Original 1968 Master Cylinder (Power Disc)

Discussion in 'The whoa and the sway.' started by HLohio, Jan 5, 2018.

  1. HLohio

    HLohio GS owner since 1977

    For the last 2 days I have searched every corner of the Internet looking for an answer about the correct, original master cylinder used on a 1968 GS400. I'm trying to do a manual drum to power disc conversion, but I want to use all factory correct parts. I have MOST of the components in hand EXCEPT for the master cylinder. Does anyone in Buickland know what the correct MC casting number and 2-letter stamped code is for a 1968 with power (4 piston) disc brakes? Does anyone have a survivor car or documentation that could solve the mystery? I know many will work, but trying to be as original as possible. THANKS!
     
  2. mrolds69

    mrolds69 "The Cure"

    I did not know that in 68 Buick used the 4 piston calipers. I do know Olds used them. I think...off the top of my head...the code is DC. That would be stamped in the front of the cylinder on a machined pad. I actually have a 68 Olds 442 dual piston disc master in my cellar with the other valve, too. I'm not home right now to check it for the casting code. I want to say it's a "308" code compared to a "309" code used on 69 up. Could be "408-409" I forget, I'd have to check the code. Are you interested in a 68 442 core?
     
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  3. HLohio

    HLohio GS owner since 1977

    I'd be VERY interested in knowing what the casting number is. If it turns out the Olds is the same except for the stamped letters, that would be very close to what I'm looking for. Can you post pictures?
     
  4. mrolds69

    mrolds69 "The Cure"

    I can, but not today. I'm buried in snow at my GF's and waiting for somebody to dig me out. I know it's a dual bail cylinder. From memory, it's not quite as tall as a 69 up cylinder. Maybe a day or 2 before I can get eyes on it.
     
  5. HLohio

    HLohio GS owner since 1977

    That would be GREAT! Thank you
     
  6. red67wildcat

    red67wildcat Well-Known Member

    I dont have the casting numbers but I do have pics of what was on my former low mile very orig 68 disc brake car
    now Im not claiming it hadnt been replaced at some point ,I dont know and never looked at the master cyl that close.
    but if you want a couple reference pics if it might help
     
  7. HLohio

    HLohio GS owner since 1977

    I will take any info anybody has. You can send pictures directly to me at HLohioATfuseDOTnet. Thanks
     
  8. gstewart

    gstewart Well-Known Member

    the a-body & f-body cars could be optioned with disk brakes in '67 & '68 and were 4 piston calipers (like the corvette). I would guess that the M/C would be identical for vehicles.
     
  9. mrolds69

    mrolds69 "The Cure"

  10. HLohio

    HLohio GS owner since 1977

    That's what I've been told by Steve Gregori at BrakeBoosters.com. Parts for '67/68 are hard to come by because disc only came as an OPTION. In 1969 some GM cars came with disc as standard equipment and therefore are more plentiful.

    Looking forward to seeing what the Olds MC casting number is. According to the parts books, the PART number (5468774) for Buick and Olds is the same in 1968. It should be a clue in the right direction.
     
  11. gstewart

    gstewart Well-Known Member

    thru 1970, disk brakes were still optional..
     
  12. BUQUICK

    BUQUICK I'm your huckleberry.

    I have no experience or knowledge of ‘68s but ‘67 and ‘68 are the only two years that used the 4-piston calipers. I do know a little bit about ‘67s so I went and pulled an original master cylinder and booster from my ‘67 GS parts stash.

    The casting number on the side of an original ‘67 disc brakes master cylinder appears to be 5460348.

    To confirm that this is a correct ‘67 disc brake master cylinder I looked up the master cylinder codes in the service manual and I’ve included a photo as well. The manual says FR code and that is what is stamped into the machined pad of this ‘67 master cylinder. The ‘67 disc brake setup also used brass block mounted below the master cylinder but I’m not sure if the ‘68s used this style as well or switched to the later design.

    For what it’s worth, there are still traces of black paint on this master cylinder. So it wasn’t natural, it was painted black. This was removed from a ‘67 GS400 over 30 years ago.


    E0B74327-A5B7-4A3F-B73D-85512580EDAC.jpeg B8CE8152-B6B3-4C02-A8B8-BF9B29790561.jpeg 43ECE6C7-4589-4F62-873B-0D6302349CE4.jpeg E3A4665C-730D-443F-9A01-29250AB4D1B0.jpeg B0C86E35-EB25-4698-80F2-3A54D93A9077.jpeg EE4462F1-02B7-4BB4-85B1-3486F83C7B8D.jpeg
    95BC3CDA-7D7A-4044-B8A3-E89E16FCF067.jpeg
     
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  13. telriv

    telriv Well-Known Member

    That brass thingy is the hold-off valve for the front disc brakes & was used up until 1970. It prevented the front discs from applying until there was 300 pds. of line pressure being exerted from the rear brakes.
     
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  14. BUQUICK

    BUQUICK I'm your huckleberry.

    Exactly. The ‘69-‘70 hood-off valves were cylindrical and not made of brass. I’m not sure which style was as used in ‘68? I’m not sure if it was like the ‘67 or like the ‘69.
     
  15. pbr400

    pbr400 68GS400

    image.jpg image.jpg This is from the ‘68 service manual...sorry for the neck strain.
    Patrick
     
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  16. BUQUICK

    BUQUICK I'm your huckleberry.

    Thanks for posting. That’s shows that a ‘68 uses the same hold-off valve that was used up to the end if ‘70. They are available as a reproduction thankfully.
     
  17. HLohio

    HLohio GS owner since 1977

    Not exactly. The hold-off valve on a '68 differs slightly from those of 1969 & up. Here is a picture of an original 1968 valve and a 1969 valve. Notice the larger size "nut" on front of 1968 and the taller casting where bracket bolts up. Unless you have a 1968 and 1969 side-by-side, most people won't notice the difference. They are VERY close, but not exact. True 1968 Valve.jpg True 1968 Valve 2.jpg 1968 Disc Brake Example 2.jpg
     
    Last edited: Jan 9, 2018
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  18. BUQUICK

    BUQUICK I'm your huckleberry.

    Excellent photos and information HLohio. I will be saving those photos for future reference.

    Great another one year only part :( but maybe this is the same valve used on other GM A-bodies in '68? I think you are right that most people won't notice the difference if a '69 valve is used.

    I just looked to see how many '68 Buick Gran Sports left the factories with power disc brakes and I was surprised to see that it was only 888 units. That is only 4.12% of the total production of 21,514 cars (GS350 & GS400). It breaks down as GS400 hardtop 545, GS400 convertible 158, and GS350 185. This info was pulled from Mike Trom's 1968-1972 Production Total Quick Reference Guide which was derived from the Buick Daily Car Reports.
     
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  19. HLohio

    HLohio GS owner since 1977

    BUQUICK, thanks for the production info. I didn't know that. Kind of explains why I've had such a hard time finding original parts LOL. With regards to 69/69 hold off valves, keep in mind that many 1968's were replaced with '69 valves if/when they went bad. The shop manual says they must be replaced and are not repairable. Therefore it's completely "normal" to see a '69 valve on a '68. I doubt GM stocked many '68 style valves as replacement parts.
     
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  20. HLohio

    HLohio GS owner since 1977

    Well, Even though this is supposed to be a thread about 1968 MC casting numbers, we might as well be thorough. Here's the casting/part number on underside of 1968 hold-off valve. The number is 2225831. 1968 Metering Part Number.jpg
     
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