Technical question: RT 1200
A friend of mine has asked me this question:
The rear brake master cylinder on my RT has sprung a leak. Do you know whether that cylinder is part of the ABS system. In other words will it affect the functioning of the ABS?
Can anyone shed some light on this please?
Yes it will.
1 Is it only leaking when pressure is applied?
Is it weeping fluid slowly even when no brake is applied?
The fact that it is leaking suggests the bike is >6yrs old. if it was still within warranty, then it was never a question, return-to-vendor.
It should never leak.
Period.
It most certainly will drain the reservoir and the leaking fluid will corrode the duco paint layer and leave indelible etching in the paintwork.
He should treat this as reasonably urgent and flush the area with warm water to remove the fluid that has leaked.
The ram is inverted, thus fluid leaking past the ram seal will gravitate down the shaft past the brake lever.
Best take it to a mechanic.
If he is going to dally, then ensure the reservoir is topped up.
Never heard of a master cylinder seal go on a BMW with less than 20 years.
A leaking master cylinder can introduce air into the braking hydraulics. ABS is part of the hydraulics.
The real question should be will the leaking cylinder affect braking? It is much, much more important to be able to brake than to have ABS. And the answer to that is also yes.
So, if the question is being asked because the rider wants to know how urgently to fix the problem, I would say it is pretty urgent. If the question is actually in relation to a warranty claim on an ABS system, I would say that unless the leak was there for a long time, air in the system should not damage the ABS. If it was a long time then moisture may have ingressed and caused damage.
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