¿Qué pasa si se mezcla líquido de frenos DOT 3, DOT 4, DOT 5 o DOT 5.1?

Recomendaciones sobre la mezcla de líquidos de frenos según especificaciones DOT.

¿Por qué el pedal se va al fondo si el sistema ha sido purgado y no hay fugas visibles?

Causas de fallas en los sellos que pueden provocar que el pedal se vaya al fondo.

¿Cómo diferencio si un pedal duro se debe al servofreno (booster) o a una manguera del sistema hidráulico obstruida?

Prueba de rueda bloqueada por obstrucción en manguera del sistema hidráulico: El síntoma es que el pedal se siente duro. La prueba permite diagnosticar si el pedal está muy duro y auto frena en forma recta y cuando se libera el pedal el sistema de frenos se libera permitiendo que las ruedas giren.

¿Cómo compruebo si una pulsación en el pedal es por discos alabeados o por una activación falsa del ABS?

Diagnóstico de discos alabeados: El síntoma es alta pulsación o vibración a altas velocidades disminuyendo a medida que la velocidad del vehículo disminuye; adicional el volante de la dirección también vibrará en el momento del frenado. Si los discos son los traseros se sentirá la vibración en la parte trasera del vehículo. La vibración aparece a muy baja velocidad (entre 30 y 10 km/h) y se mantiene justo hasta antes de detenerse el vehículo. Se produce ruido en el módulo ABS.

¿Cuál es el orden de purgado exacto para el sistema hidráulico de frenos sin ABS?

El proceso que se debe seguir incluye precauciones después de hacer el proceso de purga.

¿Cuál es el orden de purgado exacto para el sistema hidráulico de frenos con ABS?

Secuencia tradicional, secuencia en diagonal, purga del módulo ABS y proceso combinado.

¿Por qué una sola rueda se queda bloqueada (frenada) de forma intermitente?

Primera causal: Falla mecánica en la rueda. Segunda causal: Problemas hidráulicos. Tercera causal: Fallas en el módulo ABS o cilindro maestro. Determinación del origen exacto del bloqueo.

¿Es estrictamente necesario usar un escáner automotriz para purgar los frenos?

No se necesita escáner para purgar el sistema hidráulico de frenos en ciertos casos. Se necesita escáner para purgar el sistema hidráulico de frenos en otros casos específicos.

¿Cada cuánto hay que cambiar el líquido de frenos?

La periodicidad de cambio depende de varios factores. Periodicidad de cambio según DOT.

¿Por qué cambiar los cilindros de freno si aún funcionan, pero presentan herrumbre u oxidación?

Las razones técnicas para cambiar los cilindros ante herrumbre son: Contaminación del líquido de frenos, pérdida súbita de presión, y bloqueo o atascamiento.

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What happens if you mix DOT 3, DOT 4, DOT 5, or DOT 5.1 brake fluid?

DOT 3, DOT 4, and DOT 5.1 brake fluids are compatible because they share a glycol chemical base, which means they dissolve well into one another.

DOT 3, DOT 4, and DOT 5.1 fluids must not be mixed with DOT 5 fluids, as DOT 5 has a silicone chemical base. Mixing it with a glycol-based fluid creates resins (a thick sludge) that damage the hydraulic brake system.

When mixing fluids with compatible chemical bases, the mixture adopts the quality of the lowest-rated fluid. The boiling point of DOT 3 is 205°C; the boiling point of DOT 4 is 230°C; the boiling point of DOT 5.1 is at least 270°C. Mixing them will lower the boiling point to that of the lowest-rated fluid.

Recommendations:
• Do not mix DOT 3, DOT 4, and DOT 5 brake fluids; it is preferable to replace the fluid entirely with one of the same specification.
DOT 3 can be mixed with DOT 4 in an emergency.
• Do not mix DOT 4 with DOT 3, as this reduces the boiling temperature.
• Do not mix DOT 5.1 with DOT 4 or DOT 3, as this reduces the boiling point.
• Never mix DOT 5 with other fluids.

Why does the pedal go to the floor if the system has been bled and there are no visible leaks?

The pedal goes to the floor due to a loss of hydraulic pressure inside the system.

