S Type Brake Bleed

[actros]

Hi Guys

Having recently replaced the brake master cylinder on my 2004 2.7, I have tried bleeding the brake system several times using an compressor operated vacuum pump but for reasons unknown, I cannot get the brakes right on this car.

There is no leaks anywhere in the system.

Back left, Back right, Front left and Front right. not forgetting to bleed the master cylinder as well but still no joy.

Does anyone know if the engine needs to be running or am I doing something wrong - HELP!!!!!

Martyn

[david moore]

hi martyn,    when ever I do my brakes I do it the old way.... someone  sits  in the car and pushs the pedal down while the other person turns the bleed nipple with a pipe attached into a glass jar with brake fluid in. until all corners are done. then its test the pedal for how hard its gone ?  if the pedal is still spongey and it goes down slow when pushed, it maybe the rubber seals in the master cylinder are worn and need replacing. but most of the time it nearly always works first time when we have bleed the brakes as ive said doing it the old way. good luck as they can become a nightmare..... dave. 

[Guest]

Hi Martyn,

I recalled seeing a post from Raistlin, dated a couple of years back, concerning the same problem; see copied text below. May be an idea to reach out to hime directly.

Raistlin - Having acquired a vacuum brake bleeding tool, we set about the bleeding process from square one. ie. near-side rear.

I have NEVER seen so much air in brake fluid. The stuff being drawn out under vacuum was so gassy it looked like milk.

The same thing happened with the other three calipers but as a result, the car now has perfect brakes.

Highly recommend the vacuum brake bleeding kits.

It could also be that the servo is the problem so I've posted a copy of some guidance I got from another site that will help with diagnosis to rule this in or out.

 

If the pedal feels "hard" while the engine is running, the brake servo isn't operating correctly. 
Test 1
 

1. With the engine off, pump the brake pedal to remove any residual vacuum in the Servo.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the Servo is working properly.

Test 2
 

 

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight Servo.

Test 3
 

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the Servo is airtight.

Inspect the Check Valve
 

1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the Servo. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Vacuum
 

1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly  tuning the engine, checking for vacuum leaks and blockages in vacuum lines

 

Hope this helps but keep us posted.

Cheers,

Steve

 

 

[Roger S3]

Hi guys 

Mega problems with the brakes on my SType 2004 3.0 v6

having changed both the vacuum servo and the master cylinder I the brakes will not release . The system has been bled but the brakes wil not release. The electric park brake seems to be ok as the release light on the dash goes out when there is pressure on the gas pedal !!

The brake pedal is hard to depress any one got any ideas