Mitsubishi 3000 GT User Manual

Brake Upgrade Options for the AWD 3000GT/Stealth

or "If it won't brake, fix it"

by Jeff Lucius

Topics

Introduction
Stock Brakes
Braking Torque
Brake Fluid
Brake Lines
Brake Pads
Brake Bedding
Rotors and Calipers
Synopsis
Acknowledgments

Introduction

Before you go out and spend possibly $2000 to $3000 or more for the "ultimate" stopping power for our
cars, consider first that the stock brakes on all years of Mitsubishi 3000GT VR4 and Dodge Stealth R/T
Twin Turbo are some of the best on production cars for the time period (1991-1999). The stock brakes
are entirely adequate for street use but can benefit from better fluid, stainless-steel braid-protected brake
lines, and Metal-Matrix or carbon-blend brake pads. For track or other performance use, an investment
in a rotor and caliper upgrade should be seriously considered.

In the table below are some performance results for stock brakes on new production 3000GT/Stealth (3S)
cars from popular car magazines. Braking distances from 60 to 0 mph approaching 110 feet are
considered outstanding for street cars. For comparison, Road & Track presents these selected 60-0 mph
stopping distances in their Dec 2000 and Dec 2004 issues (with 10' significant distances): Porsche 911
GT1, 98'; Lotus Elise, 105'; Mitsubishi Lancer Evolution, 108'; Ferrari Enzo, 109'; Ferrari 360 Modena,
110'; Mazda RX-8, 110'; Volvo S40 T5, 110'; Subaru Impreza WRX STi, 111'; Lexus IS 300, 113';
Mercedes-Bens SL500, 113'; Dodge Viper SRT-10, 114'; Audi TT Coupe, 116'; Chevrolet Corvette,
116'; Acura NSX, 117'; Ford GT, 117'; Volkswagon Toureg V8, 117'; Porsche 911 Turbo, 119'; Nissan
Skyline GTR, 120'; BMW M Roadster, 121'; Panoz Esperante, 122'; Saleen S7, 125'; Lamborghini
Diablo VT, 126'; Ameritech McLaren F1, 127'; Chevrolet Camaro SS, 129'.

3S Stock Braking Performance

Magazine Issue Car 60-0 mph 80-0 mph 100-0 mph

Sports Car Int'l 9/90 '91 TT 120 ft 214 ft
Road & Track 9/90 '91 VR4 135 ft 237 ft
Motor Trend 3/91 '91 VR4 117 ft
Sports Car Int'l 12/93 '94 VR4 123 ft 223 ft
Sports Car Int'l 8/95 '95 VR4 123 ft
Road & Track 8/96 '97 VR4 347 ft in 4.5 s
Sports Car Int'l 10/96 '95 Spyder 134 ft
Motor Trend 5/97 '97 VR4 116 ft
Road & Track 1999 spec. '99 VR4 122 ft 218 ft

The Road & Track 9/90 issue also tested for brake fade on their '91 VR4. Cool brakes required 15 lb of
pedal effort to execute a 0.5 g stop. After six of these 0.5 g stops in a row, pedal effort remained at 15 lb;
that is pretty good for street brakes.

The Road & Track 8/96 issue published the results of their 0-100-0 mph competition. The stock '97 VR4
did not do so well overall except that it had the best 100-0 mph stopping time of 4.5 seconds (347 ft). No
car in the competition decelerated faster. The four-wheel ABS system contributes to this success. Other
cars did stop in a shorter distance in this competition: HKS-modified Supra in 326 ft (5.1 s), BMW M3
in 334 ft (4.5 s), and Mercedes-Benz C36 in 340 ft (4.9 s). The Porsche 911 Turbo stopped in 363 ft (4.6
s). Interesting that the Supra had to be modified to be in this competition. I wonder ho w well a modified
VR4 would have done?

