I have recently purchased a 1999 Audi A4 Quattro 1.8T. I am a new Audi owner, but have worked on many myself. So, I was hoping that someone could possibly help me with a problem that I am having simply trying to bleed the brake system.

Problem:

I am unable to get any fluid travel from the right rear and left front calipers. The bleeder valves were fairly aged, so I went ahead and replaced them.

A few weeks ago I replaced the master cylinder because it had failed, since then the peddle had been a little spongy. So, as a favor to my wife I decided to bleed them tonight.

To let you know now, I do not have any diagnostic scanners other than a simple Snap-On ODB-II reader. Since the R.R. and L.F. wheels were the only ones not bleeding my first instinct was to check for a proportioning valve that I could reset. Unbeknownst to me, the proportioning valve is integral to the ABS module. So, I cracked the lines and bled the module until fluid was flowing through satisfactorily.

To make sure the calipers were working, I placed a line into a clear cup of brake fluid and let my wife pump the peddle slowly where I observed air bubbles release once or twice, but never got anymore. I did this at each wheel, only the L.F. and R.R. positions filled the cup with additional brake fluid.

Is there a manual reset procedure to this ABS module, or an optional bypass? I am in no position to be purchasing additional tools or parts at this time, and it is our only means of transportation at this point.

I do not know if it is related, but the brakes recently began to become problematic after repairing the breather system going to the PCV valve. This system ties into the vacuum system for the brake booster, but does not seem to be the main supply.

A little light on this subject would be nice. If there is a manual reset procedure, or bypass for the module this would be acceptable, anyhow. The module has not worked since purchase anyhow and has never caused an issue.

 

Did you bench bleed the master cylinder before installation? There is a way to activate the ABS pump using VAG-COM, but is probably not accessible with your generic OBDII scanner.

I assume you're using the traditional 2 person method for bleeding. I've had good luck using a homemade power bleeder. I got a spare master cylinder cap at a junkyard and used a cheap yard sprayer to pressurize the reservoir. Open the bleeder screws until clean fluid flows through.

Have you been able to bleed the fronts? I've also had good luck bleeding the fronts before the rear. The exact opposite of the traditional RR, LR, RF, LF.

 

I appreciate the swift response to this question. I would have responded sooner, but I was having issues logging in.

The master cylinder was bench bled. Luckily, I kept the tubes and adapters that came with the kit. I went ahead and bled the master cylinder again tonight (just in case) to rule it out as the culprit.

I am using the traditional method. I have my wife apply the brake pedal as I crack open the bleeders. (While reading forum threads I came across a suggestion that said not to pump the brakes because it causes a "foamy" effect.)

The spare reservoir lid like you suggested may work. I am sure I can rig something with a valve stem and a pressure regulator off of a spray gun. Does this pressurized method somehow work better than using "foot power"?

I am able to bleed the front left (driver's side front) and rear right calipers. That is why I am speculating it is internal to the ABS module. As where I would presume if it were indeed the master cylinder that would affect either just the fronts or just the rears.

I was out tinkering with it in the yard a few minutes ago (yes, it's pitch black and 1:00 AM outside). I was attempting to gravity bleed it, so I have just left the bleeders cracked open for about an hour. Still nothing.

 

Okay, I see that I forgot about this post. I replaced the master cylinder (once again) and all is well again. Guess I just got a bad one.