Straightening new brake pipe

[Pugglt Auld Jock]

I've always really enjoyed making up and fitting new metal brake pipes - not so much stripping the old corroded ones with their seized tube nuts etc though! One thing I really like is to have straight runs of pipe "dead straight". I hate to see them with little kinks and bends. Unfortunately, as we all know, brake pipe is supplied in rolls - it could hardly be otherwise with some 25ft to a roll:



But getting it truly straight by hand is very difficult so, with Becky's rear brake job imminent, I've been looking at proper straightening gear. Trouble is the ones that look like they would work best aren't cheap and the "cheap and cheerful" ones look expensive for what they are and maybe won't work all that well? Anyway I found myself thinking "Those cheap ones? I'm sure I could make something that worked along those lines"? So, with Mrs J having taken charge of the TV viewing I retired to my garage to give it some thought.

I'm going to need something "slippy" which will act as a guide for the brake pipe and but not mark it either. I soon found a piece of hard nylon pipe - which was a piece of the old tubing from my Hydrolastic pressure pump when I rebuilt it - which was quite a good fit for the brake pipe. It's a wee bit over 5mm internal bore, probably an imperial size seeing how old it is. The 3/16" 4.75mm diameter brake pipe just slides in nicely without snagging. However it's not stiff enough to persuade the brake pipe to uncurl. I found a length of, quite thin wall, steel tube which I think came out of my old Ambassador when I re-piped the Hydragas system. It has an I.D. of about 10mm or 3/4" and the nylon tube slides in very snugly without requiring a lot of force to get it fully inserted:





The steel tube has a slight bend in it:



I thought about trying to straighten it but decided I'd try a piece of brake pipe through it first just to see if it looked like working at all and made a few discoveries. The first is that because the nylon tube is not an absolutely perfect fit in the metal tube it doesn't quite straighten the pipe because the ends of the nylon tube move one way and the middle arches the other. The same can be said for the fact that the brake pipe is not a perfect fit in the nylon tube so again it doesn't quite straighten it.. It's the play between the nylon tube and the steel outer tube also the play between the brake pipe itself and the inside of the nylon tube that's the problem. It does do a pretty good job of straightening it but there's still a noticeable curve in it. I thought that was going to be almost impossible to solve until I realized that perhaps if I turned the forming pipe (the steel outer pipe) so that it's curve was in the opposite direction to the curve of the brake pipe then that might compensate for the clearances in the forming pipes:



And eureka! the pipe came out as near straight as you could wish! I then slightly "adjusted" the amount of bend in the steel pipe and very soon found it was straightening the pipe pretty much perfectly:



I think that probably you could compensate for differences in size of nylon and steel tubing by simply putting in more or less of a bend in the steel tube - Of course you wouldn't want to be outrageously out in your sizes!

So far I've been working with copper pipe and I suspect I'll need to make another one with a slightly different bend in it for the Kunifer because it's a stiffer material and I think I'll make it a foot long instead of 10 inches if for no other reason than that it'll make it easy to differentiate between them in a hurry when they are in my toolbox. The only other thing is that the inner nylon tube tries to creep out of the steel tube as you are pushing the brake pipe through but I think I can cure this by swaging over one end of the steel tube slightly and then always pushing the brake pipe towards that end.

Anyway, here's my latest addition settling in with his new friends in the brake tools drawer of my tool chest:



Looks like he's always been there don't you think?

 

[Pugglt Auld Jock]

Thought I'd tidy this up and complete the thread by recounting how I swaged the end of the steel pipe over to stop the nylon tube slipping out.

I tried simply "persuading" it with a hammer but couldn't get a nice even turn over. Then I tried heating the end of the pipe to make it malleable but I couldn't find anything to shove down the middle to use as a mandrel and without something to work against it all ended up a bit uneven, certainly not to my high standards!

Then I remembered that when you use a pipe cutter (as in when doing plumbing or cutting brake pipe to length) you always end up with a bit of a flange on the inside of the pipe's cut end which you have to then remove before carrying on. I wondered if this flange would be big enough to retain the nylon pipe? Only one way to find out. I cut about 4 or 5 mm off the end of the metal pipe with my plumbing pipe cutter and it worked beautifully:



If you compare this to the third pic down in the first post you can see how much the tool turned the end of the pipe over by. The nylon pipe is now retained perfectly. The one remaining problem is that the metal pipe is just a little small in diameter to get a really easy hold on when you are pushing the brake pipe through. It's quite "livable with" but what would make it absolutely perfect would be if I could find something like the handle on the end of the chain from an old high level cistern toilet: https://www.bes.co.uk/high-level-cistern-lever-pack-11208/ I could bore a hole down the middle and slide the metal pipe in.

So now, with the weather improving, I suppose I really don't have a good excuse not to get welly'd into Becky's rear brakes any more.