1966-67 HCS Brake Warning Light reset problem

[TexAg]

I had a leak at my distribution block, which ultimately led to a low fluid situation and subsequent Warning Light activation. I have the repair manual and have tried unsuccessfully to reset the light.

From Page 2-5 of the 1967 Mustang Shop Manual.

"Centralizing The Pressure Differential Valve

After a failure of the primary (front brake) or secondary (rear brake) system has been repaired and bled, the dual-brake warning light will usually continue to be illuminated due to the pressure diffenterial valve remaining in an off-center position.

To centralize the pressure differential valve and turn off the warning light after a repair operation, a pressure differential or unbalance condition must be created in the opposite brake system from the one that was repaired and bled last.

1. Turn the ignition switch to the ACC or ON position. Loosen the differential valve assembly brake tube nut at the outlet port on the opposite side of the brake system that was repaired and/or bled last. Depress the brake pedal slowly to build line pressure until the pressure differential valve is moved to a centralized position and the brake warning light goes out; then, immediately tighten the outlet port tube nut to the specified torque.

2. Check the fluid level in the master cylinder reservoirs and fill them to within 1/4 to 1/2 inch of the top with the specified brake fluid, if necessary.

3. Turn the ignition switch to the OFF position.

4. Before driving the vehicle, check the operation of the brakes and be sure that a firm pedal is obtained."

So, the problem is that as I carefully attempted to bleed the brakes in the opposite position, the brake warning light fluttered quickly on/off for a second, and then was on again. I'm afraid that i went too far the other direction, but I can't be sure. So now, I really don't know where the slide is, and which way to try and go. Without spending hours trying back and forth, does anyone have a secret?

Since the light never really went completely off, how do I know when enough is enough? How "slowly" do you "depress" the brake pedal?

Any help would be appreciated. I'm tempted to just unplug it and drive on.. FIDO!!:grin:

 

[dalorzo_f]

You are using the pressure of the system, and the open end on the other side (if you know which it is) to emulate a leak and push the switch back to its original position. Basically you just push the pedal lightly until the light goes off. as you have found it is a fine line.

If it is well off center and you just "drive on" you risk compromised braking.

Hate to say it, but the easiest fix is to pull it, center the switch (redoing the seals is not a bad idea at this time) buy one of these

http://www.npdlink.com/store/produc...ntial_valve_switch_lock_tool-178818-2981.html


And then reinstall. Remove the holding pin last and then reattach the switch.

 

[TexAg]

Oh well, there's never a simple trick. I guess I'll try to bleed it again. If that doesn't work, I'll go ahead and pull it. I'm always afraid of messing with brake lines. It's seems that it always results in a bigger problem.

Thanks for the info. That's a handy tool!

 

[TexAg]

Thanks, dalorzo_f! I was finally able to disassemble the distribution block. Turns out the "slide" was stuck. I never would have gotten it out without your suggestion of using the grease gun. :grin:

I've rebuilt it, but haven't put it back together yet because, well, I really hate bleeding brakes!! But I hope to get it finished this weekend.

I love this site! The knowledge and experience here is AWESOME!!

 

[dalorzo_f]

Yep, after banging many on blocks of wood for hours, fabbing up a nipple and some caps and using the gun makes it a 15 second job to get a stuck shuttle out... :wink:

Glad it helped.