Master cylinder leaking?

[gdizzle]

Hello
On my 66 slant dart, sporting the original style brake system (drums , 9in, cast iron single master cyl), I am having to replace fluid every few weeks, about 3/8in drop. At the front (towards front of car) on the master cylinder there is a threaded plug that goes up from the bottom. It is maybe 1/2in threaded plug. I am not sure what would ever get connected there, but is has a slow drip coming from it. I have tightened it to the point where i feel I might ruin the threads, but it doesnt seem to make a difference. The leak is slow, gathers, then drops straight onto the dust cover on the steering joint, thus the dust cover is completely deteriorated.

Any ideas how to stop this leak? I don't suppose there is teflon tape that can withstand brake fluid? Or ???

 

[Sedanman]

I have the same issue with mine so I am going to swap it out for the 2 bolts style DrDiff sells. I didn't notice mine leaking until I saw the bubbled fresh paint on the outside of my firewall.

 

[66fyssh]

I don't know what that "extra" plug might be for. My 66 Barracuda one pot m/c didn't have any other ports. Mine was leaking at the plunger seal so I went with safety over originality and put in a dual reservoir (I have factory KH Discs so that's why different sizes). You should be able to get an original style replacement m/c for your car or it may be a good time to do the swap. Don't forget to bench bleed (I did it after it was mounted) Here's mine.

 

[BillGrissom]

I had one a single pot w/ both a front and bottom port, as you state. Might have been on a new booster I bought for my 65 Newport, and think I sold it. I now run dual reservoir MC's on all 3 old Mopars. Teflon tape would work fine. Main thing is to never remove the plug since little shreds of teflon could get everywhere in the brake system. Also, don't over-tighten the plug. Those are tapered pipe threads, so overtightening will easily crack the cast-iron body. I had that on the single port of one such MC and had to fix it w/ epoxy. Probably the crack was already there from the rebuilders since I am careful.

Re what would have used the dual ports, perhaps the PN crosses to other manufacturers. I think GM used 2-bolt MC's in the 60's, so not them. What about Ford? Some MC's today have a separate port for each front wheel (rather than a distribution block). My 80's M-B is like that, as are 90's Chrysler "cloud cars" w/o ABS (why ABS MC is better for my classics). My M-B cars don't appear to have a F-R pressure imbalance switch like 70's Mopars do, so perhaps that wasn't a fed mandate or was dropped.