Many do not understand that being able to slow down, quickly, consistently, and repeatedly, is just as important
to turning fast lap times, as a powerful engine and a good handling suspension. The more quickly and more dependably
that the driver can rapidly reduce speed, then the driver can take straight track sections faster, hold that speed
longer, brake later, haul the speed down more rapidly to a controllable level to execute a turn, and then move on
to the next straight. Picking up a second, or even a fraction of a second, on every corner, quickly adds up to big
reduction in lap times.
By 1990’s standards, the factory original brakes on the Geo Storm were above average. In all of the comparison
tests, the Storm rated in the top of the crowd. And the Isuzu sister cars, with their rear wheel disk brakes,
where pretty much the benchmark for stopping ability. But in the following decades, cars got heavier, wheel
fashion called for larger rims (and larger brakes to fill those rims), roads became more congested with traffic,
and people began to expect more out of the braking systems of their cars. By comparison to the current lineup
of cars in showrooms today, the original Storm brakes are rather small and underpowered. If kept in good working
order, they are certainly more than adequate for driving on the street, but for road racing, autocross, or
spirited driving on the streets, upgrading the brakes provides huge benefits and very noticeable improvement in
Something to further consider is that the Geo Storm brakes were designed around 1987, to stop a 2,400 pound car,
riding on mid-1980’s vintage Bridgestone Potenza RE-92 tires, likely in 185 or 195 tread width. Tire technology
has come a long way in 25+ years, and chances are that no one is still driving around on those hard, slippery,
original tires. Today’s extreme-summer-performance category tires are just short of R compound race tires in
grip and traction. Bolt a set of sticky tires onto a Geo Storm, accelerate to 60 or so miles per hour, and one
will quickly find out that the friction of the tire against the road is more powerful than the friction of the
stock brake pad against the stock brake rotor. The front brakes will probably not lock up. Now consider hauling
down the front straight at your local race track doing 130+ MPH, and stomping on the binders to make that
widow-maker left hander at Turn One. Sort of brings a new meaning to the phrase “pucker factor”.
Upgrade Brake Pads and Shoes
The original Geo Storm brake pads are designed for all purpose use with primary consideration by the car
manufacturer for dust, pad wear, rotor wear, noise, and cost.
Performance brake pads, with more effective and more expensive friction compounds, are available in a plentiful
selection for the front brakes, thanks to the fact that the pad is shared with early Mazda Miata. A pad with a
higher initial bite would be suited for autocross use, while a pad with a higher heat range would be suited for
road course use.
Performance brake shoes for the rear drum brakes are a bit more difficult to find, but companies such as Carbotech
can custom reline any shoe (or pad) with modern, high performance friction material.
Another aspect of brake pads is that choice of different front and rear pad compounds can be used to adjust brake
biasing (tendency of either the front or rear brakes to lock up before the brakes on the opposite end of the car).
This is discussed further in the section on Brake Proportioning Valves below.
Stainless Steel Brake Lines / Hoses
The original Geo Storm brake hoses, between the brake pipes and calipers/wheel cylinders, are made of rubber.
Every time the brake pedal is pressed, rubber brake hoses flex under the pressure of the brake fluid. Old hoses
flex quite a bit, and after 20+ years, count on quite a bit of flexing. This flexing reduces the amount of
pressure that gets to the brake caliper piston and pad, and causes the brake pedal to feel spongy. More
importantly, the flexing delays the brake engagement and disengagement, and makes brake control sloppy. Stainless
steel wound brake hoses eliminate the flex, sponginess, and sloppiness.
Unfortunately, there are a lot of really poor quality hoses on the market, requiring a higher level of care when
shopping. Look for DOT approved hoses, because DOT has higher standards than the German TUV. Look for hoses
with a plastic wrap hose over the outside of the stainless steel, in order to keep out grit and grime that can
damage the woven layer. Look for hoses with an insert between the crimped ends and the hose, because this
insert keeps the crimped end from cutting the hose when it moves. Look for hoses with OEM type ends and line
locators, to make sure that the new hoses fit and work as well as the originals.
Goodridge and H.E.L. brands are noted for being pretty poor quality and fit. Goodridge does not match the OEM
ends and line locators. H.E.L. does not use inserts to protect the hose from the crimped ends, and H.E.L. does
not provide line locators at all, allowing the hoses to hang loose beneath the car.
Isuzuperformance has been stocking BrakeQuip brand stainless hoses, which are exact reproductions of the original
hoses for Geo Storm and nearly every Isuzu car model made, for many years.
