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Author Topic: So what's this plug do?  (Read 1602 times)

attkrlufy

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So what's this plug do?
« Reply #15 on: February 27, 2011, 04:02:50 PM »


Quote from: Snotty
I could imagine there having been a problem and someone unpluged the sending unit wire.
Funny you should write that, Snotty.  You should go into business predicting the weather.

So I start Wanda up today in anticipation of salt-free roads (aaaaany day, now...) with that cap back in place and - wouldn't you know it - the second the car starts the brake warning light is glowing red hot like the Three Mile Island power plant (too soon?).  The E-brake is off...and yet, there it is, glowing away.

So I drive around the parking lot a bit, take a few turns, the thing never waivers.  It's glowing red.  I unplug the boot - no more light.

So that's bad.  Does it mean I need a new portioning valve?

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« Reply #16 on: February 27, 2011, 04:42:00 PM »

....or you can simply keep it unplugged, as long as the brakes feel good.
 
Now, as far as the light goes, check the emergency brake up top where the wire connects to it to make this brake light come on. I have had the pedal not push against it hard enough to cancel this switch and have the light come/stay on myself, so it may have been disconnected from annoyance, not necessarily a bad brake problem. since there is a plug up there for a switch similar to the door jam dome light, unplug and see what happens. If the light does stay on, then you can start thinking about the proportioning valve itself.
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Steve

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So what's this plug do?
« Reply #17 on: February 27, 2011, 04:55:19 PM »

Quote from: dana44
....or you can simply keep it unplugged, as long as the brakes feel good.
 


 
Na Na
 
If he unplugs the Prop Valve and the light goes out, and works normally with the E Brake, then the prop valve may be stuck.  If it's stuck, you may be doing too much braking on either the fronts or the rears
 
It can be cleaned
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« Reply #18 on: February 27, 2011, 05:44:41 PM »

That's also why checking the emergency brake plug to make sure that is not the issue, as in stays on when that switch is disconnected, narrows down the two elements the light shows. One is the emergency brake, the other the ABS. If the light remains when the ebrake is verified not making it light, time for a cleaning. With it disconnected at the ABS proves the light goes out, but still  need to verify the ebrake is not the real culprit since the brakes still appear to work correctly. Usually the lights will go off unless the brake is applied, unless the ebrake switch is grounded and allowing it to remain on constantly.
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Snotty

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« Reply #19 on: February 27, 2011, 07:19:39 PM »

That's a good thought, but the e-brake and the prop valve light are on two different circuits.  I know this because I had the same issues when I changed prop-valves on my '70.   
 
Now, if his e-brake light never came on before your point would be the case.   But, he has not indicated that it never worked.  However... did it?
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Snotty

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« Reply #20 on: February 27, 2011, 07:22:44 PM »

Back to the purpose of that light on the valve itself.  If there is air trapped in the prop-valve, even if your brakes are working fine that light will come on.  If it is the wrong prop-valve, or the wrong sending unit, that light will come on.
 
I'd say there's a problem wuith the sending unit.  Find another from a wrecked vehicle, or buy a new one if possible and screw it on.  Plug the wire in and see what happens.
 
(All this is assuming that the light always worked when your e-brake was on.
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Steve

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« Reply #21 on: February 27, 2011, 07:56:58 PM »

Good point on the air Scott, but he would feel it in the brakes.  But he won't feel an imbalance.  One set would lock up brfore the other
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« Reply #22 on: February 27, 2011, 08:43:07 PM »

That's why I though to check the emergency brake switch itself. Might be a false signal. Doesn't cost anything to check the switch is not working.
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attkrlufy

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« Reply #23 on: February 28, 2011, 05:24:47 AM »

Never noticed anything wrong with the brakes - but then again, I don't drive Wanda that hard.  I DO know I wish I had a little more stopping power.  But I don't think I've ever locked any of the wheels up in normal braking situations.

The light for the e-brake worked fine while the unit was unplugged.  When the e-brake was engaged the light went on.  When the e-brake was released, the light went off.  Leads me to believe the problem is somewhere in either the sending unit or the prop valve.

