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MG MGB Technical - Master Cylinder Flare Fittings

I need to replace two of the fittings that screw into the master cylinder on my 77 MGB. The fitting is metric; no problem as I have found replacements that fit the same as the original fittings. The problem/question is the flare on the original is a "dual flare" in that it slopes down towards the fitting to create the seal. The flare goes into the fitting hole which is concaved to receive the flare. Question, can I use a standard US flare which is more of a bubble in that it does not flare down and to the side of the fitting but is rounded and goes above the fitting. I may not be explaining the flares in the most precise manner but don't really know how to explain what they look like without providing a picture of them both.

Before I go out and try to buy a metric flare kit (if they exist) has anyone used a bubble flare (normal US flare kit) to replace their master cylinder flare fitting with?

Thanks,
Jim McDowell

If I'm not mistaken, the flare is called an ISO flare, rather than a double flare typical of US brake lines, and the first step in forming a double flare on most flaring tools forms the lead eadge and trailing edge of the iso bubble.

So you take a typical US double flare tool, set it up like you are making a double flare (put the hat on the tube, put it in the clamps, and screw the taper in. Ehrn it bottoms, you will have an ISO bubble, or something so close it will pass (lay off the 'close isn't close enough' unless you can show a failure- if this thing seals, it seals. It's a metal to metal conical contact- just like a 45 degree double taper or a 37 degree A-N fitting).

IIRC, the thread size is not metric- ther are usually the typical 3/8-24 or 7/16-20, depending on fitting size
greg fast

Check out this site:

http://www.dimebank.com/BrakePlumbing.html

You should be able to find pre-made brake lines in both double (bubble) and inverted flares at your local parts store. You may need to try a few places.

Although I cannot recall that fitting (haven't had that part apart in quite a while), my cheapo-deluxe flare tool could do any flare (except AN), it just took lots of patience, care and multiple steps.

Whatever you do, don't use a single flare as it is less durable and more likely to fracture.

Mike!
mike!

Thanks for the information! Will give it a try when time permits.

Safety Fast!
Jim McDowell

Jim, suitable flares can be made with a common US flare tool, just be sure to use the flat side of the clamping piece instead of the tapered side. Also make sure you have the correct type of flare nuts for use with bubble flares. These are not chamfered on the end which fits up against the flare. Common US flare fittings have a chamfer to support the rear part of the flare.
Bill Young

This thread was discussed between 27/09/2004 and 28/09/2004

MG MGB Technical index

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