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Rear Caliper seal upgrade to Dot5

Heygus

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Hello all, I’m building this 78 CB750.
For the rear brakes it has a Honda caliper and a HD Sportster master cylinder. The master cylinder calls for Dot5. I had brakes for one day now the caliper seal is disintegrating, so it seems. Older Honda's require Dot3 and is not compatible with Dot5. Can I upgrade the Caliper seal to be compatible with Dot5. Anyone have any experience with this,,, thanks in advance.
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If you used the existing seal that had lived in DOT3 all its life, that may have been the issue. You might try to completely disassemble & clean the caliper with alcohol and replace the seal with new and try again. If using an old rubber line, replace that too with new and switch start fresh with the DOT5

I haven't actually tried to use DOT5 in Honda brakes myself, but I'm aware of several folks that have changed over after installing new MC pistons, lines and caliper seals in various Japanese DOT3 bikes
 
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I used to own a hot rod and restoration shop. A lot of the owners wanted DOT 5 in their cars because they were afraid of the DOT 3 damaging the paint. I'm here to tell you that I and my guys hated, hated, hated working with DOT 5. It's a giant pain in the ass to get all the air out of it and in 10 years of working with it I was never satisfied with the brake on any vehicle we used DOT 5 in.

As far as any of the seals in the system you have now. If they were exposed to DOT 3 and then you swapped to DOT 5, you'll have to change out every piece of rubber in the system regardless of which fluid you end up using.
 
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