Upgrading to a Big Brake Kit: What Else Changes

By Core Brake Parts Tech Team — Circleville, OH warehouse

A big brake kit changes far more than the caliper and rotor you can see through the wheel. Larger rotors and multi-piston calipers change wheel clearance, how much fluid the master cylinder has to move, front-to-rear brake balance, the brake hoses, and how the new parts must be bled and bedded before you drive hard. Plan for all of it up front and the upgrade feels like a factory option; skip it and you can end up with a long pedal, wheels that rub, or a car that stops worse than stock.

What a Big Brake Kit Actually Replaces

Most front big brake kits are a complete corner package. Brembo describes its GT kits as aluminum opposed-piston calipers, upsized one-piece or two-piece discs, performance pads, braided stainless hoses, adapters and mounting hardware. Wilwood kits follow the same pattern: a caliper mounting bracket, a rotor bolted to an aluminum hat, the caliper, pads, and a stainless braided flexline hose kit. EBC's Apollo kits add something many buyers overlook: rear pads and rear brake lines matched to the original rear caliper, because EBC calculates brake bias against the car's stock rear brakes and master cylinder.

That means you are not just swapping brake calipers and brake rotors. You are changing the geometry, hydraulics and heat capacity of the whole front axle, and every other part of the system has to agree with that change.

Wheels: Clearance Is the First Thing That Changes

A bigger rotor pushes the caliper outward, closer to the wheel barrel, and a wider multi-piston caliper sits closer to the back of the spokes. Clearance has to be checked in both directions before you buy, not after the old brakes are off the car.

• Use the manufacturer's template. EBC tells buyers to print its wheel fitment template to scale, glue it to cardboard, cut out the profile and place it inside the wheel. Its template guidance calls for at least 5.0 mm between the caliper face and the spokes and between the top of the caliper and the wheel barrel.
• Do not assume by wheel size. EBC points out that two wheels with the same diameter, width and offset can still clear differently because spoke shape and barrel profile vary.
• Every kit has its own number. The wheel clearance diagram for Wilwood's 12.88 inch Superlite 6R kit for the Scion FR-S and Subaru BRZ requires at least 0.080 inch of clearance between the wheel and caliper in all areas, and Wilwood notes that its diagram is not meant for designing custom wheels.
• Check through full travel. After fitting, EBC says to cycle the suspension through its travel and turn the steering lock to lock to confirm clearance is kept everywhere.

If the template hits, the fix is a different wheel. Spacers are a judgment call: EBC's template page leaves that decision to the owner or installer, while the installation manual for its Apollo kit says the company does not recommend separate wheel spacers. Wilwood also warns that wheel track can change with aftermarket disc brakes, so check wheel offset before final assembly.

Master Cylinder, Pedal Feel and Brake Balance

Caliper pistons need fluid to move. A kit with more total piston area asks the master cylinder to displace more fluid for the same pad travel, and that shows up at the pedal. Wilwood explains the leverage side of it: pedal ratio is the distance from the pivot to the footpad divided by the distance from the pivot to the pushrod, and more leverage means more force into the master cylinder but also more pedal travel. Wilwood lists typical ratios of 4.5:1 to 5:1 for power-boosted pedals and 6:1 to 7:1 for manual systems.

Street kits from the big brake makers are generally engineered to work with the factory master cylinder and ABS. EBC states its Apollo kit bias is calculated against the original master cylinder, rear calipers and rear discs, and warns that a different bore master cylinder or larger rear discs will change bias. So the rule is simple:

• Keep the stock master cylinder unless the kit maker says otherwise. Changing its bore changes the balance the kit was designed around.
• Expect a slightly long pedal at first. EBC notes new or resealed calipers can take up to 300 miles to fully bed in, with the pedal improving as the seals settle. If it still feels spongy after that, re-bleed.
• A pedal that goes to the floor is different. Wilwood says to check for leaks and re-bleed first; if continued bleeding does not fix it, a master cylinder with a larger bore may be needed. On a custom or non-ABS build, make that decision with the kit maker's guidance and choose from master cylinders sized for the new calipers.

Balance is why a front-only kit is not automatically better braking. Adding a lot of front brake torque without considering the rear can move the car toward front lockup, which ABS then has to manage. That is why balanced kits either leave the rear untouched on purpose or include matched rear pads. If a kit includes rear parts, install them; EBC says leaving them off may degrade system performance.

Hoses, Fluid and Hardware

New calipers usually mean new hoses. Wilwood notes that OEM rubber brake hoses generally cannot be adapted to its calipers, which use a pipe-thread inlet, and its kits ship with stainless braided flexlines. The installer is responsible for routing them so they never touch the suspension, rotor or wheel at any steering angle or ride height. If your kit does not include lines, plan on braided brake lines or the correct brake hoses for the caliper fitting.

Banjo fittings need fresh crush washers. EBC warns that leaving out a copper washer on either side of the banjo fitting can cause a leak and loss of pressure under braking.

Fluid should be fresh and high-temperature rated. EBC includes a litre of its DOT 4 fluid with the Apollo kit. Wilwood specifies its Hi-Temp 570 grade fluid or higher, says old fluid must be flushed out completely, and states that silicone DOT 5 fluid is not recommended for performance driving. Check your owner's manual for the fluid type your system is designed for before you mix anything.

