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Thread: Wide L SWB brake caliper piston problems

  1. #1
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    Wide L SWB brake caliper piston problems

    I am changing gaskets and seals in my wide L rear calipers for vented rotor (67-68S/L) with the 38mm pistons.
    Problem is when I put the pistons back in the caliper the inside tube is too tight for the pin inside the cylinder? I have now taken the small tube out of piston and it does not go on the pin with normal Power used. When dismounting I used air to blow the pistons out.
    The calipers have been renovated before I bought them but when I turned the pistons for correct angle they destroyed the sealing ring so brake fluid flushed out of calipers (all four pistons).
    Could I bore up the hole in tube in piston so it moves freely on pin in cylinder?

    On picture, the screwdriver point on the tube which goes inside the piston.

    Any body experienced the same problem?
    Attached Images Attached Images   
    '67 911S Sunroof, Polo Red(Project disguised as a G-model)
    '67 912 Sunroof, Light Ivory(Alive and kickin')
    '67 912 SWTarga, Signal Red(Project in the making)
    X: 67 911 Coupe + 67S Targa, 912, 924, 944, 928, 356

  2. #2
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    The usual procedure is to remove the pistons, then when re-installing ensure they are aligned correctly while being pressed in.
    The pistons will need significant force to get started on the pins. I have done from 30 to 40 of these calipers over the years.
    The best authority I know on calipers is Eric Shea @ PMB Performance.
    Porsche Historian, contact for Kardex & CoA-type Reports
    Addicted since 1975, ESR mbr# 2200 to 2024 03
    Researching Paint codes and Engine Build numbers

  3. #3
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    Thanks for your input Dave!
    I will try to align and press hard to get the piston in. Is it ok to lubricate with brake fluid as I am going to put on car right away or should I get some Ate grease?

    Thanks again!
    '67 911S Sunroof, Polo Red(Project disguised as a G-model)
    '67 912 Sunroof, Light Ivory(Alive and kickin')
    '67 912 SWTarga, Signal Red(Project in the making)
    X: 67 911 Coupe + 67S Targa, 912, 924, 944, 928, 356

  4. #4
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    Brake fluid should be okay. That said, I have used the ATE brake cylinder paste (pale blue) for 40 years. This product is for internal use unlike most brake lubes which are for external use ONLY on sliding metal parts.
    By the way, I never use air to pop out pistons; that just turns the pistons into cannonballs. I use a spare pedal cluster with master cylinder and lines along with my bench vise.
    Porsche Historian, contact for Kardex & CoA-type Reports
    Addicted since 1975, ESR mbr# 2200 to 2024 03
    Researching Paint codes and Engine Build numbers

  5. #5
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    I just did exactly same calipers (among others), ATE paste is good lubricant and I use that. Then when you press piston in, do it in small steps ant let piston without pressure every few millimeter. Seal will seat nicely with this method.
    (Just one observation, calipers should be yellow zinc)
    - Ville -

    1967 911 Slate Grey/red, fully restored + 66' "r-ish" hotrod project

  6. #6
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    Thanks, will source some ATE paste.
    Thanks for your input on this issue, great!

    I hold a rag in my hand when I used air to pop the pistons, but I fully understand a more carefully method

    Yes, yellow sink should have been correct, I have done this to all other bolts, brackets etc but calippers were already done in silver... next time

    Thanks again Dave and Will!
    '67 911S Sunroof, Polo Red(Project disguised as a G-model)
    '67 912 Sunroof, Light Ivory(Alive and kickin')
    '67 912 SWTarga, Signal Red(Project in the making)
    X: 67 911 Coupe + 67S Targa, 912, 924, 944, 928, 356

  7. #7
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    Quote Originally Posted by 91167coupe View Post
    I hold a rag in my hand when I used air to pop the pistons, but I fully understand a more carefully method
    It really depends on how stuck the pistons are, and thus the air pressure required to move them. You were very lucky. When they are good and stuck, the air pressure is high, and so will be the muzzle velocity! Hydraulic pressure is far superior in this regard.

    Have you got a CoA or Kardex on this car?
    Porsche Historian, contact for Kardex & CoA-type Reports
    Addicted since 1975, ESR mbr# 2200 to 2024 03
    Researching Paint codes and Engine Build numbers

  8. #8
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    Thanks, the calipers have been rebuilt some years ago and the pistons were not stuck so they came out fairly nice. I used a air gun So I could adjust the intensivt.

    Another thing, the last dust jacket and retaning ring, I cant get it to sit, it just pops up again. Any tricks? I have dryed of the inside so it does not get so slipper.

    The car is a 912, July '67 deliver as a 67my car. Sunroof and chrome wheels and Light ivory/black. It gets the S-package though with vented brakes, 15mm ARB front/rear etc. And deep6/7R.
    '67 911S Sunroof, Polo Red(Project disguised as a G-model)
    '67 912 Sunroof, Light Ivory(Alive and kickin')
    '67 912 SWTarga, Signal Red(Project in the making)
    X: 67 911 Coupe + 67S Targa, 912, 924, 944, 928, 356

  9. #9
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    Is the inside wall of the groove tapered? I always ensure that the groove is cleaned well before plating or painting. That means using sharp tools to clean everything out of the groove, to have a sharp corner at the bottom. The retaining ring needs to be flat on the inside, and go deep into the groove. You do have to be careful how the ring is installed. I use special pliers to open the ring and drop it over the rubber seal. If you just try to push the ring into place, then it can push the seal down as well, which can just spring back up and pop off the ring. There are a lot of little tricks, and tools, that make working on calipers easier, but it takes years of experience to develop them.
    Porsche Historian, contact for Kardex & CoA-type Reports
    Addicted since 1975, ESR mbr# 2200 to 2024 03
    Researching Paint codes and Engine Build numbers

  10. #10
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    Thanks again. I will check if it is tapered. It looks like the two calipers are a little different, the rings went very easy on the first one, the second feels some bigger and harder to get over the rings.

    Kardex,
    We mailed regarding special paint on a 67 SWT 912, signal red. This car will be on its way later this winter and I will get a kardex for this car. I will come back to you.
    Thanks again!!
    '67 911S Sunroof, Polo Red(Project disguised as a G-model)
    '67 912 Sunroof, Light Ivory(Alive and kickin')
    '67 912 SWTarga, Signal Red(Project in the making)
    X: 67 911 Coupe + 67S Targa, 912, 924, 944, 928, 356

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