Your MGB's braking system is the most critical safety component on the vehicle. Whether you drive a chrome bumper roadster or a rubber bumper GT, understanding how to inspect, maintain and service your brakes will keep you safe on the road and preserve the enjoyment of driving your classic British sports car. This guide covers the MGB braking system from front discs to rear drums, including hydraulics, handbrake mechanisms and popular upgrade options.
Understanding the MGB Braking System
The MGB uses a conventional hydraulic braking system with front disc brakes and rear drum brakes. This configuration was advanced for its time when introduced in 1962 and provides effective stopping power for a car of this size and performance level. The front discs handle the majority of braking effort under normal conditions, with the rear drums providing the remaining stopping force plus handbrake functionality.
Throughout its production run from 1962 to 1980, the MGB's braking system evolved significantly. Early cars used single-circuit hydraulics with a single master cylinder feeding all four wheels. From late 1967, a dual-circuit system was introduced for improved safety, separating front and rear braking circuits so that a failure in one system would not result in complete brake loss. Servo assistance was fitted to some models, reducing pedal effort and improving brake feel.
The MGB GT V8, produced from 1973 to 1976, uses larger front discs to cope with the increased performance. V8 owners should ensure they source correct V8-specific components rather than standard 4-cylinder parts.
When to Inspect and Service Your Brakes
Regular brake inspection should form part of your routine maintenance schedule. Check your brakes at least every 6,000 miles or annually, whichever comes first, and more frequently if you notice any changes in braking performance. Always consult your workshop manual for model-specific service intervals.
Warning signs requiring immediate attention include: a spongy or soft brake pedal that sinks towards the floor, the car pulling to one side under braking, grinding or scraping noises when braking, excessive pedal travel before brakes engage, a pulsating brake pedal indicating warped discs, fluid visible around wheels or beneath the car, and the handbrake requiring excessive travel to hold the car.
If you experience any of these symptoms, inspect your brakes promptly before continuing to drive. Catching problems early prevents more expensive damage and keeps you safe.
Front Brake Inspection and Service
The front brakes do most of the stopping work on an MGB and typically wear faster than rear components. With the wheel removed, you can assess pad thickness through the calliper inspection aperture or by removing the pads entirely for closer examination.
Brake Pad Inspection: MGB front brake pads should be replaced when the friction material reaches approximately 3mm thickness. Uneven wear across the pad surface suggests sticking calliper slides or a seized piston. Always replace pads as a complete axle set to maintain balanced braking, and never mix different friction materials on the same axle.
Brake Disc Inspection: Run your fingernail across the disc surface to feel for scoring or lip formation at the outer edge. Light scoring is normal, but grooves you can catch your nail in indicate the disc should be replaced. Check both sides of the disc for wear. Measure disc thickness using a micrometer at several points around the circumference to check for uneven wear. The Lockheed minimum disc thickness specification is 7.6mm (0.30 inches) for standard MGB front discs. New discs are typically 8.8mm (0.344 inches) thick, and the minimum thickness is often stamped on the disc itself.
Calliper Service: MGB front callipers are robust units, but the pistons can seize from corrosion or lack of use. Signs include uneven pad wear, the car pulling to one side, or a dragging brake that causes the wheel to run hot. Calliper rebuild kits containing new seals and dust covers can restore function to callipers with sticky pistons. Severely corroded callipers may require replacement.
| Component |
Service Interval |
Minimum Specification |
| Front brake pads |
Inspect every 6,000 miles |
Replace at approximately 3mm thickness |
| Front brake discs |
Inspect with pad changes |
Minimum 7.6mm thickness (Lockheed specification)
|
| Rear brake shoes |
Inspect every 12,000 miles
|
Replace at approximately 1.5mm thickness
|
| Brake fluid |
Replace every 2 years
|
DOT 3 or DOT 4 specification
|
| Flexible hoses |
Inspect annually
|
Replace every 5 years
|
Component
Front brake pads
Service Interval
Inspect every 6,000 miles
Minimum Specification
Replace at approximately 3mm thickness
Component
Front brake discs
Service Interval
Inspect with pad changes
Minimum Specification
Minimum 7.6mm thickness (Lockheed specification)
Component
Rear brake shoes
Service Interval
Inspect every 12,000 miles
Minimum Specification
Replace at approximately 1.5mm thickness
Service Interval
Replace every 2 years
Minimum Specification
DOT 3 or DOT 4 specification
Service Interval
Inspect annually
Minimum Specification
Replace every 5 years
Rear Brake Inspection and Service
The rear brakes use drum assemblies with shoes that press outward against the drum's inner surface. Although they handle less braking force than the fronts, proper rear brake function is essential for balanced stopping and handbrake operation.
