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Brake light comes and goes

I bled the brakes again last night. Once again there were air bubbles coming up from each of the front bleeders, although they were smaller than the first couple of times I did it. This time I didn't pump the brakes, I used that one man bleeder bottle thing and just opened and closed the bleeder valves until I didn't see any more air bubbles coming up. After I bled them I pumped the pedal a few times (after I added some fluid to the MC) and the light stayed off. However, the very first time I hit the brakes this morning to come to a stop, it came on again. So I guess I need to start looking at what I need to replace. I made sure all the fittings were tight on the hoses, MC and prop. valve. I guess the cheapest thing to buy first would be new bleeder valve screws. Can you buy them by themselves?

Also, I installed the longer brake hoses that are meant for an '88 and up truck (I think) about a year ago. When I first put them on, the tires rubbed them for a couple of days in one spot and kinda wore the rubber down a little before I noticed it and moved them out of the way. No fluid or anything ever leaked out and that's been a while back. Could these brake hoses be the cause?
 
scottystills said:
Maybe I'm looking at it wrong, but isn't the parking/ebrake a cable system that's completely separate from the hydraulic brakes' normal operation? In my mind the only thing that can trip the parking brake indicator light is the switch/relay on the parking brake pedal.

...or possibly a short in that circuit somewhere...
Click to expand...

Unfortunately you are wrong on this. There is in fact a portion of the brake warning system that detects pressure differences between the front and rear systems. It is the proportioning valve that has a single wire running to it. If, for instance, a wheel cylinder in the rear fails it will trip the light. I have also seen it trip when Krusty blew out a rear hard line. Many brake systems are this way and have been for many years. I know my 75 F100 had it as did my Dad's 74 highboy.
 
If you are still getting air out of the front system there is something else wrong, especially if the hoses are not showing any signs of leakage. It is possible the caliper seals are bad, but you would likely only see that on one side or the other, usually not from both sides.

Check the proportioning valve, and all lines for any signs of leakage. Have someone pump the brakes a few times while watching at each and every connection. Leave the engine off while doing this and you might hear a hiss.

If the master cylinder is full, unless you have a loop somewhere in the hoses that is allowing the air to get trapped, then there is a leak somewhere allowing air into the front system. You said longer front lines, are they looped or otherwise in a position that could trap air bubbles?
 
They are kinda curved because they're a little longer, but they've been like that the whole time. I'll take a picture after the sun comes up.
 
andyblack said:
They are kinda curved because they're a little longer, but they've been like that the whole time. I'll take a picture after the sun comes up.
Click to expand...

Would yousay after bleeding it improved?
If so, there is more air in the system and you need to get it all out, if youfeel it went back to the same, then there is a problem, most likely in the PV.
Did you reset the button on the PV?
there is a button you sometimes need to reset if it doesn't by itself, you might have air trapped in there.
The PV is two fold:
It evens out the pressure between front and rear, but also works as a plug, in case front or rear had a failiure, it plugs that side and keeps some brake action on the good axle, that valve inside can trap some air.
Air in systems is always hard to get out, as you can see from all the posts about bleeding the air from: Diesel engines, power steering systems, brake systems...
Sometimes it takes a few trys not just one.
 
I would say that after I bled them and got all the air out (or so I thought) and the light went out, the brakes felt like normal. When the brake light comes on, the brakes still seem to work fine, but the feel at the pedal is noticably firmer, almost like the vacuum booster isn't doing quite right or something.

I had no idea there was a button to reset the valve. Where might this button be located?
 
andyblack said:
I would say that after I bled them and got all the air out (or so I thought) and the light went out, the brakes felt like normal. When the brake light comes on, the brakes still seem to work fine, but the feel at the pedal is noticably firmer, almost like the vacuum booster isn't doing quite right or something.

I had no idea there was a button to reset the valve. Where might this button be located?
Click to expand...

The button is on one side, left or right can't remember, but if the brakes are acting normal, it probably doesn't need it.
I would suggest a little more bleeding, you probably only have a little left, enough to trip the light and then off.
That is what is happening right?
the light goes off a little after you release the brakes?
If it stays on, then you have more than a little air, if it come on and goes off after you release, it means you are almost clear of air.
I would probably drive it around a bit like this so all the air accumulates at the calipers and then do it again.
 
The light comes on and goes off as I apply and release the brakes at first, and then it just stays on after I use the brakes a few times. When I first start the truck, the light will usually be off. Mainly the light being on is just bugging me, but I certainly don't want the brakes to stop functioning right when I need them.
 
andyblack said:
The light comes on and goes off as I apply and release the brakes at first, and then it just stays on after I use the brakes a few times. When I first start the truck, the light will usually be off. Mainly the light being on is just bugging me, but I certainly don't want the brakes to stop functioning right when I need them.
Click to expand...
Yeah drive it for a day and go back and bleed it again, there is a little bit of air left in there.
 
the reset should be on the side of the proportioning valve...its covered by a little rubber boot. it is possible, if you had a leak or drew air into the system, to have air in the p-v.

I had the PO run the MC dry...I replaced the fluid but the MC was old...so really the piston inside had been damaged by this action. I replaced the MC and bled the system. Still had the light. Air in the system somewhere...argh. Long story short, it was the calipers mounted upside down so I started from scratch...bled the new MC, flipped the calipers correctly, then slightly opened the p-v lines to allow fluid to escape (IE, gravity bleeding for a bit). Tightened the lines, then bled the crap out of the front lines.

