The Pedal That Creeps Down at the Traffic Light

Fault 1 - the sinking pedal. A pedal that holds, then creeps down at constant force with no external leak is fluid escaping past the master cylinder primary cup seal and returning to the reservoir. Nothing is lost, so the level never drops and there is no wet spot. An internal ABS hydraulic unit leak can produce a similar symptom but is far less common.

Fault 2 - the long pedal and 9-click handbrake. With 4 mm of shoe-to-drum clearance, the wheel cylinder pistons must travel 4 mm before the shoes touch the drum. That fluid has to come from somewhere, so the pedal sits low and extra travel is used before any braking force appears. The self-adjuster cannot catch up because the adjuster strut was never set after the drums were machined. Pumping restores height until the extra clearance is taken up again.

The two faults feel similar to a driver but are mechanically different.

The separating test: clamp the flexible hoses - only the rubber ones, never braided or ABS lines - or plug the master cylinder outlet ports. If the pedal still creeps with the outlets blocked, the master cylinder is bypassing internally. If it now holds, the leak is downstream: caliper, wheel cylinder or ABS unit. Do this before ordering parts, because it changes what you fit.

1. Master cylinder - replace or reseal; do not just top up and hope. Bench-bleed it before fitting.
2. Fluid - at 3.6 % moisture the boiling point has dropped enough to risk vapour lock under hard or repeated braking, and the two-year-old opened bottle is itself a moisture source. Flush the whole system with fresh DOT 4 from a sealed container until clean fluid runs at every bleeder. Do not mix DOT 5 (silicone) with DOT 4.
3. Rear brakes - set the self-adjusters, fit the shoes, adjust to a light drag and back off, confirm the adjuster actually ratchets, then set the handbrake to 4–6 clicks.
4. Bleed in the manual's sequence, usually right rear, left rear, right front, left front, keeping the reservoir above MIN throughout.
5. ABS - scan for stored codes and run any required bleed or calibration routine with the scan tool.
6. Verify - a stationary one-minute hold at firm pressure with no creep, then a controlled road test including an emergency stop in a safe area, checking for straight stopping and no pull.
7. Record the fluid moisture reading, the master cylinder test result and the adjustment figures on the job card.

Four millimetres of clearance per side means the wheel cylinder must displace a significant volume of fluid before the shoes touch. That volume comes out of pedal travel, so:

• Pedal reserve shrinks. If normal braking already uses that travel, there is less left for the emergency stop that matters.
• The wheel cylinder piston sits further out than designed. The lip seal then runs on a part of the bore it does not normally sweep - often rougher or lightly corroded - so it can weep or seize, especially with 3.6 % moisture fluid behind it.
• Oversize drums make it worse. Drums machined 0.8 mm oversize with standard-thickness linings give a smaller contact arc and need more travel for the same force.
• The handbrake becomes ineffective, and on a hill that is a real hazard.
• If the self-adjuster stays dead, clearance grows as the linings wear until the pedal reaches the floor before full braking force is developed.

Now the shortcut. Over-tightening the adjusters gives a hard, high pedal on the hoist, but the shoes then drag. Drag generates heat, heat boils old fluid and fades the brakes, and the linings wear out in weeks. Correct procedure is a light drag, then back off to the specified clearance, with a working self-adjuster - not compensating for a dead adjuster by preloading the shoes.