The original brake fluid used in the Geo Storm is DOT 3. Chances are, if you don’t remember changing the brake
fluid in your car, it is probably 20+ years old, and badly in need of being replaced. Regular brake fluid absorbs
water out of the air, becomes contaminated over time, and turns to sludge. Bleeding the old fluid out of the
system and replacing it with new DOT 3 will do a lot to restore braking performance to the car.
Upgrading to a better brake fluid can provide more resistance to boiling (heat) and moisture contamination.
DOT 4 brake fluid is an easy and inexpensive and readily available upgrade, providing higher heat resistance and
a higher boiling point. (This is sometimes labeled “Dot 3 / 4” to indicate that it can be mixed with either DOT
3 or DOT 4 that may already be in the braking system). The big advantage of DOT 4 is that it is available at most
auto parts stores.
DOT 5, 6, and synthetic brake fluids offer even more temperature and moisture resistance, and can be a necessity
for road course and circuit racing. However, these are more difficult to find, and may be available in some areas
only by mail order. This may become a big issue when the inevitable night-before-the-race-brake-fluid-leak
erupts, immediately becoming an emergency when you realize that you do not have enough of the expensive and hard
to find brake fluid on hand to refill the brake system.
Converting Base to GSi Front Brakes
The Geo Storm Base/SOHC model was originally equipped with 9.06 inch diameter front brake rotors. The GSi model
was originally equipped with 9.8 inch diameter front rotors. The rotor diameter difference makes a noticeable
difference in stopping distance. Upgrading from the Base front brakes to the GSi front brakes is reasonably
easy, requiring only the rotor and caliper. The same pads, hoses, and brake master cylinder are shared between
the two, and if the originals are usable, they will not need to be replaced.
The spindles, front bearings, hubs, and axles of the GSi model are heavier duty, and it may be desirable to upgrade
these all as a unit, with the brake rotors and calipers.
One word of caution concerning used brake calipers: 20 year old brake calipers off of a junk yard car that has
150,000-250,000 miles on the odometer, are probably not going to function like new brake calipers. This may
require rebuilding the used calipers, or purchasing rebuilt/remanufactured calipers, which usually do not include
the mounting bracket. An inexpensive brake upgrade, using salvage yard parts, can become very expensive, very
quickly, after the used calipers are repaired so that they will work.
Impulse / Stylus DOHC Rear Disc Brakes
The Isuzu Impulse, Stylus XS and RS, and Asuna Sunfire, were all originally equipped with rear disk brakes.
The rear brakes from these sister cars will bolt directly onto the Geo Storm, and make for an easy upgrade to
improve stopping ability.
This will require the rotors, calipers, caliper brackets and dust shield assemblies, brake hoses, and emergency
brake cables. In that this is a little more involved, it may be advisable to obtain a Impulse or Stylus factory
shop manual for full disassembly and reassembly instructions.
Be aware that these vehicles are becoming less common in salvage yards, and finding the needed parts to do this
upgrade is becoming more and more difficult. And several of these parts have been discontinued by Isuzu, so new
parts are no longer available.
One word of caution concerning used brake calipers: 20 year old brake calipers off of a junk yard car that has
150,000-250,000 miles on the odometer, are probably not going to function like new brake calipers. This may
require rebuilding or purchasing rebuilt/remanufactured calipers, which usually do not include the mounting bracket.
An inexpensive brake upgrade, using salvage yard parts, can become very expensive, very quickly, after the used
calipers are repaired so that they will work.
And one additional word about combination brake calipers with the emergency brake built in: These calipers are
not easy to rebuild or service. They can be a serious source of annoyance.
Multi-Piston Brake Calipers
The front brake calipers on the Geo Storm and Isuzu sister cars, (and rear brake calipers on the Impulse and
Stylus sister cars), are single piston, floating calipers. They have one piston per caliper, pressing against
the back side of the rotor, with a floating bracket assembly that squeezes against the opposing side, or outside
face of the rotor. These are the most common brake calipers on automobiles, because they are inexpensive to
make. More modern performance model and high trim level cars usually have multi-piston, fixed type calipers.
This type of brake caliper is bolted rigidly in place and pistons facing the inside and outside of the rotor,
in order to squeeze against the rotor from both sides. These calipers are less common because they are more
expensive. But fixed calipers also provide better braking, which is why the higher performance cars are equipped
Single piston, floating calipers do not work smoothly or well. They depend on slide pins to move, and those pins
usually stick or do not move freely. Most people using them will notice that the inside surface of a vented
rotor will wear more quickly, becoming noticeably thinner than the outside. This is because the inside engages
with more force, and usually sticks in place, dragging even while the driver is not using the brakes.
