2004 114,000 miles. ABS still fitted. Master cylinder losing fluid.

[ELIMINATOR]

Well, got on the bike the other day, ABS lights performed as normal. Brake lever seemed to come back further than usual. Rode the bike 120 miles, it was preying on my mind. Hit the brakes hard a few times, stopped ok. Got home, couldn't see any fluid in the master cylinder sight glass. Topped it up, never had to do this before in nearly 20 years of ownership.
I wondered where it could have gone, no oil running down the engine anywhere.
Today I looked, no oil in sight glass.

Oil under the bike, dripping from one of the breather hoses, beside the brake pedal.

Any thoughts? Apart from.... yes, it's a leak.

 

[Steptoe]

Servo or non servo ?

 

[ELIMINATOR]

Servo or non servo ?

servo

 

[Steptoe]

Oil under the bike, dripping from one of the breather hoses, beside the brake pedal.

servo

That will be brake fluid dripping out from the servo modulator fluid reservoir overflow pipe.

 

[Ian J Hartley]

I shall try to elaborate.

Most probably a leak in the Servo unit, likely across the front brake control circuit.

The detected fluid leak is likely to be coming from one or both of the servo unit reservoirs..

You are going to need to look at the levels in the Servo unit reservoirs to be certain.

As the pads wear, the fluid level should decrease. So any level increase has got to be fluid from the front brake master reservoir. The fluid has to go somewhere.

The front Brake circuit controls both front and rear brakes, so you may find that either or both servo resevoirs have captured the fluid from the master reservoir.

Without the servo running there is residual braking, all be it poor, but the front brake lever pressure does go directly to the front calliper and brake pads. So my guess would be, it’s that portion of the servo unit which is passing fluid.

Of course this is only information, the bottom line is it points to an internal failure of the Servo.
Maybe a flush and full brake service may fix it if the fluid is old and contaminated. Maybe not.

 

[ELIMINATOR]

I shall try to elaborate.

Most probably a leak in the Servo unit, likely across the front brake control circuit.

The detected fluid leak is likely to be coming from one or both of the servo unit reservoirs..

You are going to need to look at the levels in the Servo unit reservoirs to be certain.

As the pads wear, the fluid level should decrease. So any level increase has got to be fluid from the front brake master reservoir. The fluid has to go somewhere.

The front Brake circuit controls both front and rear brakes, so you may find that either or both servo resevoirs have captured the fluid from the master reservoir.

Without the servo running there is residual braking, all be it poor, but the front brake lever pressure does go directly to the front calliper and brake pads. So my guess would be, it’s that portion of the servo unit which is passing fluid.

Of course this is only information, the bottom line is it points to an internal failure of the Servo.
Maybe a flush and full brake service may fix it if the fluid is old and contaminated. Maybe not.

Thank you Steptoe and Ian, seems like it's time to remove the servo.