How to Choose a Racing Brake Master Cylinder

The right racing brake master cylinder matches your pedal box mount, has a bore sized to your calipers and pedal ratio, and is fed by the right reservoir. But if your pedal is already sinking, start by confirming the master cylinder really is the problem.

Founded in August 2005 by racer Ryan McLeod, Racer Industries was built to solve a clear problem in Australian motorsport: eliminating out-of-stock parts, inflated prices, and guesswork with genuine, track-proven gear.

This guide works through it in order: symptoms, how the part works, rebuild or replace, then choosing a racing unit from our racing brake master cylinders range. View the Tilton 76 Series installation sheet (PDF).

 

Is it your master cylinder? Symptoms to check

A pedal that slowly sinks under steady foot pressure, with no fluid lost anywhere, usually means fluid is leaking past the piston seals inside the master cylinder. The fluid isn't escaping; it's slipping back past the seal, so pressure never builds.

 

How to isolate the master cylinder

• Road cars with rubber flexible hoses: Clamp each hose in turn with proper hose-clamp pliers, never vice-grips. If the pedal is firm with everything clamped but sinks once a particular hose is released, the fault is at that corner. If it still sinks with every hose clamped, look at the master cylinder.
• Race cars with braided lines: Don't clamp braided or PTFE hoses, because it damages them. Cap the master cylinder outlets with AN plugs instead. If the pedal still sinks with the outlets capped, the master cylinder is bypassing.

 

What does a brake master cylinder do?

Think of a syringe connected by a hose to a second syringe. Push the first plunger and the second one moves, squeezing the pads onto the disc. The master cylinder is the first syringe, the brake lines are the hose, and the caliper pistons are the second syringe.

It turns force on the pedal into hydraulic pressure at the calipers (or wheel cylinders on drum brakes). Pressure equals force divided by piston area, which is why bore size matters so much.

Master cylinder vs brake booster

On most road cars, a vacuum booster sits between the pedal and the master cylinder and adds to the driver's push. The booster only adds force. The master cylinder creates the hydraulic pressure. Most race cars have no booster, so the pedal ratio and master cylinder bore have to make the pressure on their own.

 

Replace, rebuild or upgrade?

On a race car with a pedal box, swapping the cylinder is usually a bolt-in job. Most of the work, and most of the care, goes into bleeding.

Bench bleeding and bleeding: two non-negotiable steps

Whichever route you take, do both, every time:

1. Bench bleed the new master cylinder before you fit it. Clamp it in a vice, fill the reservoir, and run bleed tubes from the outlets back into the reservoir. Stroke the piston until no bubbles come out. A cylinder fitted dry traps air that is hard to shift from the car.
2. Bleed the whole system after you fit it. Air left in the lines gives a soft pedal no matter how good the master cylinder is. Racing brake systems should have the fluid replaced and bled before every event.

 

Which brake fluid to use

DOT 3, DOT 4 and DOT 5.1 are all glycol-based and can be mixed, but the mix only boils at the lower of their boiling points. DOT 5 is silicone-based. Never mix it with glycol fluids, and it isn't generally used in racing systems. See our racing brake fluid guide for boiling points, or shop brake fluid.

 

Rebuilding, resleeving and reservoir sizing

 

Rebuild kit or resleeve?

If the bore is smooth, a seal kit usually brings a master cylinder back to life. Tilton makes rebuild kits for its master cylinders; see master cylinder spares and rebuild kits. If the bore is pitted or corroded, which is common on older Ford and Holden cylinders, new seals won't seal for long. The options are a specialist resleeve (a stainless or brass sleeve pressed into the bore) or a new cylinder.

Why front and rear reservoirs are different sizes

On a dual master cylinder, the reservoir chamber for the front discs is usually larger than the one for the rear drums. As disc pads wear, the caliper pistons sit further out and hold more fluid, and that fluid comes from the reservoir. Drum brakes self-adjust, so the rear circuit needs less. If you convert a classic to front discs, check that the master cylinder's front chamber is big enough. On a race car, a remote or multi-chamber brake fluid reservoir lets you size each circuit separately.

