Brake Pedal Stuck? Check Master Cylinder Now!

Hello everyone,

My car:

Volkswagen Golf IV TDI (136 hp), year of manufacture 1998.

My problem:

'When I press the brake pedal (with force), it loses pressure within about 10 seconds and drops to the floor of the vehicle. This doesn't cause a 'spongy' feeling. Therefore, I can rule out water or air in the system. I also haven't experienced any brake fluid loss, because otherwise my reservoir would be empty by now (I pressed the brake pedal about 10-15 times and then checked the reservoir).'

The only diagnosis that comes to mind is: a leak in the master cylinder seal.

Okay, here are several questions:

Do you agree with my diagnosis?

Doesn't the master cylinder have two seals (one for each circuit)?

How do you replace the seal of a master cylinder?

My car, like most newer cars, has an ABS system. When replacing the main brake cylinder, the entire braking system needs to be bled by a workshop using special bleeding equipment (due to the potential for air in the ABS system and ABS pump). Is there a way to avoid this?


Thank you in advance for 'constructive' responses.

E.

Hello.
would not rule out air.

See:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

You will also find answers to your questions about bleeding (airing) there.

Have you already checked the error memory?

Hi there,
That could be anything really. In your situation, I would recommend taking it to a trusted mechanic (or having it towed there!) and have both the ABS and hydraulic brake booster checked.
A spongy brake pedal under constant (slight) pressure indicates leaks in the master cylinder seals. Typically, this effect is not noticeable when applying strong pressure to the pedal because the seals provide a better seal due to their design.
Air would theoretically be conceivable, but it would have to have a cause.
Also possible:
In all Volkswagen Group (VAG) cars, since time immemorial, there has been the unfortunate practice of installing brake hoses from the factory that are made of a material similar to chewing gum.
Typically, the TÜV (German technical inspection agency) will reject them within a maximum of 5 years due to cracks or porosity. If the outer casing is still intact but the inner part is leaking, you essentially pump the fluid into the brake hose, and the braking effect then depends only on the elasticity of the casing. We had something like this a few years ago in a 35i, but only on one side. When the brakes were applied, you could see a grape-sized bubble forming.

Best regards from Berlin.

Olli.

In all Volkswagen Group cars, since time immemorial, there has been the unfortunate practice of installing brake hoses from the factory that are made of a material similar to chewing gum.
Typically, the TÜV (German technical inspection agency) will reject them within a maximum of 5 years due to cracks or porosity. If the outer casing is still intact but the inner part is leaking, you essentially pump the fluid into the brake hose, and the braking force then depends only on the elasticity of the casing. We had something like this a few years ago in a 35i, but it was only on one side. When the brakes were applied, you could see a grape-sized bubble forming.

Best regards from Berlin.

Olli

Congratulations, Olli won (almost, lol)!

This morning, I figured it out myself. After driving a few kilometers yesterday and then finding that the brakes didn't work when I applied them this morning (which was, of course, terrifying), I realized:

Compensation tank empty (insane).

'Brake fluid is leaking from somewhere in the rear left brake line, near the brake calipers. This is strange; it shouldn't normally happen.'

Die genaue Stelle habe ich noch nicht lokalisiert, da ich jemanden brauche der pumpt während ich schaue. Das blöde ist nur, daß ich jetzt wahrscheinlich Luft im gesamten System habe und wahrscheinlich in einer Werkstatt entlüften muss. Aber wegen dem Entlüften schaue ich mir den o.g. Link turn it on.

Thanks for the tips, I'll get back to you when I know more.


E.

@golfschrauber1981

You once wrote:

'Bleed brake system, vehicles with and without ABS, ABS/EDL.'
Vehicles equipped with ABS/EDL.

The 'Basic Adjustment' function is only necessary for vehicles where the brake fluid reservoir has completely emptied (e.g., due to leaks in the braking system). In such cases, initiate the 'Basic Adjustment' process => Refer to the vehicle's chassis and diagnostics manual; start the basic adjustment.

Am I understanding this correctly now?

I'm installing a new hose, and then I'm going to ATU to have the entire brake system bled. Or do they not offer that kind of service?

Okay, here's a very basic question (sorry about that): After repairing the brake line, can I bleed the system myself while the engine is running? Wouldn't the air from the ABS system also be expelled at the same time?

E.

Hello,
It should also work with home remedies.

The original literature specifies the following procedure:

Bleed the brake system on vehicles equipped with ABS Mark 60.
Bleed the brake system without a brake fluid filling and bleeding device.
- Build up pressure in the braking system using pedal pumps.
- Open the vent screw while the hose is still attached to the vent bottle.
- Close the bleed screws when the pedal is depressed.
- Repeat the process until no more air escapes.


Bleeding the brake system when a chamber of the brake fluid reservoir is completely empty (e.g., due to leaks in the braking system).

Ventilation sequence => Initial ventilation followed by normal ventilation



Bleed the brake system if a chamber of the brake fluid reservoir is completely empty (e.g., due to leaks in the braking system).

Ventilation sequence.

1 - Front brake caliper, left and right.
vent simultaneously together.

2 - Wheel brake cylinder / Brake caliper
at the same time, both the left and right rear.
vent together.

- Keep the bleed screws open on the bleeder bottle while the hoses are attached, until brake fluid without air bubbles flows out.

Normal ventilation:

Ventilation sequence.

Front brake caliper, left side.

2 - Front right brake caliper.

