Brake System light revisited

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str12-340

str12-340

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So I'm building a 1970 Dart and completely (and I mean COMPLETELY) replaced the brake system. It's a factory KH front brake system wiith 10 inch drums out back. When you start the car the Brake System light comes on on the dash. When you put moderate pressure on the pedal it goes out. It's this last part that is new (just started test driving it this week). I know there is a piece in the distribution block that is supposed to be centered and when you have a partial system failure the light comes on to warn you. The brakes seem to work well and I can't find any leaks. Suggestions??? If all else fails I'll return the valve to Classic, but it was a pain getting the system all sealed up in the first place and I'd rather not start all over with the multiple fittings in the block.
 
So the distro block switch piston should be self centering.

If it's new I would expect it to work properly.


Assuming you got everything connected correctly...

You could try assisting in centering the piston by bleeding the front or the rear which will move the piston one way or the other.

When the e brake is engaged that also lights up the brake warning light, so be sure that is not the case, during your testing.

The fact that it goes out with brake application could be from air in the system allowing the piston to move, but does not explane why the piston will not self center.


You could remove the switch from the distro block, and physically check that the piston is centered.

IIRC there should not be any brake fluid where the switch is.
 
Pull the wire off the switch at the block. Does it still act the same? If not, then your problem is elsewhere.
 
If he pulls the wire off, that's a guarantee the light won't work but it doesn't answer his question.

The fact that the piston DOES center when you apply pressure shows it is working properly in that regard. But why it is moving off center when you release pressure is the mystery. (You didn't say if the light comes back on when you release the pedal but I assume it does). Even in the factory manual, it is noted that if you have some sort of failure and the light comes on, you are only supposed to fix the issue then the piston will re-center itself so the light goes out.

Is the master cylinder the right type? Does the car have the proper hold-off valve as used on the disc cars of that year? This is a smaller brass block, independent of the main prop valve.
 
gregcon said:
Is the master cylinder the right type? Does the car have the proper hold-off valve as used on the disc cars of that year? This is a smaller brass block, independent of the main prop valve.
Click to expand...
In the 67 to 70 something KH front disk brake system.

There is a distribution / brake warning block. It's only function is to distribute the front and rear brake fluid and alert if the system is unbalanced.

Screenshot_20230102-181933.png


The proportioning valve is down stream of the distro block and a separate unit.



Screenshot_20230102-181636.png
 
Yes, when I let up on the pedal it comes on again. Yes I have the other block (which I understand to be the real "proportioning valve") in line in the back brake line as it is supposed to be. If I pull the electrical plug on the distribution valve the light goes out and then it works with the emergency brake as intended. I'll try bleeding it one more time...
 
OK so here's the deal. Do this with the key on. You'll need 2 people. First crack one of the rear bleeders loose and push and hold the brake pedal down. Tighten the bleeder and release the pedal. Now go to the front wheel and crack the bleeder and slowly push the pedal down till the light goes out and stop! Tighten the bleeder and release the pedal. Fixed. You just centered the valve. ps either side of the car will work but the driver's side works better, because you can talk to each other and not scream.
 
Don't forget the light also comes on if the parking brake switch isn't made. Small chance putting the brakes on flexes stuff enough to make that movement to close the switch if it's not quite being made when static.
 
dadsbee said:
Don't forget the light also comes on if the parking brake switch isn't made. Small chance putting the brakes on flexes stuff enough to make that movement to close the switch if it's not quite being made when static
Click to expand...
Parking brake switch makes a path to ground when the handle is pulled out, turning the light on. When the handle is in there should be a no gap between the switch and the shaft braking the path to ground

Applying the brakes would not effect the switch on the shaft.
 
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LO23M8B said:
OK so here's the deal. Do this with the key on. You'll need 2 people. First crack one of the rear bleeders loose and push and hold the brake pedal down. Tighten the bleeder and release the pedal. Now go to the front wheel and crack the bleeder and slowly push the pedal down till the light goes out and stop! Tighten the bleeder and release the pedal. Fixed. You just centered the valve
Click to expand...
Agreed this will center the valve BUT...