Installation Checks That Change With a BBK

A big brake kit is a bolt-on job for an experienced installer, not a pad swap. EBC allows 3 to 5 hours for its front-and-rear kit. The steps that trip people up are the ones that do not exist on a stock brake job:

1. Inspect the corner first. EBC says wheel bearings, suspension bushings, axle shafts, wheels and tires must be checked against the factory manual and replaced if worn, or the new discs can be damaged and cause steering wheel or pedal vibration soon after installation.
2. Verify the hub. Wilwood says to confirm the hub center register and lug pattern match the new hat, and that the hat must sit flush on the hub flange or rotor runout will be excessive.
3. Measure runout and centering. EBC's manual has you check disc runout with a dial indicator and confirm the caliper is centered over the disc, using shims where needed. Wilwood uses shims to center the caliper and set pad height flush with the rotor edge.
4. Handle the pad wear sensor. Many kits do not use the factory sensor, so the connector has to be secured or bypassed so a warning light does not stay on.
5. Torque to the kit's sheet. Bracket, caliper, banjo and bleeder torques come from the kit's own instructions and the vehicle service manual. Do not reuse stock values for new brackets.
6. Bleed and leak test. Bleed from the caliper farthest from the master cylinder, outboard bleeder before inboard on two-bleeder calipers. Wilwood's pedal check calls for a firm pedal that stops at least 1 inch from the floor under heavy load.

Testing, Bedding and the First 1,000 Miles

Never drive on untested brakes. Wilwood's minimum test procedure starts with hard stops at 2 to 5 mph while turning the steering full left to full right, then a wheels-off check for rubbing or leaks, then moderate and hard stops at 15 to 20 mph, all in a safe place away from traffic.

Bedding matters more with performance pads and new rotors. EBC asks for about 200 miles of gentle driving until the discs show an even dull grey layer, then three staged sessions of progressively harder stops with cool-down drives between them. Wilwood's version finishes with 8 to 10 hard stops from 55 to 65 mph down to 25 mph. Both warn against sitting stopped with your foot on the pedal while the brakes are hot. EBC also says to lift the car after 1,000 miles and inspect every line and connection for rub marks or leaks.

Finally, the legal side: Brembo tells road users to check the regulations in their country before running upgrade kits, and local inspection rules may apply too.

If a full kit is more than your driving needs, better brake pads and quality rotors on the stock calipers are often the right first step. Browse all brake parts to compare options for your vehicle.

Frequently Asked Questions

Do I need a new master cylinder with a big brake kit?

Usually not for vehicle-specific street kits. Makers such as EBC calculate brake bias around the factory master cylinder and rear brakes. A new master cylinder is typically only considered on custom builds, or when the pedal still goes to the floor after leak checks and proper bleeding.

Will a big brake kit fit my factory wheels?

Often not, especially with smaller factory wheels. Print the kit maker's template and test it in your exact wheel, because wheels with identical size and offset can still differ in spoke and barrel shape.

Does a big brake kit work with ABS and stability control?

Vehicle-specific kits from established makers are designed to work with factory ABS. The key is keeping brake balance close to what the ABS system expects, which is why balanced kits and supplied rear pads matter.

Why does my pedal feel longer after installing a BBK?

Air left in the new calipers is the most common cause, so re-bleed first. New caliper seals also take time to settle; EBC says new calipers can take up to 300 miles to fully bed in.

Can I use my old brake hoses?

Generally no. New calipers usually have different inlet fittings, and Wilwood notes OEM rubber hoses generally cannot be adapted to its calipers. Use the lines supplied or specified for the kit.

Do I have to bed in a big brake kit?

Yes. Skipping bedding risks uneven pad deposits that feel like vibration. Follow the procedure in your kit's instructions before any hard driving.

Sources

1. EBC Brakes Racing - Brake Kit Wheel Fitment/Clearance Templates - template method, 5.0 mm clearance guidance, same-size wheels clearing differently, lock-to-lock and suspension travel check, spacer decision
2. EBC Brakes Racing - Apollo-4/6 Big Brake Kit Installation Instructions - bias matched to stock master cylinder and rear brakes, rear parts included, 3-5 hour install, worn suspension check, runout and centering, banjo washers, pad sensor, DOT 4 fluid, bleeding, 300-mile caliper bed-in, bedding, 1,000-mile inspection
3. Wilwood - Superlite 6R Front Brake Kit Assembly Instructions, Scion FR-S / Subaru BRZ - 0.080 inch wheel clearance, hub register and hat fit, OEM hoses not adaptable, fluid grade and DOT 5 note, pedal test, larger-bore master cylinder note, wheel track change, minimum test and bedding procedure
4. Wilwood - Pedal Ratios and How to Find Them - pedal ratio definition, typical boosted and manual ratios, leverage versus pedal travel
5. Brembo - GT Kit: Choose the Right One for You - contents of a GT kit, professional installation recommendation
6. Brembo Parts - Upgrade GT Kit - check local regulations for road use