Servo Problems

[zorgman]

fault just appeared on me car, driving along and went for brakes and a solid pedal as no servo working so pulled up and its working so checked all the normal vac lines and all intact now its at least 4-5 times a day with no apparent reason why it happens the servo just stops working with a rock hard pedal then it works next time i use brakes so any thoughts on this fault.

[cyborg]

Because servo's are work or fail

 

my assumptions are is that vac line is leaking, snaged or collapsed as the engine moves under braking alternativly the chamber from which the vac line is conneted to servo has some blockage however found this.

 

From VW AUDI FORUM.

 

From some research I have done, problem seems to be one of following:

 

1. Servo and vacuum hose failure (pricey);

 

2. Vacuum hose from manifold collapsed in on itself and broken on metal pipe that comes upward from the manifold;

 

3. Water drawn into servo (caused by blocked plenum drain, etc). Need to remove master cylinder and check;

 

4. Vacuum hose crimped or split;

 

5. Vacuum hose too thin on older A4's - need a newer one that is reinforced and won't crimp;

 

6. When pressing the brake pedal twice quickly in succession, it can cause the brake to become hard. The brake hose goes through the engine compartment bulkhead and naturally passes through a grommet. When you press the brake the first time it causes the hose to

[seatkid]

Because servo's are work or fail

 

my assumptions are is that vac line is leaking, snaged or collapsed as the engine moves under braking alternativly the chamber from which the vac line is conneted to servo has some blockage however found this.

 

From VW AUDI FORUM.

 

From some research I have done, problem seems to be one of following:

 

1. Servo and vacuum hose failure (pricey);

 

2. Vacuum hose from manifold collapsed in on itself and broken on metal pipe that comes upward from the manifold;

 

3. Water drawn into servo (caused by blocked plenum drain, etc). Need to remove master cylinder and check;

 

4. Vacuum hose crimped or split;

 

5. Vacuum hose too thin on older A4's - need a newer one that is reinforced and won't crimp;

 

6. When pressing the brake pedal twice quickly in succession, it can cause the brake to become hard. The brake hose goes through the engine compartment bulkhead and naturally passes through a grommet. When you press the brake the first time it causes the hose to “pull in” to the grommet (normal) but when you press the brake for the second time, the hose pulls in further and crimps thereby removing the servo assisted part of the brakes. Solution: change the grommet.

 

No 6 looks lilkey as it all over the web on vag cars.

 

None of the above apply! (Looks like a list of faults on old Audi petrol models)

 

On Shalaxy Tdis the brake servo is in the engine compartment. No pipes go through the bulkhead. Vacuum is supplied by a mechanical vacuum pump mounted on the engine at the front near the gearbox end.

 

Most likely failures are

 

1. Perished internal seal(s) in the servo (requiring replacement of entire servo unit) - unlikely to be intermittent however, rather a constantly leaking servo that gives little or no reserve of vacuum.

 

2. Check the stiff plastic vacuum pipe that is attached to the servo. Check both ends for splits - when they split they are a loose fit. Note there is also another similar stiff pipe going to the vacuum pump.

 

3. There is a whole load of minor vacuum pipes also that feed the turbo control system - but I find it hard to imagine a fault that gives intermittent brake effort.

 

4. They are reports posted of failed vacuum pumps (rare)

 

Are you sure this is not a case of little or no vacuum reserve? (i.e. a vacuum leak somewhere or poorly vacuum pump). With the engine running and stationary, press the brake moderately firmly a number of times in quickish succession (say once a second) - if the brake pedal goes hard on the 2nd or 3rd push - you have a leak. When the brake pedal goes hard, it should recover within a 2-3 seconds.

Edited April 10, 2011 by seatkid

[seatkid]

Because servo's are work or fail

 

my assumptions are is that vac line is leaking, snaged or collapsed as the engine moves under braking alternativly the chamber from which the vac line is conneted to servo has some blockage however found this.

 

From VW AUDI FORUM.

 

From some research I have done, problem seems to be one of following:

 

1. Servo and vacuum hose failure (pricey);

 

2. Vacuum hose from manifold collapsed in on itself and broken on metal pipe that comes upward from the manifold;

 

3. Water drawn into servo (caused by blocked plenum drain, etc). Need to remove master cylinder and check;

 

4. Vacuum hose crimped or split;

 

5. Vacuum hose too thin on older A4's - need a newer one that is reinforced and won't crimp;

 

6. When pressing the brake pedal twice quickly in succession, it can cause the brake to become hard. The brake hose goes through the engine compartment bulkhead and naturally passes through a grommet. When you press the brake the first time it causes the hose to

[zorgman]

right late reply here but noticed its only at low speed it happens but tried the test and after 3rd push it goes hard but does recover tho when it went other day it stayed hard untill i released pedal then it did recover so going to have to pull all the main pipes off as ive renewed all the small vac pipes.

[Shabazmo]

Zorgman did you ever fix this problem.  I have the same problem but only when the weather is wet and it happens once every few months