The most common cause is an internal leak through the seals in the master cylinder.

Damage to the internal seals of the master cylinder that reduces or compromises the seal allows fluid to pass from one chamber to another within the pump itself instead of being sent to the wheel cylinders.

Causes of seal failure:
• Wear from use. Over time and with use, the seals crystallize and crack, losing elasticity and sealing capacity. For this reason, it is recommended to periodically replace the master cylinder and brake cylinders even if they do not show external leaks.
• Damage generated during bleeding. Avoid pushing the pedal all the way to the floor manually during the bleeding process. In normal operation, the pedal never reaches the floor; by forcing it to the floor, the seals move beyond their normal range, passing through areas that may have accumulated rust or dirt. Any particle inside the pump will tear the rubber of the seals.
• Air trapped in the ABS module. If the system ever ran out of fluid in the reservoir, air enters the system. When bleeding the system mechanically or conventionally, the module cannot expel the air (because air is highly compressible); the air acts like a spring, compressing and absorbing all the hydraulic pressure, causing the pedal to go to the floor.
• Hoses with excessive extreme flexing. Even if the hoses do not show leaks, the rubber fatigues, which leads to the rubber expanding when braking instead of the pressure reaching the cylinder or caliper pistons, thereby reducing pressure.
• Damage to the self-adjustment mechanism of the drum brakes. If the mechanism gets stuck or jammed, the system requires very high pressure to transmit hydraulic pressure to the pistons.
• Inverted calipers. If calipers are mounted inverted, the bleeder screw or port remains facing upward, preventing the complete exit of air.

How do I differentiate if a hard pedal is due to the brake booster or an obstructed hydraulic system hose?

• The brake booster uses the vacuum generated in the engine (by moving a diaphragm) to increase or multiply the braking force or pressure.
• In the hydraulic system, the hoses transmit oil pressure to move the pistons and press the brake linings or pads.
• First, verify if the brake linings or pads release when the brake pedal is pressed and released, or if they remain stuck. When the fault is the brake booster, the pedal becomes hard when pressed and "releases" when the brakes are let go. A hydraulic system hose acts like a one-way valve (toward the linings or pads); if the problem is an obstruction when releasing pedal pressure, the brake system remains locked.
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Test for a wheel locked by an obstruction in a hydraulic system hose:
➤ The symptom is that the pedal feels hard.
The test:
◦ Lift the car.
◦ Press the brake pedal and release it.
◦ Try to turn the wheel.
Diagnosis:
◦ If the wheel or wheels are locked, open the bleeder port; if a jet of brake fluid comes out at high pressure, the hose is obstructed.
‍
➤ The symptom is that the pedal is very hard and self-brakes in a straight line, and when the pedal is released, the brake system releases, allowing the wheels to turn.
The test:
◦ With the engine off, pump the pedal at least 5 times to eliminate the vacuum in the lines and inside the brake booster.
◦ Keep the brake pedal pressed and start the engine.
◦ If the pedal does not sink slightly, the brake booster or its vacuum line is not working.
◦ If you hear an air leak sound, find the leak point and replace the component.
◦ If no leak is heard and the vacuum hose is not obstructed, the problem is internal to the brake booster.

How do I check if a pedal pulsation is due to warped discs or a false ABS activation?

• First, determine at what speed the pulsation occurs.
• With warped brake discs, the pulsation is proportional to the vehicle's speed when the brake pedal is pressed. The higher the speed, the more vibration will be felt in the brake pedal.
• A fault in the ABS unit activates at very low speeds (almost when the vehicle is coming to a stop) and generates a noise (knocking), and usually turns on the fault light on the instrument cluster.
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Diagnosis of warped discs:
➤ The symptom: high pulsation or vibration at high speeds that decreases as the vehicle's speed decreases; additionally, the steering wheel will also vibrate when braking. If the discs are the rear ones, the vibration will be felt in the rear of the vehicle.
The test:
◦ Lift the car.
◦ Remove the wheel.
◦ Install a dial indicator (magnetic base on the chassis and the tip of the indicator on the disc).
◦ Rotate the disc.
Diagnosis:
◦ If the needle variation on the indicator is greater than 0.05 mm, the disc is warped.
Diagnosis of false ABS module activation.

