I think you may be on to something here, but you need to get more detail and get in the engine bay.

FWIW the motive works fine, I have one and used it many times with no problems. It's actually much easier to use than doing it the old school way. Sounds like you had your bleeder open too long, and/or you let it run out of fluid, and that would shoot air into the system. But all you would need to to is re-bleed, just watch that bleeder reservoir!

14psi is the max you want to push the system to (I don't go over 10psi, that's plenty), but the system should accept way more than that. It's possible you blew your suction jet pump in half - that valve supplies the booster with pressure. That would explain the stuttering/misfires.

So, take a look. And (no offense) learn to use the power bleeder the right way and it will be your best friend for brake jobs.

[A4SoftWalker]

Eh, I think you may be on to something here, but you need to get more detail and get in the engine bay.

FWIW the motive works fine, I have one and used it many times with no problems. It's actually much easier to use than doing it the old school way. Sounds like you had your bleeder open too long, and/or you let it run out of fluid, and that would shoot air into the system. But all you would need to to is re-bleed, just watch that bleeder reservoir!

14psi is the max you want to push the system to (I don't go over 10psi, that's plenty), but the system should accept way more than that. It's possible you blew your suction jet pump in half - that valve supplies the booster with pressure. That would explain the stuttering/misfires.

So, take a look. And (no offense) learn to use the power bleeder the right way and it will be your best friend for brake jobs.

No offense taken no ones BORN knowing all there is to know. I have a 11mth old suction jet pump valve. Changed it out last Christmas.

My guess is there is probably a ton trapped air in there somewhere that is out of the pathways of the regular brake lines.

I still cant figure out why it leaked like 2-3 litres of brake fluid out onto the pavement or more importantly "where" it possibly was coming from when pressurizing the system with the Motive.

Seen plently of videos on the internet and the Bentley says to pressurize to 2bar!!!

I did pressurize below 15psi thats for sure so plus atmospheric pressure that = 2bar approx.

[old guy]

14psi is the max you want to push the system to (I don't go over 10psi, that's plenty), but the system should accept way more than that.

15 to 20 PSI is fine for bleeding the brakes. When you go to bleed the slave cylinder you will probably have to pump it up to 30 -35PSI.

It's possible you blew your suction jet pump in half - that valve supplies the booster with pressure.

You are correct in that a faulty suction jet pump can cause braking issues, but it won't cause the pedal to go soft. In fact just the opposite happens. The suction jet pump supplies vacuum to the booster. when it splits the brake pedal goes firm, just as it does with the motor turned off.

[MikeWire]

OG, I was speaking from my experience but I suppose everyone's is different - very good input as usual. 2bar is correct, but 10psi worked just fine for mine and my buddies A4. When my jet pump split a few months ago, my pedal was so soft, at first I thought I had blown out a brake line.

I have to add though, if you are just doing brakes, I wouldn't mess with the clutch cylinder. And it might be a good idea to cycle the ABS pump using VCDS, I dunno, I have always done it on the cars I have flushed and they turned out fine.

Again, just going off my experience, which can be taken with a grain of salt considering there is more than one way to skin a cat.

Rep to you for doing your own work!

[A4SoftWalker]

I have to add though, if you are just doing brakes, I wouldn't mess with the clutch cylinder. And it might be a good idea to cycle the ABS pump using VCDS, I dunno, I have always done it on the cars I have flushed and they turned out fine.

I do have the full version of VAG-COM

Cycling the ABS pump does what for the system?

I see the option in the screen not sure what it does or how to do it.

Do u pressurize the system?

Do u leave the brake fluid cap on /off

Checked Bentley no mention of the procedure

I'll look harder perhaps

Thanks for the info soo far guys.

[EBG 18T]

I do have the full version of VAG-COM

Cycling the ABS pump does what for the system?

I see the option in the screen not sure what it does or how to do it.

Do u pressurize the system?

Do u leave the brake fluid cap on /off

Checked Bentley no mention of the procedure

I'll look harder perhaps

Thanks for the info soo far guys.

Last time i used the ABS pump cycling on the Vagcom i used these instructions: Ross Tech instructions for ABS Pump Cycling

i left the lid on the resivoir and didn't pump the pedal. After i did the ABS Pump Cycling i re-bled the brakes the old fashion way and everything was perfect.

[A4SoftWalker]

Last time i used the ABS pump cycling on the Vagcom i used these instructions: Ross Tech instructions for ABS Pump Cycling

i left the lid on the resivoir and didn't pump the pedal. After i did the ABS Pump Cycling i re-bled the brakes the old fashion way and everything was perfect.

