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Greg, Technician
Category: Volvo
Satisfied Customers: 7279
Experience:  Automotive diagnostic tech
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hi i have a 99 s80 with a brake problem when the engine is

Customer Question

hi i have a 99 s80 with a brake problem when the engine is not running there is normal presure at the pedal but as soon as i start the engine the pedal slowly goes down i have checked for fluid leaks but found non hope you can help charlie
Submitted: 4 years ago.
Category: Volvo
Expert:  Greg replied 4 years ago.
Hi Charlie .

This is a typical sign of your master cylinder starting to fail or should i say has failed .

You can bleed the brakes and have great pressure but as soon as you have the engine running and have power assisted then you will notice that the brake pedal will traval slowly to the floor and not have any brake fluid loss , this is due to the internal seals letting fluid draw from one side to the other .

If you don't have any brake fluid loss replace the master cylinder , and to be even more 100% block off each four brakes with a hose clamp and see if the pedal still drops down to the floor ,if it does replace the master cylinder .

Need further assistance with this issue then pleas eget back to me .

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Rgds Greg