Parking Brake light 1999 Adventurer

Sk8Surfr · 11-01-2023, 07:47 PM

1999 Adventurer - Ford v10.

I added some from LEDs - when I was installing them - I 'thought' I bumped and broke the brake differential pressure switch - so I ordered a new one (boy were those plastic pieces of threads fun to get out).

Anyways, I replaced it - and now the red parking brake light won't go off... unless I unplug the switch...

The manual says the parking brake light would stay illuminated (if obviously parking brake is illuminated) or if brake fluid is low (which it's not).

I assumed the 'yellow' brake light would be if there was a fault with the brake differential switch...

Morich · 11-01-2023, 08:59 PM

Are you sure you are not confusing the light that is on and it is actually the light to alert you to a problem with the brakes, not the parking brake?
If I read what you are saying and disconnecting the lead to the new switch turns THAT light off, I might guess it means there is a difference in pressure between the front and rear brakes sections.
That would be explained if you did not do the correct procedure to recenter the switch reading on the new switch?

I'm not into the mechanical stuff any more and long forgotten how to do the process to clear the light.
I would think it is info found in a repair manual for the chassis and not RV specific info.

Foggy memory that should not be trusted? Perhaps bleeding fluid off either front or rear to center the switch?

Sk8Surfr · 11-05-2023, 07:49 AM

Thanks... I did some basic troubleshooting today... If i unscrew the switch - and leave it plugged in - the light is off. So you're right - the switch is triggering that light

Here is the weird thing... If i manually press the metal plunger/spring in - the light does not illuminate. It only illuminates if it's screwed in.... How does this work? I'm guessing it's making a basic continuity connection or grounding itself out inside the brake resevior?

Morich · 11-05-2023, 03:22 PM

I don't have much on those switches and it's been a long time! I think it id more a matter of the sensor being in the middle? Not too far left nor right and that is the way it tells us that something is wrong but not being very specific about what.
There are now two systems, front and rear where they used to only have one combined. On the other, when any one wheel lost fluid, ALL the brakes were gone. But with about early '50"s (maybe?) they made it two and we can lose all the fluid out of one and still have brakes on the other end to still stop.
I think that is where the sensing comes in as it turns on the light if it goes too far in either direction if we lose front or back brake fluid.

How to get that recentered is my thought? Really, really guessing now, but I think it was a matter of pushing the brakes while somebody opened the line to release pressure??
But that is one to check on chassis builder info for when we have had to change wheel cylinders, etc.

I did a quick search and got way into the stuff for newer cars and found none for what I think needed. You may need to find an old hammer-head car guy that keeps up on the older methods.

Morich · 11-05-2023, 03:47 PM

Ok, Got better ideas after talking to my older brother who is the car guru for the family!
One doesn't have to go under to let the fluid out as there are two lines on the master cylinder!
He tells me it is a two person job, one to press somewhat gently on the brake pedal while the other just barely cracks open one line on the master. The idea is to let a little fluid out and watch carefully for the light to blink.
He stated to not press hard and watch carefully as it is likely you will either be on the wrong end and the light won't blink OR you will let too much out too quick and you go beyond the center point.
Idea being that it is easy to go too far and the light stays on when you have let too much out on that side, so you get to close that one and try to let the right amount out on the other side!
Also be sure to keep fluid in both sides of the reservoir to avoid having to bleed the brakes to get air out of the lines!

See if that makes sense but I'm not at all sure I will know how to answer any questions!!

Sk8Surfr · 11-06-2023, 12:34 PM

Thanks for the info.- tried. a little last night. Couldnt get it to blink. Will try again later.

Called a local RV guy... he actually said a lot of times when it moves you can't get it back and might need an entire new master cylinder... he also said the entire system wasnt great back then and a lot of people had those issues... He said I'm probably getting brakes to all wheels - but maybe not the 60/40 it should be or whatever...

Morich · 11-06-2023, 03:42 PM

While we all have our own opinions, that sounds like a bit of a half thought out idea! It is a 20+ year old system and they have likely improved in that time but to say it never worked for those 20+ years?
Is he saying everybody who had a wheel cylinder leak or a line break had to change out the master cylinder to fix the light?
I think I might move on to somebody who has been around long enough to know a bit more!
Some basic questions to ask before deciding? Were the brakes okay up to the point the sensor got broken?
If they were, isn't it likely they are still the same now except for the part that got broken?
I'm for suggesting you find somebody who has some more experience with resetting the sensor as all the rest is just like it was ? Got any small truck shops around that might know more about it ? They don't have to pull it in the shop, just walk out in the parking lot and fiddle with the master cylinder but it does sound like a job that takes a certain amount of "touch".
My brother and I had old cars and this was the sort of stuff we grew up doing but that was a lonnng , long time ago! We came along after they went to the two section master but way before they turned it all over to computers!

Maybe look for a car repair group online for somebody who has done it recently? I think what you need is an old boy who may have a few old cars jacked up on blocks and setting around the yard. They likely know about that stuff!

Sk8Surfr · 11-07-2023, 10:41 AM

Took the RV for a spin around the block - then checked the inside rotor temp.

Front Left - 195 degrees
Front Right - 215 degrees
Rear Left - 195 degrees
Rear Right - 245 degrees

It would seem the brakes are at least all working...

Morich · 11-07-2023, 11:30 AM

I would assume breaking the sensor would not change the brakes but just the alarm.
the idea of it when they changed from a single to the dual section was to get better safety. when there was just one single system, the first warning we got was when we tried to stop!
So they went to dual and with the alarm, when one single item like a wheel cylinder or one brake line to a wheel failed, the alarm would come on and we still had half the brakes but knew to fix the problem.

If you don't fix the alarm, the first warning you will get is when you can't stop! The brakes will work-----until they don't!

Sk8Surfr · 11-07-2023, 12:54 PM

Just found this picture that looks like how the switch works... I wonder if I can remove the bolt on the left side and adjust the slide...

Morich · 11-07-2023, 02:13 PM

That's an interesting idea and may be totally right but not something I've ever seen before. Possibly an improved version of what my brother has done?
Logical thing for them to do after a few years of doing it the hard way and needing two people, they do tend to come around to better ideas!