Thanks for the info bro will give it a go then.

[EBG 18T]

Thanks for the info bro will give it a go then.

let us know how it works out.

[diagnosticator]

15 to 20 PSI is fine for bleeding the brakes. When you go to bleed the slave cylinder you will probably have to pump it up to 30 -35PSI. You are correct in that a faulty suction jet pump can cause braking issues, but it won't cause the pedal to go soft. In fact just the opposite happens. The suction jet pump supplies vacuum to the booster. when it splits the brake pedal goes firm, just as it does with the motor turned off.

Just to clarify, there is no connection between the hydraulic system pressure, as applied by the Power Bleeder, or via brake pedal application, and the booster housing or connected vacuum system components.

[old guy]

Just to clarify, there is no connection between the hydraulic system pressure, as applied by the Power Bleeder, or via brake pedal application, and the booster housing or connected vacuum system components.

Thanks for the clarification. I wasn't trying to imply that the two systems were connected but after re-reading my post I can see how that could be misconstrued.

[A4SoftWalker]

Well here's the long awaited update:::

followed these instructions here and got the car all jacked up:





Then I got this interesting error message:





I tried all the different settings I could find but nothing worked.

So anyways I decided to use the Motive again pumped it up to 15psi and followed the Bentley and not the traditional bleeding method.

Closest to furthest. No bubbles out of the front or rear... hmmm pumped the brakes a little with my hand on the rear... not sure what I was doing.

Yesterday bought 5 500ml (half liter) bottles of EXPENSIVE Motul 600... yeah I was gonna do it, This was it.


Armed with the Bentley knowledge that I can assist slightly with pedal pressure to help bleed the system I was certain to succeed.

Filled Motive up with 3 bottles of fluid.



Pumped it up to 20psi bled the fronts (driver then passenger) and assisted with pedal pressure no air bubbles. Bled out a little over 500ml for both total.



Next focused on the rear: Maintain pump at 20psi gentle steady foot pressure on the pedal. I could feel/hear something gurgling in the master cylinder.

Kept checking the rear and then... bubbles out of the driver's side rear for a good 5 minutes. Bled out 500ml on this side.




Now on to the last side passenger rear. This was it I was going to get all the air out this time. That sucker bled about 200ml then the bubbles started coming and coming.



Filled up the Motive with another container number 4/5 still bubbles filled the last one in there still bubbles then I started recycling the last bleed did that another 2 times and got tired of the bubbles.



Test drive pedal grabs real low after 3-4 pumps

Will update after another mega-bleed with a full Motive container.

[diagnosticator]

The Bosch 5.7 ABS is not supposed to require pump cycling to purge air from the pump, but it can't hurt. You need to run the output test for the ABS to run the pump.

Also, don't second guess the factory requirement of 2 bar bleeder pressure.

[A4SoftWalker]

The Bosch 5.7 ABS is not supposed to require pump cycling to purge air from the pump, but it can't hurt. You need to run the output test for the ABS to run the pump.

Also, don't second guess the factory requirement of 2 bar bleeder pressure.

Good to know diagnosticator - most people on here state 10 -15 psi. Not being a B6 trailblazer I just learn by following.

However, many things I have done by the Bentley bible NEVER fail.

In my case with air in the brakes seems like only the Bentley/factory way to do it.

2bar = 29 psi on the guage? Not including atm pressure???

That little Motive is gonna weep.

[diagnosticator]

That is 2 bar gage pressure, so that includes atmospheric. Gage pressure starts at 1 bar absolute pressure so 0 bar gage=1 bar absolute pressure.

[EBG 18T]

a4softwalker - i am not sure why you received the error message with the vagcom. I used it last time and it worked fine. I will try to go cycle it again today and document my steps incase they are different from the link i gave you from rosstech.

Also i did a manual bleed with out the motive powerbleeder after i cycled the abs. i had my wife in the driver seat and i bled the calipers. have you tried the old school bleed method or just with the motive?

[A4SoftWalker]

a4softwalker - i am not sure why you received the error message with the vagcom. I used it last time and it worked fine. I will try to go cycle it again today and document my steps incase they are different from the link i gave you from rosstech.

Also i did a manual bleed with out the motive powerbleeder after i cycled the abs. i had my wife in the driver seat and i bled the calipers. have you tried the old school bleed method or just with the motive?