The objectives of braking system improvements are to reduce stopping distances (especially from high
speeds), tune the feel of the brakes (subject to the driver's preferences), and improve thermal control
(heat dissipation and temperature sensitivity). Though the tire-to-road interface always limits rapid
deceleration, I don't discuss tires here. Quite often a switch to stickier tires may be the easiest way to
improve your stopping distances. However, if repeated application of the brakes causes fade in the
application that you are using your car, whether it is the street or the track, then thermal control must be
a priority. Some of the information presented here is applicable to any automobile. However, I have
concentrated on improvements for the AWD 3000GT/Stealth braking systems.

The following steps (in order) should be considered when improving your braking system.

1. Improved brake cooling.

2. High-performance brake fluid.

3. Steel braided brake lines.

4. High-performance brake pads.

5. Larger rotors and calipers.

6. Master cylinders.

There are no commercial brake-cooling kits for our cars that I know about. Improved brake cooling for
3S cars generally takes the form of homemade combinations of venting, heating, and roof-drain parts
that direct cool air from the front of the car onto the rotors and calipers. Also, I am not aware of any
aftermarket master cylinders that are available. The master cylinder converts the force generated by the
brake pedal assembly into hydraulic fluid pressure. The stock master cylinder seems to provide a good
balance between fluid capacity (sufficient for our ABS system) and hydraulic pressure (1.133 times
pedal force). So I will concentrate on items 2 through 5 above. But first, I'll summarize the stock setup
and present the concept of braking torque.

Stock Brakes

The front brakes for all years of the AWD models use ventilated, iron-disc rotors with 4-piston, rigid,
iron calipers. The outside dimensions of the calipers changed in 1994 because of the larger rotors but the
internal parts (such as the pistons) and the brake pads did not change. The rear brakes for AWD models
up to 1993 use ventilated, iron-disc rotors with single-piston, floating, iron calipers. Starting with the
1994 model year, the AWD cars have rear brakes with twin-piston, rigid calipers. The drum-type
parking/emergency brakes are incorporated into the hat of the rear rotors. The master cylinder is the

2

same for all model years, with a 26.9 mm (1.06") inside diameter, as is the vacuum-type brake booster,
with an approximate 7:1 boosting ratio of the brake pedal force. Mitsubishi recommends DOT3 or
DOT4 brake fluid for all years. Though not directly related to the brakes, the following wheel
information may be relevant when upgrading. All wheels (all sizes, all years) on all models (FWD or
AWD) have a 46 mm (1.81") offset with 5 lugs in a 114.3 mm (4.5") pitch circle diameter. The relevant
"performance" dimensions of the stock brake systems are summarized in the table below. Note that rotor
sizes are the actual outside diameters. The service manual specifications are "effective diameters", which
is likely near the middle of the brake pad.

Stock Dimensions

Front Rear

AWD year

1991-1993

1994+

Rotor

O.D. mm (in)

295 (11.62) 30 (1.18)

314 (12.36) 30 (1.18)

Rotor

Thickness mm (in)

Cylinder

ID mm

40.4 x 2

+ 42.8 x 2

40.4 x 2

+ 42.8 x 2

Rotor

O.D. mm (in)

284 (11.19) 20 (0.79) 38.1 x 1

295 (11.62) 20 (0.79) 38.1 x 2

Rotor

Thickness mm (in)

Cylinder

ID mm

The 3000GT VR4 and Stealth TT utilize a 4-wheel, 2-channel ABS braking system, as shown in the
illustration below. The master cylinder contains two pistons which effectively divide the brake lines into
two separate hydraulic systems. One system is the left-front and right-rear brakes, and the other is the
right-front, left-rear brakes. This is done for safety in case a leak develops in one of these systems.
These two hydraulic lines go from the master cylinder to the ABS hydraulic unit (HU). The HU controls
the four output brake lines as two channels. One channel for each side of the car. However, because of
the use of select-low valves between the two rear wheels and between two wheels on one channel (same
side of car), a total of 3 wheels are controlled hydraulically at the same time. In order to prevent lock-up
of the rear brakes during heavy braking, a proportioning valve is used on the two brake lines going from
the HU to the rear brakes. For the hatchback AWD models, the output pressure will be the same as the
input pressure until there is 533 to 604 psi pressure in the rear brake lines (called the split point). At
pressures greater than this, the output pressure to the rear brakes will drop 34 to 42 percent. For the
convertible AWD models, the split point is higher at 704 to 775 psi and the pressure drop is lower, 25 to
34 percent. The preceding is for North American and European models. The proportioning valve for
vehicles bound for Australia was yet a third model. It had a split point in the range of 391 to 462 psi and
a pressure drop of about 25 percent.

