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Technical GM metric low drag calipers *FIXED*

Discussion in 'The Hokey Ass Message Board' started by Bullit68, Aug 12, 2020.

  1. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

    So, I have the GM metric calipers on the front end with the 70’s Ford type master cylinder. I’m always having to pump the brakes one time to get a good pedal because of the “low-drag” calipers. From what I’ve read, I need square cut seals for these. Anyone know if these are correct? I bought another set of calipers that supposedly had a good PN, but they are same as my old ones.
    https://www.napaonline.com/en/p/UBP...er+Boot+Kit+-+Front&keywordInput=caliper+deal
     
  2. I've never heard them called "low drag" calipers. I've used them on many cars both stock and custom application. I've never had a problem with them.
     
  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
    ALLIANCE MEMBER

    There are "low drag" calipers. They are not the same ones found in generic disc brake kits for older cars (or at least they should not be).

    http://www.remaninc.com/pdfs/lowdragcalipers.pdf

    They require a stepped-bore quick take-up master cylinder. Without one, they are downright dangerous.
    [​IMG]

    Whey I find them, they go in the metal recycling bin, after I cut a mounting ear off of them.
     
  4. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

    Well, they changed in 1980 for better fuel economy from the previous years. It lets the piston retract in a little so the shoe isn’t dragging on the rotor. I have almost .020” clearance between inside pad and rotor. I know they need the step bore master, as far as I know the 78-88 GM metric calipers ARE the “low drag” style... changed in 1980
     

  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    Low drag calipers are different internally. You need a correct set, not just seals.

    upload_2020-8-12_19-59-3.png
     
    Truckdoctor Andy likes this.
  6. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    Both low drag, and non low drag versions exist.
     
  7. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

    Supposedly, it’s the seal on the piston that changed from square to a “taper” style.
     
  8. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    I am not making it up that the calipers are different internally. It is not just the seals.
     
  9. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

    I’m not debating that, just something I’ve read. I just need to know where I can find the pre-1980 “conventional” style. Any info would be appreciated...
     
  10. Jibs
    Joined: May 19, 2006
    Posts: 1,525

    Jibs
    Member

    ^^^^^Me too.
     
  11. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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  12. bobscogin
    Joined: Feb 8, 2007
    Posts: 1,761

    bobscogin
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    Weren't the metric calipers introduced in 1978 on the GM A-G bodies?. Couldn't you just get a pair for a '78 or '79?
     
  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
    ALLIANCE MEMBER

    Yes, they were, but finding a set may be a needle in a haystack, as they get freely mixed in with later calipers, since they fit in the same spot.

    That is the very reason why Allied Signal sent out that bulletin on not mixing calipers.
     
  14. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

  15. gimpyshotrods
    Joined: May 20, 2009
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    gimpyshotrods
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    If you look in the comments on the Summit page, it calls out that feature specifically!
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    Just make sure that your master cylinder is for disc fronts, and has the correct size bore.
     
  17. Mimilan
    Joined: Jun 13, 2019
    Posts: 644

    Mimilan
    Member

    The easiest way to determine what you have is by the bleed screw. Low drag calipers have metric bleed screws.
    The difference is in the way the groove is cut into the body, so they flex [and retract] more
    upload_2020-8-13_15-53-22.png

    @Bullit68 Keep the low drag calipers , but switch to a Stepped Bore [aka, quick uptake] master cylinder.
    A Chevy S10 M/C is the solution
    There is 2 different models but both have the same 24mm pressure bore size.

    The non-boosted S10 M/C has a slightly smaller "Step" in the bore [31.75mm bore]
    The boosted S10 M/C has a larger "Step" in the bore [36.5mm bore]

    We've used a stepped bore M/C with conventional callipers on a race car. This allows the use of smaller bores [for pressure increase] with the pedal remaining high.
     
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  18. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,534

    Mr48chev
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    Napa and Rock Auto lump them all together. Eckler shows quick take up master cylinders being 84 and later on El Caminos but no stock style calipers to check 4 master cylinder styles between 78 and 87 with those brakes.
     
