The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: 1972R60 on April 12, 2014, 09:12:06 PM
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I am getting myR65 ready for the first ride of the seasom.Brake fluid level is low in the master cylinder. It seems to be leaking where the plastic cylinder attached to the metal base. Anyone ever encountered a situation like this? Any help much appreciated.
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If you have the round reservoir master cylinder, you may have to get a replacement .
The round reservoir master cylinder is bonded to the reservoir, not meant to be seperated .
Havn't heard of anyone having success in repairing this .
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If you do go with a replacement, make sure to measure your master cylinder bore size. There are several options available.
Also, if you do replace I'd get the rectangular 1981+ unit as it has a replaceable o-ring between the reservoir and master cylinder.
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It seems to be leaking where the plastic cylinder attached to the metal base. Anyone ever encountered a situation like this? Any help much appreciated.
These rely on a mechanical seal formed when the plastic part is driven under pressure into the metal part. It is a one-time deal and if the components are ever separated the piece that forms the seal is destroyed and you need a new plastic part. New plastic parts are NLA since about 2004.
My experience is that they all leak after a while due to age related deterioration of the plastic, aided where I live by the generally high UV.
As others have suggested, measure the diameter of the bore and replace with the newer "square" type, which is a direct bolt on to your existing lever/throttle assembly.
Having just looked at the Motobins site, you can still buy the "round" brake master cylinder, but unless you are a stickler for originality I would pass on that and buy a square one as a round one is just as likely to fail on you in the same way as your existing one.
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Normally, the inside diameter is moulded UNDER the cylinder.