3

Braking Torque

Torque is a force acting to rotate a body about an axis. Torque can be directed to increase or decrease
rotation. Torque is the magnitude of the force times the perpendicular distance between the line of action
of the force and the axis. Braking torque (TB) then is the force applied by the caliper to the rotor (FB

)

C

times the effective radial distance the brake pads are from the center of the wheel (RE). The force
applied by the caliper is determined from the pressure in the hydraulic lines (PH) times the total piston
area in one half of the caliper (AP) times the brake pad coefficient of friction against the rotor (µ) times 2
(there are pads on both sides of the rotors). The complete expression is below.

TB = FB

x RE = [PH x AP x µ x 2] x RE

C

The pressure in the hydraulic lines (PH) is determined from the pressure exerted by the driver on the
brake pedal, the length of the brake pedal "arm", the brake booster, the size of the brake master cylinder,
and the condition of the brake fluid.

Please note that ultimately it is the friction of the tire acting against the road surface tha t actually stops
the car. If there is little friction, such as "balled" tires on ice, the car will not stop well regardless of
brake torque. On the other hand, if tire-road friction is good a car can come to a stop (eventually) with
no application of the brakes (let's imagine the drivetrain and its "drag" have been removed, as well as
aerodynamic drag).

The upgrades and maintenance discussed here are designed to optimize braking torque. Keeping the
brake fluid free of water and from excessive heating maximizes transfer of pressure from the master
cylinder to the calipers. Stainless-steel braid-protected brake lines reduce pressure transfer time from the
hard lines through the soft lines to the calipers. Good brake pads provide the optimum friction
coefficient, which is heat dependent, as well as assist in heat dissipation/absorption management. Rotors
can increase brake torque if they have a larger effective diameter, and can assist in heat dissipation.
Finally, better calipers provide optimal management of heat transfer to the brake fluid, and of force
multiplication using piston area, reduced pad vibration, reduced mounting flex, and optimized offset
loads.

4

Before proceeding, let's look at how the braking torque is biased in the factory system. For all AWD
models, both front brakes have a total of 5441 mm2 of piston area and both rear brakes have a total of
2280 mm2 of piston area. When pressure is the same in all hydraulic lines, that is, when the ABS is not
activated and pressures are below the split point in the proportioning valve, there is a front bias of
5441/2280 or 2.38:1, or equivalently, the rear brakes pads get about 42% less pressure than the front
pads. The difference in effective diameter of the rotors further increases the front bias to an overall bias
F/R of 2.5:1 for 1991-1993 AWD models and 2.58:1 for 1994 and later AWD models. When braking
hard enough to exceed the split point pressure in the proportioning valve, overall front bias will increase
to about 3.85:1 for hatchback models and to about 3.38:1 for convertible models. For track use, there
may be some advantage in swicthing to the convertible's proportioning valve (higher split point), or if a
person could find one, the proportioning valve used in vehicles exported to Australia (lower split point).
For example, if the front brake bias has been increased through the use of larger rotors and same-as­stock or greater piston area, then an increase of rear bias (about 12% or so) to balance this could be
achieved under hard braking by using the convertible's or Australian proportioning valve on the
hatchback.

Brake Fluid

The Haynes Automotive Reference Manual defines brake fluid as "A compounded liquid for use in
hydraulic brake systems, which must meet exacting conditions (impervious to heat, freezing, thickening,
bubbling, etc.)." Well, being impervious to heat is certainly the goal! The car's brakes convert the kinetic
energy of the car into thermal energy, or more simply, they heat up as they slow the car down. The heat
(energy) generated by the brake pads and rotors heats up the brake fluid in the calipers. If the fluid heats
up enough, it will boil creating vapor in the system. Vapor in the hydraulic system (whether it is from
brake fluid, water dissolved in the fluid, or air) is bad because it is compressible, reducing braking
efficiency, possibly to the point of loosing the brakes entirely. This is called brake fluid fade.

