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Brake light came on while driving

Discussion in 'The Garage' started by TrcksR4ME, Apr 16, 2002.

  1. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I just swapped in new axles, and had to disconnect the rear brakes and bleed them. I bled them quite a bit but the pedal is still soft.

    The problem is I was driving and hit the brakes and the brake light came on and stayed on. Is the brake system connected to the light in some way, truck is a '77. Or is this some other dash light malfunction?

    The brake pedal is still soft and i bled enough fluid through to where it comes out clean now. Would one of those bleeders you can get for like $40 at the auto parts store bleed the brakes well? Or is it better to just take it to a shop?
     
  2. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    Yeah, I question the damn light too, what is it connected to and why does it come on? I just replaced front calipers rotors etc, rear drums etc, master cylinder, bled the whole system still got a brake light on. No soft pedal or anything but still a red annoying light.
     
  3. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I didn't figure an older truck like mine had anything high tech that would tell the brake light to come on, and the light has never done this before. The 14bff probably has larger calipers than the stock unit and maybe this has changed how the brake system functions-and if there is a sensor maybe it thinks more fluid being needed to stop is bad...err something. I have no idea though, just guessing
     
  4. Triaged

    Triaged 1/2 ton status

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    The light comes on when there is a difference in pressure in the front and rear lines. My guess is it came because your master went out on you while you were bleeding the brakes (but it could be a leak anywere). The light is that scary red for a reason!
     
  5. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Well, how am I suppose to check this? If the master cylinder has gone out, what do I look for? There is no sign of leaks anywhere, and the fluid level has not changed in the reservoir. I am still thinking it may just need to be power bled and that there is still air in the line. But I don't know the brake system to well.
     
  6. BorregoK5

    BorregoK5 1/2 ton status

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    I think you hit it on the nose. The light is triggered by the proportioning valve which is beneath your radiator. The valve senses pressure changes.
     
  7. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I still need to know how to check and whether or not this could be air in the line. Again, no leaks that I can see.

    I can't belive the light even works, the only thing on the dash that lights up...lol

    I wanna get the truck on the road asap, and need to know what to do next. HELP!
     
  8. Triaged

    Triaged 1/2 ton status

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    There are 2 posible locations that arn't visible. The 1st one is the wheel cylinders. You have to pull back the dust boot on the wheel cylinder (both boots on both sides of the truck) to see if they are leaking. The 2nd is the master. It can leak internally (fluid goes back into the res.) or externally (into the booster). Both of these you can't see but either type of MC leak means you need to replace it.

    To tell if the MC is leaking hold down on the peddle (about 1/2 way down) and if it stays there w/ the same force on it then that is what air in the lines feals like. If it goes to the floor under the same force that is the MC.
     
  9. BorregoK5

    BorregoK5 1/2 ton status

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    If the pedal is still soft with no leaks then you have one of three possibilities. Either there is still air bubbles in the line (Sometimes difficult to do without power bleeding, just keep circling longest to shortest path fluid path), the seals in the master cylender have gone out (usually happens when you change / lose pressure as the unusual travel moves the seals into rough areas and they scuff up or tear, cheap fix for the home mechanic), or you have swelling brake lines(unusual to happen all of a sudden). Checking the system without special tools and fittings makes it hard to pinpoint an air bubble from an bad master cylender, at least that I know of.
     
  10. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Well I'll have to check it all out more thoroughly. Sounds like even if it's not the MC, I should change it just for good measure at this point.

    Tips for MC replacement? I think I am gonna get a decent bleeder too, and not cause anymore problems /forums/images/icons/crazy.gif

    Neverending...did I mentioned all I wanted was 4wd when I started, and now I've swapped out both ends, rear springs, done all the bearings and brakes + all the misc crap that goes with it.
     
