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MG MGA - Brake Caliper Bleed Fittings

While bleeding my brakes I noticed that a couple of the bleed fittings were a little rounded and wanted to take the opportunity to replace them.

What i really mean is once I start to do a job on the old girl it always seems to grow. But over 30 years working on aircraft means I get a bit pedantic over little things.

So off I went to my local parts supplier they should be easily available. Well it wasn't to be, my fittings are 7/16 but all I could find locally were 3/8. Insert suitable words here.

Ok so went to my usual parts supplier, no worries have them in stock I will send them down. Great service at my home the very next day, now the fun starts, they are 3/8. Insert suitable words here again.

Ring up the supplier he checks his books and assures me they are the right ones and should be 3/8. Once again suitable words yet again.

I explained what I had and he said that the clutch slave cylinder had a 7/16 bleed fitting where the head was the same size as the threaded body. Eureka!!

So I have a way ahead, now what I would like to know is which is right. Has there been a repair done somewhere that took it to a bigger size?

A long story but I enjoy spinning a tale, if anyone could shed some light on this for me I would greatly appreciate it and thank you in advance.
S P Rossetto

The original brake caliper bleed nipple thread was 3/8" UNF. I would guess that, sometime in the past, the nipples on yours had rusted badly and on removal the caliper threads were ruined so a PO had tapped them next size up.

One of my calipers had suffered a similar fate and someone had drilled and tapped one of the holes to 1/2" then put in a 1/2"/3/8" insert. Unfortunately, the newly drilled hole must have been ever so slightly off axis compared with the original conical seating and there was always a tiny fluid leak. When I got the car I was unaware of all the history and gave the nipple a good tightening to try and stem the drip and there was a horrible cracking sound as the caliper wall broke away! The caliper was a write-off.

So my advice would be to live with the 7/16" tapped holes and not try to use 3/8" inserts...................Mike
m.j. moore

Thanks Mike

As you suggested, I have no intention to try and bring it back to the original 3/8. Now that I now know and fitting some new bits anyway I shouldn't have to worry about it for the rest of my ownership.

Impressed that after a lengthy time of ownership she still can come up with little surprises.
S P Rossetto

This thread was discussed on 14/08/2013

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