BUBBLE OR DOUBLE

[TELBOY]

Good evening all,
Need a little advice! last year I replaced most of the brake lines on EOW 1W and on checking the pipes were bubble flared, however today I was replacing the front left and upon removal I noted that this was double flared!!!! I am assuming that bubble replaced double in the mid 80's and the male nut appears with a recess to accept a double whereas the new nuts look flat so to accept a bubble flare (hope your all following this because I am now lost) What I need to know is obviously because of the nuts a bubble flare is the way to go, but is it in any way compromising the seal of the pipes?

Terry

[suffolkpete]

Sounds very odd to me.  Look inside the threaded bit to see whether it's concave or convex at the end.

[roy4matra]

Good evening all,
Need a little advice! last year I replaced most of the brake lines on EOW 1W and on checking the pipes were bubble flared, however today I was replacing the front left and upon removal I noted that this was double flared!!!! I am assuming that bubble replaced double in the mid 80's and the male nut appears with a recess to accept a double whereas the new nuts look flat so to accept a bubble flare (hope your all following this because I am now lost) What I need to know is obviously because of the nuts a bubble flare is the way to go, but is it in any way compromising the seal of the pipes?

Terry

Terry, as Peter has said, you need to check the surface inside any connection that a brake pipe is mating with.  It will either be convex or concave and the flared end of the pipe has to match it.  So if a union has a concave or dished-in surface where the end of the pipe seals then the end of the pipe needs a convex flare (what you are calling a 'bubble' I think).  A convex surface will need a concave flare end (what you are calling a 'double').  Most pipe end flaring tools create a convex first and then 'squash' that to create the concave end shape on a second operation (giving you that double material thickness).

Usually unions, cylinders or calipers will have a concave shape and need a convex pipe flare.  The most common need for a concave pipe flare is when it connects to a flexible hose which usually has a convex end shape.

There is a third flat end type, that is more rare in the U.K. and the mating flat surface has a small 'pip' in the middle of it.  However, that is not used on the Murena.  The Murena uses the metric flare system, which is similar to but slightly different to the old English single and double flare.

Roy

[TELBOY]

Thanks Guys..... I understand! photo of bubble flare fitted to old pipe.... I have discovered that if I create a double flare then remove the pipe and place it in the tool the other way up it creates a bubble flare..... now that is sorted I just have to "re-do" the pipes I had already made!!!!!! better safe than to find out I have no brakes lol.

[roy4matra]

Thanks Guys..... I understand! photo of bubble flare fitted to old pipe.... I have discovered that if I create a double flare then remove the pipe and place it in the tool the other way up it creates a bubble flare..... now that is sorted I just have to "re-do" the pipes I had already made!!!!!! better safe than to find out I have no brakes lol.

Your last photo, Terry, shows the true Murena brake pipe flare and flare nut, and it is the metric flare, which you would expect from a European made car.  The No.1 (convex) and No.2 (concave) flares are the older English brake pipe end flares and use a different flare nut to the metric one.  The metric flare nut has an almost flat end shape and the flare on the pipe as can be seen in your photo, has a 'bubble' on the very end but the other side where the flare nut contacts, is virually a right angle and flat to mate with the flat end of the flare nut.  The angle on the flare cone is also slightly different to the English flare.  So strictly when making brake pipes for a Murena, you should be using the metric flare nuts and metric flaring tool for the pipe ends.  In fact, if you are re-using the original flare nuts, then since these are the metric type, then putting a No.1 English bubble flare on the pipe would result in a mismatch.  Fortunately, as the copper or copper-nickel pipe is relatively soft, as you tighten the flare nut up, it should re-shape the end enough to seal.  However, you really should be using the correct metric flare system.

So the true answer to your heading 'Bubble or Double' is: Neither!  It should be a metric flare.

Roy