vtraudt

We replaced the master brake cylinder.
Still not sure what caused it, but assume dirt.
The entire process was:
- car came in with working brakes for auto/manual swap
- brakes not touched, other then connecting line for clutch to/from brake reservoir
- clutch not working
- replaced (used, came with manual tranny) clutch slave with metal slave
- clutch not working
- put working brake master on.
- clutch and brake working
- clutch slave line popped out. Replaced with metal braided one with secure screw type fittings
- clutch and brakes working
- 2 weeks later, brakes locking up
- removed brake master and replaced.

I assume that dried up brake fluid (from old clutch slave and clutch line) may have found its way into the system, causing the problems.

waltwlms55

[wow this is an old thread but seems to relate to my issue. I have ‘96 A4 which has been sitting for 3 years, beginning to restore. just completed full brakes, calipers, rotors, pads. front brakes lock up when engine running ie battery connected and vacuum to booster. Disconnect battery and pump brakes and brakes release. i read this allegedly resets ABS. brakes do not lock up if depressed with battery disconnected and no engine vacuum. based on what i’ve read, i’m leaning towards ABS module, please share any other thoughts or possibilities, the module is around $250, playing best odds. thanks. w

QUOTE=indoor;24599947]Looks like ABS unit is acting up. Service manual says some hydraulic abs units have to be bled via computer(VCDS). Check your abs unit type if you have the service manual(they have a picture of each type).
Maybe you got some air in the unit, or it's leaking...
P.S.: I would lube the caliper guide pins even though chanses are not all four seized up out of nowhere...oh' and clean the abs sensors too just to rule them out...[/QUOTE]

kabbyo chawdhury

[QUSame problem- my dash also says esp fault- could you email me the manual as well? OTE=thejulex;24599960]Can you describe in more detail when it locks up?

E.g. you drive normally and all of the sudden it brakes on its own?
You brake lightly and it locks? or heavily that would prompt ABS to activate?
Right after coming to a stop first time after starting the car (ESP pump self-test, ESP pump generates pressure in brake system without driver's involvement)?

Either way it sounds like a valve in ABS is acting on you, or more specifically perhaps ESP channel pressurizes the system as if traction control is needed and never let's go.

It must be ESP pump, not abs. ESP pump normally activates when traction control kicks in as at that time you naturally have zero pressure in hydraulic system (you're not pressing brake pedal when accelerating).

Send me your email, I will send you factory repair manual for brakes for fun reading (130 pages PDF... covers pretty much every nitty gritty detail)[/QUOTE]