strange brake problem

Hi i hope someone can help me,over the last few days when my girlfriend has taken the car to work a4 avant 1.9tdi shes phoned me up in a panic saying the first time in morning she puts brakes on theres just a hard pedal and no braking action,however if she releases padal and reaplies they work fine and continue to work fine for rest of journey just seems to be once car has sat all nite or all day,any help would be apreciated as every time i check it it seems fine,and i know the garage will prob say the same:1zhelp:

Sounds like you're losing servo vac overnight,try pressing the pedal before starting the engine,there should be still a vac left in the servo,enough to press the padal down,You need to sort that out pronto otherwise she'll be hitting something,ever tried braking without the servo it requires a lot of force!try looking for leaks non return valve maybe.

hi think you might be right i just drive car and it did it to me aswell twice so its getting worse,

thats 99% gonna be a servo problem.
that needs to be sorted out ASAP
do a search for plenum chamber and servo and you'll see it's a well known problem
Thankfully i've never heard of a very serious accident because of it, but please dont be the first.
get it sorted asap

I reckon your plenum chamber drain holes have been blocked and during heavy rain the plenum chamber has filled with water and killed your servo. You may have to fit a new servo and remove one or both of the drain grommets. One under battery, and one under servo.

agreed get them to justtake out the grommets when they replace your servo.
make sure every 6months you clean it out.

ive seen a few threads on here saying this was a audi recall for the bungs blocking and leading to break failure,do you think audi would fix this under this recall if its related.if not wot sort of money is in a new servo,thats got to be expensive.

You can check if the plenum chamber is blocked just lift the battery cover and check around,having said that these servos have a habit of rusting internally could of been a previous owner,anyway you can go down to audi give them your VIN number see what they say,but it may be down to having full service history?many years ago my wife wrote off my audi 100,lost servo assistance,managed to slow it down to walking speed then hit a lampost!

Hi i just checked brake fluid and around the top of the reservoir looks wet to me as if fluids been leaking out,once opening cap i found reservoir is full to brim you could not fit another drip in,in my opinion it should not be like this,i phoned audi this morning and they told me mine wasnt affected with the plenum chamber its a a4 2003 tdi,could there be water getting in reservoir,or could it be a simple break in vac hose between engine and bulkhead? iam scared to drive it,booked into garage tomorrow but as its a intermittant fault iam sure they will tell me servos fine and try and get me to get new discs and pads aswell althought they are slightly worn these are definatley not the source of no brakes and a solid pedal almost asive i have a bit of wood jammed uder pedal and cant push it down,

You are right to take it in for assessment its definitely the servo or master cylinder area, average wear on the pads and discs will not cause this,ask them to take off the vacuum pipe off the servo and see what the condition is,also check the condition of the pipe for internal collapsing,the master cylinder overfilling might be just that overfilling.when there's no vac in the servo its just like you said,a block of wood under the pedal.