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hydraulic fluid and brake fluid for Alle 2CValt

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Citroën A-Series Models: Brake Fluid for Front Drum Brakes

On Citroën A-series models with front drum brakes, standard glycol-based brake fluid is typically used, such as DOT 3 or DOT 4.

This applies to many early and mid-range models in the Citroën A-series family, for example:

  • Citroën 2CV with front drum brakes
  • Citroën Dyane with front drum brakes
  • Citroën Ami 6
  • Citroën Ami 8 with front drum brakes
  • Citroën Méhari with front drum brakes
  • Citroën AZU, AK, AKS, and other panel vans based on the A-model with drum brake systems

The important basic rule is:

  • Front drum brakes = DOT brake system
  • Front disc brakes = hydraulic brake system

Therefore, LHM must not be used in vehicles with front drum brakes. However, the actual brake system installed is always the deciding factor. Especially in older vehicles, modified vehicles, or vehicles with an unknown history, the system should be thoroughly checked before performing any work on the brakes.

Why the right brake fluid is so important

DOT brake fluid and LHM are chemically completely different fluids.

DOT brake fluid is glycol-based. LHM is a mineral hydraulic fluid. The seals, boots, wheel brake cylinders, master cylinder, and connecting parts of the brake system are each designed for the appropriate fluid.

If DOT and LHM are mixed up or combined, seals can swell, leak, or fail. In the worst-case scenario, the entire brake system must be disassembled, cleaned, and overhauled.

If the vehicle’s history is unknown, you should therefore always first determine with certainty which fluid is in the system.

Distinguishing features of a DOT brake system with drum brakes

Typical indicators of a DOT brake system are:

Characteristic Meaning
Front drum brakes DOT brake system
Rear drum brakes Standard on A-models
Clear to light amber brake fluid Indicates DOT brake fluid
No green LHM master cylinder Indicates DOT version
No front brake discs on the transmission No typical LHM disc brake system

Important: The color of the fluid alone is not conclusive evidence. Old brake fluid can be dark, cloudy, or contaminated. If in doubt, the brake system should be professionally inspected.

DOT Brake Fluid Change Interval

DOT brake fluid absorbs moisture over time. This lowers the boiling point of the brake fluid. Additionally, corrosion and deposits can form in the master cylinder, wheel cylinders, and lines.

A useful maintenance guideline is:

Replace DOT brake fluid approximately every 2 years.

For vehicles that have been idle for a long time, have an unknown maintenance history, or show visible contamination in the reservoir, the brake fluid should be completely replaced. A quick bleed is often insufficient in such cases.

Citroën A-series models with drum brakes: typical weak points and bleeding

Typical weak points in A-models with drum brake systems

1. Old or contaminated brake fluid

Old DOT brake fluid can absorb water and thus cause corrosion in the brake system. The master cylinder and wheel cylinders are particularly affected.

Typical signs include:

  • dark or cloudy brake fluid
  • rust or dirt in the reservoir
  • spongy brake pedal
  • uneven braking
  • seized wheel brake cylinders
  • Leaky seals

2. Seized wheel brake cylinders

In drum brake systems, wheel brake cylinders are a common weak point, especially after long periods of inactivity. They can seize up, become stiff, or leak.

Typical signs include:

  • uneven braking
  • damp brake anchor plates
  • Fluid loss
  • poor pedal feel
  • Brake does not release cleanly
  • Vehicle pulls to one side when braking

If a wheel brake cylinder is leaking or seized, the brake on the affected axle should always be fully inspected.

3. Incorrectly adjusted drum brakes

On Citroën A-series models with drum brakes, mechanical adjustment is particularly important. An incorrectly adjusted drum brake often results in a long pedal travel, even though the brake system has already been bled hydraulically.

The brake shoes must be adjusted so that they engage cleanly and evenly with the brake drum. If the eccentrics, adjusters, or brake shoes are incorrectly adjusted, braking performance may be uneven.

Typical consequences of incorrect adjustment are:

  • long pedal travel
  • poor braking performance
  • uneven braking
  • vehicle pulling to one side when braking
  • poor parking brake performance
  • Increased wear on brake shoes and drums

Therefore, drum brakes should always be mechanically adjusted correctly first before the brake system is evaluated or bled again.

4. Worn brake shoes and brake drums

Brake shoes and brake drums are subject to natural wear. If the linings are glazed, oily, heavily worn, or worn unevenly, braking performance can be significantly reduced.

Worn or out-of-round brake drums can also cause problems.

Typical signs include:

  • brake squeal
  • uneven braking performance
  • Noises when braking
  • poor pedal feel
  • frequent readjustment required
  • Poor handbrake performance

Oily brake pads should not be used any longer. Oil or brake fluid on the pads significantly reduces braking performance.

5. Leaking master cylinder

A leaking or internally worn master cylinder often manifests as decreasing pedal pressure or fluid loss. Even if no major external leak is visible, pressure may be escaping internally past the piston.

Typical signs include:

  • Brake pedal sinks slowly
  • Pedal feels soft
  • Fluid loss in the reservoir
  • Moisture in the pedal well or dashboard area
  • Uneven brake pressure

If a defective master cylinder is suspected, do not put any further load on the brake system until the cause has been determined.

