master cylinder cap

[MikeP]

so i wanted to add some dot 3 to my brakes to see if i could get any pressure for a quick test drive and so i unscrewed the access port and tried to unscrew the cap and couldnt its a square nut that takes a 3/4 wrench but when i go to turn the wrench i hit the edge of the hole before i get any movement and i tried from the top and thats even harder to do so how the * do i get the cap off

[stony]

Take the fender off.  Probably easier than going through the �access� hole.[ch128540]

[MikeP]

that might be the way to go but the steering box is still in the way and not alot of space for a wrench

[Rus Curtis]

I've been struggling with this also.  My first m/c had two tabs where I could use a screwdriver or channel lock pliers to get it started.  My current m/c has a different style (hex head) that takes a large wrench (either 1 1/16" or 1 1/8") and I can barely get a box end in there to turn and loosen - and it's slow.  I've been wondering what cheap wrench idea I could use to alter the tool to make it better.

Yours has a square nut shape on the top.  Different.  Having something shallow that would fit and still be able to turn is a challenge.

Some ideas:
A palm ratchet could fit but you'd still need a socket.  Perhaps you could get your hand in there but then not be able to see or twist.
A crowfoot open end wrench could be set with a ratchet attached and you could then back it off.
Outside the box - a bottle opener adapted to work.

I've also used several extensions and a universal joint on similar hard to reach spots.

Once you do remove it, consider making a custom tool that fits and is easy to twist.

Some use a remote reservoir up on the firewall to avoid this but this alteration still requires cap removal to add plumbing.

[SteveKfl]

Would a "Basin Wrench" work?...  https://www.thespruce.com/how-to-use-a-basin-wrench-2718720

[Bruce_W]

  I don't fool with the "access" cover on the floor. I use a socket, a universal joint, a long extension and a ratchet to loosen the cap from above, then scratch up my hand and arm to remove the cap. You may be able to find an old eight-sided socket the right size to fit your square cap, or a twelve-point socket. Then I use a long "Zep" funnel that I keep dedicated to brake fluid and brake fluid only.
  When you replace the cap, remember that it does not hold the wheels on - it only needs to hold itself, it doesn't need to be as tight as you can get it.   BW

[johnrb3b]

I've done all that as well.
My last attempt was socket, universal, two (2) 12" extensions and my impact wrench.
No go.
So now I'm taking it off the frame and putting it in a bench vise.

I won't be surprised if I end up buying a new one. If so, it will get a remote fill system high on the firewall.