How-to flare a brake pipe.

Little Dog

Little Dog

A2OC Donor
European-Union
Increasingly our A2s are failing MOT tests due to corroded brake pipes. Members are sourcing Audi pipes and having pipes made but sourcing pipes is becoming more difficult. Some members have advised that it is better to make your own pipes and I would agree. Facing this task for the first time is daunting and I have not been able to find any instructions to share.
The purpose of this How-to is to guide a first time DIY brake pipe maker on how to produce pipes that will be safe and reliable in use.
 
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Step 1.

Know what union threads and flares you have on your car. These are the common options:

Pipe flares.jpg


The two most common are 3/16" SAE and 4.75mm DIN.

SAEDIN.JPG


SAE is a double convex flare that is secured with a 3/8" UNF union with a concave front to match the flare rear. These are commonly found on American cars and vintage British cars.

DIN is a flat rear convex front flare that is secured, most commonly, with a M10 * 1 union with a flat front to match the flat rear of the flare. The flat front is more easily seen on the M12 union. Both M10 and M12 have a small chamfer to prevent a stress raiser on the pipe that could result in the flare breaking off. I've never found any other flare on a German car, however there are some oddball unions as the M12 illustrated.

3/8" UNF will easily screw into a M10 female thread. This is very bad practice and should be avoided. SAE is not interchangeable with DIN.
 
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Step 2.

Source your materials.

I like Kunifer (also reffered to as Cunifer or Cupro-Nickel) brake pipe diameter 3/6" (4.76mm), it is strong (stronger than copper), easy to cut and flare (unlike steel) and is easy to bend (like copper). It is also very corrosion resistant:

brake pipe.JPG


For most repairs on an A2 you will need standard length M10 * 1 male unions:

M10.JPG


Long male unions and female connectors are useful for connecting a Kunifer repair to original steel. I have them behind the sills under the B post on my A2:

M10 long.JPG


M12 male unions, I believe (it is raining and I can't just lift the bonnet), are used on an A2 ABS controller:

M12.JPG


3/8" UNF have no place on an A2. I have them for a classic mini:

UNF.JPG


I have tried unbranded and branded but aftermarket fittings are rubish and rust very quickly. If you want them to last you have to strip the factory plate and apply a good coat of zinc.
 
Step 3.

Source tools.

Tools don't have to be expensive, but don't buy the cheapest, they will mark your pipes and produce substandard flares. My tools:

Tools.JPG


I am only going to comment here on the flaring tools (I'll cover the others when I use them); the most important thing is buy the correct flare profile. The bench tool above comes with a range of dies to suit various pipe sizes and both SAE and DIN flare profiles. If you are doing this job for the first time and only have a small number of flares the hand held tool is more than adequate and produces good flares:

hand tool.JPG


4.75 DIN is the tool you need for working on A2.
 
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Step 4.

Cut pipe and deburr.

If the pipe has been cleanly cut you only need to cut the length. Ill cover length and bending in a future How-to. I will cut a sort legth to illustrate the process.

cut.JPG


Both the inside and the outside of the pipe are burred:

burred.JPG


Deburr inner and outter diameters allowing swarf to fall away from the pipe:

swarf.JPG


You don't want those flakes of metal in you braking ststem.
 
Step 5.

Form the flare.

Don't forget to put the union the correct way; yes I've got it wrong many times. The pipe goes in long:

X1.JPG


At this point the second half of the die would be fitted so the pipe can still move, just imagine it is. Then the depth of pipe in the die is set by fully screwing in the depth end of the former:

Edit 240222, when you form the flare you may find that the DIN flat is not as well formed as it should be. This is something I have noticed since preparing this guidance. I think the problem is caused by these tools being designed for steel pipe. I think Kunifer either deforms differently or the wall thickness is different to steel. I do tests where the depth is not fully set and measure the gap between the setting tool and die with a feeler gauge. Once I have the perfect flare I note the gauge thickness and use it to set the gap between the die and setting tool for future flares. I now do this for every new roll of pipe.

X2.JPG


The die halves are now fully tightened, just imagine they are. The former is then lubricated with "special punch grease"; anything that is brake fluid compatibe and does not degrade rubber will do. I use Castrol red rubber grease but I've also found that it is only really required for steel pipes: The former is screwed to a stop and the flare is formed:

x4.JPG


Let's see what we get:

X5.JPG


Considering I've not flared one for a while with the hand tool I'm pleased with that. The pipe where clamped is unmarked, I have the DIN flat back to the flare and the convex front is there.

All you need to do this is:

X6.JPG



Also a compressor or canned compressed air. It is surprising how much muck blows out. If not fitting immediately seal ends with masking tape.
 
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Superb thread!!

The only thing I would add would be a small pipe bender of which I could do to purchase one myself, makes the forming of brake pipes into a fine art and something to be proud of!

With drum brakes being quoted approx 600mm and 1500mm this could become an offered service lol??
 
Howey said:
Superb thread!!

The only thing I would add would be a small pipe bender of which I could do to purchase one myself, makes the forming of brake pipes into a fine art and something to be proud of!

With drum brakes being quoted approx 600mm and 1500mm this could become an offered service lol??
Click to expand...
Thank you, I will cover pipe benders and string when I do a brake pipe bend How-to. I just don't have one to do at the moment. The simple tools I hid from the camera are:

String.JPG
 
 
Very well illustrated and written guide. for the novice, practice on a small length of pipe by flaring the end and also making a couple of bends to get the feel of the pipe. If copying and existing pipe difficult to go wrong with the bends.

Nice to show examples of pipe cutter and bending jig.

🤞🤞🤞
 
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