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Thread: Question on 100M front brake cylinder

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    Jedi Knight bighealeysource's Avatar
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    Question on 100M front brake cylinder

    Hey y'all,
    Been a while since I posted as usually just reading what everyone else is talking about. But got a question on the front brake wheel cylinders. I have a 1956 100M, March of 56 production date, and trying to figure out which cylinders I have on it. During this COVID 19 situation, doing some minor projects on the Healey. One of which was to flush and bleed the brakes. Ordered the minor rebuild kit from Moss for a BN2 which are for a 7/8 inch bore cylinder per their catalog versus a 1 inch bore cylinder for a BN1 up to chassis # 221403. My chassis is 231xxx so should call for a 7/8 bore. BUT, the rubber dirt cover from the 7/8 kit is not even close in size to the one on my existing cylinders. No way it would fit so I cleaned up the old ones and put back on. I looked at the Moss catalog again and the 1 inch bore dirt cover is close to 1.375 inches in diameter and the 7/8 is 1 inch. After all of this my question is - if I seem to have 1 inch bore wheel cylinders and choose to replace with new ones, can I only go back with the 1 inch so everything fits properly or can I replace with the correct 7/8 bore cylinders ? I do not know if the existing cylinders were replaced by the previous owner going back to 2000 but they do have raised letter ID on them "Girling 303310W". BTW, since I got everything finished up now and brakes are working better than before with all new fluid I probably will not do anything at this time but for a future project trying to figure out which way to proceed.
    Thanks,
    Mike
    Mike Lewis, 1956 Austin Healey 100M - Registry Confirmed

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    Jedi Trainee Joe Schlosser's Avatar
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    Re: Question on 100M front brake cylinder

    I cannot be positive on this but I assume that the brake cylinders are matched to the master cylinder bore.
    Joe Schlosser
    SCCA National License, Retired
    60 Bugeye, since 1966
    SCCA FP, sold but not forgotten

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    Yoda steveg's Avatar
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    Re: Question on 100M front brake cylinder

    Looking up the repair kits on Moss' website, bores are given in catalog and on site:

    Fronts: ..............Moss PN:.. Bore
    Early BN1.......... 513-015.... 1"
    Late BN1, BN2... 021-145... 7/8"
    BN4, BN6 ..........513-015.... 1"

    Rears:
    Early BN1.......... 513-015.... 1"
    Late BN1, BN2, BN4, BN6
    .........................513-093.... 1"
    Ft Disc cars........ 583-020... 3/4"

    Years ago on the email list IIRC there was a discussion about one of the BN1 or BN2 setups resulting in unstable braking.

    Before converting to 4-wheel discs, my all-drum BN6 exhibited stable braking, so I'd guess the BN6 setup of 1" all around is a good setup.
    Last edited by steveg; 04-08-2020 at 12:27 AM.
    Steve Gerow
    Altadena, CA, USA
    Maker of most complete Big Healey rear disc kit
    Check out my galleries:
    http://www.pbase.com/stevegerow


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    Jedi Knight bighealeysource's Avatar
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    Re: Question on 100M front brake cylinder

    I'm replying to my own post but looking at the existing brake cylinders, could they be the originals since they are Girling and do appear quite old ? Of course could have been put on anytime prior to the Healey being wrecked back in early 60's.
    Mike Lewis, 1956 Austin Healey 100M - Registry Confirmed

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    Re: Question on 100M front brake cylinder

    Mike, 7/8" is correct for your car. My 100M is 233xxx. It's been in my family since 1963 w/33,000 miles. It's been mine since 1971(w/48000 miles) and I am the only one who has done any brake work on it. I replaced cylinders on one side and kitted the other back in 1990. I replaced all 4 a few years back and kept the ones I removed. All 4 are 7/8". I also have a boot left from the kit used in 1990. The dust boot is a very difficult fit---I tried it on one of the old cylinders. I also have a complete 1" cylinder kit. Those dust boots are an extremely sloppy fit on the 7/8 cylinder. I wonder if, as has become too common these days, the "reproduction" kit is just a really poor fit.

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