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Thread: Seized Caliper Piston?

  1. #1

    Seized Caliper Piston?

    My Brake pedal is hard as a rock.... if you stand on it it'll go down a tiny bit, but not even far enough that when you get off of it the pedal retracts. I disconnected the front brake line from the master cylinder, and the pedal went down fine. So I went to the brakes and the LF pad is still kinda clamped to the rotor... You can turn the wheel by hand but as soon as you stop turning, the brakes stop the wheel.. the RF turns fine.. It'll spin freely. I haven't had a chance to disassemble the LF brakes yet... What do you guys think? I'm thinkin a seized piston.....

  2. #2
    Senior Member MASTER BUILDER
    Join Date
    May 2003
    Location
    Owingsville, Ky
    Posts
    157
    I just repaired a "sticking caliper", by replacing the rubber hose. They can go look OK on the outside, but get a crimp on the inside and only allow fluid to pass in one direction. One way that you can check is to open the bleeder screw on the suspect caliper and see if it releases and allows the rotor to spin freer. This would mean that the pressure is still being applied in the lines even though the pedal has been released.

    On your other posts, you had spoke of changing your race car from dual master cylinders to a single one with dual outlets and of having drum brakes on the rear. Your hard pedal could be due to other problems, which could be the mechanical ratio or too small a master cylinder bore. Here is a link to an article on brakes, bias, and pedal ratios. http://www.hotrodheaven.com/tech/bra...kes1_index.htm

    Master cylinders have different bias ratios and bore sizes depending on what application they are to be used on. Also, the front port on a lot of master cylinders goes to the rear brakes because of the bias. I am thinking that the Mopar one that I have is a 69%/31% split.

    For the ratio, you want to be around 6:1, this is determined by the length of your pedal from the point of pivot and the distance down to where you connected the master cylinder rod at. If your pedal is 12" long from the pivot point and the rod is connected at 2" down from the pivot, then this is a 6:1 ratio. But, if the rod is connected at 3" down (usually the spot where the power brake rod connected) then your ratio would only be 4:1 and have a much harder pedal.

    Be safe on this and get some help if you need it. You need for this to be correct and there is a lot more to it than just bolting on pieces.

    Bill M

  3. #3
    I bled that caliper several times before I removed the master cylinder. Each time I opened the bleeder fluid came out. I stopped when my reservoir was about empty... The brakes worked fine when I parked it. It sat outside for a few days (covered but outside) till I could get back to it with my trailer. When I was driving it to the trailer the LF tire went flat then I went to brake and realized the pedal was hard as a rock.

  4. #4
    I was able to compress the piston back into the bore.. Is there anything I can lube the piston up with that won't damage the rubber seal?

  5. #5
    Senior Member MASTER BUILDER
    Join Date
    May 2003
    Location
    Owingsville, Ky
    Posts
    157
    The rubber seals have to stand up to brake fluid, so they should be fairly hard to damage with any lubricants. But you have to be careful to not contaminate the brake fluid, so I have just coated the seals and bore with brake fluid to install. If the bores have rusted enough to sieze the piston, you will probably have issues with leaks and sticking when the pads wear down some. (been there done that with factory Ford 4-piston calipers, next step will be to get the stainless steel ones)


    Bill M

  6. #6
    Heh... If it's gonna cause problems down the road, I can get some remanned ones for 10 bucks a piece at the local part store

  7. #7
    Senior Member MASTER BUILDER
    Join Date
    May 2003
    Location
    Owingsville, Ky
    Posts
    157
    For the 20.00 or so, I would recommend putting the remanufactured ones on it. When I rebuilt the ones for my Mustang they were only a 2 year option and I couldn't buy rebuilt ones except for the stainless steel ones ~400.00.

    Bill M

  8. #8
    Wow. 400. Those must be some damn nice calipers! Thanks for your help....


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