Replacing the main brake cylinder on a VAZ-2110: checking, repairing the GTZ

A smooth or sharp dip in the brake pedal, or its floating and vibration during braking, usually indicates a malfunction of the brake master cylinder . Most often, the reason for its malfunction is the loss of tightness of the rubber sealing cuffs or improper operation of the bypass valves.

To distinguish its malfunctions from other malfunctions of the brake system and find out how to check whether the master cylinder is working, read the article.

How to understand that the GTZ is bypassing brake fluid?

Vehicles use a system with two separate hydraulic circuits. You can read in detail about its task and work separately. The general principle is that when the brake pedal is pressed, the vacuum booster rod acts on the first piston of the GTZ, which, by compressing the brake fluid supplied from the reservoir, creates excess pressure in circuit 1 directly, and in circuit 2 indirectly by moving the second piston.

If the piston seals are severely worn, the GTZ bypasses: the liquid passes between the walls of the housing of the first, second or both pistons in the opposite direction and returns to the expansion tank. As a result, necessary to act on the brake cylinders is not created

There are two simple ways to check the operation of the brake master cylinder for bypass of brake fluid:

Method number 1 (performed with an assistant)

1. Unscrew the cap of the expansion tank in the engine compartment.
2. Have an assistant press the brake pedal while observing the condition of the fluid.
3. If, when pressed, the level decreases and remains until the pedal is released, the cylinder is in good condition.
4. If the fluid level begins to increase when the pedal is pressed or bubbles appear and gurgling is heard, the GTZ is bypassing.

Designation of GTZ terminals

Method number 2 (you can do it yourself)

1. Disconnect the brake pipes from the GTZ terminals.
2. Plug the fittings with bolts with suitable threads.
3. Depress the brake pedal.
4. If, after pressing the pedal, it sags a little, but does not go further and resistance is felt, the cylinder is properly maintaining high pressure.
5. If, when pressed, the pedal smoothly sinks to the end, this indicates a slight bypass, and if it quickly fails, the wear of the turbocharger is critical.

On cars where the braking system is equipped with pressure sensors, problems with the turbocharger can be indicated by glowing indicators on the dashboard and errors in the ECU memory. For example, P0557 - low signal level of the brake pressure sensor or C1301 - the pressure does not correspond to the position of the brake pedal limit switch.

Error 01435 and its interpretation on the VW Golf dashboard

Most manufacturers use their own problem numbering. In particular, for VAG cars, the following codes indicate problems with the GTZ:

• 01435 – problems with pressure sensor 1;
• 00813 – problems with pressure sensor 2;
• 02847 – front left wheel pressure sensor;
• 02848 – front right wheel pressure sensor;
• 18108 – incorrect signal from the brake pressure sensor.

These errors can occur both in case of problems with the gas turbine unit that cause a drop in pressure, and in the event of failure of the sensors themselves.

It is possible to determine 100% that the master brake cylinder is bypassing only by measuring the pressure at each outlet of the turbocharger.

Disassembly

To replace and repair a damaged master brake cylinder

• Carefully disconnect all pipelines from a part such as the main cylinder;
• Disconnect the block equipped with wires from the emergency brake fluid indicator. They are connected by terminals;
• It is necessary to prevent fluid leakage and contamination of the mechanism; to do this, it is necessary to cover the openings of the unit and pipelines;
• Next, you need to remove it along with the tank; to do this, unscrew the fastening nuts that secure it to the vacuum type amplifier;
• After the VAZ 2110 fluid level sensor is removed, you need to drain all the brake fluid from the cylinder and basque;

Signs of a faulty master cylinder

Among the symptoms indicating a malfunction of the master brake cylinder, the main signs can be identified:

Checking the GTZ in 5 minutes without removing it from the car: video

• pulling the car to the side when braking;
• overheating of the pads on one wheel;
• squeaks when pressing the brake pedal;
• pedal travel is too soft or hard;
• shortened pedal travel;
• brake pedal failures;
• holding the wheels with blocks after releasing the pedal;
• fluid leaks on the GTZ housing.