WARNING. Brake fluid is poison. Keep it away from skin and eyes. Do not

allow brake fluid to contact painted surfaces.

The DOT brake fluid classifications (
guidelines for manufacturers as to how impervious their fluid is to heat. The dry boiling point (when the
fluid is fresh and contains no water) is the temperature at which the fluid turns to vapor. The wet boiling
point (measured when the brake fluid contains 3.7% water) is related to how easily the brake fluid will
absorb water (or how hydroscopic the fluid is). The lower the wet boiling point, the more water the fluid
will absorb. Absorbing water is bad, so a higher wet boiling temperature means better brake fluid. And,
of course, a higher dry boiling point is good too.

The table below summarizes the DOT guidelines plus the relative advantages and disadvantages of each
fluid type. The actual performance may exceed the DOT guidelines and should be printed on the
container. For example, Pyroil Premium DOT 3 Brake Fluid states a minimum wet boiling point of
291ºF. DOT 3 and DOT 4 are polyglycol-based fluids and can be mixed with each other. DOT 5.1 can
also be mixed with DOT 3 and DOT 4, even though it is based on a different chemical and has about
half the viscosity. If DOT 5.1 is specified for an ABS system, do not add or use any other fluid type.
DOT 5 is silicone-based (not less than 70% by weight of a diorgano polysiloxane) and must not be
mixed with or contaminated by DOT 3, DOT 4, or DOT5.1.

49CFR571.116) include a set of minimum specifications that are

5

Standard Brake Fluids

DOT 3 DOT 4 DOT 5 DOT 5.1
Dry BP ºF (ºC)
Wet BP ºF (ºC)
Kin. Viscosity

mm2/second
Advantages

Disadvantages

401 (205) 446 (230) 500 (260) 500 (260)
284 (140) 311 (155) 356 (180) 356 (180)

1500 max @ -40ºF

1.5 min @ 212ºF

- Inexpensive

- Readily available

- Attacks paint!

- Most hydroscopic

1800 max @ -40ºF

1.5 min @ 212ºF

- Available at auto parts stores

- Less hydroscopic than DOT3

- Attacks paint!

- More expensive than DOT3

900 max @ -40ºF

1.5 min @ 212ºF

- Does not attack paint

- Does not absorb water

- DOES NOT mix with DOT3, DOT4, DOT5.1

- Water may "puddle" in the system

- Careful bleeding required

- Slightly compressible near its boiling pt.

- Very expensive, hard to find

900 max @ -40ºF

1.5 min @ 212ºF

- Superior performance

- Attacks paint!

- Expensive, hard to find

Probably the best thing you can do to maximize the performance of your brake fluid (any type) is to
change it regularly (at least once a year) to minimize the amount of water in the system. According to
the Car Care Council and SAE field tests, brake fluid can become contaminated by water (2% on
average) within 1 to 2 years, and in substantially less time in humid climates. Brake fluid (other than
DOT 5) readily absorbs water from the air in the master cylinder. This cannot be prevented and
changing (flushing) the brake fluid is the only solution. Alternating the use of different-colored fluids
can aid in knowing when the flushing process is complete. The dry boiling point of DOT 4 is higher than
the wet boiling point of the best brake fluid (Castrol SRF excepted). Speed Bleeder Products makes a
replacement bleeder screw for the brake calipers that allows one-person bleeding. Speed Bleeders cost
$7.00 each; you'll need 4 plus one for the clutch release cylinder if desired. For the Stealth and 3000GT
turbo models, use Speed Bleeder model SB1010 for front calipers and rear calipers, except use SB7100
for rear calipers on cars with 3/92-5/93 production dates. SB1010 also works for the clutch release
cylinder.

While our brake system will perform as designed using standard DOT 4, you may want to consider one
of the popular high-performance brake fluids, especially for racing situations. Some of these are Ate's
(Alfred Teves Engineering's) Super Blue Racing and "Super Gold" (same fluid but different color; also
called Ate Typ 200), Motul's 5.1 and Racing 600, AP Racing's 550 and Ultra 5.1, and NEO's "Super
DOT".

