Brake line unions

[pmm316]

I have installed disc brakes on my trailer that previously had no brakes, and have a problem/question. What is the proper torque for inverted flare fittings to unions? Since this is my first ever experience with brake lines and fittings I have no reference for proper installation. I have leaks (under pressure) at the unions where I had to join two lengths of steel line together. Is it possible to over-torque the lines/fitting or is it not tight enough? The unions are inverted flare, brass. The lines are 3/16 steel.<br />Any help is appreciated.

 

[boater4life]

Re: Brake line unions

Most likely they are not tight enough. They have to be good and snug.

 

[Bondo]

Re: Brake line unions

About 25/35ft.lbs.......<br /><br />Either they're Loose, Or you've Already Stripped them............

 

[Pascal]

Re: Brake line unions

pmm316<br /><br />There are torque specs available for flared fittings but they are not easy to apply.<br /><br />A much easier method is to use the pitch of the threads. Your 3/16 tube fitting has 24 threads per inch. dividing 24 into 1.000 shows that the fastener will advance 0.042" per revolution or about .007" per flat on the nut.<br /><br />With a new flare you want about 0.020" of crush on the union. on a used flare about .015" of crush will do.<br /><br />This is a standard method of tightening flared hydraulic fittings. see this web site.<br /><br />(a 3/16 tube = a dash 3)<br /><br /> http://www.insidersecretstohydraulics.com/hydraulic-fitting.html <br /><br />If the fitting still leaks when you have used this method, check the flare face and the fitting seat for any defects. <br /><br />If you flared the end of the steel line your self, don't feel bad if the flare face is off center and won't seal. Steel brake lines are very difficult to double flare properly with the standard flaring kits. Best flaring kits for steel lines are the ones that use a hydraulic cylinder and provide a straight linear push rather than the added twist and flex of the forcing screw on a regular flare kit.<br /><br />This is one website that shows the hydraulic flaring tool.<br /><br /> http://www.enjoythedrive.com/content/?id=10024

 

[pmm316]

Re: Brake line unions

Thanks a lot. That's just the information I needed. Turns out I had not torqued them enough. Since I wasn't sure how tight to make them I just went a little more than hand tight. After tightening a little they sealed up.<br />Thanks again.