  19. Mimilan
    Joined: Jun 13, 2019
    Posts: 644

    Mimilan
    Member

    Most 80's G Bodies are stepped bore.
     
  20. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    The thin black line outlining the seal represents the circumferential seal groove in the piston bore.
    upload_2020-8-12_21-22-33.png
    This is why you cannot simply change the seals.

    The caliper body has been machined differently.
     
  21. Jibs
    Joined: May 19, 2006
    Posts: 1,525

    Jibs
    Member

    The non-boosted S10 M/C has a slightly smaller "Step" in the bore [31.75mm bore][/QUOTE]

    What year S10?
     
    Last edited: Aug 12, 2020
  22. This is why i keep coming back to this site. The knowledge here is impressive. Thanks for the info.
     
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  23. Mimilan
    Joined: Jun 13, 2019
    Posts: 644

    Mimilan
    Member

    1984-85 S10 4 cylinder with Disc / Drum manual brakes

    https://www.amazon.com/Cardone-Sele...---14--------3&vehicleName=1984+Chevrolet+S10

    Edit: if you want a smaller Step than the S10 [but same pressure bore] but a 28mm step look at Audi [Cardone # 13-2042]
    or 1976 -80 Mercedes [same pressure bore with 28mm step]
    https://www.ebay.com/itm/Brake-Master-Cylinder-Cardone-11-1919-Reman-/324244358777
     
    Last edited: Aug 13, 2020
  24. southcross2631
    Joined: Jan 20, 2013
    Posts: 4,012

    southcross2631
    Member

    I have low drag 4 wheel drum brakes . No issues. 65 Comet drums and shoes. 67 comet master cylinder for safety.
     
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  25. Bullit68
    Joined: Sep 16, 2009
    Posts: 107

    Bullit68
    Member
    from Verona, PA

    It sure is, thanks again for the info!
     
  26. gnichols
    Joined: Mar 6, 2008
    Posts: 10,796

    gnichols
    Member
    from Tampa, FL

    Of all the topics that come up here, I can't think of one more important than braking. Thanx so much for this... however, comma, would it be possible to list all the available (within reason) caliper / master cylinder combinations that are confirmed to be correct, please? I've built two rods (street or otherwise) and neither one has had good brakes. Pretty sad when your Honda SUV brakes better than your custom-built performance car, eh? Or should we just call them Cold Rods instead? While I plan on Wildwood gear for my next one, I'm sure there are thousands out there with GM derivative systems that have a serious need to know what the correct caliper / MC matchups are and where to get them. Thanx everyone, Gary.
     
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  27. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
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    Good for you.

    In traffic, where I live, that would be an accident waiting to happen.

    I have 10,000 feet of elevation change to deal with on fun runs, and 60+ miles of closely-spaced traffic, going 85, daily. I live 250 feet from a neighbor with a $2,500,000.00 car, and similar others.

    I hope you realize that not everyone lives or drives under the same conditions as you, and that shaming people for wanting and installing better than what you settled for may be rightly seen as a negative indicator of character content.
     
    BJR, VANDENPLAS, Atwater Mike and 4 others like this.
  28. This is good info, we need the low drag calipers for our race car.
     
  29. WZ JUNK
    Joined: Apr 20, 2001
    Posts: 1,669

    WZ JUNK
    Member
    from Neosho, MO

    I am currently struggling with a GM caliper problem. ( These are the Tornado/Eldorado/Rivera emergency brake calipers) I have a low pressure situation in my rear brake system. By taking pressure measurements I have determined that I have about 400 psi drop in my rear brake calipers. In round figures about 1100 psi before the calipers to about 700 psi with the calipers connected in the system. Both of these measurements are with the system fully bleed of air. I have tried every method I know to get air out of the calipers and when they are tested I get the same results. I do not know what is going on but I could use some help.
     
  30. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,656

    gimpyshotrods
    ALLIANCE MEMBER

    Do you have any sort of metering or combination valve in the system?
     

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