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Brake fluid help

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I

ichthos

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I need some help with brake fluid. I am installing a new Lucas brake master cylinder. On the cap it says to use only DOT3 brake fluid. I am running Castrol GTLMA in my clutch sytem. Is it OK to use the Castrol in my brake master cylinder also? Any help would be greatly appreciated.
Kevin
 
GTLMA will do fine. The cap was made before the DOT 4 standard was introduced.

Of course some of us feel that DOT 5 is even better, but that's a different discussion
grin.gif
 
Thanks, Randall as always. I am still baffled as to why my last master brake cylinder failed after only two years. It was rebuilt by Apple Hydraulics which I have always had good luck with in the past. I don't know if the brake fluid was the culprit. I had to run new seals in my clutch sytem and decided to use the GTLMA. I was noticing a black tint in the clutch master cylinder, which I figured meant that the seals were being dissolved. I did not notice this in the brake master cylinder.
 
That can happen if you happen to get the old-style seals, and use non-Girling DOT 3 or DOT 4. The original seals were natural rubber; and unfortunately the DOT standard does not specify testing with natural rubber. So with the old seals, the important thing was not DOT 3 or DOT 4; but using a brand of fluid (like Girling) that was compatible.

Dunno if that was your problem or not; but I'm convinced the problem is real. Or was, since AFAIK any seal made in the last 10-15 years is SBR, not natural rubber. Might be some old ones still on the shelf, though.
 
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