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Thread: NC (third gen) Miata Brake Booster and Master Cylinder

  1. #1
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    NC (third gen) Miata Brake Booster and Master Cylinder

    So I decided on how I want to tackle the brakes. Knowing that there are mixed opinions on the manual brake setup, I wanted to keep boosted brakes. However, the Subaru booster and master cylinder simply don't fit well in the area provided by FFR and likely provide too much brake pressure.

    So I scoured the internet for small car brake booster options to find one that has the same firewall bolt pattern as the Subaru. This turned out to be extremely difficult because the bolt pattern info for most cars is not easy to find on the internet. Out of luck, I managed to determine that NA and NB miatas should have the same 80mmx60mm brake booster bolt pattern as the Subaru. The miatas also had small 7.5" or 8" (will measure mine when it's delivered) single diaphragm brake boosters. Perfect for the 818! Even better, the Subaru master cylinder might bolt on if you wanted since they're both horizontal mount. Haven't confirmed if MC bolt spacing is the same.

    But I didn't buy a NA or NB booster/master cylinder... I bought an NC auto transmission booster and master. There was a downside to doing this, the Subaru master cylinder will for sure no longer bolt up and the common Mazda 929 1" master cylinder won't bolt up either. So I've limited my ability to mess around with master cylinder sizes besides the 7/8" stock. But, the NC master cylinder is very short and side ported! So I think this will resolve all of the fitment issues of the Subaru setup and has a decent chance of giving good brake feel and function. I believe I will also be able to trade my NC setup for a NA/NB setup with a local miata parts guy if I determine the NC setup won't work for me.

    Take all of this info with a heavy grain of salt for the moment. I have not received the booster yet, but I will have it in this week to test fitment. It will be quite some time before I'll be able to comment on pedal feel, but I thought I'd get this info out there for any others interested in brake options. I will update this thread once I fit the booster and hopefully remember to later once I have the brakes functional
    .
    NC miata booster.JPG
    Last edited by lsfourwheeler; 08-07-2018 at 11:25 AM.

  2. #2
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    7/8 might be just fine. My brake pedal on the stock master doesn't move very much AT ALL. As for testing, I managed to pump mine down with a hand-held mighty vac. I didn't get full vacuum because it's an old pump (maybe 15 inches), but it should allow you to get a comparison to NO vacuum. I compared that to no-vacuum-travel with me pushing as hard as I'd have to in order to complain about the brakes. I got somewhere around an extra inch or two with the same perceived effort.

  3. #3
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    I'm hoping for OEM brake pedal feel, but my Subaru Calipers are significantly bigger than the Miata ones this setup was designed for. We'll see how big of a difference it makes in the end.

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    Update on the NC brake setup:

    I got the booster installed onto the firewall. The good news is that the booster and master cylinder fit into the space provided by FFR. The bolt patterns do indeed match up and the level sensor is even the same plug! That was a nice thing that I was not expecting.

    The bad news is that they BARELY fit. By that, I mean there is less than a millimeter of clearance between the booster and the frame and there's just enough room to wiggle it in there. The NC booster is actually 10" in diameter. Maybe the NA/NB are smaller or maybe my miata forum info was wrong (not unusual). The other bad news is that the front port, despite the very short master cylinder, is partially blocked by the frame. However, I think there's just enough space for me to be able to install the brake line without notching the frame. The master will have to come off in order to install the line, but I don't think that's a big deal since I won't be removing that frequently.

    I did some further inspection on a NA booster (my dad has a 1991 model). The booster itself is smaller but I'm not sure if it would fit any better because of the design of the master cylinder and proportioning valve it has. The NA/NB reservoir might be too tall for an 818 as well.

    IMG_20180810_120810.jpgIMG_20180810_120817.jpgIMG_20180810_120824.jpgIMG_20180810_120849.jpg

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    Just some validation

    Good morning,
    I just wanted to give you some validation that you're on the right path. I used to have a NC Miata and ran 12.88" wilwoods on it. And it weighed 2400-2500lbs. The braking force was fantastic. Dropped my 0-60 stopping distance by 10 feet and I could almost always overwhelm the grip of the summer tires (a 195 section).

    You're going to love it.

    IMG_2238.JPG

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  7. #6
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    I forgot that we talked about the different caliper cylinder volumes. On a positive note, it looks like you have just a WEEEEEEEEEEEE bit more room for that brake line than I had.

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    It's a tight fit for sure but I think it'll work.

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