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Old 01-02-2014, 02:03 AM   #1
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Default Brake Boosters

Has anyone played with swapping boosters? I think the brake booster is weak in this car and just seeing if anyone has found a PNP stronger booster for the NA miata's. Car is a 1995 with stock brakes.

Edit: I found a huge thread on miata.net with lots of good info from Bbundy. Looks like he used custom bent lines and T fittings. Still looking for something a little more Plug and Play.

Last edited by jacob300zx; 01-02-2014 at 11:10 AM.
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Old 01-02-2014, 02:14 PM   #2
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Isnt it the OEM 15/16ths master with that years booster the heaviest pedal setup? I think thats non-ABS sport brakes cars and all MSM (including ABS).
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Old 01-02-2014, 02:30 PM   #3
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This cars brake booster is terrible, like its not there. Heel toe is nearly impossible because the brake gets pushed down so far.
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Old 01-02-2014, 02:34 PM   #4
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A non-working booster would give you a super short but hard pedal.
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Old 01-02-2014, 03:09 PM   #5
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Originally Posted by jacob300zx View Post
This cars brake booster is terrible, like its not there. Heel toe is nearly impossible because the brake gets pushed down so far.
I think you're complaining that the brakes are over boosted, not under boosted. I've seen threads on m.net where people have removed the brake booster altogether. You can see if you want to go this route by turning the car off while in motion and trying the brakes.
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Old 01-02-2014, 03:38 PM   #6
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Remove and plug vacuum line and report back if it was actually working or not. I'm curious.
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Old 01-02-2014, 04:34 PM   #7
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"overboosted" does not cause a pedal to drop too far. Bleed your brakes, bleed your master, then upgrade to the 15/16" master and non-ABS Sport booster if you're still dissatisifed.

If the non-ABS Sport master/booster doesn't satisfy you, I'd suggest a Porsche or a Ferrari.
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Old 01-02-2014, 04:51 PM   #8
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Quote:
Originally Posted by jacob300zx View Post
This cars brake booster is terrible, like its not there. Heel toe is nearly impossible because the brake gets pushed down so far.
Check for bad wheel bearings, a leak, or bad master cylinder seal.
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Old 01-02-2014, 05:24 PM   #9
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Check for bad wheel bearings [...]
I've not heard this one...I'm curious - how would wheel bearings would have any effect on the brake pedal stiffness. not saying you're wrong, just looking for a little free education.
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Old 01-02-2014, 05:37 PM   #10
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I believe your car may be suffering from the same issue as buffon's was.
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Old 01-02-2014, 05:46 PM   #11
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Originally Posted by krazykarl View Post
I've not heard this one...I'm curious - how would wheel bearings would have any effect on the brake pedal stiffness. not saying you're wrong, just looking for a little free education.
Pad kickback. Same reason having the rear parking brake adjusters loose can change pedal feel and rear brake grab.
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Old 01-02-2014, 06:10 PM   #12
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Quote:
Originally Posted by Leafy View Post
Pad kickback. Same reason having the rear parking brake adjusters loose can change pedal feel and rear brake grab.
...usually this is a long, but firm pedal. The pedal drops a few inches and then gets hard.
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Old 01-09-2014, 08:44 PM   #13
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Jacob what you are describing is what I fought as well. Now my pedal stays high under braking allowing for easy heal toe. Here is what I suggest.

Upgrade MC and booster to sport version (03+)
Install FM master cylinder brace
Install SS lines
Check pads for taper
Check wheel bearings for slop
Adjust pedal free play as per factory manual. Set it on the tight side of specs.

Are you running V8R brakes by chance?
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Old 01-09-2014, 10:13 PM   #14
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No, stone stock brakes for a 94-97. Did your 03+ booster bolt right up? Which master did you use? Did you rebend any lines?

Pads and rotors are new, pads are bedded in per ctbrakes.com, rear brakes are adjusted very close to drag .25-.5 turn off drag. I do have a possible bad drivers rear wheel bearing. Even if the wheel bearing which I have replacements makes it feel better I still want more boost (power per peddle effort). Info found on miata.net below.

Quote:
Originally Posted by Keith View Post
As part of one of my projects, I've been diving into Miata brake master cylinders and power boosters. I've uncovered a couple of things I didn't know about. This information is true for the US and Canada as best as I can tell, I don't know about other countries. This information comes from checking the 1990, 1996, 2002 and 2004 factory manuals and various parts fiches. Unfortunately, our 2006 manual is on loan to a third party for some product development so the NC version of this information will have to wait.

A lot of this information is going to appear in my new book. It's nearly a year out (my publisher is very slow at layout), but it's a taste of what to expect

First, I've always stated that the non-Sport 1990-02 brakes all use a 7/8" master cylinder. Turns out that's not correct. 1990-00 cars use a 7/8" master and all 2001-05 cars use the 15/16". I confirmed this with a non-Sport 2002 that's sitting in the shop right now. If you want to know what size your master cylinder is, by the way, it's cast into the top of the master just under the reservoir. You can easily read it with the parts installed. If you discover your car came from the factory with a different master, I'd love to hear about it.

