I've got this 65 Valiant that I redid the entire braking system on. All original components replaced. New lines, hoses, wheel cylinders, shoes, springs, drums, and master cylinder 6 times now. I've tried Cardone several times and Dorman new master cylinder once. I got the new reproduction lines at Right Stuff and they suggessted DOT 5 Silicone fluid so that's what I'm using. Well every single master cylinder I've put on has leaked at the secondary plug at the bottom of the master cylinder just drips overnight. Well I got tired of everyone of them leaking so I jb kwik'd over it with the plug in so it quit leaking. But now it's pushed the leak out of the line to master cylinder fitting which never leaked on any of the prior master cylinders. I had the original master cylinder which didn't have a spot for a plug on the bottom and tried to have Cardone rebuild it but they just sent me one of their junky remans. So mine is now gone for good. I've tried teflon many times. It will bleed and build up pressure and look like it's not going to leak. I come back the next day and see fluid dripping from the bottom fitting or in this case now the line fitting. No matter how tight you tighten these fittings they always leak. I believe this is the 6th or 7th master cylinder I've tried. It's keeping me from putting it on the road. Does anyone know what the problem could be?

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1965 Plymouth Valiant 200 4DR 2.8L 170CID
1973 Dodge Charger 6.6L 400CID
1986 Plymouth Reliant SE Wagon 2.2L 135CID

The guys that make the lines might like DOT 5 fluid but it's pretty likely that the rubber pieces in the master cylinder and in the wheel cylinders are not compatible with DOT 5 and are being damaged by the incorrect fluid. AFAIK DOT 5 is specific to Porsche, Harley Davidson and maybe only a few other manufacturers.

Use DOT 3, DOT 4 or DOT 5.1 to be sure of compatibility with typical internal rubber parts.

This may not have anything to do with your leaks but it is a serious safety concern. Use the right fluid, your life may depend on it.

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I solved the leaking plug by using this:

http://www.permatex.com/products-2/prod ... een-detail


Says it penetrates, but I took the plug out cleaned the threads and applied like normal thread lock.

I used the same thread locker on my AC gauge set that had a slow leak (vacuum or pressure) with Teflon, no leak with this stuff.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Have you changed out both the hydraulic line from the MC and the plug? Perhaps the tubing has been nicked or slightly damaged, and ditto for a plug.

BTW, what kind of plug are you using? Does it actually have a reverse inverted flare and is made of softer metal like brass?

The whole situation with DOT 5 fluid and rubber compatibility seems to be variable and not settled. Here is some info from somone who actually contacted some manufacturers:
http://www.adlersantiqueautos.com/articles/brake1.html