It is supposed to be self centering, so why is it not self centering?

And then why is it moving when the brakes applied?

Something is wrong
 
Dana67Dart said:
Parking brake switch makes a path to ground when the handle is pulled out, turning the light on. When the handle is in there should be a sizable gap between the switch and the shaft.

Applying the brakes would not effect the switch on the shaft.
Click to expand...
Ya.. thinking B body there. Pedal up is on the switch and it takes very little downward movement to come off the switch and turn the light on. Hand brake in the A is right there with the brake pedal assembly, or closer to it so I'd still be looking at it.

Other than that.. sumting wrong.. LOL
 
Dana67Dart said:
Agreed this will center the valve BUT...

It is supposed to be self centering, so why is it not self centering?

And then why is it moving when the brakes applied?

Something is wrong
Click to expand...
It is not self centering. If it comes on after you center it then something is wrong.
 
LO23M8B said:
It is not self centering
Click to expand...
If you are saying that the distro / warning block does not self center look at the section view. Two opposing springs keep the piston centered.


If you are saying the OPs new distro / warning block is not self centering like it should, then I agree with you.
 
The piston does self center when the pressure is the equal on both sides...which it will be if the brake system is not experiencing any problems.

As for the drawing that shows the added valve as a 'proportioning valve', that is interesting as B Bodies have the same valve and it's called a 'hold-off valve'.
A hold-off valve allows the rear drum brakes to apply first before the front discs begin to apply. A prop valve reduces rear drum application in proportion to front disc application, the goal being to reduce or eliminate rear wheel lockup.
 
Can't speak to B body but it's a pressure reducing valve on A bodies.

Maybe a Symantec issue?

Inline Tube Hold Off Valve

TomAto / Tomato

Wouldn't a hold off valve work the other way around. Fronts apply first then rears apply.
 
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No, they are two different functions.

The hold-off valve allows the rear brakes to apply first - the idea is that while discs apply directly, the drums must first overcome the resistance of the return springs and move the shoes out a little before any braking happens. So, the hold-off valve is intended to give the drums a "head start". Also, it's generally recognized that a vehicle stops in a more controlled fashion if the rear wheels come in first, even if it's only a little. Then, once the 'heavy braking' starts, the prop valve reduces the rear pressure to prevent the rear brakes from locking up.
 
I do know that "back in the day" there were tools you could buy--you unscrew the switch, and screw in the tool, which locks the piston centered until you are done bleeding the brakes.

THE NEW IMPROVED SOFTWARE REFUSES TO DISPLAY THE LINK

httpsCOLON//wwwDOTamazonDOT.com/

Combination-Prevents-Unwanted-Tripping-Compatible/dp/B08BT816MS
 
That tool is a cap screw with the end machined a little lol. Notice that is says it only keeps the piston centered but does not center it.

But the centering of the valve doesn't affect normal bleeding...only if you are using a pressure bleed system.
 
gregcon said:
That tool is a cap screw with the end machined a little lol. Notice that is says it only keeps the piston centered but does not center it.

But the centering of the valve doesn't affect normal bleeding...only if you are using a pressure bleed system.
Click to expand...
.............And you completely missed the point. It keeps the piston centered while bleeding. I posted this mostly because many younger guys don't know about them
 
I do see the point. But I also noted that the factory manual notes there is no need to keep the piston centered.
 
I think we are off the OPs question here.

He needs to determine why his distro block is not self centering.
 
67Dart273 said:
.............And you completely missed the point. It keeps the piston centered while bleeding. I posted this mostly because many younger guys don't know about them
Click to expand...
Fyi. That is for ford's and they don't have centering springs.

Screenshot_20230103-140907.png
 
For your consideration : on a stock mopar -

If you set the line lock while the foot brake is applied, the imbalance lite remains off.
Release the foot brake and the imbalance lite comes on, release the line lock, the imbalance lite goes off.
Why does the lite go off when the linelock is released ?
 
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