I did the following:

Motive power bleed fronts only

Manual bleed old-school style brake-pedal rear furthest to front

Combination old-school style with vacuum bleeder

Motive power bleeder 15psi Bentley style front to rear Sat

Motive power bleeder 20psi Bentley style front to rear Sun

Motive power bleeder 30psi Bentley style front to rear Today

Still only reduction is a pump of the pedal - now 2 or 3 to get good braking action instead of 4 or 5 this morning.

Verdict there is tons of air in there. Or I'm totally incompetent.

Bled about 1 bottle through the fronts

Bled 2.5 bottles through the driver rear.

BLED 3 FULL POWER BLEEDERS THROUGH THE PASSENGER REAR = 10 bottles.

[MikeWire]

One thing I noticed on the A4 calipers: If you crack the bleeder valve more than 1/4 turn, it seems to suck air back into the caliper and/or the line. I went through about 1 bottle until I figured that I was opening the line too much - I was seeing bubbles in the line that appeared to be coming out of the caliper, and they wouldn't stop coming. As as soon as I only opened the valve 1/4 I saw a steady stream of fluid coming out of the bleeder valve with no air bubbles.

Maybe something to consider, just trying to help!

[EBG 18T]

a4softwalker - i think it might be time to limp it to the local shop and make them do it. I hate to see you keep wasting $ on the expensive fluid. While you are there at the shop watch them to see what they do different. Maybe we are missing something simple.

[A4SoftWalker]

a4softwalker - i think it might be time to limp it to the local shop and make them do it. I hate to see you keep wasting $ on the expensive fluid. While you are there at the shop watch them to see what they do different. Maybe we are missing something simple.

yup my thoughts this morning on making an appt to get it done...

I was recycling the brake fluid, its clean as a whistle

but still $60 for a 5 liter jug is no joke when I got 2 of em...

Next time i'll pay closer attention to not getting air in there (bleeding the pump dry) while using the Motive.

Thanks to everyone for all the help and ideas offered.

[A4SoftWalker]

One thing I noticed on the A4 calipers: If you crack the bleeder valve more than 1/4 turn, it seems to suck air back into the caliper and/or the line. I went through about 1 bottle until I figured that I was opening the line too much - I was seeing bubbles in the line that appeared to be coming out of the caliper, and they wouldn't stop coming. As as soon as I only opened the valve 1/4 I saw a steady stream of fluid coming out of the bleeder valve with no air bubbles.

Maybe something to consider, just trying to help!

U are right I noticed that too... ...but at my bleed pressures btw 20 and 30 psi.

That should not have been an issue with air getting back into the system from the bleeder screw.

[A4SoftWalker]

BRAKES DONE

I broke down and took it in to Carlson Audi. They hadn't seen me since my warranty went out many a moon ago at 50k in 2005 (109k now) - Same set of guys still there over 4 years later.

Anyways they had me car on the rack in no time and bled the system in a little over an hr.

Still got a ton of bubbles out of the passenger rear where Ive been getting stuck at.

but

bled in reverse of the Bentley furthest to nearest

and more importantly bled the INNER and OUTER bleed screws on the Alcons.

According to the tech there was a ton of air in from the INNER front bleed screws too.

In total he got less than a quart of fluid out of the WHOLE system - unlike the bottles and bottles I got using the Motive.

Not a bad way to spend $125.

I was considering buying the electric diaphragm machine myself but unless I went into business the $400 price of admission is steep.

So YEAH - Happy New Year with new firm Alcon brake pedal again.

Lessons learned:

1>>> Never let ur Motive bleed dry - it INJECTS a ton of air into the system
2>>> Alcons and most multi-piston brake setups have more than one bleed point funny how I remember that now.
3>>> There is no replacement for a lift - the Audi techs were able to bleed the brakes with the wheels ON THE CAR using a lift
4>>> Do not use the flat black rubber washer like device with a little hole in it in the Motive cap - it will allow pressure to build btw the cap and the Motive and spill ur precious brake fluid all over.

[EBG 18T]

glad you finnally got it taken care of. Sometimes it gets to the point of frustration it is best to just let someone else do it for you.

[A4SoftWalker]

glad you finnally got it taken care of. Sometimes it gets to the point of frustration it is best to just let someone else do it for you.

Happy New Year and Thanks for ur help all the same getting me pointed in the right direction.

Rep to ya my man.

