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hydraulic fluid and brake fluid for Citroën 2CV 2CV6

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Brake fluid reservoir with locking cap, for the brake system LHM. Suitable for Citroen 2CV6 with

front disk brake system. The reservoir is green dyed and has a white cap. The connection on the master brake cylinder is from center to center: 70mm. Or.Nr.: 95554585

LHM+ green, hydraulic fluid. 1 liter. Suitable for Citroen 2CV starting from year of construction

1981 as brake fluid (vehicles with disc brake). Citroen DS starting from year of construction 1967, Citroen CX, GS, etc. for hydraulics.

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Brake fluid for the Citroën 2CV6: DOT or LHM?

With the Citroën 2CV6, it’s not just the model designation that matters. What’s important is which brake system is installed.

For a 2CV6 with front disc brakes, LHM or LHM+ should be used in the brake system. This is the green, mineral-based Citroën hydraulic fluid. DOT brake fluid must not be used in this system.

The situation is different for a 2CV6 with front drum brakes. These vehicles typically use classic glycol-based brake fluid, either DOT 3 or DOT 4 depending on the model.

The simple basic rule

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

Therefore, please always check the actual brake system installed and do not rely solely on the designation “2CV6.”

Why the right fluid is so important

LHM and DOT are chemically completely different fluids. LHM is mineral-based, while DOT brake fluid is synthetic or glycol-based. The seals, boots, hoses, wheel brake cylinders, brake calipers, and the master cylinder are each designed for the appropriate fluid.

A common and serious mistake is topping off an LHM system with DOT brake fluid. This can attack, cause swelling, or destroy seals and rubber parts. In this case, the entire brake system must be overhauled. We have put together a special brake fluid set specifically for this oversight.

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

Identifying features of the LHM brake system on the Citroën 2CV6

Typical indications of an LHM brake system are:

Characteristic Meaning
Green fluid in the reservoir Indicates LHM
Green master cylinder or green marking Indicates LHM version
Front disc brakes on the transmission Late 2CV6 models from 1981 onward, LHM
Front drum brakes Earlier brake system up to 1981, DOT

Important: Color alone is not always a reliable indicator. Old, contaminated, or improperly mixed fluid can discolor. If in doubt, the brake system should be professionally inspected.

Brake fluid change interval

LHM also ages in the brake system. Although LHM absorbs less water than traditional DOT brake fluid, dirt, debris, and moisture can accumulate in the system over time.

A sensible maintenance guideline is:

Replace LHM in the brake system at least every 40,000 km or every 5 years (according to Citroën). However, we recommend changing it every 2 years.

For vehicles that have been parked for a long time, simply bleeding the system is not enough. In such cases, it is advisable to completely replace the fluid and thoroughly inspect the entire brake system.

Typical weak points of the Citroën 2CV6 brake system

1. Mixing up DOT and LHM

Using the wrong brake fluid is one of the most critical mistakes with the 2CV6. LHM and DOT must not be mixed together. If you are unsure which fluid was used, do not drive the vehicle until the brake system has been inspected.

If you suspect the fluid was filled incorrectly, simply topping it off or a quick flush is not enough. The master cylinder, brake hoses, wheel cylinders, brake calipers, and seals must be carefully inspected and, if necessary, replaced or overhauled. We have put together a special brake kit in case the brake fluids have been mixed up.

2. Seized rear wheel cylinders

The rear drum brakes are often affected by corrosion in stationary vehicles. Wheel brake cylinders can seize up or develop leaks.

Typical signs include:

  • uneven braking
  • damp anchor plates
  • Fluid loss
  • gradually decreasing pedal pressure
  • poor braking performance on the rear axle

3. Incorrectly adjusted rear drum brakes

The 2CV has rear drum brakes. Their correct adjustment is crucial for a short pedal travel and consistent braking performance.

If the eccentrics or adjusters are set incorrectly, the brake pedal may have a long travel, even though the system has been properly bled hydraulically. Therefore, the rear drums should always be mechanically adjusted correctly before assessing the brake system.

