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I just finished rebuilding the manual drum brakes on my 67FB. I replaced everything, other than the lines and MC. While having the lines disconnected, the MC leaked all the fluid out. I put everything back together, and proceeded to bleed the lines. All bled ok. I then cranked up the car, and the brake light is now on, where it wasn't before. I didn't mess with the connector on the top of the firewall block where the lines connect to, but once I noticed the problem, I reseated it anyway. No help. So what could be the issue? The brakes seem to work fine, although they are slightly mushy. I'm not sure if I just didn't bleed them good enough, or if I should go ahead and replace the MC, since I rebuilt everything else.

Any opinions?
 

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Most likley the valve on your brake distribution block is causing the problem. When it is not centered a little bump on the shaft closes the circuit in turn causing the brake light to come on. I have got it to go off by re-bleeding the system starting with the wheel furthest away from the dist. block (right rear)If it still does not go off, but braking seems to be good you can unplug it,(not recommended) or remove the dist block, clean it out, replace the O-rings, and recenter the shaft.. That is what I finally had to do and my light has not come on since. If you got that route use new brake fluid to clean the dist. block.
 

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The brake light is triggered by a pressure differential switch within the distribution block. Later style redundant braking systems are actually two separate brake systems, as opposed to early braking systems which were a single system. In the early systems, loss of a single soft line would result in total loss of all brakes, not a good thing.

With the later style brake systems, loss of a soft line will result in only half of your brakes failing. The brake light is an indication that there was a large differential in the brake system pressure between the front and rear brakes. Of course, when you open up the bleeding valves, this does drastically reduce the fluid pressure and unless you are extremely lucky you will end up with the brake light on after bleeding the brakes.

As stated by an earlier poster, there is a shuttle within the distribution block that needs to be centered for the light to go out. This is really a two person job. Most frequently, you will need to open up a rear bleeder to do this since the last brake to be bled on a standard brake job is the front driver side brake. With a rear bleeder open have someone else gently apply the brakes until the brake light begins to flicker and finally goes out. At this point close the bleeder. If you press to hard on the pedal, you will send the shuttle to the other side and have to open up the front brake system and try again.

Good luck
 
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