I swapped out the master brake cylinder and the proportioning valve today. I bleed the entire brake system from each corner, got all the old brown brake fluid out of there.

And now the brake light is on. I test drove the car, its stops fine (but not as good as I think it should). Also, the pedal travel is alot more than it was before the change.

Note: I changed out these parts because several years ago I installed the 1LE brake upgrade from SSBrakes (kinda wish I never bothered).

So why is the brake light on?

 

Cuz your brake pressure is too low in one of the lines. Re-bleed the system. Did you bench-bleed the MC properly?

 

I dont know anything about bench bleeding the MC.

So, the answer is no.

Can you describe the procedure, please.

Maybe its important now to say that I swapped out the MC and prop. valve in two steps. First, I swapped out only the MC, bleed the entire system using a vacuum pump, then test drove the car. The brake light was not on during the test drive.

Second job was swapping out the proportioning valve. Once again bleed the entire system, and test drove the car. On this second test drive the brake light was on, and it stays on.

 

The brake light switch is sort of a toggle thing.

It "flips" to ON whenever there's significantly higher pressure on one side than on the other, and then stays there; forever, if it's never reset.

To reset it, there has to be high pressure on BOTH sides of it. So, if the brake system is now repaired, stand on the brake pedal with the car sitting still to get high pressure, and it should "flip" the switch back to OFF.

 

Thanks, I'll try that.

If that does not work, then I'll rebleed the system.

 

OK, I tried that and the light is still on.

 

Then either the brakes aren't repaired yet (i.e. they don't create equal pressure in the fronts and rears), or the combo valve is defective.

Since you swapped the MC, I'd bet money the problem is, there's still air in it. Which if there is, you can bleed those brakes 24 hours a day from now til Doomsday with the MC installed on the car, and they'll STILL have air in them, because the place the line attaches to, isn't the highest point of the cyl. The air will remain trapped.

If it was my car, that's where I'd start; is bleeding the MC properly.

 

Well, the brake light did not come on after changing out only the MC.

Now that the new MC is in along with the prop. valve, can I bleed the MC while it is mounted?

 

Hmmmm.... I'm not sure.... is "mounted" something like "installed"? my linguist/translator is out to lunch... I'll have to get back to you on that.

 

Yep, sorry, mounted means installed. I agree installed is better than mounted.

So, how does one bench bleed an MC? I would figure that I would fill both parts of the resevior and pump the actuator end.

With the MC and proportional valve both installed:
If I disconnected the two bottom fittings and the one off of the back/top side of the proportional valve (or better yet just loosen them) can I bleed the MC?

BTW: I just bought Russels steel brake lines for the car.