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TR4/4A Master Cylinder Corrosion Do I replace?

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rnpennington

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I have this corrosion on my Master Cylinder, yet nothing on the Clutch Master cylinder. A few questions:
1) First and Foremost How and why did I get it?
2) Can I just clean the cylinder or should I replace it?

Attached are pictures

Inquiring Minds want to know.
 

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It looks like the cap for that reservoir leaks a bit...are you using DOT3 fluid? If so, that is the culprit. DOT3 and 4 are hygroscopic, so once it spills it attracts moisture, and between the 2 it will cause corrosion. Since it is entirely external, so long as the cylinder operates fine I would just use a wire brush and/or toothbrush to remove the waxy scale and coat with a corrosion preventer, like LPS3 or other light oil. Of course, be sure to either tighten the cap more or replace the leaky cap seal.
 
I have found that some of the caps on the newer TR4 M/C's do not seat correctly. The ones that I was dealing with had a cap thread that did not seem to fit the M/C thread. Even with a new seal i still had problems. I had several old caps and one other new cap and finally found one that fit tight. I know that this does not sound helpful. But I say it to give you something to look at. There is a lot of sloshing around of the brake fluid inside the M/C in normal driving. Or at least my kind of "normal driving".
 
Charley, I think that's true. Recently I had to replace my original clutch MC with a new reproduction one. The old cap, which I wanted to use, almost fit the new MC, but not quite. As I remember, the thread pitch was a little different and the thread depth was shallower. So, I stuck with the new one's plastic (ugh!) cap.
 
More worrying, than the external scale and waxy coating on the body of the brake master cylinder, is the visible corrosion on the master cylinder brake line visible in your pictures.

M
 
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