And if your 2CV6 also has front drum brakes, precise adjustment is even more important.

4. Sticky front brake calipers on disc brake models

On the 2CV6 with disc brakes, the front brake calipers are located on the inside of the transmission. There, they are exposed to heat, dirt, and oil mist.

Possible problems include:

  • sticky pistons
  • leaky calipers
  • contaminated brake pads
  • oil on the brake discs
  • uneven braking

5. Parking Brake

On the 2CV6 with disc brakes and a front drum brake, the parking brake acts on the front brake discs or drum, respectively, and not on the rear wheels. This is due to the vehicle’s design and is initially unfamiliar to many.

Poor handbrake performance is often caused by:

  • incorrect adjustment
  • worn handbrake pads on disc brakes, incorrectly adjusted brake shoes on drum brakes
  • stiff operation
  • dirty or oily components

6. Old brake hoses

Brake hoses may still look fine on the outside, but may already be swollen or damaged on the inside. This can cause poor brake pressure return. But note: Only very early 2CV6 models from the early 1970s have brake hoses.

Typical consequences are:

  • Brakes release slowly
  • One wheel remains warm or hot
  • uneven braking performance
  • spongy pedal feel

7. Leaking master cylinder

A defective or leaking master cylinder is often indicated by decreasing pedal pressure, fluid loss, or moisture in the area of the pedal well and dashboard.

In a hydraulic brake system, pay particular attention to green, oily traces.

Bleeding the Citroën 2CV6 brake system with disc brakes

The following description applies to the late-model 2CV6 with front disc brakes and a hydraulic brake system.

Preparation

You will need:

Part / Tool Note
LHM or LHM+ Use only for LHM brake systems
Transparent hose Fits the bleed nipple
Collection vessel Clean and stable
8 mm ring wrench For opening the bleed nipple
Helper or pressure bleeder Use pressure bleeder only at low pressure
Brake cleaner and rags LHM is oily; brake discs and pads must remain clean

Before bleeding, check the following:

  1. Park the vehicle securely and jack it up.
  2. Clean the reservoir to prevent dirt from entering the system.
  3. Check for the correct fluid: For front disc brakes, use LHM or LHM+.
  4. Adjust the rear drum brakes mechanically to the correct settings.
  5. Check the master cylinder, lines, wheel cylinders, and brake calipers for leaks.

Bleeding sequence

In practice, work from the longest to the shortest line:

  1. rear right
  2. rear left
  3. front left (both calipers are bled via the left caliper)

It is crucial that the system is completely bled, the reservoir never runs dry, and work is performed on each wheel until bubble-free, clean fluid emerges.

Bleeding with an assistant

  1. Fill the reservoir with brake fluid up to the mark.
  2. Connect 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 fluid and air to escape (but only depress the brake pedal 3/4 of the way to avoid damaging the seals).
  5. Close the bleed nipple again.
  6. Only then release the brake pedal.
  7. Repeat the process until no more air bubbles escape.
  8. Check the fluid level after each wheel and top up if necessary.
  9. Clean all bleed nipples and check for leaks.

The brake pedal should be pressed slowly. Pumping too quickly can cause air and 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 suitable range is usually around 0.5 to 1.0 bar, provided the cap fits tightly and the system is designed for it.

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. Therefore, when bleeding manually, the pedal should also only be pressed about 3/4 of the way down.

Check after bleeding

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

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

A hot wheel can indicate a grinding brake, a seized piston, or a swollen brake hose on the inside (on early 2CV6 models).

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 performance Rear 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 Brake hose swollen on the inside or piston stuck
Parking brake does not work properly Handbrake pads, adjustment, or mechanism faulty

Important Note

On the 2CV6 with disc brakes, do not experiment with the brake fluid.

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

If the vehicle has been parked for an extended period, the brake system should not only be bled but also thoroughly inspected. In particular, the wheel brake cylinders, brake hoses, master cylinder, brake calipers, and the adjustment of the rear drum brakes are crucial for ensuring that the 2CV brakes safely, evenly, and reliably.