Removing the Drum: With the wheel removed, the drum should pull off the hub studs. If stuck, ensure the handbrake is fully released and tap around the drum edge with a soft mallet to break any corrosion bond. On wire wheel cars, the drum is integral with the hub assembly and secured by the knock-off spinner.
Shoe Inspection: Examine the friction material for wear, checking that the thickness remains above approximately 1.5mm at the thinnest point. Look for contamination from oil or brake fluid, which appears as dark staining on the friction surface. Contaminated shoes must be replaced as they will not provide consistent braking. Check that return springs are intact and properly positioned.
Wheel Cylinder Inspection: The wheel cylinders push the shoes outward when hydraulic pressure is applied. Peel back the rubber dust covers and check for fluid leakage around the pistons. Any visible fluid indicates failed seals requiring cylinder rebuild or replacement. Wheel cylinders that have leaked may have contaminated the brake shoes, necessitating their replacement as well.
Drum Inspection: The inner braking surface of the drum should be smooth and free from deep scoring. Light glazing is normal, but heavy scoring reduces braking efficiency. Measure the drum's internal diameter to ensure it has not worn beyond the maximum limit stamped on the drum casting.
Brake Hydraulics Service
The hydraulic system transfers pedal effort to the wheel brakes through fluid under pressure. MGB brake hydraulics include the master cylinder, brake hoses, rigid brake pipes, wheel cylinders and calliper pistons.
Brake Fluid: The MGB was originally specified for DOT 3 brake fluid (such as Castrol LMA), though DOT 4 fluid is also compatible and commonly used today. Both are hygroscopic fluids that absorb moisture from the atmosphere over time, lowering the boiling point and causing internal corrosion. Replace brake fluid every two years regardless of mileage. When topping up, only use fresh fluid from a sealed container, as opened containers absorb moisture rapidly. Do not mix DOT 3 or DOT 4 with silicone-based DOT 5 fluid.
Flexible Hoses: The flexible rubber brake hoses connecting the chassis-mounted rigid pipes to the moving suspension components deteriorate over time. Inspect for cracking, bulging, chafing, or soft spots. Replace hoses showing any deterioration, and consider preventive replacement every five years. Uprated braided hoses offer improved pedal feel and longer service life.
Rigid Pipes: Original steel brake pipes corrode from the inside out, making visual inspection unreliable. If your car still has original pipes, replacement with copper-nickel brake pipe kits is strongly recommended. These corrosion-resistant pipes come pre-formed with the correct fittings for straightforward installation.
Master Cylinder: A failing master cylinder typically causes a spongy pedal that gradually sinks under sustained pressure. Internal seal failure allows fluid to bypass the piston rather than building pressure. Rebuild kits are available, but replacement master cylinders often prove more reliable. Dual-circuit cars require the correct twin-bore master cylinder.
Servo Service and Diagnosis
The brake servo uses engine vacuum to multiply pedal effort, reducing the force required to achieve effective braking. Not all MGBs were fitted with servos from new, but many non-servo cars have had them retrofitted.
Testing Servo Function: With the engine off, pump the brake pedal several times to exhaust the vacuum reserve. Hold the pedal down firmly and start the engine. The pedal should drop slightly as vacuum assistance becomes available. If no change occurs, the servo may be faulty, or the vacuum supply may be inadequate.
Common Servo Problems: A hissing sound when pressing the brake pedal indicates a vacuum leak, often from a failed internal diaphragm. A hard pedal with no assistance suggests complete servo failure or a disconnected vacuum hose. Servo repair kits can address some failures, though replacement is often more practical for units with severe internal damage.
Handbrake Service
The handbrake mechanism operates the rear drum brakes mechanically through cables and levers, independent of the hydraulic system. Proper handbrake function is essential for parking security and provides an emergency backup if hydraulic brakes fail.
Adjustment: The handbrake should hold the car securely with the lever pulled three to five clicks from the released position. Excessive travel indicates stretched cables, worn rear shoes, or maladjusted rear brakes. Adjust the rear brake shoes first using the adjusters on the backplate, then take up any remaining slack at the cable adjuster under the car or at the lever mechanism.
Cable Replacement: Handbrake cables stretch over time and eventually require replacement. Different cables are fitted depending on model year and whether the car has wire or steel wheels, so verify the correct cable for your specific vehicle. Lubricate the new cable before installation to ensure smooth operation.
Bleeding the Brake System
Air in the hydraulic system causes a spongy pedal and reduced braking efficiency. Bleeding removes air bubbles and should be performed after any work that opens the hydraulic system, including hose replacement, calliper rebuild or master cylinder service.
Bleeding Sequence: For single-circuit systems, bleed in order from the wheel furthest from the master cylinder to the nearest: right rear, left rear, right front, left front. Dual-circuit systems should be bled in the same sequence, ensuring both circuits receive attention.