No more brake light :)
 
Despite replacing the master cylinder on my 82 K2500,along with the rear wheel cylinders,all the brake lines except the right front and having good calipers only 5 years ago,and bleeding the thing with all the usual methods,the dam brake light wont go out completely,sometimes it comes on bright too,but the brakes are working perfectly....I tried using my home brewed vacuum bleeder thats never failed me yet,but that lamp just refuses to stay off.............................................................................................................................................................................................................This isn't my first truck with this issue,my 72 K5 had the same thing occour after a brake line blew...I ended up replacing the proportioning valve,though I doubted it was "defective",--but once I put a used one on and bled it again,it went out and stayed out......................................................................................................To get a sticker on my '82 ,I had to take the bulb out of the dash ,and I stuck it in the ash tray...its been there a couple of years now,and the brakes still work fine....only trouble I have had is now the rear chamber in the master cylinder started losing fluid,just like the one I replaced---and if I let it sit too long and fail to top it off soon enough,it'll let air in and need to be bled again..........guess its hard to get a decent master cylinder any more,rebuilt or new.................its about 25 bucks for one,so its not the end of the world,but still irritating to have to try another one...I suppose I'd have to put another P-V on it,to get the brake light to stay off...the piston in it must be stuck just off to one side of center,where it would shut off the light...
I have had to replace a few other P-V too,when I tried pushing in or pulling out on that pin on it under the rubber bootie..(some you had to push in,others need to be held out)....my friend who's done brake jobs for 20 years said he's rarely had to mess with that pin,and just about every time he did,it resulted in it needing replacement,so I dont touch them !...we have bled a lot of brakes at his shop and never had to mess with one in at least 5 years..
 
I have had problems with getting that light out too. I wish I could find a diagram of how it works.
The piston that trips the light is not spring loaded. Its centered by brake pressure being equal on both sides.
If it ever gets shoved all the way over, such as a line bursting, it can stick.
Had one on my Ford that would not center, and a brake place just pressed really hard on the pedal and it moved.

But, another time, that did not work on another truck that had had a line failure.
That time, the brake place put light pressure on the pedal with the booster empty, and another guy slightly loosened a line on the other half of the system just enough to let about a drop out.

The pressure imbalance moved it right back.

I don't think I have ever had one I could not get to go out with a stock system.
 
It is a ground switch system, the PV must be mounted on a grounded surface for it to work. As J said, it can get stuck at times and realistically most of these valves are getting old with little to no actual flushing of the brake systems in many cases, and they should be replaced.
 
imiceman44 said:
I know it doesn't make sense, but the smaller compartment is the one for front.:waytogo:
Click to expand...

I'll take your word for it. You have almost certainly worked on one more recently than me.

Its interesting, I was going by the fact that it seems most MCs have the back chamber power the front brakes and the front the back.
And the back chamber is the biggest.

But, I double checked, and I see where my memory played me false. On a GM product, the rear chamber is the smaller, but on a Ford, the front is the smaller.

If I worked on these things on a regular basis, I could keep them straight, but I might work on a GM one day, Dodge the next, Subaru on a weekend, and then tinker with my Ford.
That is not a problem. The problem is, there might be a year between them, and I think its been almost two years since I pulled the cap off of one other than my 1966 F600.
And its only got a single chamber with a screw cap...........
 
My truck's original master cylinder had 2 different sized fluid chambers,the smaller one to the rear,next to the booster....which is for the rear brakes I am pretty sure,because if I had let it sit long enough for the fluid to leak out thru the seal in the rear of the master cyl,I'd lose the REAR brakes,and have to bleed them to get the pedal back to normal..................................................................................................The rebuilt master I put on it has 2 equal sized chambers for the fluid....and the rear one closest to the booster operates the rear drum brakes on that one too.....when I first installed it ,I discovered the steel lines would screw in the ports on the master cylinder if I swapped them front to rear,and it would lock the rear wheels instantly even if you used a feather touch on the pedal,I could not safely drive it--after buying brass adapter fittings to allow the lines to be installed where they were originally,solved that probem....it felt like it had ONLY rear brakes with the lines reversed,so I assume that proved the rear chamber isn't big enough to operate a caliper (or the piston in the master might be 2 different sizes or steps to provide the correct volume and pressure to each end of the truck)...
 
On mine, the front (smaller) chamber is definately for the front brakes because after bleeding the front brakes, the fluid level on the front chamber went down.

I bled it a few more times the other day with the same results. This weekend I hope to get someone to press on the brake pedal while I get up under there and listen to see if I can hear any air escaping from anywhere. Then if I still can't determine what the faulty component is, I guess I'll start by replacing the front brake lines. I need some braided stainless steel brake lines anyway.
 
Just wanted to update this thread and let everyone know what the problem was. Apparently the wheel cylinder for the left rear drum had been starting to go bad and let air in the system, because when I went out to look at it Saturday morning, there was a huge puddle of brake fluid on the ground by the left rear tire and the master cylinder was almost empty (but only the front chamber :confused:). Of course the shoes were soaked back there too so I got a new wheel cylinder for each rear wheel and went ahead and replaced all the shoes and springs and had the drums turned while I was at it. Man I hate messing with drum brakes! :mad: How can something be so complicated and still not really work all that good?

Anyway, thanks to everyone for their advice. After bleeding the brakes, the light went out and stayed out and the brakes worked waaaaay better than before. So of course it was time for the transmission to break yesterday afternoon. Wouldn't you know. Guess I'll be starting a new thread pretty soon... :doah:
 
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