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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.

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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.

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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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    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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    alternative would be a corolla ke30 brake booster with a mr2 spider master cylinder (has both ports on right side of master cylinder.
    see this thread for dimensions of brake booster
    http://www.toymods.org.au/forums/thr...attern-spacing

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    you sure that setup would work ^

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    Quote Originally Posted by Newkitguy View Post
    you sure that setup would work ^
    I think only way you could be sure would be to take the risk and buy the components for fitment. It's always a gamble with this kind of stuff.

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    I am going through this same issue with mine right now. I am about 40% done with my build and I just got the opportunity to drive a finished one with willwood manual brakes and I refuse to go manual brakes. It's not happening. I was going to try and make the subaru brake booster work but was looking around to see if there were issues with that, and stumbled across this thread. Love your photos and I love the idea of using a Miata booster to get the sensitivity correct.

    One question..... Have you considered the JDM versions? wouldn't this one be a better option since the side ports are on the opposite side? (I am assuming the proportioning valve is unneeded)
    Let me know your thoughts. If you agree, I am willing to buy it and test it out for the group on my unfinished car. (I am also going to be doing ABS on mine)

    jdm miata booster.jpg

    EDIT: I think this one might be better still since it has the low profile reservoir. Although the photo leads me to believe that the diameter is larger on this one. Is this the same as the one you tested above? but with ports on the opposite side?

    jdm miata2.jpg

    Thanks

    Eric
    Last edited by e-rue; 11-13-2018 at 12:49 PM.

  12. Thanks lsfourwheeler thanked for this post
  13. #12
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    Quote Originally Posted by e-rue View Post

    EDIT: I think this one might be better still since it has the low profile reservoir. Although the photo leads me to believe that the diameter is larger on this one. Is this the same as the one you tested above? but with ports on the opposite side?

    jdm miata2.jpg

    Eric
    That's actually a fantastic find! If you get the JDM right-side port version then you've solved all of the fitment issues. It's certainly still a tight fit, but the ports will be fully accessible. I guess the pedal feel part is still up in the air but I see no reason why the Miata setup shouldn't be an improvement over the manual brakes.

    Edit: And yes the second photo you sent is of a NC Miata booster which is identical in size to the one I purchased. It's a larger diameter but with some wiggling you can get it in. See all my photos for what the fitment will look like.
    Last edited by lsfourwheeler; 11-13-2018 at 02:34 PM.

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    Bought the second one. Should be here this Saturday. I will keep you guys posted!

    Also, what difference does it make if its an automatic trans or not? Mine is automatic (i completely redesigned the back of the 818 frame to hold a modified 4EAT) But I wasn't sure what if any difference it makes to the brake booster.

    I should probably start a build thread...... my 818 is "different" for sure. The donor is a 2004 Forester XT, with a baja TCU, trans, and shifter, with jdm paddle shift behind the steering wheel.

    Eric
    Last edited by e-rue; 11-13-2018 at 03:30 PM.

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    Quote Originally Posted by e-rue View Post
    Also, what difference does it make if its an automatic trans or not? Mine is automatic (i completely redesigned the back of the 818 frame to hold a modified 4EAT) But I wasn't sure what if any difference it makes to the brake booster.
    Eric
    No difference in the booster, but the NC Miata uses a shared clutch/brake fluid reservoir. The Subaru WRX uses a separate reservoir for the clutch master cylinder. So for any 818, manual or auto, you want a automatic transmission NC booster/master cylinder so you get a reservoir that does not have the lead for the clutch master cylinder as well.

    So there's no differences generally for automatic vs. manual brake boosters/masters but you have to keep an eye out for shared reservoirs on manual vehicles.

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    Quick update, tracking says it will be here the 20th. I will get it installed over the thanksgiving break and report back with photos etc. Thanks for the help and advice guys!

    Eric
    Last edited by e-rue; 11-14-2018 at 02:22 PM.

  17. #16
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    Finally got the package after fighting with USPS..... worst shippers ever.
    I really wanted to get it installed yesterday (friday while I was off work) but I might be able to get to it tonight or tomorrow.

    IMG_1756[1].jpg

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