Procedure: Attach a clear tube to the bleed nipple and submerge the other end in fresh brake fluid in a container. Have an assistant pump the brake pedal several times and hold it down firmly. Open the bleed nipple until fluid flow stops, then close it before your assistant releases the pedal. Repeat until no air bubbles appear in the expelled fluid. Keep the master cylinder reservoir topped up throughout the process.
Upgrading Your MGB Brakes
For spirited driving or track use, several upgrade options improve MGB braking performance beyond standard specifications.
Uprated Pads: Performance pad compounds such as EBC Greenstuff offer improved bite and fade resistance over standard materials. These are a simple upgrade requiring no other modifications and suit fast road driving well. Explore the front brake kits for matched disc and pad combinations.
Four-Pot Calliper Conversions: Uprated brake kits with four-piston callipers provide significantly improved braking through better pad coverage and more even clamping force. These bolt-on conversions use the standard disc but may require 15-inch wheels for clearance. The transformation in braking confidence is substantial.
Vented Disc Upgrades: For the most demanding applications, vented disc conversions offer enhanced heat dissipation. These require specific callipers and brackets but deliver genuine performance improvements for track day use or heavily laden GT models.
Browse the complete range of MGB performance brake kits for available upgrade options.
DISCLAIMER: THIS GUIDE PROVIDES GENERAL INFORMATION FOR EDUCATIONAL PURPOSES. ALWAYS REFER TO THE OFFICIAL WORKSHOP MANUAL FOR YOUR SPECIFIC MODEL AND CONSULT A QUALIFIED MECHANIC IF YOU ARE UNCERTAIN ABOUT ANY PROCEDURE. RIMMER BROS ACCEPTS NO LIABILITY FOR WORK CARRIED OUT BASED ON THIS GUIDE. BRAKE SYSTEMS ARE SAFETY-CRITICAL, AND IMPROPER MAINTENANCE CAN RESULT IN SERIOUS INJURY OR DEATH.
Frequently Asked Questions
What is the difference between single-circuit and dual-circuit MGB brake systems?
The distinction between single-circuit and dual-circuit brake systems represents one of the most significant safety improvements made to the MGB during its production run, and understanding which system your car has is essential for ordering correct replacement parts and maintaining safe operation.
Single-circuit brake systems were fitted to early MGBs from the model's introduction in 1962 until late 1967 (approximately). In this design, a single master cylinder with one piston pressurises a common hydraulic circuit that feeds all four wheel brakes. The advantage is simplicity, with fewer components and straightforward servicing. However, the critical disadvantage is that any leak or failure anywhere in the system results in complete loss of hydraulic braking, leaving only the mechanical handbrake for emergency stopping.
Dual-circuit systems, introduced in late 1967, use a tandem master cylinder with two separate pistons feeding independent hydraulic circuits. On the MGB, one circuit operates the front brakes and the other operates the rear brakes. If a leak develops in either circuit, the other continues to function, providing at least partial braking capability. A pressure differential warning switch illuminates a dashboard light if one circuit loses pressure, alerting the driver to the problem.
Identifying your system is straightforward. Check the master cylinder mounted on the bulkhead: single-circuit cars have one outlet pipe, while dual-circuit cars have two. The fluid reservoir also differs, with dual-circuit systems using a divided reservoir or separate reservoirs for each circuit.
Parts are not interchangeable between systems. Master cylinders, brake pipe layouts, and some associated components differ significantly. When ordering parts, specify whether your car has single or dual-circuit brakes, and provide your chassis number if possible so that parts advisors can confirm the correct specification. Converting from single to dual-circuit is possible but involves significant work, including a new master cylinder, pedal box modifications, revised pipe routing, and a warning light installation.
How often should I replace MGB brake fluid and why is it so important?
Brake fluid replacement is one of the most frequently neglected maintenance items on classic cars, yet it directly affects braking safety and system longevity. The recommended interval for MGB brake fluid is every two years, regardless of mileage, and understanding why this matters will help you appreciate the importance of this simple service.
DOT 3 and DOT 4 brake fluids (both compatible with the MGB) are hygroscopic, meaning they actively absorb moisture from the surrounding atmosphere. Even in a sealed system, water vapour passes through flexible rubber hoses and the microscopic pores in reservoir caps. Over time, this moisture accumulates in the fluid, causing two serious problems.
First, water dramatically reduces the fluid's boiling point. Fresh DOT 4 fluid has a minimum dry boiling point of 230°C (446°F), more than adequate for normal braking. However, as water content increases, this boiling point falls significantly. The DOT 4 wet boiling point specification (measured at 3.7% water content, representing approximately two years of service) is 155°C (311°F). During heavy braking, friction generates significant heat that transfers through the calliper and piston into the fluid. If the fluid boils, it creates vapour bubbles that compress under pedal pressure instead of transmitting force to the brake pads. This phenomenon, called vapour lock, results in a pedal that goes to the floor with minimal braking effect, often occurring precisely when you need maximum stopping power.
