Detailed gear ratio specifications for the 3000GT and Stealth transmissions, tabulated for easy reference. These specs mostly come from published Mitsubishi or Dodge factory service manuals, but some pieces were filled in from counting the teeth on gears from the physical trans. This covers all AWD and all FWD transaxles in the US Domestic Market (USDM) and the notably different models in the Japanese Domestic Market (JDM).

Key: MT = Manual Transmission, AT = Automatic Transmission, Z11A = FWD chassis, Z16A = AWD chassis w/ 4WS, Z15A = AWD Chassis w/o 4WS

USDM AWD Models:

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Virtually every modification I have made to a car has been in the name of increased performance, whether improving power, handling, or braking. A few months ago, in light of ever increasing gas prices, I decided to try something that would help my fuel economy. My 1994 Protege LX, like so many other economy cars, has a very short fifth gear. So short that the engine runs at 3,500rpm when driving at 70mph. If fifth gear were taller and the engine ran slower, the highway milage could be improved significantly.

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First of all, yes, there is a different technique for driving on the street with racing brake pads. General braking technique doesn’t change, for the most part. But, there are a few things that you should do, and a few things you should not to, to help keep your racing brake pads happy.

Why Does it Matter? - Different Operating Temperatures for Racing Brake Pads
The whole reason why there is an issue with driving on the street with racing brake pads is because race pads are designed to operate in a much hotter temperature range than normal street tires. In regular street driving (e.g., when your mother drives to the store), braking is mild and spaced far apart. That means that there is very little heat generated each time she stops, and enough time in between stops that the brakes can cool down sufficiently. Thus, street pads are designed to operate in a much cooler temperature range, since the pads are never heated up on the street.

Now think of what your braking looks like on the track: 1) full acceleration until the last possible second, 2) full braking, 3) full acceleration until the last possible second, 4) full braking. Repeat for 20 minutes. Needless to say, braking so hard so often generates a LOT of heat - so much, in fact, that if you use street pads, you will overheat them and then you’ll have no brakes. That would be bad. So, instead you want to use a compound designed to work in a much hotter temperature range, something like Hawk Blues or Carbotech XP8 or AX6 pads. Read the rest of this entry »

Last week Chris’s protege sacrificed itself for our purposes. The B6 (SOHC 1.8, 102hp for those who do not know) in my Protege is probably a little tired after 248,000 miles, a bunch of track days, and only 2 oil changes in the last 103,000 miles. The BP (DOHC 1.8L, 125hp) in Chris’s Protege is in it’s infancy, relatively: 148,000 miles. The engine/transaxle assembly is an easy direct swap, so I pulled the it out of Chris’s car. Here’s what it looked like to begin with:

The left front had been damaged in an accident, so there was a lot of cutting, hacking, and other violence required just to get the radiator and some other normally easy stuff out. But soon enough the engine was out of the car…

…and then Chris went to work taking other stuff:

The best part about pulling engines out of cars you don’t care about is the recklessness with which you can work. A/C, power steering line, or other part in the way? Hack it in half, dump the fluid all over the place, and move on. A bolt won’t come out? Just cut parts around it until it doesn’t matter, like I had to do with the shifter rod. Need to relieve fuel pressure? Cut the lines with a knife. Gas goes all over the place and pressure is relieved.

The Protege engine is very easy to pull. Someone with moderate mechanical skill can have it out in just a few hours. If, like me, you’re swapping (or planning on swapping) the DOHC BP into an SOHC Protege, make sure you also take the driveshafts, ECU, wiring harness, and ignition coil from your donor car. All those are unique to the DOHC model.

Check out the picture gallery of the engine pull. A bit later, we also tipped the car on its side in Chris’s driveway. You may be amused.

From the last article on this subject, we know that a planetary differential is capable of distributing torque unequally to its outputs based on its design. We discovered that torque split is constant for any rate of speed and irrespective of which output rotates faster, neglecting the viscous coupling (VCU) action– but what sets this ratio? Can it be changed? How can we easily determine the design torque split of a planetary differential?

Despite how complicated it looks, the ratio of a planetary differential is simple to find. When the ring gear is the input, as with the 3000GT/Stealth AWD center differential, the ratio of the sun gear to the ring gear gives us the proportion of input torque supplied to the sun gear output. In other words if we have a ring gear with 100 teeth, a sun gear with 40 teeth and the ring gear is the input, the sun gear receives 40/100 or 40% of the input torque. If 10ft-lbs is the input torque, 4ft-lbs is applied to the output (neglecting friction).

And the torque supplied to the planet carrier? That’s the remaining 60% in this example, or 6ft-lbs.

Let’s look at a model of the actual 3/S center differential. If the stock sun gear is 27 teeth and the ring gear is 60 teeth, we find a ratio of 27/60 to the sun gear (front output), or 45% of the available torque. The remaining 55% goes through the planet carrier to the center output shaft and to the rear wheels.

What if we wanted to change this ratio? Someone with the knowledge and resources to cut his own gears could modify the factory center differential with a new sun gear and a redesigned planet carrier (the original planet gears could be reused). Such a modified differential could achieve significant changes in torque split just by adding or subtracting three teeth from the sun gear:

And so a rear-biased 60:40 ratio is hardly out of reach. For someone going to the effort of fabricating a new sun gear and modified planet carrier, more radical torque splits are a minor design change away. Getting a radical 65% of drive torque to the rear wheels could be done with a 21-tooth sun gear!

