braking system split

Discussion in 'Suspension, Steering & Brakes' started by Frankenchevy, Feb 17, 2018.

  1. Frankenchevy

    Frankenchevy .

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    another question, but close enough to not need a new thread...

    do our trucks have a residual valve in the rear portion of the master cylinder or is this function carried out by the metering/hold-off valve?
     
  2. Craig 85

    Craig 85 Supporting Member Supporting Member

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    When you put the rear brake lines back in, ditch the weight sensing valve on the rear axle. You'd be amazed how much better your rear brakes will work.
     
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  3. Frankenchevy

    Frankenchevy .

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    Was yours symptomatic prior to removal? Mine seems to work fine, but I’ll give it a go without it. Must be a reason they discontinued the part.
     
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  4. Craig 85

    Craig 85 Supporting Member Supporting Member

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    This valve was GM's anti-lock brakes prior to computers. I had an issue with an '87 K20 after I lifted it. I had a shop lift the truck back in the early 90's. They raised the valve off the differential, but not enough to compensate for my 4" lift. I was towing my El Camino on a trailer that did not have the electric brakes hooked up (I was young and dumb). When I suddenly had to stop for a red light, it was like having no brakes at all. I ripped out the valve the next week. I don't recall having any lock up issues after removing it, but it's been so long I don't recall.

    I removed the one in the K30, knowing I was going to lift it and I would have more rolling mass with new tires and wheels. I think you said you were not lifting your's, so if it works it may not be an issue.
     
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  5. Dougnsalem

    Dougnsalem Full Access Member

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    If you take it off, you may not want to just toss it. I have no idea what that would be worth, but here's one for sale....

    https://m.ebay.com/itm/CUCV-Chevy-k30-d30-proportioning-valve-14-bolt-rear/372223976376?_trkparms=pageci:a140260a-159b-11e8-9756-74dbd180b7ea|parentrq:af24ce571610aa14438934cbfff2bda1|iid:1&_trksid=p2481888.c100675.m4236

    CUCV Chevy k30 d30 proportioning valve 14 bolt rear
    $80.00

    s-l400.jpg
     
  6. Frankenchevy

    Frankenchevy .

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    I wonder if he will actually get that much..
     
  7. Dougnsalem

    Dougnsalem Full Access Member

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    I don't have a clue. Looks like the guy is parting out a CUCV m1008. Has a 14 bolt posi carrier for sale too.
     
  8. Frankenchevy

    Frankenchevy .

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    Posi or Detroit?
     
  9. Goldie Driver

    Goldie Driver Full Access Member

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    Back from the dead, but figured I would try it.
    I have an issue where the left front and right rear run hotter (by feel and temp gun ) than the others.

    Is our system on an X pattern, or just front to back ?

    Loosening the master cylinder from the power booster seemed to have no effect on the lf caliper, and the rears are new including drums as of Saturday.
    I thought I had both rears pretty even with a slight drag.

    Thanks!
    Britt
     
  10. bucket

    bucket Super Moderator Staff Member

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    Nope, just a basic front/rear system.
     
  11. chengny

    chengny Full Access Member

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    Probably not your problem, but just something to look at.

    On the hot RR drum, what kind of condition are the contact pads in - and are they lubricated?

    Look closely at the condition of the contact pads on the backing plate. Although there is not any relative rotary motion between the brake shoes and the backing plate, there is a certain degree of linear motion that occurs - as when the wheel cylinders force the shoes out against the drums. Even though the shoes are held tightly against the backing plates (by the mounting/hold down springs), the brakes are engaged by hydraulic pressure so they rarely (if ever) stick on the way out.

    But when the brakes are released, the only force that returns them to the free wheel position is what is provided by the return springs. For that reason, the inboard edges of the shoes must be able to move freely across the 6 contact pads. If the pads are trashed they tend to prevent the shoes from fully releasing. In that case, it is possible that the linings then stay in contact with the drums causing heat and premature wear. Or, as noted below, if the pads are modified - in an attempt to restore the smooth surface - this results in misalignment and grabby/noisy brakes:

    Cab_interior__left_brakes_014.jpg

    Nickel Never-seize seems to work best as a lubricant - and it stays put between brake jobs:

    Cab_interior__left_brakes_016b.jpg

    From the GM service manual:

    BACKING-PLATE INSPECTION

    Contact Pads - Clean the contact pads thoroughly and verify they are not burred or grooved. Burrs may be removed with very light sanding. If the contact pads are grooved the backing-plate should be replaced.

    contact pads.JPG

    NOTE: Grooved contact pads may cause the rear brakes to drag or stick. If you attempt to remove the grooves by grinding or filing, the new shoes/linings will not line up correctly with the drum. This may result in the problems noted above.

    The contact pads should be coated with a high temperature silicone lubricant prior to reinstalling the shoes/linings.

    Mounting Bolts - Verify the mounting bolts are secure. A loose backing-plate will cause the rear brakes to be very sensitive or grabby.


    On the hot LF disc brake, while there could be any number of causes, a good place to start is at the contact points - are the slide surfaces smooth and lubricated? Use a file to clean the surfaces shown below and apply Never-seize:

    CaliperSlideLube.jpg
    CaliperLube.jpg
     
    Last edited: Oct 11, 2018
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  12. Goldie Driver

    Goldie Driver Full Access Member

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    Finally! My account was locked for about a week because I updated my email address and could not get a confirmation email to come through...

    At any rate, how about MC for the answer?
    Had the pedal stick halfway down twice on me - hung the brakes so bad I could barely move.
    Shut her off, wiggled the pedal, and no more problem that day. Did it once the next day , too- parked today with a new MC due in tomorrow.

    Never had this failure mode before - buddy of mine says he has heard of it before after a cold snap.
    Which we had Monday, the first day of the spazz out...

    Pretty weird.

    Britt
     

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