Multi-piston calipers provide more even braking, because the pistons press evenly on both sides, and release
evenly on both sides. The braking action is more accurate, with the force spread more evenly on the pads. The
pads are usually larger providing more surface area for the brake pad against the rotor, and providing more
braking ability. Even on the stock GSi front rotors and Impulse/Stylus rear rotors, multi-piston calipers make
a huge difference in stopping ability.
There are several drawbacks, including requiring different brake hoses, custom mounting brackets, and that
multi-piston brackets are usually larger, and may cause clearance problems with the rear face of the wheel.
Also, multi-piston calipers are not available as a combination caliper, with a built in emergency brake. So
installing multi-piston calipers on the back means either adding a dedicated parking brake caliper (such as
Brembo or Wilwood) or eliminating the emergency brake (acceptable for road racing, prohibited in Street
Prepared autocross class).
But considering the cost of purchasing used calipers, and then rebuilding them so that they work properly, the
cost and added performance level make them worthy of serious consideration.
Big Brake Kits
Larger brake rotors and larger brake calipers are a straightforward way to improve braking. Larger rotors and
brake pads provide more area for friction between the two. A larger diameter rotor moves the point of friction
farther from the axis of rotation, which gives the caliper more leverage to apply braking force on the rotor.
The larger rotor also provides more volume to absorb the heat produced by the friction of the pad rubbing
against the rotor.
A well designed and built big brake system will dramatically improve braking ability, but a poorly planned and
thought out brake system can result in little or no improvement, and waste a lot of time and money.
- Brake Calipers
Single piston brake calipers are not adequate for a big brake system. Larger size floating calipers are going
to do just as poor a job as the original floating calipers. Single piston, floating calipers do not work
smoothly or well. They depend on slide pins to move, and those pins usually stick or do not move freely. Most
people using them will notice that the inside surface of a vented rotor will wear more quickly, becoming
noticeably thinner than the outside. This is because the inside engages with more force, and usually sticks in
place, dragging even while the driver is not using the brakes.
Used single piston calipers, are a waste of time and money, as they will need to be overhauled and rebuilt to
bring them up to even their like-new, inadequate level of performance.
New, multi-piston, aftermarket calipers provide better braking, even braking pressure to both sides of the
rotor, smoother operation, and the added value that there is no need to service or rebuild them because they
are new. Taking into consideration the cost of obtaining used calipers and rebuilding them to return them to
usable condition, new, multi-piston, aftermarket calipers provide significant savings.
Matching the caliper’s hydraulic size (piston volume) to the original brake caliper, is important, if the
original master cylinder is to be used. The original brake master cylinder is more than adequate to operate
a big brake system, but caliper selection requires research, math, and careful consideration.
- Brake Rotors
Brake rotor selection can be a challenge. Larger diameter one piece rotors, that fit, are not available. So
multi-piece rotors, with a cast iron rotor bolted to an aluminum top-hat style center, is required.
Rotor diameter is a serious issue. 12.4 inch diameter rotor discs are the most widely available, and the least
expensive. But these large diameter rotors require the use of a 17 inch diameter wheel, and this size rotor,
with the brake caliper, will not fit within a 15 inch wheel. The racing tire size for a Geo Storm is 205-50R15.
Racing tires simply are not available in 205-40R17, and 205-45R16 are so uncommon as to be irrelevant to the
decision. To fit behind a 15 inch wheel, the rotor diameter limit is a little bigger than 11 inches.
Rotor thickness is the other serious issue. Thicker rotors would be desirable, because the additional metal
would provide more volume for heat absorption. But the offset between the outside face of the brake rotor,
and the mounting surface of the wheel, is very shallow. There is no space for additional brake rotor thickness,
and barely enough space for a larger brake caliper between the factory thickness rotor and the back of the
wheel. In fact, the factory 15 inch wheels will not fit over larger brake calipers on the front of the car.
The diameter and thickness limitations of the rotor decrease the selection of available sizes, to those that
are less common, less readily available, and more expensive.
