Originally Posted by jacob300zx (Post 1087879)

This cars brake booster is terrible, like its not there. Heel toe is nearly impossible because the brake gets pushed down so far.

Originally Posted by jacob300zx (Post 1087879)

This cars brake booster is terrible, like its not there. Heel toe is nearly impossible because the brake gets pushed down so far.

Originally Posted by hustler (Post 1087934)

Check for bad wheel bearings [...]

Originally Posted by krazykarl (Post 1087942)

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.

Originally Posted by Leafy (Post 1087949)

Pad kickback. Same reason having the rear parking brake adjusters loose can change pedal feel and rear brake grab.

Originally Posted by Keith (Post 4311953)

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.

Originally Posted by Savington (Post 1087932)

"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.

Originally Posted by jacob300zx (Post 1090178)

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?

Originally Posted by jacob300zx (Post 1090178)

Pads and rotors are new, pads are bedded in per ctbrakes.com. I still want more boost (power per peddle effort)

Originally Posted by k24madness (Post 1090796)

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.

Originally Posted by Scrappy Jack (Post 1087947)

I believe your car may be suffering from the same issue as buffon's was.