➤ Symptom: The vibration appears at very low speed (between 30 and 10 km/h) and continues right up until the vehicle stops. Noise is produced in the ABS module.
The test:
◦ Disconnect the ABS system fuse.
◦ Disconnecting the fuse will deactivate the ABS system, leaving only the normal operation of the brake system; the ABS fault light will turn on.
◦ Perform a road and braking test in a safe place.
◦ If the vibration and noise disappear, the problem is a false activation of the ABS module.
◦ Follow the ABS system diagnostic process established in the service manual.

What is the exact bleeding order for a hydraulic brake system without ABS?

The bleeding sequence in a brake system without ABS must start from the wheel furthest from the master cylinder.

The hydraulic fluid must be completely changed using exclusively the DOT specification established by the vehicle manufacturer.

The process to follow is as follows:
1) Ensure all lines and hoses are connected correctly.
2) Verify or check that the fluid level in the master cylinder is above the "MAX" mark.
3) Connect a transparent hose to the bleeder valve of the furthest wheel and submerge the other end in a container of brake fluid.
4) Ask an assistant to press the brake pedal several times and finally hold it pressed all the way down.
5) Open the bleeder valve to let air and old fluid out. Close the valve before the assistant stops pressing the brake pedal.
6) Repeat steps 4 and 5 until the brake fluid comes out clean and free of bubbles.
7) Check the brake fluid level in the master cylinder. Add fluid until the level reaches the "MAX" mark.
8) Repeat the cycle in the same order for the remaining three wheels.

Precautions after performing the bleeding process:
1) Verify that the brake fluid level is above the "MAX" line. Add more if necessary.
2) Pump the brake pedal several times with the engine off: It should feel firm, not "spongy."
3) Verify that there are no visible leaks at the bleeder valves, line and hose connections, the base of the master cylinder, or the junction between the reservoir and the master cylinder.
4) Secure the master cylinder reservoir cap correctly.
5) Clean any residue and fluid from the calipers and drums, as brake fluid is highly corrosive.
6) Dynamic speed test:
◦ Low-speed test: Start the vehicle and take a short drive in a straight line.
◦ At low speed, press the brake pedal and confirm that the vehicle comes to a complete stop.
◦ Verify that the vehicle does not pull to one side during braking.

What is the exact bleeding order for a hydraulic brake system with ABS?

The bleeding sequence in a brake system with ABS is based on the physical distance from the main brake pump or master cylinder and the ABS module, starting from the wheel furthest away and ending at the closest wheel. Some manufacturers require a diagonal order or a specific sequence controlled by the diagnostic scanner.
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Traditional sequence:
1) Rear right wheel.
2) Rear left wheel.
3) Front right wheel.
4) Front left wheel.

Diagonal sequence:
1) Rear right wheel.
2) Front left wheel.
3) Rear left wheel.
4) Front right wheel.

Bleeding the ABS module:
1) This type of process removes air bubbles trapped inside the ABS module.
2) The scanner must be connected.
3) Look for the specific function in the ABS or ESP bleeding menu.
4) During the bleeding cycle, the pump inside the ABS module will turn on, opening and closing the valves to expel air bubbles from inside the unit.
5) The sequence for this process is indicated on the scanner screen: the order indicated on the screen must be followed strictly. The traditional bleeding method is not used; instead, it is performed wheel by wheel:
◦ The scanner activates the internal valves of the ABS module for one wheel at a time, indicating when to open and close the bleeder valve.
◦ The exact order depends on the programming of the vehicle's brake system manufacturer.
◦ Bleeding with a scanner generates high-pressure pulses to extract air from inside the module.

Combined process:
1) Bleed the ABS module with the scanner.
2) Final manual bleed:
◦ After bleeding the ABS module with the scanner, a round of manual bleeding must be performed using the traditional sequence starting from the furthest wheel to ensure no bubbles remain in the lines.

Why does a single wheel stay locked (braked) intermittently?

