hi fellars
i've recently come across an 2003 A3 with a brake pedal that nearly goes all the way to the floor when applied with the engine running, i've power bled the system, i get an ok high n hard pedal when pumped a couple of times with engine off..... but as soon as its started the pedal drops...

input will be greatly appreciated thank you

 

Has there been a brake in the line at some point, in other words have you taken a brake caliper off or loosened any brake lines. If air has got into the system, its possible its travelled all the way to the ABS solinoid. I had to bleed that thing seperatly and it was a real bitch. As long as its hard with engine off, its just a case of getting that air out, its in there somewhere

Luke

 

Don't know if you have fixed this but there must be air trapped in the lines. Best thing to do if you did a pressure bleed is to do a gravity bleed. get all fours up off the air. Start with the rear right, then rear left, front right, then last front left. Go ahead and open your brake fluid reservoir, pump the brakes with the car off! till it gets stiff before you open any of the bleeder valves. let each one drip for about 5 seconds the first round, 10 the second round, and finally 15-20 the third time. Pump the pedal before you start each round. refill to proper level, close reservoir, pump one last time and hold it when it gets stiff. It should be even or really close to the same level that the gas pedal sits at. Start it while you're holding it down, and it should drop slowly. if you notice ANY bubbles coming out while it's bleeding then keep letting them drip till all the air is out. I'm sure you know most of this but just trying to help out

 

thanks heaps for reply DSG n just_e

to DSG: yes the rear calipers were disconnected so i can wind pistons back on a vice,

to just_e: i have'nt performed a gravity bleed in a long while, i'll try to get the customer to come back then i'll do wht you suggested.. wont hurt to try right..

The thing is guys it has a good high firm pedal after its pumped a few times with the engine off.... if it was spongy or dropping to the floor i'd say it was the master cylinder right?
But as soon as its started it falls close to the floor.. should'nt it just drop an inch or so?
please correct me if i'm wrong...

 

Hi Zenonimus,

I have the same problem with a 2000 reg A3. All the symptoms exactly as you describe! I have replaced front and rear discs and pads, master cylinder and done a brake fluid change. There is no leaks in the system and all calipers are good, yet the pedal still goes almost to the floor!
I'm getting it in the ear from the owner to get it sorted and i'm all out of ideas. I did think about the servo? But could this cause the problem? Surely the servo can only provide assistance untill it comes up against the pressure of the fluid being compressed? I will look into possible air in the ABS solenoid. But then again surely it will have a spongy pedal when the engine is off? Anyone know how to bleed it seperatley?
Any other info will be gratefully recieved!!
Thanks!!

 

Hi Everyone,

If you have a power bleeder try that repeatedly, raise the rear as high as you can, connect the power bleeder to the fluid reservoir and that forces fluid through your whole system and out the rear callipers. If you haven’t used one before let me know but its pretty straight forward. Air is in there somewhere.

The thing about the ABS solenoid can’t be a bitch. Basically behind the battery is a metal block with maybe 6 to 8 metal pipes coming out of it. Each tube has a nut. With all bleed nuts tightened around all four corners of the car, get an assistant to press the brake pedal and then loosen a nut on the ABS solenoid, fluid and hopefully air will trickle out. Tighten the nut when you’re confident its just fluid coming out. Then move to the next nut and do the same process. The top of the solenoid is probably where the air is if anywhere in that block, so concentrate on the top tubes. This advice is based on a Golf V5 I was working on and this where I found the air after I too had taken off the callipers.

In future when changing discs and pads, take the cap off the brake fluid reservoir, apply a G clamp around the calliper, and force the cylinder back into the calliper, that way no air can get into the system, fluid is just pushed out of the fluid reservoir.

Thanks

Luke

 

hi fellars...many thanks for adding more tech to this old techhead.... it was the m/cylinder... the much added info helped make the repair a 100%...

highoctane! keep in mind wat the guys have mentioned.........and in addition....bleed clutch slave cyl and master cyl if u're still not happy... bleed ABS by loosenin the pipe nuts on top of ABS module, one at a time though, and if still not satisfactory,,.... replace master cyl