I've never done any brake work before, so just a point of clarification: If I unscrew the sending unit on the proportioning valve to replace it with another, won't that either a) introduce air into the brake line and/or b) send brake fluid shooting everywhere?  Even if it's not under pressure, since the prop valve is lower than the fluid reservoir, won't the liquid pour out as it seeks a common level?  This sounds like it'll make a mess.


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« Reply #24 on: February 28, 2011, 07:00:10 AM »

Well, if the brake light worked with the ebrake being used and disengaged properly, then yes, it has to be the switch that was unplugged itself. It would be a real shame if it was the wire itself and not the switch, so, check the wire and the fluid level itself first, an imbalance in pressure will make the switch go off for starters (My 68 Charger, just last month, drove it ten miles after sitting four years in storage, was low fluid in the back, so filled it up, drove it home, light for the brake was on for the first 20 or so times I pressed the brake pedal then went off), so low fluid is the next verification. Next would be a wheel removal and check each is not leaking and that they are not frozen (I have had two rear wheels with frozen cylinders and the brakes worked enough on the front that it wasn't noticed initially), and a simple tire off the ground, have someone press the brake while you are spinning the tire and if it stops, no need to remove the drum unless you see fluid or can't hear or feel the brake engage (you should hear the springs move and the wheel will stop spinning when the brake is applied).
 
If all this turns out good, well, I guess the switch is the bad thing (you just rule out everything else out first), so, think about what happens when you poke a hole in the side of a sealed can....the drip is very slow. Since the master cylinder reservoir is sealed, unscrew the sensor and have the replacement real close and change out real fast, you may get one or two drips but it won't gush out. Be fast and clean, brake fluid is a paint eater. 
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Corey

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« Reply #25 on: February 28, 2011, 07:55:41 AM »

Actually having it lower is a good thing if you do it quick enough pull the old sending unit fluid coming from the place it is screwed imto will help prevent air getting in you may still want to bleed the system afterwards but there shouldnt be much air at all in a sense what you would be doing is gravity bleeding the prop valve and as long as you leave the cap on the master in place it shouldnt shoot out. on another note you said you would like more stopping power on thing to check for that is the adjustment of the rear brakes drum brakes have that self adjuster but those dont always work properly raise the rear end and free up the wheels so they spin and give them a turn like you spinning that price is right wheel lol if properly adjusted you should get no more that one and a half turns out of each wheel if they spin more than that they need to be adjusted. stinger11702011-02-28 12:57:09
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Snotty

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So what's this plug do?
« Reply #26 on: February 28, 2011, 04:16:52 PM »

Agreed, it won't drip much.  It should be bled after anyway.
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attkrlufy

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So what's this plug do?
« Reply #27 on: March 01, 2011, 11:53:23 AM »

Sorry, guys, it's not that I don't believe you, I just don't understand how the SENDER can be the problem.

My understanding of the way this system works is that within the prop valve is a metal "slider" that has a notch in its center.  If the fluid levels are balanced F&R the slider is centered in the valve.  And if there's a pressure imbalance of some kind, the slider moves either F or R towards the low pressure zone.  The sender is just a metal rod that sticks down and fits within the "gap" on the slider.  If the pressure is equalized, the sender doesn't touch the slider.  But when pressure drops, and the slider moves, it comes into contact w/ the sender - completing the circuit - and thus the warning light goes on.  It's the same principle behind the board game "Operation."

So how can the sender - a passive piece of metal - be at fault?  That's what I don't get.  To me it would seem more likely to be a problem with the prop valve or downstream in the lines, somewhere.


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« Reply #28 on: March 01, 2011, 01:25:53 PM »

Case in point, why I said it may be a wire grounding problem, not the valve, unless the reason it was disconnected was because the "slider" is jammed one way or the other and can't get unstuck by itself. A small piece of debris may have made it ground out. It the brakes work and you don't have a pulling issue or the brakes don't lock up, ummmm maybe there was a safe reason to unplug it for less than the hassle of trying to repair a simple light being stuck on.
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Snotty

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« Reply #29 on: March 01, 2011, 05:12:30 PM »

[/QUOTE]


 
When I swapped my front drum brakes for disks I needed to swap the sending unit.  I asked the same question, "Why?"  Because it was not calibrated for the amount of fluid that flows to disks, which is considerably more than that of drum brakes.  That's how I learned about the unplugged wire - I did it to mine because I was getting a false reading.
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