Wrench for brake master cylinder size

R

robert shreveport

Senior Member
Want to build a long wrench to reach down and unscrew the master cylinder cap on a 46 ford car for a friend. He wants it long enough so he doesn’t have to bend over so far. I will make him one but want to know what diameter the cap may be. And about how long it should be. Anyone have some ideas? Thank you
 
The configuration for master cylinder caps has moved about over time. The OE versions were mostly raised ridges and not rounded.
 
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robert shreveport said:
Want to build a long wrench to reach down and unscrew the master cylinder cap on a 46 ford car for a friend. He wants it long enough so he doesn’t have to bend over so far. I will make him one but want to know what diameter the cap may be. And about how long it should be. Anyone have some ideas? Thank you
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Um, like me all too often, I believe you are overthinking this. A four-point socket works perfectly. Those are readily available from places like McMaster-Carr.

The cap on the master is about 3" below the floorboard. Again, with a socket, your friend can use as many extensions on hos ratchet as he feels necessary.
 
Some of the later caps have a long hex shape drive instead of the square. Should be able to fit a deep well 6 sided socket and extension length of your choice.
 
On my 1951 Ford I use a 6" extension for a 3/4" socket wrench. It fits the master cylinder cover, and I turn it with a 3/4" open end wrench.
 
I didn't offer a dimension as we have no clue what cap is currently in place. The original cap was square, 3/4" between flats.
 
Its been a long time since I've opened the brake cylinder on my 39 but I have some memory of using a piece of 1 inch steel square tubing that fit right over the square head on the cap.
 
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