The connection between the rotor and the center top hat will determine durability and streetability. In this
case, floating is better. The cast iron rotor and the aluminum top hat center will expand and contract at
different rates when exposed to heating and cooling. A fixed connection, with round holes and bolts, will be
problematic. The expansion and contraction of the metal will loosen the bolts. A fixed rotor assembly is
considered acceptable only for track use, where the car sees service before and after each race event and in
between race heats, so that the rotors can be retightened. A floating connection has slotted mounting holes
and special hardware to allow the rotor and center top hat to expand and contract independently. The special
hardware keeps the nuts and bolts from loosening themselves. A floating rotor assembly is considered
necessary for street use.
- Brackets, Hats, and Hardware
Any discussion of big brake upgrades and/or kits should also consider the smaller and less visible parts and
pieces that hold the larger, more recognizable pieces, to the car. The caliper mounting brackets and center
top hats for the rotors are arguably the most important parts of a big brake kit. These are the most difficult
to obtain, and most expensive to make items. They must be made to match the vehicle, and the parts being
attached to the vehicle. They must be strong enough not to break, because you are depending on these parts to
stop the vehicle you are driving. And if they are to last long, they must be finished and coated to keep them
protected from water and brake dust.
Isuzuperformance has developed several big brake kits for Geo Storm and Isuzu cars, and has 15+ years
experience building big brake kits for these cars.
Junk Yard Big Brake Kits – A Bad Idea
Many a industrious shade-tree-tuner have tried and failed to build an effective big brake kit utilizing used
parts from the salvage yard. Most underestimate the complexity and details involved, and dive straight into
a search for cars that share the same bolt pattern, with a larger diameter brake rotor. In the odd event
that a close match is found with another brand and model of vehicle, the entire rest of the brake system is
expected to fit onto a Geo Storm, only to cause disappointment when it doesn’t.
Quite quickly, the cost of the brackets and hardware to attach the salvage yard parts to the car, will dwarf the
cost of the salvage yard parts themselves. The cost will quickly climb into the range of doing the job right,
with a professionally built big brake kit. And the difference in braking performance between a junk yard big
brake kit, and a professionally built big brake kit, is like night and day.
The 4x100 bolt pattern for the wheels of the Geo Storm is shared by a large number of cars, but that is only
one of the many dimensions and measurements of the brake rotor, which soon limits the range of possible
donor cars to few or none. Brake disc outside diameter, disc thickness, hub diameter, bore diameter, and
offset are all concerns. The last three of these typically eliminate all of the likely candidates, because
the rotor has to fit over the hub, the bore must match the raised ring in the center of the hub, and the
offset must be shallow enough to clear the spindle, and deep enough that the caliper will not rub the back
of the wheel.
Some have suggested redrilling calipers with different bolt patterns to match the hub of the Geo Storm. At
best, this will throw the assembly out of balance, and weaken the rotor. At worst, a hand-drill-re-drill job
is going to result in lug holes that are not properly positioned, and a rotor that is no longer centered on
Matching the caliper’s hydraulic size (piston volume) to the original brake caliper, is important.
Most of the other cars on the road use floating calipers. It has already been pointed out numerous times that
floating calipers do not work well or smoothly, and do not provide very good braking performance. Changing
from the original floating calipers, to a different set of floating calipers, is not going to improve braking
performance or feel. If the goal of putting larger brakes on the car is to make the car stop more quickly,
and make as much improvement to the braking performance as possible, then floating calipers are not
Used multi piston calipers are rare, usually more expensive than aftermarket racing multi piston calipers, and
normally used only on vehicles with much larger brake master cylinders than the Geo Storm. Attaching one of
these calipers to a Geo Storm brake system would probably make it necessary for the driver to pump the brakes
several times each time the brakes are to be used.
And it is worth mentioning again, that used brake calipers are probably going to need an expensive rebuild to
be restored to good working condition.
- Brackets, Hardware, and Attaching It To The Car
This seems to be the detail that dooms most of these projects, because consideration is seldom given to how
these things are going to be attached to the vehicle, and what it is going to cost to do it. It should be
rather obvious that the project is based on taking parts that were not designed for the vehicle, and attaching
them to that vehicle. And most of the difficulty and cost is going to be involved in this part of the effort.
These pieces have to be made from scratch, because they aren’t sold in stores or used on another vehicle.
And making things from scratch is seldom inexpensive or easy.
A bracket will have to be made to attach the caliper to the spindle. This bracket will have to hold the caliper
in a specific position, not only in relation to the diameter of the rotor, but also in relation to the offset
between the mounting surface and the cross section of the rotor. Disparate mounting hole positions and directions
must be resolved. Do these attach from the same side or opposite sides? Is there adequate space to for enough
threads to allow for secure and sold mounting? Do the mounting tabs on the spindle and the bracket overlap and
want to occupy the same space when the caliper is positioned correctly?