[billyhoyle]

I like when threads like this have a resolution, so I'm going to post mine here even though it's 6 years old (I found this thread when searching for a solution to my problem, which was the same as OP's).

I bled my brakes, but accidentally let the reservoir run dry...twice. Yeah...anyway, I bled again with the power bleeder until there were no bubbles coming from the lines, and still had no brakes when I turned the car on. If I pumped them 4 or 5 times they would firm up for a second, but that's it.

The solution: rebleed each caliper with the power bleeder but pump the brakes 5-10 times (until you no longer see bubbles in the line) for each one. Problem solved. Air clearly got somewhere where a simple pressure bleed wouldn't push it out. Pumping the brakes (or possibly having the pedal partially depressed during the whole process, but I didn't test this) was the key.

Note: Apparently it's bad for the master cylinder to press the brake pedal all the way to the floor, so don't do that.

[Petabell]

I haven't touched my brakes in over a year and just started having a similar issue. Brakes are hard when the car is off, but super soft when the engine is running. Brake fluid level is good.

My question is, should I start bleeding (even though brakes have worked great for over a year) or should I look elsewhere in the system?

[poormanrich]

I just dealt with this before doing my pads and rotors. I bled them (two man method) 3 times before I got am good feeling brake pedal. I never let the resi get dry just make sure you take care to keep the resi full of fluid and don't introduce any more air in the system. My brakes feel better now then when I bought the car.

[Petabell]

My soft brakes ended up being a 1/4" long crack in the brass line going into the caliper. Couldn't get the brass fittings loose without destroying them (of course that would happen too) so I removed the caliper and quick braise job did the trick.

[texasboy21]

I haven't touched my brakes in over a year and just started having a similar issue. Brakes are hard when the car is off, but super soft when the engine is running. Brake fluid level is good.

My question is, should I start bleeding (even though brakes have worked great for over a year) or should I look elsewhere in the system?

Brakes should be bled once a year, so perform the service and see whats happening after.

[tegraphile]

Woke up yesterday to drive and had the same issue. Brakes, rotors, and fluid were done 7K miles ago with no issue. Worked the night before without issue either. No leaks on the ground and reservoir is full. I have a feeling the MC may be going out, so I bought one pre-emptive to take to the mechanic on Monday.

My symptoms are similar: brake pedal firms up when off, then softens and presses to the floor when the car is running in neutral. When driving at low speed, the initial press gives about 10% of the full braking force and begins to go to the floorboard. Each subsequent pump brings on more braking power, but as you continue to hold pressure, the pedal presses down to the floor and you get back the original 10% of braking power. Am I right in thinking its the MC?

[old guy]

Yep. Sure sounds like a defective brake master cylinder. The primary seals are failing and the secondary seals are pushing the brake fluid back into the reservoir.

[tegraphile]

Yep. Sure sounds like a defective brake master cylinder. The primary seals are failing and the secondary seals are pushing the brake fluid back into the reservoir.

Thanks. Hope it's addressed on Monday so I can enjoy the Motoza Stage 1 in the mail. :)

EDIT: Thanks for the advice. Ending up need a new MC and vacuum boost along with a rusted out left rear caliper. Price was steep, but glad it's done (until the next issue).

[noods]

I like when threads like this have a resolution, so I'm going to post mine here even though it's 6 years old (I found this thread when searching for a solution to my problem, which was the same as OP's).

I bled my brakes, but accidentally let the reservoir run dry...twice. Yeah...anyway, I bled again with the power bleeder until there were no bubbles coming from the lines, and still had no brakes when I turned the car on. If I pumped them 4 or 5 times they would firm up for a second, but that's it.

The solution: rebleed each caliper with the power bleeder but pump the brakes 5-10 times (until you no longer see bubbles in the line) for each one. Problem solved. Air clearly got somewhere where a simple pressure bleed wouldn't push it out. Pumping the brakes (or possibly having the pedal partially depressed during the whole process, but I didn't test this) was the key.

Note: Apparently it's bad for the master cylinder to press the brake pedal all the way to the floor, so don't do that.

+1 to this. I had this problem too.
I spent countless hours tstuffing around with vagcom in a bid to activate the abs pump thinking this was the root cause to my pressureless brake pedal. This was my first brake bleed attempt BTW. Couldn't figure out how to activate it on an a4 b6 and there wasn't posted in forums specifically for our car. Then read diagnosticators post that the abs module doesn't require bleeding... So persevered and bled another 2 times being concious to depress pedal to its limit albeit gently.