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Stainless steel brake line problem


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IMHO, stainless steel is one of the most difficult (if not THE most difficult) material to work with for brake and fuel lines.  The hardness of SS makes it more difficult to get leak-free connections as compared to softer metals.  If the leaks are on the smaller/slower side, you may be able to resolve via loosening and tightening several times....helping the metal to take a "set" within the connection.  It also helps to do this with the fixture unbolted from its mounting point (e.g. leave the Master Cylinder unbolted, or at least loose, on the brake booster when tightening the front and rear lines to the MC.)  This will help ensure that the incoming/outgoing lines have optimal geometry WRT the fixture they are connecting to.  This is particularly important when working with a non-malleable material like SS.

 

Just out of curiosity, what style flares did the brake line kit come with?  Also, did you visually inspect all your original hardware (tee connections, prop valve, etc) before installing the new lines to ensure you had no damage on any of the nippled connection points? 

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The flares are double flares. So far I have replaced the master cylinder with a brand new one. I have tried two different brake  light indicators, have a third one yet to try. Three of the five connection on the brake light indicator are fine. The one going to the rear ,and the one going to the passenger front leak. Both of the proportioning valve leak , and one of the three in the block that splits to the rear brake leak. The two rear brake connections are not leaking the two front do. I have assembled the whole master cylinder brake light indicator connections out of the Z except for the connections going to the rear and passenger front and still get the leaks. All connections were threaded in finger tight to avoid cross threading, then tightened, backed off, retightened four times. Some seal ,some do not.

I will keep trying , may be they will eventually seat. Hope full someone else has had this and has an answer. Thanks

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Have you taken a good closeup look at the sealing surfaces?  Use bright light and a magnifying glass.  There's probably a clue there.  You got single or double but they're both just a cone that sits on a cone.  You can even put a final finish on the surfaces with abrasives.  Look for cracks, imperfections, or crud on the sealing surfaces.

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71 240Z takes a double inverted flare, not a bubble flare. Talked to Don at Classic Tube. The suggestion is to keep doing the tighten, back off ,retighten scenario, it will eventually do the job. As he said they have sold quite a few of the kits so that’s not the problem, the problem is the hardness of stainless versus the softer original tubing. Their site even mentions replacing the old parts you are connecting to with new. We all know that’s not going to happen.

 

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The all SS sealing surfaces is poor engineering practice  IMO. Hydraulic systems often couple a hard metal with a softer metal for precisely this reason. I don’t think any of the “kits” out there have gone through this effort but I suppose it’s not a big enough problem to warrant a change. All SS coupling in other industries, like swagelok compression fittings, are machined to tight tolerances and include a “blighting” surface to overcome this problem.

 

also, be careful not to gaul the threads. This is a process of over-working or overtightening matted metal surfaces. Most common in SS due to the hardness. Once gauled, it will be near impossible to uncouple the connection without ruining the threads. To avoid this, do not over-tighten the connection past the point where you no longer witness leaks under pressure. 

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