6. Corroded brake lines and connections

Brake lines and fittings can corrode in older vehicles. Areas under the vehicle, at junctions, brackets, and fittings are particularly at risk.

Typical signs include:

  • Rust on brake lines
  • Damp fittings
  • Fluid loss
  • Bleed nipples that are difficult to loosen
  • uneven brake pressure

Brake lines should not be inspected only superficially. Hidden areas and mounting points are also important.

7. Problems with the parking brake

On many Citroën A-series models, the parking brake acts on the front wheels due to its design. On vehicles with front drum brakes, it engages the front drum brake system.

Poor handbrake performance is often caused by:

  • incorrectly adjusted brake shoes
  • sticky handbrake mechanism
  • worn linings
  • oily or dirty drums
  • incorrectly adjusted cables or linkage
  • Worn brake drums

The parking brake should always be checked separately and adjusted correctly.

Bleeding the brake system with front drum brakes

The following description applies to Citroën A-series models with a DOT brake system and front drum brakes.

Preparation

You will need:

Part / Tool Note
DOT 4 brake fluid Use only for DOT brake systems
Clear hose Fits the bleed nipple
Collection container Clean and stable
Matching ring wrench For opening the bleed nipples
Helper or pressure bleeder Use pressure bleeder only at low pressure
Brake cleaner and rags Carefully remove brake fluid and dirt

Before bleeding, check the following:

  1. Park the vehicle securely and prevent it from rolling away.
  2. If necessary, jack up the vehicle securely.
  3. Clean the reservoir to prevent dirt from entering the system.
  4. Check for the correct brake fluid: DOT fluid is typically used for front drum brakes.
  5. Adjust all drum brakes mechanically to the correct settings.
  6. Check the master cylinder, brake lines, wheel cylinders, and connections for leaks.

Bleeding sequence

In practice, work from the longest to the shortest line. Depending on the model and line routing, the order may vary slightly.

A common order is:

  1. rear right
  2. rear left
  3. front right
  4. front left

It is crucial to work on each bleed point until clean, bubble-free brake fluid emerges. The reservoir must never run dry during bleeding, otherwise air will re-enter the system.

Bleeding with an assistant

  1. Fill the reservoir to the mark with the appropriate DOT brake fluid.
  2. Attach the hose to the bleed nipple and place the end of the hose into a collection container.
  3. Slowly press the brake pedal two to three times and then hold it under pressure.
  4. Briefly open the bleed nipple to allow brake fluid and air to escape.
  5. Do not fully depress the brake pedal all the way to the floor to avoid putting unnecessary strain on older seals in the master cylinder.
  6. Close the bleed nipple again.
  7. Only then release the brake pedal.
  8. Repeat the process until no more air bubbles escape.
  9. Check the fluid level after each wheel and top up if necessary.
  10. Clean all bleed nipples and check them for leaks.

The brake pedal should be pressed slowly. Pumping too quickly can cause air and brake fluid to foam, making bleeding more difficult.

Bleeding with a pressure bleeder

A pressure bleeder can be used, but should be used with caution on older vehicles. With old reservoirs, caps, and seals, only low pressure should be used.

A reasonable pressure range is usually around 0.5 to 1.0 bar, provided the cap fits tightly and the system is suitable for this.

The advantage of this method: The master cylinder is protected because the brake pedal is not pressed all the way into otherwise unused areas of the cylinder.

Check after bleeding

After bleeding, the brake pedal should feel firm. Then check the following points:

  1. Press the brake pedal several times. It must not sink slowly.
  2. Check all bleed nipples and connections for moisture.
  3. Check all drum brakes again and adjust them correctly.
  4. Adjust and check the parking brake separately.
  5. Take the vehicle for a careful test drive.
  6. After the test drive, check whether individual wheels become unusually warm.

A hot wheel may indicate a dragging brake, a seized wheel brake cylinder, a drum brake set too tight, or a hydraulic return problem.

If the brake pedal remains soft

If the pedal remains soft after bleeding or the pedal travel is too long, the following causes are often possible:

Symptom Possible cause
Pedal soft, no visible leak Air still in the system
Long pedal travel, weak braking effect Drum brakes incorrectly adjusted
Pedal sinks slowly Master cylinder has an internal leak
One wheel barely brakes Wheel brake cylinder seized, line clogged, or air in the system
Brake releases poorly Wheel brake cylinder seized, return mechanism malfunctioning, or brake set too tight
Vehicle pulls to one side when braking Uneven adjustment, seized wheel brake cylinder, or dirty brake pads
Handbrake does not work properly Brake shoes, adjustment, cable, or mechanism faulty

Important note

For Citroën A-series models with front drum brakes, the appropriate DOT brake fluid should always be used.

  • Front drum brakes = DOT system
  • Front disc brakes = LHM or LHM+
  • Never mix DOT and LHM

If the vehicle has been parked for an extended period, the brake system should not only be bled but also fully inspected. In particular, the wheel brake cylinders, master cylinder, brake lines, drums, brake shoes, and the correct adjustment of the drum brakes are crucial for ensuring that the vehicle brakes safely, evenly, and reliably.