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MOTRS

MGB Roadster

1962-1980 / Roadster / United Kingdom

All MGB Roadster problems All workshop problems
Minor Brakes

Brake Master Cylinder Failure

Symptoms

A spongy brake pedal that sinks to the floor under sustained pressure. Brake fluid weeping from the master cylinder body or around the pushrod seal. Air in the system despite repeated bleeding.

Cause

The internal seals in the master cylinder harden with age and allow fluid to bypass. On later dual-circuit cars (1975 onwards), the tandem master cylinder has twice as many seals to fail. Brake fluid absorbs moisture over time, which corrodes the cylinder bore from within.

Fix

  1. 1 Rebuild kits are available ($30--50) but a new or remanufactured master cylinder ($80--150) is more reliable. Flush the entire brake system with fresh DOT 4 fluid every two years -
  2. 2 this single maintenance item prevents most master cylinder failures
Cost mentioned in fix
$30$80

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Other known issues

Minor Brakes

Brake Servo Failure (Later Cars)

Hard brake pedal with dramatically reduced braking assistance. In the worst cases, reported by MGB Register members, fluid can leak internally into the servo canister -- the pedal feels normal until you press it, then all the fluid disappears into the servo and you have no brakes at all.
Critical Brakes

Seized Rear Brake Cylinders

One rear wheel locks or drags. The car pulls to one side under braking. A burning smell from one rear wheel after driving.
Minor Body and Structure

Sill Corrosion (Inner and Outer)

The outer sill skin bubbles, softens, and eventually perforates. In advanced cases, the outer sill crumbles when prodded. The inner sill -- the structural member -- rots from inside the box section and loses its load-bearing capacity.
Critical Body and Structure

Floor Pan Corrosion

Soft or perforated floor pans, particularly in the footwells and under the seats. Wet carpet is a telltale sign. In severe cases, you can see the road through the floor.
Minor Body and Structure

A-Post Corrosion

Rust at the base of the windscreen pillars where they meet the scuttle panel. This area can be invisible until advanced.
Minor Body and Structure

Door Skin Corrosion

Rust along the bottom edge of each door, working upward from the inside.
All MGB Roadster problems