2005 A4 Quattro 2.0T Brakes Soft at cold start

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pilotie

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• Jan 30, 2014

• #1

I have a 2005 Audi A4 Sedan Quattro 2.0T automatic VIN WAUDF68E65A43xxxx. When I first start the car, and back up or go forward, the brake pedal is soft and I have hardly any brakes. If I drive the car for 1-2 minutes, the brakes are fine. I suspected a vacuum leak and have looked in the hoses, checked around the brake booster hoses and can feel no leak or cracks or hear no hiss sounds. I disconnected the vacuum host where it goes thru the rubber grommet and the firewall joining with another hose leading to the booster after letting the car sit overnight - there was a small hiss of vacuum indicating at least some residual vacuum - I guess there would be a check valve somewhere in the vacuum lines heading from the engine to the booster to prevent loss of vacuum so brakes would be good on startup ?
The car has 75K miles.

No brake light, No CEL, no codes.

can anyone suggest a diagnosis/fix for this issue ?
Thank you.

 

geordiestig

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As a test, from a cold start pop the bonnet with the engine running and look to the back of the engine where the firewall is, you will see the vacuum pump located on the back of the engine with a black pipe terminating in to a black connector on the side of the vacuum pump, does this appear to vibrate or pop in/out slightly from the pump housing?
Either way, go back in to the car and pump the brake pedal and if it is a failing pump assembly the pedal should firm up.

Rob.

 

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pilotie

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I will try the test after work tonight. On the coldstart previously, the pedal is not soft - it just goes down a bit, is hard, and there is very little braking force - hardly makes the car stop when backing up a little slowly or going forward slowly.
I will post the results of doing coldstart and observing the vacuum pump connection.
Thanx for the quick response.

 

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pilotie

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I started the car cold. The black hose coming out of the vacuum pump does vibrate with the engine running.
I pumped the brake pedal, seemed to make no difference in the brakes when I backup or go forward - hard pedal, car barely stops at low speed even tho I pushed hard on the pedal.

 

geordiestig

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• #5

Does it pop in an out of the pump housing ever so slightly?

 

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pilotie

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No it is just vibrating at the hose. I can not see or feel it popping in and out at all.

 

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• Jan 31, 2014

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http://i.ebayimg.com/00/s/NTA0WDM5NA==/$(KGrHqR,!iYF!9,nzK7,BQfHd6pMLg~~60_12.GIF?set_id=880000500F

I think that is the pump - any more thoughts Rob ?
Thank you