  11. bobsurf

    bobsurf 1/2 ton status

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    Ditto to what Borrego said. Spongy brakes should be your indicator that things aren't right. Recently revamped my braking system (MC, Booster, Pads, shoes, etc.) and bleeding them took a long time. Make sure you're getting good pressure release when your opening the line. We probably did at least 10 laps around the truck before getting a solid pressure release for all 4 wheels. You should also notice a difference (at least in my 73) between the "floor" of the brake pedal for the back and front brakes. I think the front was significantly higher in mine.

    You might also want to think about having them power bled at a shop. Any input on that from anyone? I've never done it. I'm also curious about those $40 one man bleeder kits. Has anybody ever used one?
     
  12. MudFrog

    MudFrog 1/2 ton status

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    This happened with me as well, I ended up having to replace my master cylinder because I couldn't get the rear brakes to bleed properly. Once I replaced the master cylinder the pedal was stiffer and the brake light went off.
     
  13. fulltopblazer

    fulltopblazer 1/2 ton status

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    I've been going down this road for weeks know. Everything in my entire system is new, and I still can't get a good pedal. When the pedal is about 3/4 down the light comes on but when I release it goes off. Yesterday I ordered extended steel braided brake lines hopefully they will help. I'm tired of trowing parts at this and not getting any results.
     
  14. KBK5

    KBK5 Registered Member

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    A cheaper way is to "gravity bleed" the system. Park on a hill with the rear downhill, open the driver's rear bleeder first and let the fluid run into a bottle, bucket, etc. and stand around and drink beer, whatever, and keep an eye on the MC. Fill as necessary NOT letting air enter the lines in the MC. Figure how much you need to run the length of the line before closing and going on around the truck. Takes some time but that was the last straw on my '77. WORKED!!
     
  15. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Heh, I did the gravity feed where all the fluid came out on acciedent, so there is a chance of air still in the system. The MC is old though, and it leaked from somewhere either where it bolts to the booster or the cover, but only a little and stopped.

    I think I should go ahead and do the MC for good measure, and I want to bleed the brakes well this time.

    Anyone have experince with one of those $40-50 vacuum one man bleeders they sell at the Auto parts store? I dont want to go to a shop if I dont have to. Wanna get it done right this time though.
     
  16. Overkill

    Overkill 1/2 ton status

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    Never tried the vacuum one but tried one of those "fill the cup half way with fluid and pump the brakes" jobs. Wasn't worth a hill of beans. Still had to enlist the help of a friend to complete the bleeding succesfully.
     
  17. JIM88K5

    JIM88K5 1/2 ton status

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    I got one. I did a satisfactory job but I used up 2 or3 bottles of brake fluid. It took a little bit to figure out how to get the best results. Got a good firm pedal. I changed all 3 of my brake lines (extended). I think summit or jegs has bleeder valves with a check valve for the one man system. I have also done the earth sucks bleeding procedure on my car and it worked for me.
    Jim
     
  18. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I used the tube into brake fluid method, and it did not work so great. One side did not bleed very well, was really slow. The bleeder valve must be screwed up cause fluid would leak out around the threads, but slowly through the valve. Should this be replaced?

    How much do MC's go for? Auto parts store wise, not online or Mail order.
     
  19. 70~K5

    70~K5 1/2 ton status

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    I replaced the MC on a 77 K20 I had 15 years ago. After I got the new MC on I found the front bleed screws were cloged with crap. Proably didn't need the new MC. Changed it cause I couldn't get the front brakes to bleed right. Take a smaller than the center hole drill bit and try and clean out the bleeder screws off the truck. Also clean them through the holes on the side of the screws. If you can't get them cleaned out then replace them. Also buy some little rubber boots to cover the end of them to keep the crud out. The boots come stock on some brands of trucks. They look like the caps to block off vacum ports.
     
  20. KBK5

    KBK5 Registered Member

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    One other possibility that comes to mind after 25 years. A buddy of min had a '65 shortbed chevy w/ a 3/4 ton Dodge army running gear under it. He had to pinch off one of the rear brake lines to make the brakes work because the wheel cylinders were too big for the MC. If you can't get any results the way you are going, you may need to consider a larger MC. Just food for thought.
     

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