Most signs of a brake system malfunction appear when the brake pedal is pressed and are similar to other problems with the brake system. In particular, the failure of the pedal may indicate congestion or depressurization of the lines. Therefore, before checking the serviceability of the master brake cylinder, it is necessary to at least check the level of brake fluid in the reservoir, as well as the condition of the pads, discs and hoses .

How to Diagnose a Malfunctioning Master Cylinder

Symptoms of problems

The general technical condition of the car (including the brake system) can be checked using a personal diagnostic adapter - a car scanner. These types of devices are widespread and have a wide price range. We would like to draw your attention to the budget model of Korean production Scan Tool Pro Black Edition.

At a cost of about 2 thousand rubles. This scanner is capable of fully diagnosing your car (engine, gearbox, transmission, abs, srs and much more), which will pay for itself in 1-2 trips to the service station. The adapter is quite easy to use, has Russian-language software and is compatible with most cars produced in 1993. The device will also be useful when buying a used car, as it can show its real mileage and VIN.

The fluid brake system consists of many parts that can become unusable: pipes, wheel cylinders, calipers, drums and pads. Typical signs of a faulty master cylinder:

1. After pressing the pedal, the car stops slowly. The reason is that the cuffs of one or two pistons have lost their tightness - they have cracked or “floated”.
2. To slow down, you need to press the brake pedal hard. The phenomenon occurs due to swelling of the rubber of the piston seals.
3. The brake pedal travel is too short. The fluid inside the cylinder has nowhere to go because the compensation hole is clogged. Another option is that the passage is blocked by a swollen rubber seal.
4. A common symptom is pedal failure, the brakes coming on at the end of the stroke. This indicates complete wear of the cuffs; as a result, liquid penetrates behind the piston and rushes into the expansion tank - the cylinder “bypasses.”
5. The pads do not release the brake discs and drums and get very hot when driving. Options: one of the pistons is jammed or the bypass hole is clogged.

The listed symptoms of a GTZ malfunction are similar to malfunctions of other elements. Pedal failure also occurs when a large amount of air enters the tubes or loss of fluid in one of the working cylinders. Sluggish deceleration and increased force on the pedal are often caused by a breakdown of the vacuum booster - a cracked membrane or a lack of tightness at the joints of the hose that takes off engine vacuum.

There are signs that clearly indicate the performance of the main hydraulic cylinder and the malfunction of other elements:

• during braking, the car pulls to the side - the problem lies in a certain circuit or wheel;
• jamming of the brake mechanisms of one wheel;
• creaking and squeaking when braking;
• heating the discs and pads on one wheel.

If you eliminate these symptoms, it will become easier to check the brake master cylinder in a garage. This also includes obvious brake fluid leaks and the knocking sound of worn calipers.

Checking the brake master cylinder

A full check of the gas turbine engine for operability is carried out using a special high-pressure pressure gauge (0–250 atm). Using connecting fittings of the appropriate diameter, they are connected to the outlets of the master cylinder instead of tubes. A working turbocharger should create a pressure of up to 180–200 atm when the pedal is pressed. (bar). If the measurement results are lower, the cylinder is worn out and requires replacement or repair.

Brake Pressure Measuring Kit

The cost of a set of pressure gauges with adapters is about 15,000 rubles, so not every service station has it. Without a pressure gauge, you need to check the gas turbine engine using indirect signs. For diagnostics you may need the following materials and tools:

• brake union wrench (split or clamp), usually 10, 11, 12 or 13;
• a bottle of brake fluid (if there are leaks, the level is below normal);
• bolts with threads similar to the threads of the GTZ tube fittings.

For a full check, you will also need an assistant who will press the brake pedal during the diagnostic process.