When a wheel locks up or remains "braked" intermittently, the problem is that the hydraulic pressure is not being released completely or correctly after releasing the brake pedal, or that a mechanical component is sticking due to movement or temperature.
‍
First cause: Mechanical failure at the wheel.
1) Guide pins or bolts lacking lubrication due to rust buildup or loss of grease. The caliper moves well sometimes, but at other times, it misaligns.
2) Caliper piston rusted due to wear, which creates a "neck" in the cylinder or tears the seal, allowing dirt to enter. The piston moves when the brake pedal is pressed but does not return smoothly.
3) Parking brake mechanism stuck due to internal corrosion or a frayed cable.

Second cause: Hydraulic problems.
1) Brake hose collapsed internally; as the rubber degrades, it creates a loose layer that acts much like a one-way (check) valve, preventing the fluid from returning.
2) Excess fluid in the reservoir creates thermal overpressure, as it does not allow the fluid to expand, keeping its temperature high.

Third cause: ABS module or master cylinder failures.
1) ABS valve or solenoid stuck due to dirt or corrosion, which traps pressure.
2) Obstruction in the master cylinder return ports due to corrosion or dirt.

Determining the exact source of the lockup:
1) Lift the wheel.
2) Open the bleeder screw on the lifted wheel.
3) If the wheel releases immediately, the problem is hydraulic in origin.
4) If the wheel remains stuck, the problem is mechanical in origin.

Is it strictly necessary to use an automotive scanner to bleed the brakes?

No, it is not strictly necessary to use a scanner to bleed the brakes in most cases.
‍
A scanner is not needed to bleed the hydraulic brake system when:
1) Routine maintenance: Only if changing the brake fluid without removing or draining the fluid from the ABS module.
2) Routine maintenance: In systems that do not have an ABS module.
3) Basic component replacement: When changing brake linings, shoes, pads, discs, or calipers.

A scanner is needed to bleed the hydraulic brake system when:
1) Replacing the ABS module.
2) Disconnecting and/or removing the ABS module.
3) Replacing the master cylinder.
4) If the system has drawn air in from the main reservoir.
5) If the brake pedal remains "spongy" after having previously performed the bleeding procedure with a scanner.
6) If the vehicle manufacturer's service manual requires the use of a scanner to activate the ABS module after any brake system maintenance work.

How often should brake fluid be changed?

Brake fluid should be changed based on either mileage or time, whichever comes first.
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The change interval depends on:
1) The system having no leaks. Leaks allow moisture to enter and shorten the life of the brake fluid. If a leak is discovered, the fluid must be completely replaced after the problem is fixed.
2) The fluid specification; it differs for DOT3, DOT4, DOT5.1, and DOT 5.
3) In general, it is recommended every one (1) to five (5) years or between 40,000 and 60,000 kilometers, depending on the DOT rating of the fluid.

Change interval by DOT:
1) DOT 3: Change at least every year (1 year), as its polyglycol base absorbs moisture rapidly.
2) DOT 4: Features an improved polyglycol base, allowing for slower degradation than DOT 3. It is recommended to change it at least every two years (2 years).
3) DOT 5.1: Also polyglycol-based, but with an additive package that increases its boiling point and allows for greater fluidity in ABS systems. It is recommended to change it at least every two years (2 years).
4) DOT 5: Silicone-based, which allows it to repel water and makes it non-corrosive. It is recommended to change it every 3 to 5 years.

Why replace brake cylinders if they still work but show signs of rust or oxidation?

Oxidation is the result of a chemical reaction where metal gives up (loses) electrons in the presence of oxygen in the air.

Rust, the product of oxidation, is progressive and irreversible damage that weakens rubber seals and erodes cylinder material, eventually leading to partial or total cylinder failure. Cylinders should be replaced immediately if rust is present.
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The technical reasons for replacing rusted cylinders are:
1) Brake fluid contamination: Rust particles (iron oxide) enter the brake fluid and travel through the system, acting as abrasive elements that damage hydraulic system components through contact and friction (due to pressure).
2) Sudden pressure loss: Rust gets inside the pistons and the rubber-to-housing seal, causing them to seize and preventing movement.
3) Locking or seizing: Rust formation causes metal material to flake off, creating a rough surface that will tear seals and eventually cause leaks.

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