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Rear Brake Problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by cegusman, Jul 8, 2001.

  1. cegusman

    cegusman 3/4 ton status

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    About a month ago I did my brakes all the way around (calipers,pads,wheel cylinders, and shoes. Well on the forth July I went wheeling and my rear brakes started grinding, after closer inspection I found out I must have been driving that whole month with them locked up. Today I replaced my shoes and wheel cylinders again. When I go to bleed the I am getting veyr little pressure (The fluid only shots out about 2 inchs or less) and is not consistant every time. If i take the wheel cylinders off the and step on the brakes the fluid shoots out of the lines about 6 foot. I have tried gravity bleeding them.

    1. open both bleeders.
    2. take top of M/c
    3. Keep a close eye on the M/C and make sure it has fluid at all times.
    4. let drain for a while getting about 2-3 M/c full of fluid through the lines.
    5. Close the bleeders.
    6. reinstall the mc/ lid.

    but have still no strong pressure with wheel cylinders on. The pedel is spungy the whole time and goes all the way to the floor. I checked my fronth calipers and the spay like old faithful so the front are fine.
    What should I try next?
     
  2. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Dam, you must have cooked everything back there. Are you sure the drums are not cut too far? Even with a good bleed, if they are cut too far you will never get a good pedal. Might be worth trying a new set. just my $.2

    [​IMG]<font color=red>[/b]"Rid'in HigH in my K5"[​IMG]
    ....[​IMG]<font color=blue>[/b]"6" Lift -<font color=purple>38.5's"[​IMG]....
     
  3. cegusman

    cegusman 3/4 ton status

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    Could the master cylinder cause a problem like this? Or what about the proportioning valve. The drums are fine
     
  4. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    I would think that you would be having probs with the front brakes also.
    this is what I know:
    -the back brakes need careful adjustment
    -they still don't work well
    -bleeding is a pain and the source for most probs


    Dave

    Beauty is in the eye of the beer holder.
     
  5. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Yes the proportioning valve could do this but it's kinda weard to have that happen right after the other problem. What caused the lock up (parking brake?). It might be worth having a good mech. take a look for a few bucks and maybe do a power bleed. Does the parking brake work good? When bleeding them, you did have a friend work the peddal while you worked the bleeders didn't you?

    [​IMG]<font color=red>[/b]"Rid'in HigH in my K5"[​IMG]
    ....[​IMG]<font color=blue>[/b]"6" Lift -<font color=purple>38.5's"[​IMG]....
     
  6. cegusman

    cegusman 3/4 ton status

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    Both wheel cylinders failed and caused the lock up, and my ebrake is not being used at the time.I did have a friend work the peddal while I worked the bleeders, What kind of problems would a bad master cylinder cause? What is a power bleed
     
  7. mpascino

    mpascino 1/2 ton status

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    did you try opening the bleeders up some more, since you said the fluid shoots out 6 feet with just the open line there must be some resistance in the wheel cylinder. I had the same problem with mine before I realized that the bleeders were not open enough. I losened them to the point they were just still in the wheel cylinderand bleed them again. Since then II have had no problems. Give it a shot.


    You call that dirty!?
     
  8. cegusman

    cegusman 3/4 ton status

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    I will give that a try and see if that works.
     
  9. cegusman

    cegusman 3/4 ton status

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    I tried opening the bleeders more but still have not enough pressure.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd be guessing master cylinder myself. I changed fluid, and could never get a firm pedal back. Spongy all the time, 2 hours of bleeding no difference. Drove it anyway. Got bad enough that twice, at lights, the truck started to roll while the pedal was to the floor. (good thing it's a stick!) FWIW, from what I have read, bleeding brakes is a great way to get the MC to fail, since the pedal, and thus MC piston, travels further than it usually does, pushing the piston seals into crud that has built up, ruining the seals, which causes that spongy feeling.

    The front and rear brakes are on a different "circuit", so fronts are independent of the rear. Depending on MC, some have a channel for the front and rear brakes to share fluid, but thats MC only, once its to the two lines, its seperate front to rear. Ground out the proportioning valve light (go from the drivers side fender, light brown (?) wire plugged right into the proportioning valve. If the "brake" light comes on in the cab (key turned to "run" position) the proportioning valve should be working correctly. Very rarely do they fail. Extremely simple. Check my page below for a picture of the inner workings of one if you care to.

    My vote is MC cylinder. Spongy pedal, not much velocity in the brake fluid, all lead me to that, or a leak in one of the lines, but you should notice that now. Just tell yourself its a good idea to repalce it, since its so old, and it will be easier to do. that way even if its not the problem (which it probably is) you don't feel so bad.

    Dorian
    My tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
    No anti-theft measures on your truck? No pity when its stolen
     
  11. cegusman

    cegusman 3/4 ton status

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    Got my rear brakes working today. The brand new wheel cylinders I bought were defective.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Wow. I guess it goes to show what kind of products are being put on the market. TWO defective wheel cylinders is bad. I hear the ignition modules out there are pretty prone to not working as well. Just yesterday I was fixing a miss on another engine....2 out of the 8 (cheap) Autolites didn't work at all. Less than 30 minutes of run time, no driving. And of course no warranty.

    Dorian
    My tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
    No anti-theft measures on your truck? No pity when its stolen
     

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