Weird braking behaviour from my VW Polo 1.6, despite low usage

No error warning/lights are popping up on the dashboard though.

BHPian 2000rpm recently shared this with other enthusiasts.

I am facing weird behaviour on my 1.6 Polo w.r.t braking. The symptoms are below

• Behaviour 1 - On some occasions, when I brake lightly while slowing from a far distance, the pedal tends to slowly go in. When I start braking, the brake bites but then to maintain the same level of braking, the pedal tends to compress more and more slowly, until a certain point.
• Behaviour 2 - The brake bite point is variable, sometimes lower than a normal point. When this happens, if I quickly do a pump, the brake point then comes to a higher point
• Behaviour 3 - The brake bite point is observed to be lower (more occurrences) when the car is going downhill

More data.

1. No errors on the Dashboard.
2. The car was not in use much for the last 1.5 months, only occasional start-up, as I had broken my foot.

Diagnosis

• Diagnosis 1 - Master cylinder failure.
• Diagnosis 2 - Air in the line. I have bled all the brakes and will see the behaviour for a couple of days of low running. If the problem does not get solved we will replace the master cylinder.

Any views by experts here??

Here's what BHPian SS-Traveller had to say on the matter:

Your brake booster is leaking. It's usually a sealed unit and will need to be replaced.

Here's what BHPian Jeroen had to say on the matter:

I agree with Ss-Traveller. Sounds like the booster or a problem in the vacuum system.

Try this simple test. With the engine switched off press the brake pedal several times. The pedal should go hard and sit up high. With your foot on the brake pedal, start the engine. You should feel the brake pedal going down quite a bit.

If it doesn't it's the booster or something wrong with the vacuum.

Another possibility - one or more brake hoses have split on the inside. This happens on older hoses. It won't leak, the split is on the inside, but because of the split/tear, there is a larger volume inside the hydraulic system.

You can measure the vacuum if you have a vacuum gauge. Check the check valve and vacuum hoses. If ok, I would replace the brake booster and if that doesn't solve the problem, replace the brake lines.

Here's what BHPian Jaggu had to say on the matter:

You got your answers here ^ Do a complete checkup of the brake system including brake bleed, check for leaks, brake/master cylinder and vacuum efficiency. With the symptoms you described, am leaning towards an airlock / weak hoses. Even a worn-out or weak hose can cause issues if it bulges when pressure is applied. Hope the fluid levels are intact.

This is a simple system so any competent dealer or non-dealer garage can sort this.

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