Podster Posted July 26, 2015 Share Posted July 26, 2015 I just had the master cylinder for my 40 Special bored and sleeved. I decided to buy a rebuild kit and do the rebuild myself. Piece of cake thought, except for one problem . It leaks from the copper seal ring between the master cylinder body and the treaded port base. I torqued the heck out of the threaded base with a pair of Channel Locks but it still leaks. Is there some kind of trick to sealing this area up, like Teflon tape on the threads? Link to comment Share on other sites More sharing options...
Guest gmorse Posted July 26, 2015 Share Posted July 26, 2015 I had the same problem on my '39 at least 10 years ago. If my memory is correct, after I took it apart, and used a straight-edge on the casting, there was a very small defect in the casting. Did not leak before, so the tiny area must have been filled with rust, or some other junk. Again, if my memory is correct, I had the casting very slightly machined to be completely flat. I have also heard of the fitting that screws into the cylinder being not flat. I did not have that problem, just the old casting was not flat enough to fully seal.Also, closely examine the brass washer for any defects which could cause the same problem.Gary Link to comment Share on other sites More sharing options...
39BuickEight Posted July 27, 2015 Share Posted July 27, 2015 Loosen and tighten it 100 times. That's what I did. Seated eventually. Link to comment Share on other sites More sharing options...
pont35cpe Posted July 27, 2015 Share Posted July 27, 2015 May need new copper/brass washers on the fitting, the leak is probably coming from the washers not the threads.. Link to comment Share on other sites More sharing options...
DonMicheletti Posted July 27, 2015 Share Posted July 27, 2015 First, the sealing surfaces must be smooth. Then you have to fully anneal the copper seal ring.You anneal the ring by heating it until it is fully red hot and then quench it in water. Taught to me by an old pipe fitter.Some say that you do not have to quench it, but I always do and it always works Link to comment Share on other sites More sharing options...
Podster Posted July 28, 2015 Author Share Posted July 28, 2015 Thanks for responding. All your responses gave me some information to work with. I considered having the machined seating area kissed, and I may do that. However I noticed that the wall thickness at the bottom end of the bore diameter is no more than 1/16" thick while the top end is about 1/4 " thick. That is not much of a sealing surface on the bottom. It is not a very good sand casting and may have shrink in that area.I also compared the old copper seal ring to the one I received in the repair kit. The old one was .066" thick the new one is .039" thick. I good reason to buy NOS.They are both scratched up from assembly and disassembly. Anyone know where I could buy copper seal rings?Billy, when you loosened and tightened it 100 times, was it a quarter turn back and forth each time? Sounds like you made a groove in the sealing ring which increased the sealing surface. Don's idea about annealing the ring does the same thing except the soft ring is being squished. Did you use an Oxy-Acetylene torch? The ring didn't warp? Link to comment Share on other sites More sharing options...
39BuickEight Posted July 28, 2015 Share Posted July 28, 2015 Yes that's basically what I did, just turned it enough to separate it and snug it. I said 100 times, but it wasn't really that many. Maybe 1/2 turn. Never really tightened it but every 10 times or so. After a few rounds it stopped leaking. Link to comment Share on other sites More sharing options...
DonMicheletti Posted July 28, 2015 Share Posted July 28, 2015 You just need a propane torch to get the copper to red hot. (you can even di it with a cigarette lighter)You do not need to worry if the ring gets distorted. Since it becomes dead soft, the process of tightening will flatten it out.The idea behind the annealing is to make it very soft so it will conform to any irregularities on the sealing surfaces. However, the smoother the better. You do not have to worry about the copper getting to soft and blowing out. It still has plenty of strength Link to comment Share on other sites More sharing options...
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