Parking Brake light keeps coming on - update 5/17

[AJMBLAZER]

So since late last year Big Ugly's parking brake light keeps coming on increasingly often. Now, the truck drives fine and the parking brake works just as it should when I activate it and releases as it should when I pull the lever.

So anyone got any thoughts on where it's getting the signal saying it's on?




Only thing that makes me nervous is the truck was surplused out from the Minn NG because some Private Doofus drove it around with the parking brake on and locked the rear axle up solid. Cheaper for them to just get rid of it than to fix it.

 

[dremu]

Two things make the parking brake light come on.

One is the switch on the brake lever. It could be flaky, wiring could be chafed, that sort of thing.

The other is the combo valve; if it detects a sizable difference in brake pressure between the front and rear circuits, it turns the light on. This can be caused by low fluid level, but is more likely indicative of a leaky master, or maybe leaky wheel cylinder or caliper. (Or bad rubber hoses on one of the corners.)

I'd go over the electrical to the switch with a fine-toothed comb (well, a flashlight ) first, 'cuz that's less scuzzy than brake fluid, but I have a sneaking suspicion you'll be replacing something hydraulic and then bleeding the hell out of the thing.

-- A

 

[sandawgk5]

Check your brake fluid level. If it gets low and there is a differential pressure between front and rear brakes it will cause the light to come on. It has to do with the switch/valve thing on the front crossmember.

That switch could also be bad too.

Dik

 

[sandawgk5]

Two things make the parking brake light come on.

One is the switch on the brake lever. It could be flaky, wiring could be chafed, that sort of thing.

The other is the combo valve; if it detects a sizable difference in brake pressure between the front and rear circuits, it turns the light on. This can be caused by low fluid level, but is more likely indicative of a leaky master, or maybe leaky wheel cylinder or caliper. (Or bad rubber hoses on one of the corners.)

I'd go over the electrical to the switch with a fine-toothed comb (well, a flashlight ) first, 'cuz that's less scuzzy than brake fluid, but I have a sneaking suspicion you'll be replacing something hydraulic and then bleeding the hell out of the thing.

-- A

Damn I'm too slow

Dik

 

[AJMBLAZER]

Okay, I'm back...sorta forgot about this in all the hubbub of the last week.

Finally managed to check the level. How full is it supposed to be? The front is a ways down but not empty and the rear is mostly full (say...3/4?)
Been a long time since I had a truck with a master cylinder you couldn't just look at and tell.

No brake fluid appears to be leaking but I haven't started really crawling around under it. Plenty of oil leak, maybe some diesel and coolant...but haven't noticed any brake fluid.

Now to figure out if this thing has DOT 5 or DOT 3 in it...hopefully not both...


Stops just fine. I sold the Tracker today so I'm DDing it until I get the K5 next month.
Lemme just say two dogs and me on a bench seat is fun. Especially considering one is 75lbs.
[dog voice]I WUB YOU I WUB YOU I WUB YOU! WATCHA DOING? HEY SQUIRREL! WHAT? I WUB YOU I WUB YOU I WUB YOU...[/dog voice]

 

[AJMBLAZER]

Okay, dinked with it today.

-It has DOT 3 in it and not DOT 5. I guess the Minn NG never got around to putting DOT 5 in it. Lucky for me as I'm clean out of DOT 5 and had two bottles of DOT 3 on the shelf.
-Front chamber was empty and rear was about 1/4 to 1/3 down.
That means the rears were missing the fluid...right?
-I still can't see any leaks or anything under the truck but it sorta looks like under all the grime and such that there's brake fluid coming out from under the cap? Slimy brake fluid like stuff all over that thing and the steering shaft below is a bit shiny/grimy too. Vacuum thingy behind it isn't.

I'd take pictures but I'm using a loaner phone and this thing's camera SUCKS.

I filled up the reservoir and I guess we'll see. About all I can do right now.

So any thoughts all might brake gurus?

 

[AJMBLAZER]

Oh yeah, NAPA and Rock Auto mention two different master cylinders with 1605 and 1925 on them...any one know where these numbers would be? Cast in? Can't really see anything on mine.

 

[AJMBLAZER]

 

[Jason4x4]

sounds like wheel cylinders leaking, pull the drums and see.

 

[AJMBLAZER]

Yeah...well, was going to be taking the tires off to groove and sipe them anyways...

 

[dremu]

Oh yeah, NAPA and Rock Auto mention two different master cylinders with 1605 and 1925 on them...any one know where these numbers would be? Cast in? Can't really see anything on mine.

Huh. So does CSK/Oreilly.

In the "see what other vehicles this fits", the 1605 is listed as working for lots of stuff 73+, P and G vans, etc

The 1925 is listed as fitting newer vehicles, like the R and V series on up through some mid-90's.

I suspect then, that the master design changed halfway through '86.

Now, CUCV's are special -- they're all 1984 parts. When I went to get a wiper motor for my '85 M1009, I discovered that, for standards purposes, all the CUCV's use 1984 parts. That is, even if GM changed the parts on the civvy trucks, they kept delivering the original style to the military.

If I had to guess, then, I'd say that your truck has the 1605 style cylinder, just on the premise that it's likely the earlier design.

The other possibility is that the two have something to do with GVWR and brake type (i.e. dually or SRW, and which size drums) but usually the parts listings say "for 13x3.5 drums" or whatever.

If it's the early-vs-later, I betcha it's fitting-related, i.e. different sizes or front-vs-back. Worst case, take the old one in and match it at the store.

And bleed that thing! The motor guys say "oil is cheap; steel ain't" and the same applies to brake systems. Fluid is cheap, calipers aren't. (Well, they're not as pricey as motors, but you get the idea )

-- A

 

[AJMBLAZER]

Yeah, it's on the list.

They definitely work better now. Locked them up this morning when an old man in a dump truck pulled out in front of the lady in front of me and I and we both nearly rear ended him. (Old bastard just drove on in first or second all the way up the hill at 15mph.)

Question about the rear cylinders...if they were leaking wouldn't that show on the back of the brake drums? Nothing.

 

[dremu]

Yeah, it's on the list.

They definitely work better now. Locked them up this morning when an old man in a dump truck pulled out in front of the lady in front of me and I and we both nearly rear ended him. (Old bastard just drove on in first or second all the way up the hill at 15mph.)

Question about the rear cylinders...if they were leaking wouldn't that show on the back of the brake drums? Nothing.

Might. They can also leak all over your nice new expensive shoes (as in brake shoes ... they cost more than the shoes I was wearing!)

Pull the drums for the old "visual inspection", and adjust the non-self-adjusting self-adjusters whilst in there.

-- A