1.6L to 1.8L Brake Rotor and Booster Upgrade

With more power comes the need to increased stopping power. It's hard to see above 90mph on a 1/2 mile straight shot of track in a N/A miata. Whereas it's easy to see +120mph with an added turbocharger.

When Mazda added 200lbs. and about 10rwhp in '94 they upgraded a lot of components, including the brakes. Luckily, they also shared a lot of the same parts to make things easy for an upgrade.

The 94-97 rotors are about 1" diameter larger and your braking surface area is dramatically improved. All you need to perform this mod are the brackets from a 94-97 donor, pads, and rotors.

Front Rotor Comparison:


Rear Rotor Comparison:


Pads comparison:


Left: Rear | Right: Front

Noticed the beveled edge on the 1.6L front pads. I've seen this on a few brands,
the friction surface on a flat 1.8L pad is dramatically increased over the 1.6L pad.

Tools Required:

Metric Sockets & Wrenches
Allen Wrench
Caliper Grease
Tin Snips
Large U-clamp

Front Installation Procedure:

  • Jack the car up on all four corners.
  • Take off the wheels.
  • Remove the caliper bracket from the hub. (2) 14mm bolts.
  • Remove the top slider pin that holds the caliper to the bracket. (1) 17mm bolt.
  • Slide the caliper off the bracket.
    • The bottom bolt will stay in place and slide out.
  • Remove and replace the rotor.
    • Bend the Dust Shield away from the rotor.
  • Install the new 1.8L bracket.
  • Slide the caliper back in place. (Lube it generously).
  • Swing the caliper on the bottom hinge and install the new 1.8L pads.
  • Swing it back over the pads (Use your U-clamp and squeeze the piston to retract out of the way if it won't fit, watch your fluid level)
  • Lube the 17mm bolt and reinstall.

Rear Installation Procedure:

  • Your new rotors will be just as large as the dust shield behind the rotor.
  • Remove the dust cap off the lower caliper bolt and remove. (1) 10mm bolt.
  • Swing the caliper up and push the caliper inward and it will slide off the top slider.
  • Remove the Bracket. (2) 14mm bolts.

*Trim the dust shield to fit the larger rotor.

  • Install your new rotor and fit the new bracket in place. (*NOTE* must install rotor first.)
  • Remove the bolt on the back of the caliper to access the caliper adjustment screw. (1) 12mm bolt.
    • Use your allen wrench to turn it counter-clockwise until the piston is pushed in all the way.
  • Lube and replace the caliper.
  • Install the new pads.
  • Lube and tighten the lower bolt.
  • Tighten the caliper adjustment screw to push the caliper against the pads, loosen back 1/8th turn so it's not clamping down on the rotor.

That's it. Enjoy all the new stopping power.

Also, posted by Keith @ Flyin Miata (http://forum.miata.net/vb/showthread.php?t=363284) :

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.

I bolted a 7/8" master to a non-ABS Sport booster last night as part of a test fit, so they do bolt up. I need to check a couple of things on the pushrod length, but the bolt pattern is the same at least.

Going with the 2001-02 non-Sport booster and master will make your brake pedal firmer and require less effort. That might make it a bit harder to modulate, though. The difference between locked and not locked will be smaller. Bob's plan to use the big booster and a big master will make his pedal even firmer - his piston sizes are comparable to a non-Sport car.

Brake lines and the vacuum lines will change between the two, although none of the hard points on the car (firewall mounting, clearance, etc) are affected.

Bias is determined by the proportioning valve and everything downstream. It's not affected by changing the master or booster.

Caliper piston sizes. Note that ABS and non-ABS Sport cars use the same calipers even though the booster is different.
non-Sport, front: 2.01"
Sport, front: 2.125"
non-Sport, rear: 1.25"
Sport, rear: 1.375"

Bob adds:
I’m pretty sure the push rod thing wont work right.
The 323 GTX community has been doing a similar swap for years with a 929 master cylinder. It required using a booster from a later model Protégé I don’t think anybody got one to work with a stock booster. The 929 master has the same push rod interface as the 2001+ miatas.

The piston in the master cylinder sticks deep in the booster on the 2001+ versions while on the earlier ones the push rod of the booster sticks out and into the piston of the master cylinder. The early master will bolt up to a later booster but it wont work right without a longer rod I don’t think the later master will bolt up to a early booster because there is no way to make the push rod short enough.

ZakRabbit adds: I installed the '01 master and booster in my '90. I tried to install just the master, but didn't want to modify the rod in the booster. Using both parts, it's pretty much a bolt-in affair. The lines to have to be re-bent, but they are quite long enough. Like bbundy above says, the later masters' contact point for the booster's rod is about 1" behind the mount point and the matching booster has a correspondingly shorter rod. Another thing to mention is that the 01-02 non sport model with the huge booster has an interference problem with the master cylinder and the '01+ shock tower brace.

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