Residual pressure valves: 10 psi for drums, 2 psi for discs

   

Never fit a 10 psi valve to a disc circuit, because it can make the pads drag. Mounting the reservoir above the calipers also stops drainback; Tilton recommends it in its installation notes.

A residual valve isn't the same as a proportioning valve. A residual valve holds a small pressure in the line. A proportioning valve, such as the Tilton Proportioning Valve – Lever Style, reduces rear line pressure to set front-to-rear brake bias.

 

How to choose a racing brake master cylinder: 6 checks

Once you know the master cylinder needs replacing or upgrading, work through these six choices in order:

1. Mounting and pedal box: Match the bolt pattern to your pedal box. The Tilton 76 Series, for example, is a direct replacement for cylinders on a 2.25" spaced, 2-bolt mount.
2. One cylinder or two: Most racing pedal boxes use separate front and rear cylinders with a balance bar between them, so you can set brake bias from the pedal. Fine-tune it further with a brake proportioning valve or bias adjuster; see our proportioning valve guide.
3. Bore size: A smaller bore makes more line pressure for the same pedal force, with more pedal travel. A larger bore gives a firmer, shorter pedal with less pressure. The right size depends on your caliper piston area, pedal ratio and how much pedal effort the driver wants. If you've fitted bigger calipers from a brake upgrade kit, check the bore again. The Tilton 76 Series comes in 0.625" to 1.000" bores. Not sure which one you need? Contact us 1300 722 374 and we'll help you size it.
4. Reservoir: Choose a direct-mount reservoir for tight installs, or a remote reservoir for flexibility. A 3-chamber remote reservoir can feed the front brakes, rear brakes and clutch together. Shop brake fluid reservoirs.
5. Fittings and lines: The Tilton 76 Series uses a 7/16"-20 (-4AN) inlet and AN3 outlets. Plan your brake hose and fittings and brake lines before you order.
6. ABS: Some racing master cylinders, including the Tilton 76 Series, may not suit cars running ABS. Pressure pulses from the ABS unit can damage the high-pressure seal. If your car keeps its ABS, ask us before you buy.

Shop Tilton master cylinders and spares

Every Tilton master cylinder we stock is listed below with its matching rebuild kit, so you can buy the cylinder and its spares together.

Racing brake master cylinders

 

Master cylinder spares and adapters

Browse the full ranges: racing brake master cylinders · master cylinder spares · brake fluid reservoirs · pedal boxes · Tilton 76 Series installation sheet (PDF)

 

Brake master cylinder FAQs

Is it safe to drive with a failing brake master cylinder?

No. If the pedal sinks or feels soft, park the car until it's fixed. A master cylinder that fails completely can leave you with no braking.

Why does my brake pedal sink to the floor with no fluid leak?

Fluid is usually slipping past worn seals inside the master cylinder, so pressure never builds. Cap the outlets with AN plugs, or clamp the rubber hoses on a road car. If the pedal still sinks, the master cylinder is the cause.

Do I have to bleed the brakes after replacing the master cylinder?

Yes, every time. Bench bleed the new cylinder before fitting it, then bleed every caliper to remove any air left in the lines.

Can I rebuild my master cylinder instead of replacing it?

Yes, if the bore is smooth: a seal kit is enough. If the bore is pitted or corroded, it needs a resleeve or a new cylinder. Shop master cylinder rebuild kits.

What size master cylinder do I need?

It depends on your caliper piston area, pedal ratio and the pedal feel you want. A smaller bore gives more pressure and more travel; a larger bore gives a firmer, shorter pedal. Compare bore sizes in our racing brake master cylinders range, or ask us to help size one.

Can I use a racing master cylinder with ABS?

Not always. Tilton warns that the 76 Series may not suit some ABS systems, because pressure pulses can damage the high-pressure seal. Check with us before fitting one to a car that keeps its ABS.

Do I need a residual pressure valve?

Drum circuits typically use a 10 psi valve. Disc circuits only need a 2 psi valve when the master cylinder sits below the calipers. Never fit a 10 psi valve to discs, because it can make the pads drag.

Can I mix DOT 4 and DOT 5.1 brake fluid?

Yes. Both are glycol-based, but the mix only boils at the lower of their boiling points. Never mix either with silicone DOT 5. See the racing brake fluid guide.