Dash BRAKE light stays on?

[custom10nut]

I just finished doing the Disc Brake conversion on my 70 (CPP kit, fairly simple to install), and after getting everything put back together and bled (I think), I turn the key on and the BRAKE light won’t go off.
Now, it may be that I don’t have the system bled enough, because when I press the brake pedal, it will gradually go to the floor.
I’m thinking I still need to bleed the system more.
Here’s my question:
What causes the BRAKE LIGHT to come on?
Is it lack of pressure on the nipple inside the Prop Valve where the warning light wire hooks to it?
I took that fitting out, and that nipple does move, so I know it’s not frozen.
As I said, I probably have to bleed it more, but I don’t ever remember having this much of an issue any other time I worked on the brake system.
Thank y’all for your patience

[Steeveedee]

You probably still have air in the lines. Did you bench bleed the master? Are the bleeder valves on the calipers at their high point? Some calipers can be installed on the wrong side and will never bleed properly. Did you put rear calipers on? If so, they need to be adjusted to reduce their movement.

As for the light, the shuttle valve has likely shifted due to the imbalance in pressure when bleeding the brakes. You'll need to recenter that shuttle, but getting the brakes bled properly is first.

BTW, pushing the pedal all the way to the floor may damage the master's internals.

[vics stuff]

Just as STEEVEEDEE says . I would try bleeding them with some help.
Vic

[Rust_never_sleeps]

Originally Posted by Steeveedee

<snip>
As for the light, the shuttle valve has likely shifted due to the imbalance in pressure when bleeding the brakes. You'll need to recenter that shuttle, but getting the brakes bled properly is first.
</snip>

To be fair, you’ll need to recenter the shuttle to bleed the brakes. Valve has blocked off fluid from flowing to the side that’s low pressure

That said…..it’s worth checking that the switch isn’t lying to you before d1cking with the mechanicals(this may have been mentioned/verified already)

[PbFut]

Rust N S is correct.

1 verify the wire was not damaged. Simply unplug at the combo valve connector. This will break the circuit to the suspected closed switch and confirm the shuttle valve has moved. The valve rod will slide out of position to the circuit with low pressure. You can ground the connector checking the circuit manually for extra assurance. Grounding will light the warning lamp and will not hurt anything. Make sure key is on when testing the light.
2 Confirm no leaks and reset the shuttle valve. There are a few ways to reset the valve. Once reset, the light will be off.
3 Use a combo valve (often referred to as proportioning valve) lock tool to lock shuttle valve in place. Many say you do not need the lock tool. It may be they have an old stuck valve. I can assure you the valve moves with very little variance relative to front/rear circuit fluid flow.
4 Bleed your system making sure all air has been expelled. Vacuum bleeders work well on the system.
5 Remove lock tool and replace switch and wire connection. If you did everything right, you will have brakes and no warning light lit.
Last note. I like the plastic lock tool. Less chance of nicking the shuttle valve rod.

[PbFut]

ooops. double post

[Steeveedee]

Originally Posted by Rust_never_sleeps

To be fair, you’ll need to recenter the shuttle to bleed the brakes. Valve has blocked off fluid from flowing to the side that’s low pressure

That said…..it’s worth checking that the switch isn’t lying to you before d1cking with the mechanicals(this may have been mentioned/verified already)

Good catch!