# 97 Audi A6: Spongey brake pedal only with engine running??



## MEDEL514 (Jan 12, 2002)

Long sorty short, I took my car to a mechanic for a ball joint replacement and then I call saying that I need a brake job. I just changed my pads a couple weeks ago and everything was working great, so I didn't believe him. I picked up the car and the brake pedal was very spongey and would only slowly come to a stop with the pedal down to the floor. WTF?

Today I bled all four calipers and got no signs of air in the system and clean fluid comming out. The calipers were working great, and the brake pedal was nice and tight. So I took the car out for a spin and the brake pedal got all spongey again! I brought the car back home checked everything over again, and it looked all good. The brake pedal gets nice and tight by the second pump with the engine off and will stay tight, but as soon as I started the car up, the brake pedal went back to mush! 

At this point I'm thinking it has to be something with the ABS. So I unplugged the ABS controller harness, pumped the brakes and got them tight, started the engien, and the brakes went to mush again! 

I don't know what else to do, and I don't know if the mechanic did anything to my car to mess up the brakes, but the car is not safe to drive anymore. Any help would be greatly appreciated.


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## MEDEL514 (Jan 12, 2002)

nobody?


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## STVR6 (Jul 6, 2010)

I think you will need to take the car to the dealer to have them exercise the ABS pump and solenoids. Somehow air got into the pressure reducing circuit of the ABS system. And with the more complex system (ABS + Electronic Brake Distribution, Acceleration Slip Reduction, Brake Proportioning, Stability Control, etc), it is not possible to do it without a scan tool. 

I'm not sure if the VAG-COM can do more than running the ABS pump. 

As to why air got into things when you have it serviced I do not know. But I don't think the shop is going to tell you either.


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## Anony00GT (Mar 6, 2002)

Try doing a complete system bleed as per the service manual. It's weird that this happened only after a shop worked on it, as a ball joint replacement shouldn't have any effect on the brakes.

It's also possible that you've got a bad master cylinder.


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## MEDEL514 (Jan 12, 2002)

I have a master cylinder coming in the mail, I'm going to change it and bleed all for brakes when i do. 

Is there anything else I should be looking for to fix this?


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## STVR6 (Jul 6, 2010)

OEM master cylinder or aftermarket? Just wondering. 

If the brake is firm when the engine is off, and the pedal doesn't drift lower with light pressure, then the master cylinder cups should still be fine. From what you are describing, you are getting a firm brake pedal when the engine is off, but it goes mushy when the engine is on? I'd still say it's air in the ABS system. Only the dealer can purge it using their scan tool -- you have to ask for that or they'll do a normal flush without activating the ABS. (Does anyone know if VAG-COM has a bleed mode that's more than turning on the ABS motor for a while?)

I really don't know what the mechanic did, because a ball joint job should NOT cause this. But I'm sure he won't tell you. IMO he messed up. Maybe the brake hose was yanked on or something. I'd find another shop.

So in addition to ABS purging, I'd give the whole hydraulic system a good inspection. Sounds like your MC is still OK. But verify again with engine off an light foot pressure on the pedal. Does the pedal gradually sink towards the floor? If it remains nice and firm, then I think it's OK. Maybe take it in to the dealer for a diagnosis before you put the MC on. 






MEDEL514 said:


> I have a master cylinder coming in the mail, I'm going to change it and bleed all for brakes when i do.
> 
> Is there anything else I should be looking for to fix this?


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## STVR6 (Jul 6, 2010)

Also, try quickly pumping the brake pedal with the engine on several times. See if you get a slightly firmer pedal.


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## MEDEL514 (Jan 12, 2002)

STVR6 said:


> OEM master cylinder or aftermarket? Just wondering.
> 
> So in addition to ABS purging, I'd give the whole hydraulic system a good inspection. Sounds like your MC is still OK. But verify again with engine off an light foot pressure on the pedal. Does the pedal gradually sink towards the floor? If it remains nice and firm, then I think it's OK. Maybe take it in to the dealer for a diagnosis before you put the MC on.


Thanks for the help! I think it may be an aftermarket MC. It had "Lucas" stamped on the side of it, but no typican VW/Audi part number. 

How does a dealer bleed the ABS system with a VAG-COM? My car is a Euro Spec 1997 Audi A6 (C4) with OBD1, so I don't think there's anything a VAG-COM can do for me. I tried driving the car around with the ABS connection harness unplugged and the brakes did the exact same thing. Do you know another way to bleed the ABS pump? I would've assumed that it would get bled normally. I'm still waiting on my new MC to arrive in the mail, so I have time to play around with the brakes to see what I can find.


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## STVR6 (Jul 6, 2010)

The deal can bleed the ABS pressure relief circuit using their special scan tool, which is not the aftermarket Vag-Com that I know of. They do so by exercising the solenoids and pump motor to clear the air out of the circuit. 

Again, you can try, with the engine running, _repeated_, _rapid _pumping of brake pedal. If the pedal gradually firms up it's good indication air is the problem. 





MEDEL514 said:


> Thanks for the help! I think it may be an aftermarket MC. It had "Lucas" stamped on the side of it, but no typican VW/Audi part number.
> 
> How does a dealer bleed the ABS system with a VAG-COM? My car is a Euro Spec 1997 Audi A6 (C4) with OBD1, so I don't think there's anything a VAG-COM can do for me. I tried driving the car around with the ABS connection harness unplugged and the brakes did the exact same thing. Do you know another way to bleed the ABS pump? I would've assumed that it would get bled normally. I'm still waiting on my new MC to arrive in the mail, so I have time to play around with the brakes to see what I can find.


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## MEDEL514 (Jan 12, 2002)

STVR6 said:


> Again, you can try, with the engine running, _repeated_, _rapid _pumping of brake pedal. If the pedal gradually firms up it's good indication air is the problem.


I just tried this today, and that exactly what the car is doing. It starts to get firm, almost back to normal, then it get spongey again. hmmm, I'll call the dealer tommorrow and make an appt. 

Thanks for the help! I'll let you know what they say.


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## Vwsythe1 (Feb 8, 2009)

I'm havingthe same problem on my mk4 2.0 what did the dealer say?


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## MEDEL514 (Jan 12, 2002)

the dealer was booked two weeks out, so a buddy and I put it on a lift to check everything out. Turns out that the Mechanic installed the drivers side caliper wrong, mispositioning the spring lock on my caliper. We removed both calipers, inspected, lubed, and reinstalled them, and the car drove away like normal!


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## STVR6 (Jul 6, 2010)

Glad to hear it's worked out and turned out not an air issue but incorrect installation. Another reason to do own work.:thumbup: 




MEDEL514 said:


> the dealer was booked two weeks out, so a buddy and I put it on a lift to check everything out. Turns out that the Mechanic installed the drivers side caliper wrong, mispositioning the spring lock on my caliper. We removed both calipers, inspected, lubed, and reinstalled them, and the car drove away like normal!


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