3 - Wheel brake cylinder / Brake caliper
bottom left

4 - Wheel brake cylinder / Brake caliper
bottom right

- With the hose attached to the bleeder valve of the brake fluid reservoir, keep the bleeder screw open until brake fluid flows out without any air bubbles.
After bleeding the brakes, a test drive must be performed. During this test drive, at least one ABS intervention must occur!

Wow, thank you. Your response makes me very happy.

After getting 100 liters of brake fluid on Monday, I'll go ahead and do it, haha.

Three more things:

I'm only realizing this now because I've previously only opened the bleed screws while the system was under pressure during the bleeding process.

Can I repeatedly pump the brake pedal while both bleed screws on an axle are open, without closing those screws during the return stroke of the brake pedal?
(shouldn't matter during a pre-bleeding process).

Should the ignition/engine be off during both bleeding procedures?

'If there's still air somewhere in the system after bleeding (and I specifically mean in the ABS components), would I notice it when braking or when the ABS is activated?'



Wow, another lot of questions again... sorry.

Okay, I've now also located the error locally.

The hose connection on the rear left brake caliper. There are two aluminum sealing washers there. The lower one, between the caliper and the hose fitting, was completely corroded. The upper one also showed significant signs of wear. It's unbelievable that the brakes would fail in a six-year-old car simply because VW is incapable of designing a reliable braking system.

After I get 100 liters of brake fluid on Monday, I will do it, lol.

Two liters will definitely be enough.

1. Can I repeatedly pump the brake pedal while both bleed screws of an axle are open, i.e., during the initial bleeding process, without closing these screws during the return stroke of the brake pedal?
(shouldn't matter with a pre-ventilation).

It shouldn't matter, but just make sure to keep the pedal pressed down and tighten the screw (see instructions).


2. Should the ignition/engine be off during both venting procedures?

I've always left them disconnected during brake fluid changes, and it's always worked out fine so far.

3. If there is still air somewhere in the system (and I mean specifically the ABS components) after bleeding, would I notice it when braking or when using the ABS?

Yes, it shows.
The pedal is difficult to pump up firmly (it feels spongy).
The vehicle pulls to one side when braking (so don't immediately accelerate and perform a full ABS brake in traffic. Instead, start gently on a lightly trafficked, preferably wide road).

Since I'm not familiar with your expertise and don't want to be responsible for any accidents, here's another piece of advice:

Since the braking system is an absolutely vital component, it's always better to consult a professional rather than risk making a mistake for a few euros, which could potentially endanger yourself or others.

It's not meant to be rude.

The vehicle pulls to one side when braking (so don't immediately accelerate and perform a full ABS brake in traffic. Instead, start gently on a lightly trafficked, preferably wide road).

Since I'm not familiar with your expertise and don't want to be responsible for any accidents, here's another piece of advice:

Since the braking system is an absolutely vital component, it's always better to consult a professional rather than risk getting into trouble over a few euros and potentially endangering others.

It's not meant to be malicious.

@ Golf enthusiast/tinkerer.

Thank you for the kind reply. Just to reassure you:

I've been maintaining my own cars for about 12 years now (always without any problems). I've also frequently replaced brakes and other components, and have often bled brake systems (with and without ABS). In this particular case, I wasn't sure whether air entering the master cylinder could cause problems with the ABS, and whether those problems would be noticeable.

Today I'm going to replace the rear brake pads (they were due for replacement anyway) and at the same time, I'll change the aluminum seals ('on both sides'). Then I'll bleed the brakes (a brake fluid change was planned for soon anyway), and finally, I'll take it for a test drive. And since there's so much snow everywhere here, I can do the initial hard braking tests in empty parking lots without wasting too much rubber.

One thing I'm curious about:

In the repair manual I have ('How it's done'), it is strongly recommended that you take your car to a workshop and have it 'specially' bled in the situation described above, specifically because of the ABS system and another system (I can't remember the name) which regulates the distribution of braking force to the rear wheels during cornering.

You said that if something isn't right, the brakes might engage unevenly or at an angle.
If my brake tests go well, does that mean I don't have to worry about it anymore?

E.

Okay, it's done, everything is in place, and everything works perfectly.

The only thing is, there's still a little bit of air in the system, but just a little. I'll have to bleed it one more time.

Hi,

I'm experiencing a similar problem to the original poster from over a year ago.
Vehicle: Volkswagen Golf IV, manufactured in 2004, engine code AXR, station wagon (Variant), FS-III brake pads on the front axle, Lucas brake pads on the rear axle.

When I press the brake pedal with moderate force while the engine is running (meaning somewhere between lightly braking at a traffic light and applying full brakes; this test was performed with the car stationary, and the description is only for explanation), it slowly retracts and moves towards the floor of the vehicle.

Having checked all the connections, hoses, error memory, etc., over the past two days and found no faults, I'm a bit at a loss. Could it really be the much-mentioned seal on the master brake cylinder? If that seal were leaking, where would the brake fluid go? Would it leak out of the braking system, or would it remain inside? The brake fluid level has been just below the "MAX" mark since I bought the vehicle.

Here's what I've observed: When the engine is off, the brake pedal can be pumped firmly. Also, when performing the "pedal sinking test" with the engine running, it seems that a progressively increasing braking pressure builds up as the pedal is released. (Initially, I can only pull the handbrake up one notch before needing to apply additional force; when the pedal is fully depressed, I can move it past six notches.) This shouldn't be happening if the seal on the master cylinder is defective, right?

Can someone who is knowledgeable about current ABS systems provide some information on this?

Sure, here's the translation:

"Thank you in advance."

Regards,
Sure, here is the translation of the text from German to English:

"Micha"