How to understand that the brake cylinder is not working: technique

1. Inspect the wheel brakes and lines . Make sure that the problem is on the GTZ side and that the actuators are in order.
2. Inspect the brake master cylinder . Insufficient fluid level in the expansion tank and the presence of brake fluid leaks on the GTZ or VUT housing are an obvious sign of depressurization. If there is not enough fluid, but no signs of leakage are visible, add fuel fluid and check the operation of the brakes. Perhaps the GTZ is working properly and the culprit is a leak somewhere in the line.
3. If there are GTZ leaks, look where they occur .
   To search, you need to clean the cylinder body of the fluid (for example, with gasoline, solvent or alcohol), ask an assistant to pump the pedal, and in the meantime, look where the fluid leaks appear. Determining a GTZ malfunction using the example of a Hyundai Accent: video
4. Start the engine and pass the VUT hose . If, after squeezing the hose, the engine speed changes, the problem is not in the GTZ, but in the vacuum booster.
5. Start the engine (on old cars without VUT you can not start it) and press the brake pedal firmly . If it stays in one position, the GTZ is normal and maintains pressure properly, and if it sags smoothly, the cylinder is probably releasing the fuel fluid into the tank.
6. Look at the behavior of the liquid in the tank during operation . On a working turbocharger, when you press the pedal there should be no extraneous sounds, and the fluid level should drop slightly. If it remains unchanged, gurgling is heard, bubbles are visible - the piston cannot create the required pressure and the cylinder releases the fuel fluid back into the tank, which means it is not working. When you press the pedal, the level should drop and remain at that level until released. If it increases when the pedal is pressed, the GTZ does not hold pressure and bypasses fluid.
7. Plug the outlets of the turbocharger and check whether it holds pressure . To do this, you need to unscrew the brake pipes from the cylinder, and in their place screw in bolts with similar threads. After this, add fluid to the reservoir to the normal level and press the pedal. If the foot feels resistance and the pedal does not move further, the cylinder is properly holding pressure. If the pedal is pressed smoothly or fails altogether, the piston bypasses fluid, the turbocharger is faulty.

If after carrying out the manipulations it becomes clear that the brake cylinder is not working properly, you need to remove the turbocharger and disassemble it for troubleshooting, which will allow you to determine the true cause of the malfunction.

How to check a removed brake master cylinder

To dismantle and diagnose the GTZ you will need:

• split or clamp wrench for brake pipes;
• a large (from 10 cubic meters) syringe for pumping out fuel fluid and an empty container for draining brake fluid;
• a key for disconnecting the turbocharger from the VUT (most often at 13, 14 or 17) and keys for disassembling the turbocharger;

To disassemble the brake master cylinder for diagnostics, you need to:

Disassembling the brake cylinder to determine the breakdown: video

1. Pump out or drain the brake fluid from the expansion tank.
2. Disconnect the brake pipes from the GTZ outlets.
3. Unscrew the brake cylinder from the VUT.
4. Remove the GTZ from the car.
5. Unscrew the bolt plug (if any) in the front part of the GTZ and/or remove the stopper in the rear part (from the VUT side).
6. Inspect the inside of the VUT for leaks; if there are traces of fuel fluid there, the cylinder is clearly faulty.
7. Remove the pistons from the turbocharger, having previously disconnected their retainers - bolts or pins.
8. Wipe the pistons with a dry cloth, inspect them for wear, and assess the condition of the seals.
9. Wipe the inside of the cylinder body, inspect its mirror for burrs, holes, traces of corrosion and other defects.
10. Measure the gaps between the pistons and the cylinder walls, compare them with factory tolerances.
11. Inspect bypass windows, openings and outlets for blockages.

Based on the results of inspection of the GTZ parts, conclusions can be drawn about further repairs. If there are signs of wear on the rubber sealing cuffs, you can limit yourself to a small repair kit. If there is wear on the pistons, you need to buy a repair kit consisting of pistons and rubber bands. If the GTZ body itself has burrs, cavities, traces of corrosion and other defects inside, the assembly will have to be replaced.