Now, brake boosters. Boosters take the force applied by the pedal and multiply it. The ratio between the input force and the output is called the boost ratio. Say, if you put 100 lb-ft of force on the pushrod and the booster exerts 250 lb-ft of force on the master, you have a boost ratio of 2.5:1.

It turns out there are at least 3 boosters that were used in the Miata, and I didn't expect some of the variations. Here's how it breaks down.

1990-00: 4.74:1 <- this is a bit approximate, as Mazda gives a range of output pressures as acceptable
2001-05 non-Sport and Sport with ABS, except for MSM: 9.7:1. Yes, that's about double. This booster is visibly fatter, and I suspect it has dual diaphragms inside instead of a single.
2001-05 Sport without ABS and MSM: 6.4:1

There's more to it than the boost ratio, of course. That larger master cylinder in the 2001-05 cars means less pedal travel and more effort with a given caliper size. Taking both the master cylinder size and the boost ratio into account, here's how it shakes out.

1990-97:754-796 psi of line pressure for 44 lb-ft
2001-02 non-Sport and 2001-05 ABS: 1038 psi of line pressure for 44 lb-ft on the pedal
2001-5 Sport non-ABS and MSM: 638 psi for 44 lb-ft

Sport cars (all of them) use larger pistons in the front and rear calipers, so the amount of braking force is going to change. But from this, we can tell that the 2001-02 non-Sport cars will have the pedal with the least travel of any stock car, but should also have the lightest touch.

There are some interesting interchange options here. I have an MSM master and booster in the Targa car. If I wanted to make the brakes require a little more effort, I'd swap in a booster from a 1990-00 car.
Paging Bbundy, Keith Tanner, and JasonC SSB
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Old 01-10-2014, 12:49 PM   #15
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Quote:
Originally Posted by Savington View Post
"overboosted" does not cause a pedal to drop too far. Bleed your brakes, bleed your master, then upgrade to the 15/16" master and non-ABS Sport booster if you're still dissatisifed.

If the non-ABS Sport master/booster doesn't satisfy you, I'd suggest a Porsche or a Ferrari.
My brakes now feel better than a 996 I drove recently. Less pedal sink, better (a bit less) pedal force required.

1" 929 master, lower-boost 01+ booster (not the fat one), the common FM front BBK, Mazda "large-piston" sport rear calipers, and XP8 front pads.

Last edited by JasonC SBB; 01-10-2014 at 03:08 PM.
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Old 01-12-2014, 12:00 AM   #16
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Quote:
Originally Posted by jacob300zx View Post
No, stone stock brakes for a 94-97. Did your 03+ booster bolt right up? Which master did you use? Did you rebend any lines?
You will have to make changes to one of the lines. Not a big deal with the right tools. I used the booster and MC out of a 03+ non abs Miata. Booster should look almost the same as your current one. If its twice as thick its the wrong one. Best $100 I have spend. Just do it!



Quote:
Originally Posted by jacob300zx View Post
Pads and rotors are new, pads are bedded in per ctbrakes.com. I still want more boost (power per peddle effort)
More power per pedal effort can come from a few different places. Sure you can run the biggest booster possible but I think that's the wrong approach. A good high friction race pad will "bite" in a way that requires less pedal effort. I never had great luck with the Carbotech pads. If yours are not bedded perfectly that could easily be the problem (assuming you have at least XP12).

One mistake I made was not doing a BBK right out of the gate. I was burning through front pads every 2 days with stock setup and XP12. Now with Cobalt XR4's and 949 11" BBK I have 10+ days on the same pads and they are still good. The BBK paid for itself already.
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Old 01-12-2014, 10:49 AM   #17
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What tools to I need to run the newer booster and 929 Master? Got any pictures of your lines?
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Old 01-12-2014, 01:07 PM   #18
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A box flare wrench and a credit card?
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Old 01-12-2014, 02:42 PM   #19
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Quote:
Originally Posted by k24madness View Post
One mistake I made was not doing a BBK right out of the gate. I was burning through front pads every 2 days with stock setup and XP12. Now with Cobalt XR4's and 949 11" BBK I have 10+ days on the same pads and they are still good. The BBK paid for itself already.
My understanding is that this car is a nearly stock daily driver with OE-replacement pads, rotors, etc. While Jacob has a lot of track time under his belt, I thought this car was just seeing some spririted street driving.


If that is accurate, I will reiterate my previous comment:

Quote:
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I believe your car may be suffering from the same issue as buffon's was.
That is, "a misdiagnosis."



If that's not accurate, continue to ignore me.
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Old 01-12-2014, 11:49 PM   #20
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Yes this one in particular is stock, I think I made it sound different refering to ctbrakes.com, I was just stating how I bed them in. What was Buffon's issue? Regardless I like my brakes a little more sensative ie more power. My MSM brakes where awesome feeling, going to try the MSM/non-ABS Booster.
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