Raceshopper.com sells Ate Typ 200 (or Super Blue Racing) for $9.95/liter, and other brake fluids at

some of the best prices you will find. Motul Racing 600 can be purchased at
Other retailers sell AP Ultra 5.1 for about $20/liter and AP 550 for about $28/liter.

Porterfield for $18/liter.

Brake Man sells their

racing brake fluid for about $25/liter. NEO "Super DOT" 610 sells for about $12 per 12-oz can ($34/liter)
and has the highest wet and dry boiling points. Castrol SRF has very high boiling points as well, but at
about $65/liter (raceshopper.com) seems to me to be a bit expensive; but not nearly as expensive as

GS610 which sells for ~$84/liter! Ford Heavy Duty brake fluid is cheap ($6/liter) and has a very-high

dry boiling point, making it a favorite for the weekend racer that changes brake fluid frequently.
However, the DOT 3-rated wet boiling point makes Ford Heavy Duty less than desirable for street usage.
Do not mix any of these fluids, some of which are DOT 4 and others are DOT 5.1, with DOT 5 silicone­based systems.

6

Dry BP ºF

(ºC)

Wet BP ºF

(ºC)

Price

per liter

Motul

Ultra

5.1

509

(265)

365

(185)

$12-14

High-Performance Brake Fluids

AP

Ate

Ford

AP

Ultra

(270)

(191)

~$14-

Typ

200

536

392

HD

550

(288)

290

(143)

5.1

518

(280)

375

(200)

$10-15 ~$6 ~$28 $25 ~$30 $34 ~$18-21 ~$36-40 $65-75 ~$30 ~$34 ~84

20

550

563

(295)

293

(145)

Brake

Man

577

(303)

300

(149)

Earl's

Hypertemp

421

585

(307)

421

(216)

NEO

585

(307)

421

(216)

Motul

Racing

600

585

(307)

421

(216)

AP

Super

600

590

(310)

410

(210)

Castrol

SRF

590

(310)

518

(270)

Motul

RBF

600

593

(311)

420

(216)

Ate Super Blue or Typ 200

Store Price/liter

raceshopper.com
Strictly German
DaliRacing
SP Motorsports
Spec Miata Superstore
Cobalt Friction Technologies
Mach V Motorsports

$9.95
$9.95
$10.00
$10.85
$10.95
$11.99
$14.00

NEO

Super

DOT 610

610

(321)

421

(216)

GS610

610

(321)

421

(216)

Ate Super Blue and Type 200 - the best deal in
performance brake fluid for the street at $9.95/liter.

Brake Lines

The brake fluid is contained in rigid steel tubing from the master cylinder to about 1 foot from the
calipers. To allow for movement in the suspension, a flexible rubber-coated nylon hose connects the
steel tubing to the calipers. These eight short hoses (two per wheel for the 3000GT/Stealth) can expand a
small amount as pressure increases in the system. The expansion of these hoses increases the hydraulic
volume of the brake system and causes a small delay in actuating the calipers. As the hoses age, their
expandability can increase. To reduce this delay and improve "pedal feel" (increased firmness and
reduced pressure), the rubber hoses can be replaced with nylon hoses covered by stainless steel braiding.
SMC (using lines and fittings from Goodridge) supplies a steel braided brake line kit (part number
46200-M3000) for our cars ('90-'95). The SMC kit costs from $200 to $250.

MVP Motorsports has

advertised this kit for as low as $188. Pictures of the SMC lines mounted on my car can be seen at 2-

brakelines.htm. New stainless-steel braid-protected brake lines are supplied with many of the

combination rotor and caliper upgrade kits mentioned later in the web page.

Brake Pads

As mentioned above, the brakes convert the cars kinetic energy (its forward or reverse movement) into
thermal energy (heat) in order to assist in stopping the car. Notice I said assist; this is because it is the
friction of the tire acting against the road surface that actually stops the car! The brake pads are pressed
against the rotor by the pistons in the calipers. The amount of force actually exerted on the rotor is

7