After diagnosing the GTZ and rebuilding or replacing it, after installing it on the car, you should add brake fluid to the reservoir to the maximum mark and bleed the brakes.

Nuances of repair

O-rings require special attention. The time the rings are in isopropyl alcohol should not exceed twenty seconds, after which they should be dried immediately using a compressor.

The surfaces of the mirror, as well as the piston elements, must be completely clean and free of rust. Every disassembly and repair of a faulty brake master cylinder must be accompanied by replacement of the O-rings, even if they are in good condition. The cuffs of the device also require attention; if they are swollen and frayed, they must be replaced.

After all, it is necessary to check the elasticity of the piston springs; this should be done under load. The length of the spring under load should be 39.01–45.9 N (3.8–4.8 kgf) - 41 mm, with another option the following indicators should be 82.01–99.48 N (8.35–10 .15 kgf) – 21 mm. When free, the spring should have a length of 59.8 mm. If the springs do not have such indicators, then they must be replaced.

FAQ

• When the engine is running, the pedal slowly sinks to the floor with constant force, is it necessary to change the turbocharger?

  Smooth subsidence of the pedal is a frequent sign of leaking GTZ seals. In this case, it is possible to repair the part by installing new cuffs from the repair kit.

• Brake fluid leaves the reservoir, but then appears, is it the GTZ?

  Changes in the level of brake fluid in the reservoir are not necessarily a sign of a breakdown of the turbocharger. The fuel fluid can also either go down or rise due to airing, boiling due to overheating of the pads, or jamming of the actuator cylinders.

• Does it make sense to install a repair kit or is it better to replace the GTZ?

  It makes sense to install a repair kit when only the rubber parts are worn out. If the piston is severely worn or the housing is damaged, it is better to replace the entire turbocharger.

Methods for diagnosing VUT

If one of the above symptoms is detected, you should immediately check the vacuum brake booster for functionality without removing it from the car. Diagnosis is simple:

1. Start and warm up the engine.
2. Leaving the engine idling, use your hand or pliers to press down the vacuum outlet pipe leading from the manifold. Another option is to disconnect it from the fitting and plug the latter with a wooden wedge.
3. Constant behavior of the motor indicates the tightness of the system. The serviceability of the air valve is checked in another way, described below.
4. If the speed of the power unit has stabilized or increased, air is leaking through the VUT or supply hose.

Having determined that the amplifier is faulty, exclude the vacuum transmission hose from the list of “suspects”. Disconnect the pipe and inspect for cracks and tears. Check the condition of the clamps, install new clamps if necessary.

If sealing the pipe does not produce results, proceed to checking the “vacuum tank” itself:

1. Without starting the engine, sit in the driver's seat and apply the brake 3-5 times. The first presses will be light, but on the last ones the stroke will be greatly reduced. In this case, the diaphragm draws air through the hose and pumps it inside the housing; a check valve prevents it from coming out. Remember, the atmospheric channel is closed.
2. Having completed the last movement, hold the pedal depressed and start the engine.
3. After starting the engine, the pedal should go down about halfway.

This brake booster test identifies problems with the check valve or air valve. If the first one is faulty, then it will not be possible to pump air into the housing - the pedal will sag all the way. A worn air valve will not open the air passage while the engine is running and the pedal lever will remain in the up position or drop very slowly.

The tightness of the VUT housing is checked as follows:

1. Start the power unit.
2. Squeeze the brake all the way.
3. Without releasing the pedal, turn off the engine.

If the amplifier housing or diaphragm does not allow air to pass through, the pedal lever will remain depressed. Otherwise, it will return to its original position under the action of the spring. Then you need to remove the mechanism and replace it with a new one. Repairing a VUT in a garage is a rather difficult task, since the body of the element is held together by factory rolling.