Is there a spacer ring needed to adapt the rotor to the hubcentric ring in the hub. Or does the rotor need to
be bored out?
What changes must be made to the brake hoses to connect the different calipers to the vehicle?
Adjustable Brake Proportioning Valves
Control over brake biasing (tendency of either the front or rear brakes to lock up before the brakes on the
opposite end of the car) is important to getting the maximum performance out of the brake system. Ideally,
it is best to have the front brakes lock just before the rear brakes lock. But this will change based on
vehicle speed, tire compound, road surface, etc. So adjusting for the exact conditions is desirable.
Switching front and/or rear brake pads to balance braking is one technique. But controlling the pressure to
the front and rear brakes provides more control. An adjustable brake proportioning valve (or valves) will
do this. This (these) are installed in the brake line, between the brake master cylinder, and the rear brakes.
If the four channel brake system is retained, then two valves are required, one for the left rear brake, and
one for the right rear brake. The valve (or valves) is(are) used to limit rear brake force. Brake pad
selection would need to be such that the rear brakes lock up first, and the valve used to reduce rear braking
force to match the front.
An additional note: What the factory parts catalog calls a “proportioning valve” at the base of the factory
master cylinder, is actually a residual pressure valve, which keeps a minimum amount of pressure in the longer
rear brake pipes, to enhance braking response. There is no proportioning valve within this mechanism, and
the supplemental brake proportioning valve should be installed in line after the residual pressure valve.
Brake Cooling Ducts
Brake cooling ducts are a rather straight forward concept. By running duct hoses from the nose of the car
to the brake rotors, as the car rolls down the road, air blows through the hose and onto the rotor, cooling
it. This will require a custom dust shield, to hold the hose on the rotor end.
One thing to keep in mind is that these ducts provide brake cooling only while the vehicle is moving. In
autocross events, the vehicle is raced for +/-60 seconds, with hard use of the brakes, and then parked in the
grid to wait for the next run, with no air flowing through the brake ducts. If the driver us using a
left-foot-braking technique, the brakes can see rotor temperatures as high as 500 degrees, which is above the
boiling point of DOT 4 brake fluid. And if the autocross event is run efficiently, the car will be back at
the starting line and making its next run before the brakes have an opportunity to adequately cool. In such
cases, brake cooling ducts alone are not an adequate solution.
Brake Duct Cooling Fans
Electric cooling fans can be added to brake cooling ducts, providing air flow to cool the brake rotors when
the vehicle is parked, or moving slowly.
Most of the fans used for this task are adapted from marine bilge ventilation applications. It is a good
idea to look for waterproof fans, if the vehicle is going to be operated in the rain, or on a wet or puddle
surface. Water proof fans are slightly more expensive.
Provided the class racing rules allow for forced air brake cooling, this is a good solution.
Titanium Brake Pad Heat Shields
Titanium is excellent for use as a thermal barrier, because it has low heat conductivity. Placing a titanium
shim between the brake pad and caliper will prevent heat transfer and heat radiation from the pad and rotor,
to the piston and caliper body. This will prevent the boiling of the brake fluid, and allow the brake system
to be pushed harder.
Isuzuperformance offers titanium brake pad shims for Geo Storm and Isuzu vehicles.
The Impulse RS AWD Turbo, Gemini Irmscher-R JT191S, and Piazza JT221, were available with Anti-Lock Brake
System. The Piazza JT221 was available only in Front Wheel Drive. So the ABS system can be installed on a FWD
The parts needed are:
However, some owners of the AWD Turbo cars complain quite vocally that the ABS system feels mushy. For
motorsports use, the system is typically removed from the AWD cars, and the four channel standard brake system
from the FWD car is usually installed.
- Front spindles with ABS sensor ports.
- Rear spindles with ABS sensors ports.
- AWD model rear wheel bearings.
- The ABS sensors themselves.
- Struts with the ABS sensor wire brackets.
- ABS wiring.
- ABS control box.
- Two channel master cylinder.
- The pipes from the master cylinder to the ABS hydraulic unit.
- The ABS hydraulic unit.
- The pipes between the ABS hydraulic unit.
- The brake hoses at the four corners of the car.
- Front outer axle stub ends with the sensor crown wheel.
- Rear outer axle stubs with the crown wheel.
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