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Old 05-10-2015, 10:11 PM
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Default C4 master cylinder bore diameter(s)?

An '84 brake booster looks to be about half the weight of my stock '69 booster, and also small enough in diameter to clear the valve covers (IIRC, the later plastic boosters are a touch bigger diameter). In the event I can adapt this to the '69 but have to use a C4 master cylinder, can anyone tell me what the C4 master cylinder bore is (or are, in the event that there were multiple sizes during the C4 run)?

Thanks!
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Old 05-12-2015, 12:45 AM
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I've got an unknown vintage C4 plastic brake booster and master cylinder sitting on the shelf. The m/c looks to be in the region of 15/16" diameter, less than my C5 m/c (1") on the '69. I took a spare C5 m/c I've got laying around and tried to hook it up to the C4 booster, but it looks like the m/c bolt spacing is just a touch narrower than the booster studs spacing, but perhaps a slight bit of filing might allow the C5 m/c to fit a C4 booster.

The plastic booster is about 9 1/2 inches in diameter, while my stock C3 booster and the booster in my '84 are both close to 8 inches in diameter. The '84 style booster looks like it will fit (with some adapting) in my '69 while being several pounds lighter.
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Old 05-12-2015, 11:05 AM
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I had the bore diameter information but can't find it. I think there were 2 bore sizes during the C4 run. I think the last was ~15/16 because the people were swapping C5 stuff to C4's without changing the MC.
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Old 05-12-2015, 03:55 PM
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I would spec out an early/late say '85 and '93 m/s at most any decent parts house, they get the # from the mfgr, then look up the specs.....


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Old 05-17-2015, 01:23 PM
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Rock Auto shows 1984 bore = 13/16, 85-91 = 7/8, 92-96 = 15/16
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Old 06-28-2015, 03:07 AM
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Quote:
Originally Posted by BBShark View Post
Rock Auto shows 1984 bore = 13/16, 85-91 = 7/8, 92-96 = 15/16
Thanks Larry.

I'm working on an aluminum adapter to put an '84 brake booster on the '69, and I've got the '84 m/c and another unknown model year m/c (which looks like the 15/16" part). The '84 booster is 5# lighter than the '69 booster (3.8# vs 8.8#), and it looks like I can get the adapter welded up with about one pound of mass (for a 4# net reduction). The later m/c looks like it will bolt up to the older C4 booster.
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