I understand that part, but what keeps the pressure up?
specialty wiring question: brake pressure switch (1 Viewer)
- Thread starter DSRTRDR
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
I understand that part, but what keeps the pressure up?
So technically the warning light turns on for an imperceptible moment every time you step on the pedal?
Looking at the diagram - if the E-brake is on (warning light on) why would depressing the brake pedal override the completed circuit and turn off the warning light?
This thread is very confusing to me.
But perhaps that's just because I have a 1979 model. (I can't see why being "diesel" would make any difference.)
My rear brake lights are operated by a simple switch ("Stop Light Switch") that senses when my brake pedal is moved away from its "rest position" as shown here:
This sysyem is powered all-the-time. So if my stop light switch is adjusted wrong or faulty (or if my brake pedal is somehow not returning to its proper position) ... my rear brake lights will be "on all-the-time" (even when my key is out of my ignition).
I have another" rheostat device" on my brake master cyclinder reservoirs that senses "low fluid level" - And my key must be "On" for this to light the warning lamp on my dash.
And I also have a switch on my parking brake lever (which some call "emergency brake lever") sensing when that lever leaves its "off position" - And this also lights a warning lamp on my dash .. only when my key is "On".
I don't have any "brake-fluid pressure swtiches" at all?
But perhaps that's just because I have a 1979 model. (I can't see why being "diesel" would make any difference.)
My rear brake lights are operated by a simple switch ("Stop Light Switch") that senses when my brake pedal is moved away from its "rest position" as shown here:
This sysyem is powered all-the-time. So if my stop light switch is adjusted wrong or faulty (or if my brake pedal is somehow not returning to its proper position) ... my rear brake lights will be "on all-the-time" (even when my key is out of my ignition).
I have another" rheostat device" on my brake master cyclinder reservoirs that senses "low fluid level" - And my key must be "On" for this to light the warning lamp on my dash.
And I also have a switch on my parking brake lever (which some call "emergency brake lever") sensing when that lever leaves its "off position" - And this also lights a warning lamp on my dash .. only when my key is "On".
I don't have any "brake-fluid pressure swtiches" at all?
- Thread starter
- #26
I have another" rheostat device" on my brake master cyclinder reservoirs that senses "low fluid level" - And my key must be "On" for this to light the warning lamp on my dash.
And I also have a switch on my parking brake lever (which some call "emergency brake lever") sensing when that lever leaves its "off position" - And this also lights a warning lamp on my dash .. only when my key is "On".
I don't have any "brake-fluid pressure swtiches" at all?
you call it the "rheostat device"
our FSMs call it "brake pressure switch"
- Thread starter
- #27
Well I just looked at my FSM and there they call what I'm talking about a "Brake Fluid Low Level Warning Switch" with no mention of the word "pressure". (But I think my description is more accurate because it isn't a simple on/off switch but rather a "varaible resistance device"):
And this still leaves me baffled concerning many replies in this thread.
PS. I also have a "bulb check relay" (which is mistakenly labelled as a "Valve Check Relay" on the wiring diagrams in this section of my FSM. And this relay illuminates my "low fluid level warning light" whenever my key is in the "start" (cranking) position just to show me that the bulb hasn't blown and that this aspect of the safety warning system is indeed still working.
Last edited:
- Thread starter
- #29
the brake pressure switches we are talking about are not in the reservoir but below the reservoir; they monitor the pressure in the brake line, not fluid levels in the reservoirs
in my truck, there isn't a relay for the brake indicator light
Thanks DSRTRDR.
Found them:
My master cylinder doesn't have those "fluid-pressure switches" fitted (or any spare ports to screw them into).
And I've always wondered what they were (when I saw pictures of other people's master cylinders with those things dangling underneath).
(Never stop learning.)
PS. I see those pressure switches were used in landcruisers right up to the 1980s too. So I wonder what determined who got them and who didn't.
- Thread starter
- #31
yes, those are the devices we are talking about
some people don't even know they are there - often, POs remove the wires since they are not really mission critical to the brake's functioning per se, and then you never suspect
if you had any other brand master cylinder instead of OEM, they may not have a provision at all
some people don't even know they are there - often, POs remove the wires since they are not really mission critical to the brake's functioning per se, and then you never suspect
if you had any other brand master cylinder instead of OEM, they may not have a provision at all
Last edited:
Rockets2000
Space Cadet
That's how mine are. The PO had them disconnected, so they are nothing but plugs now. I now have a Cruiser Corps reman MC, so I don't even know if they would work if I hooked them up.
Originally Posted by numby
Looking at the diagram - if the E-brake is on (warning light on) why would depressing the brake pedal override the completed circuit and turn off the warning light?
Well, it does on mine. Is that bad?
Looking at the diagram - if the E-brake is on (warning light on) why would depressing the brake pedal override the completed circuit and turn off the warning light?
Well, it does on mine. Is that bad?
- Thread starter
- #34
it's not "bad" in the sense of harming you or others on the road, and it doesn't harm the truck or electrical system, either - not a safety impediment
if your goal is that the truck functions as designed from the factory, this would be a "not so correct" issue
hardly any truck here on MUD is free of those
I don't have/use these pressure switches. But when I've used them in other applications they are Normally Open because the pressure keeps them open and at loss of pressure they activate the alert.
What's the point of a pressure switch that only turns on a light WHEN you press the pedal? Your foot is going to tell you all you need to know and at that time taking your eyes off the road probably isn't a good idea.
What's the point of a pressure switch that only turns on a light WHEN you press the pedal? Your foot is going to tell you all you need to know and at that time taking your eyes off the road probably isn't a good idea.
The light will warn you if you have a non-working brake system (front or rear), you might not know that one system has failed. When you press the pedal the light gets power and turns on because the sensors are both grounded. As pressure builds both sensors have to open for the light to turn off. So every time you press the brakes the light comes on (for a short time) and then goes off, thats what mine does. If the light stays on then one system did not build pressure.
My BJ40 was never fitted with them either.
Perhaps they are "USA-market only"?
Based on the posts in this thread by Charlie and Mark ... They should be classified as "normally closed" because there is no pressure in either chamber of the tandem master until you put your foot on the brake pedal Psreno.
But without the brake warning light telling them that they have a problem, some people may not notice if only one circuit is working Psreno. (Especially if it is just the front circuit that is working because that one does most of the "braking work" anyway.)
Here are those informative posts by Charlie and Mark that I'm referring to:
Based on this, the two pressure switches are quite useful (IMO) and will tell you if you're missing either brake circuit.
Damn - FJForty beat me to the draw.
My BJ40 was never fitted with them either.
Perhaps they are "USA-market only"?
I have them on mine Tom.
Well I can say with certainty that the factory never fitted them to my July 1979 model. So there must have been a cut-off date between 77 and 79 for Aussi-market BJ40 models. (I bought mine in Oz of course.) And the Toyota epc doesn't shed any light on this. (It shows them being fitted to BJ40 models right through into the 1980s ... including the "ARL market" ... which up until now I thought meant "Australia".)
PS. I realised after posting my previous post that I shouldn't really have suggested it may be a "USA-market only thing". Because that microfiche page was for a BJ40 and I understand that model was never even sold new in the USA.
Last edited:
