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MG MGB Technical - Brake pipe size

1972 MGB
Trying to bleed the rear brakes and i couldn't get any fluid out the driver's side. Come to find out the brake pipe was sqeezed/squashed against the axle, maybe a result of being towed at some point. So pipe is off, went to the parts store and confusion.
I believe the pipe is 3/16 BUT is it a Metric thread or US ? I know its a bubble end.
I don't want to strip any treads, so please which is the right one. Also the pipe is 46in long but i can only buy 40in or 51in pipes, i'll have to hide 5ins some where.
Thanks in advance....
Gerry Lodge

The fittings vary in appearance. The Workshop Manual shows the metric fittings as having a series of 'M's stamped down one of more faces of the hex part, and it says they are coloured either gold or black. Where the pipe comes out of hex nuts with an *internal* thread is conical for UNF, flat for metric. The pipe flares on these fittings seem to be the same. For nuts with an external thread there is only space for one and a bit 'M's on the metric version, but they have a relatively short length of thread with plain sections either side. The UNF nut has a short plain section at one end but the thread goes all the way back to the hex part at the other. the flares are quite different on these two, being conical both sides of the UNF, virtually flat both sides of the Metric.
Paul Hunt

Thanks Paul.
So i take it your saying Metric.... which in a way made sense.
Gerry

The threads on the lines should be inch, not metric. Today on new lines most of them are color coded at the fitting. Bubble flair lines with red fittings are inch, blue are metric.
John H

So, out here in America, i have a choice, Metric or US, what ever US is.
So far one Metric one inch (is that US?)
Any other opinions ?
Gerry

I had the same thing happen to my 65. It had the aluminum line and somewhere along the line it got crimped closed on top of the axle by the PO.

I bought a replacement piece either from Moss or Victoria British. It was just a little long but I got it in okay and it looks good fine. I didn't want to get into fabricating custom parts but you can do that.
Robert McCoy

Robert, are you saying the piece was pre bent ? That would be ideal. Right thread and bent, Magic!
Gerry

Gerry
I don't think the pipes from Moss or VB are pre bent. They come in straight close to what you need in length for whichever wheel you are doing. You need to bend them but the fittings are correct. There is a place called Classic Tube, classictube.com. that sells preformed lines, they will do a single line for you but I checked with them about doing a single for me and the wait was way too long. Think they said 3-6 weeks!
Mike
MK Mike

No the tube was not prebent. I used the old one for a pattern. It may have even been in a coil. The tube from Moss was slightly too long but I think I just made one bend bigger than original so I could fit right up the the cylinder.

A simple tubing bender you can buy at NAPA or similar place will do the job.

From what I hear Classic Tube does fine work but not the cheapest and there is a wait.
Robert McCoy

Gerry, inch means US threads. As for length you could always stop at a brake shop and have them cut it to the exact length and re-flair the end.
John H

Gerry - the Workshop Manual implies it could be either, which is why it goes into the detail of identification of both. You have to look at yours and decide which they are. I would have *thought* they were all Imperial, but you still need to check.
Paul Hunt

I redid all my brake lines, including the fastening points. I bought the lines in various straight lengths at a big hardware store that also carries auto supplies. The lines were labeled "US thread, standard flare", or US thread, bubble flare", as both types of flares were found on my '68. These were all 3/16th inch lines. Some of their stock was labeled "Metric thread, bubble flare"; I didn't use any of those.
I cut, re-flared, and bent the lines as needed, using the old threaded fittings where required. Doing a double flare is pretty easy with the proper tool. A bubble flare is done the same way, omitting the last step, as described in the archives. In other words, the double flare 'cone' is not done.
Gerry, if you don't feel comfortable doing it that way, or don't want to buy the tools, a local Brit shop should be able to duplicate your old line. Joe
Joe Ullman

The metric bubble flairs are used in cars from the far east.
John H

Have a look at this page:
http://www.dimebank.com/BrakePlumbing.html
Lots of interesting information about brake fittings, pipe. etc.
Andy Taylor

This thread was discussed between 18/09/2008 and 19/09/2008

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