Brake fluid loss on 02 2.2HDi C5

[aramsay]

Hello.

I'm experiencing some brake fluid loss from the resevoir of my '02 2.2HDi C5.

There are no external signs of any leaks on the underside of the car nor near the servo.

I suspected the master cyclinder was leaking fluid into the vacuum system of the servo and being burnt off in the engine. However, having removed the m/cyl from the servo drum, there is no sign of leaks from past the m/cyl seals, nor any apparent wetness inside the drum of the servo.....

Any suggestions where else to look for a leak ?

I still suspect the fluid might be leaking from the small seal at the end of the actuation rod, but would like to have other options to investigate before I fork out for a new m/cyl....

Slainte, Alan.

[BX]

Did you check the clutch master and slave cylinders. The clutch uses the same reservoir even though on Irish/British cars the brake and clutch master cylinders are on opposite sides of the car.

[aramsay]

There is no sign of leaks at either the master or slave clutch cylinders.

I am also now experiencing a sinking brake pedal, despite having bled all the brakes, and had the brake master cylinder out of the servo-drum....no sign of any leaks here either.

The bore of the brake m/cyl looked fine. Do the seals "go" on these ? Car has done 130,000 miles.

As a new brake m/cyl. is in the region of £260, I want to be sure that is the where the fault is.

Any other suggestions welcome.

[BX]

If air gets into the abs unit it can give the sinking pedal symptom.
In common with several other makes and models, if air gets into the abs block the pump needs to be activated to bleed it properly. This is done using a diagnostic tool. I cannot say that the unit cannot be bled without activating the pump but I have failed to do it. I have tried the traditional 2 man method, pressure feeding fluid from the reservoir and reverse bleeding under pressure from the slave cylinders. However activating the pump a few times using any of the above methods has worked for me.
Your fluid loss is certainly a mystery. It surely has to leave some trace where it is escaping. Is there any danger of a tiny pin hole in a pipe somewhere. If the fluid sprays away from the body it might leave little or no trace. Might also cause the pedal problem as well if it gets worse.
I haven't come across a faulty brake master cylinder in a C5 yet or even heard of one. I thought I had discovered one until I read the rat manual and then tried activating the abs pump.

[mooseshaver]

Probably no help but when my c5 02 leaked fluid it appeared on the centre of one of the wheels and spread out as I drove.
That was after brake pads were fitted. The pedal lacked resistance and eventually the resovoir was empty. Only then did the garage accept it wasn't the pads bedding in.