Brake Flares, Some Questions & Answers
Q: Do metric and imperial brake pipes use the same size bundy pipe?
A: Yes
Q: What threads are in use on car brake pipes?
A: Theses days ISO Metric Course, but in the 60s and early 70s it was UNF and before that BSF. On Ford UK models the change to metric came with the introduction Escort MK2 Capri MK2, and Cortina MK3. Most earlier UK models have UNF threads. The last car to change from BSF to UNF was the Morris Minor.
Q: How do I tell one thread from another?
A: Look at the tube nuts, tube nuts with metric threads have a much squarer shape particularly the female nut, on the pipe side the UNF female tube nut tapers in a tear drop shape. UNF tube nuts should also have a little nick cut in the points.
To tell BSF from UNF is a bit harder but you are unlikely to come across BSF pipe work building a Locost.
Important: Metric flares are made using a different outer die from Imperial flares. Metric flares have a square shoulder on the "pipe" side, Imperial flares taper.
Q: My car is built from a mixture of donor parts, how do I adapt between different threads?
A: Just make a pipe up with a different fitting up at each end.
Q: What kind of spanner should I use on brake lines?
A: Get a proper 11mm slotted brake line spanner to avoid skinned knuckles, this should fit both Metric and UNF tube nuts.
Q: Can I join two lengths of bundy pipe together?
A: Yes but you must use a proper joining coupling don’t just join using a male tube nut and a female tube nut.
Q: What is a "residual pressure valve"?
A: This a small valve sometimes fitted in the line(s) to rear drum brakes to keep some hydraulic pressure in the rear brakes thus keeping the wheel cylinder sealing rubbers expanded to reduce leakage. Generally if your donor didn’t have one you don’t need one. When fitted they usually take the form of an inline coupling joining 2 steel brake pipes.
Q: I have heard about copper brake pipes, are they any good?
A: Depends what you mean by copper, standard copper brakes pipes are illegal in some countries because they age harden become brittle and fracture. However special copper based alloys are a different matter as aside from the greatly improved corrosion resistance they are much easier to flare and bend. Personally I would only recommend using Kunnifer brand pipe which is made from a complex cu-ni-fe alloy I have no experience of any other brand but would be very wary of anything advertised as "Copper".