Second, water causes internal corrosion throughout the brake system. Moisture attacks the steel surfaces of brake pipes, wheel cylinder bores, calliper pistons, and master cylinder internals. This corrosion creates pitting that damages seals, causes leaks, and eventually necessitates expensive component replacement. Corroded particles circulating in the fluid accelerate seal wear throughout the system.
The replacement procedure is straightforward: connect a clear tube to each bleed nipple in sequence, pump through fresh fluid until clean, bubble-free fluid emerges, and dispose of the old fluid responsibly. The cost of fresh fluid is minimal compared to rebuilding corroded hydraulic components, and the safety benefits of maintaining proper boiling point protection are impossible to overstate.
Can I upgrade my MGB to modern four-piston brake callipers?
Upgrading from the original single-piston sliding callipers to modern four-piston fixed callipers is one of the most worthwhile performance modifications available for the MGB, delivering dramatically improved braking confidence with relatively straightforward installation. Understanding what is involved helps you decide whether this upgrade suits your requirements.
The standard MGB front brake uses a single-piston sliding calliper that clamps the pad against the disc from one side only. As the piston extends, the calliper body slides on its mountings to bring the outer pad into contact with the disc. This design is adequate for normal road driving but has limitations. The single piston provides uneven pad pressure distribution, the sliding mechanism can stick if not properly maintained, and the overall clamping force is limited by the piston size.
Four-piston callipers address all these limitations. Four smaller pistons, two on each side of the disc, provide more even pad coverage and higher total clamping force. The fixed calliper body eliminates the sliding mechanism and its associated maintenance requirements. The result is shorter stopping distances, improved pedal feel, better fade resistance under demanding conditions, and increased confidence during spirited driving.
Conversion kits are available as bolt-on installations that use the existing disc and mounting points, minimising modifications to the original components. The callipers are typically machined from aluminium alloy for lightweight and corrosion resistance, with stainless steel pistons for longevity. Kits include matched performance brake pads designed to work optimally with the calliper configuration.
The primary consideration is wheel clearance. Four-piston callipers are physically larger than standard units and may contact the inside of original 14-inch wire wheels or small steel wheels. Most conversions require a minimum 15-inch diameter wheel. Check your current wheel size and verify clearance before ordering. Uprated flexible brake hoses with correct fittings for the new callipers are recommended to complete the installation. For MGB brake and clutch hydraulics, ensure any replacement lines match your upgraded system.
Why does my MGB pull to one side when braking?
A car that pulls to one side under braking indicates uneven braking force between the left and right wheels, which represents both a safety concern and a diagnostic opportunity. Identifying the cause requires systematic investigation, starting with the simplest and most likely causes before progressing to more involved checks.
Start with tyre pressures and condition. This is the simplest check and an often-overlooked cause of braking imbalance. Unequal pressures or differing tyre wear patterns between sides affect braking behaviour. While not strictly a brake fault, this common issue can mimic or exacerbate braking problems and takes only moments to verify with a pressure gauge.
Visually inspect the brake pads for contamination. Contaminated brake pads cause inconsistent friction, resulting in unbalanced braking. Oil or brake fluid on the pad surface dramatically reduces its coefficient of friction. Inspect both front pads for dark staining or a glossy, contaminated appearance. If one side is contaminated, investigate the source of contamination (leaking wheel cylinder, hub seal, or calliper) before fitting new pads.
Check for a sticking calliper piston or seized sliding mechanism on the front brakes. When one calliper drags or fails to apply fully, the opposite side generates more braking force, pulling the car in that direction. Signs include uneven pad wear between sides, a wheel that runs hot after driving, or visible differences in pad-to-disc clearance. A sticking calliper may be freed with a rebuild kit containing new seals, or it may require replacement if the bore is corroded.
Examine the flexible brake hoses. A blocked or restricted flexible brake hose can act as a one-way valve, allowing fluid to push the piston out but preventing it from returning. This causes the brake to drag progressively during driving. Internally degraded hoses may appear fine externally but have deteriorated rubber liner material blocking the passage. Replace any suspect hoses with new items.
Finally, investigate the rear brakes. Rear brake issues can also cause pulling, though less pronounced than front problems given the rear brakes' smaller contribution to total braking force. Maladjusted rear brakes, a seized wheel cylinder, or contaminated shoes on one side create imbalance. Ensure rear brake adjustment is equal on both sides and that wheel cylinders operate freely.
By working through these checks in order from simplest to most involved, you can systematically eliminate possibilities and pinpoint the root cause before carrying out a targeted repair.
Chris Wrigley
Commercial Manager
Chris has been a car enthusiast since the early 1990’s and got his first Triumph Spitfire in 1996, one of many classics that followed!
Read More