What about the planet gears? Believe it or not, the planet gears have no effect on the torque split of the differential — none. The factory center differential has 13-tooth planet gears, but the following differentials have the same torque split ratio:

In fact, the outer planet gears can even be different sizes than the inside planet gears without having any effect on torque split. Remember: the ratio of the ring gear to the sun gear alone determines torque split.

So why not make the planet gears as small as possible to shrink the differential down? Besides approaching a practical limit to how few teeth a gear can have and still make good contact with another gear, the simplest answer is strength. Because drive torque is still transmitted through the planet gears, they need to be large enough to carry the load.

That’s the long and short of it. Anybody want to machine some gears?

Replacing the rear wheel bearing on a first generation Mazda Protege is a very easy job. No pressing–no special tools of any kind, really–are required. Unlike the front wheel bearings, which require a press or a lot of hammering to replace, the rear wheel bearing comes as part of a bearing/hub assembly (Beck-Arnley # 051-6018).

To replace the hub/bearing assembly, remove the wheel, brake caliper, and brake rotor. The caliper is held in place with 2 14mm bolts.

• With the caliper and rotor out of the way, access the retaining nut by removing the retaining nut cover. Use a screwdriver or (better) a small chisel and gently hammer at the lip of the cap, as shown here.
• Remove the cap.
• Using a 36mm socket, remove the retaining nut. You may also use a 1 3/8 socket. If you don’t have a socket of this size, your local Sears, hardware store, or tool shop will likely have a shelf of impact sockets that run this large. The axle nuts for many cars are this size, so a 1 3/8 or 36mm socket is a good thing to have.
• Grasp the hub/bearing assembly and pull it off. It is not a press fit and should slide off the post very easily.

It’s a simple as that. Slide the new hub/bearing assembly onto the post. Reinstall the nut, then reinstall the rotor and caliper. All told, you should be able to do the job in about 30 minutes.

Last year in my more than you ever wanted to know about AWD systems article, I described the function of several types of passive all-wheel-drive arrangements. One of the most popular passive center differentials is the planetary differential. A planetary differential offers some advantages over the traditional bevel-gear differential, which is often used as the front or rear differential of a FWD, RWD, or AWD car — although some cars such as the DSM or manual transmission WRX use a bevel gear center diff.

Unlike a bevel gear differential which necessitates an equal torque split on both outputs, a planetary differential can be designed for completely symmetric through radically asymmetric output according to what the application requires. The 3000GT and Stealth AWD system has such a planetary differential, and I have an animation to help visualize it:

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Recently I put Carbotech pads on my Protege for a quick-and-dirty track outing. I chose the AX6 compound up front and Bobcat for the rear, the former (previously called Panther Plus) having performed flawlessly on my Stealth at the track while retaining good street characteristics. In the process of changing pads I replaced a seized caliper and all four rotors. No sooner had I bedded the new pads in and started driving to work did I notice my brake pedal would occasionally go to the floor. After a little cautious driving and a refill of the half-empty brake reservoir, I determined that the new rear caliper was leaking A LOT from the piston seal. Score one for rebuilt calipers from Autozone! There was brake fluid EVERYWHERE. Having the caliper replaced under warranty was a no-brainer, but how does one salvage pads that are saturated in DOT 4 brake fluid?

The answer should have been obvious, but knowing how particular they are about bedding procedures I called Carbotech to be sure. Janine took my call and was so gracious as to take my number, call the tech who had just left, Chris, on his cell phone, and call me back with the answer within a couple minutes:

Apparently it is perfectly acceptable to clean brake fluid off an oil-soaked pad surface with — would you have guessed it — brake parts cleaner. Over a pint of brake fluid on my disc, caliper, pads, and wheel well was visually intimidating; those parts just aren’t supposed to be lubricated. For that reason I fully expected to hear “oh, you’ll have to replace those pads”. Guess not.

Mazda did a really poor job of anticipating and preventing corrosion in their early-90s cars. One of the ways this lack of foresight manifests itself is in the brakes – namely the mechanical rear disc emergency brake or parking brake of the Miata and Protege. The Miata/Protege emergency brake is built into the rear calipers and is actuated by lever which is pulled by the “ebrake” cable. Over time the lever on the brake caliper will tend to stick despite a strong spring that is supposed to return it to an unlocked position. If it sticks badly enough the only solution is to buy a new caliper, but less than $5 and a little creativity can fix this problem if you catch it early-on.
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I’ve owned a lot of cars at this point in my life. No fewer than ten vehicles have come into my ownership in the past decade, most of which were beaters, and all of which had between 75k and 175k miles on them. Fully 30% of the vehicles I have owned have been Mazda Proteges of between 130k and 170k. Every one of those Proteges has had some kind of unacceptable corrosion above and beyond the norm for a New England vehicle of similar age and mileage. Some examples would include:

• rusted, leaking gas tank
• excessive underbody rust/rot
• structrual unibody rust with holes — rear strut towers, trunk
• completely unremovable rear suspension components
• rusted, seized brake components — bleeder screws*

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