Brakes are acting crazy

A

Apsaauga

Member
Hello,

today i took my wife's 1.4 tdi to a wheel service and bought a new set of tyres. After that i drove to work and noticed a scary thing that i never felt before:

I was driving behind other car that was slowing down and i pushed the brakes gently one time, and again, and again, and after that my brakes were almost "gone".

I stoped, then accelerated a bit and used my brakes again - everything was fine, untill i tried to do that "multiple push" of the brake pedal. The same thing - brakes were almost gone, like it would be with engine off.

So after few seconds brakes are "fine", but they are always dull after i push the pedal like ~3-5 times.

What is going on?

Thanks for information

Cheers
 
What do you mean "dull almost Gone"?? is the pedal sinking without noticable braking or is it stiff - again without braking?
 
Nothing was done to the brakes recently, but there is one thing i should mention. Brake pad error (yellow) on the dash started to show few weeks ago. I went to the brake garage, they lifted the car and said: - brake pads are like new, but the sensor, which gives message when pads are worn is cut off and isolated (on purpose). I did't noticed that a year ago, when i bought the car. So they said, the error of pads shouldn't come at all... But it is.

Automatic: the pedal after several deep pushes becames stiff and without braking, like it would be if you would try to brake with engine shut off and ignition on. But if i wait 5 seconds, brakes are back.
 
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Sounds like vacuum pump - diesels don't have a brake servo so have to have another means of providing the assistance
 
So brakes can disappear any time? And Is it expensive repair? Damn it, this little car starts to eat my money:)
 
Depends; repeated application of the pedal over a short period of time would deplete the vacuum leading to the symptoms you are describing. This is supported by your description that the brakes are OK after a short time so it sounds like the pump is working - maybe you have an air/vacuum leak?
 
Just a quick correction; there is a servo, it's just that the vacuum is supplied by a pump rather than directly from the inlet manifold

Dan
 
the brake booster is off the top rear of the tandem pump which is on the right side of the engine
the pipe runs under the inlet i would check that for splits or loose
on my phone so havent a pic !
 
That definately sounds like a servo problem. The servo or booster, is there to provide assistance to the driver by "assisting" and thereby increasing the force applied through the pedal. A sure fire way to test this - the only practical way in fact - is to pump the brake pedal several times whith the engine OFF. Maintain pressure on the brake pedal and then turn on the engine. As the engine fires and vacuum is built up, the brake pedal should "soften" and "sink" toward the floor by a few millimeters but enought to be felt. There is no limit as to how many times this test can be performed - the crucial aspect is to ensure that all vacuum is released and the pedal is hard prior to engine turn on. Brake servos cannot be repaired - they must be replaced!

Hope this helps and good luck, let us know how it turns out.

Blue skies

Tony
 
Tony, i did not quite understood, is it good or bad when the pedal softens when i start the engine:) what indicates in this test the failure of the servo?

Today's problems didn't end with that. (!), abs and triangle warnings came up after a while!! What is going on?!?
 
the pedal MUST sink when you start the engine. as to the warning lights - it could be an abs sensor or the wiring from it. a common problem is that the cable from the front sensors is often worn as a result of wider wheels been fitted. best to do a scan to identify where the fault is located. keep us informed, we will get to the bottom of it.

blue skies

tony
 
Hello
I have the same problem. The pedal is stiffer than usual, and several times it went really hard so I could not brake at all (on the speedway...).
We checked all the tubes and pipes, and there is seems to be no leak at the moment - vacuum pump works, and when you disconnect the pipes, you can feel it.

I think that suggestion by Hotstuff is the one the we will check next. This started to happen, after I changed my tires last week (185/65 R15).
Also, a question - is there anything that we have to check under the car?

Thank You!

A2 TDi 1.4 55kW 2002
 
Had everything checked at the garage. All of the pipes have been changed, we even dismantled the vacuum pump from the side of the engine, checked it and cleaned it - looks like it is working fine, at least there is no mechanical damage to it, or any malfunction visible. We changed all the stuff that is connected to timing belt change, double checked all the pipes, but there is still not enough vacuum. Connecting to PC, shows no error codes. Dashboard lights are also not flashing. Mechanics told me, that when the engine is running, and you pull that main vacuum tube from its place (the one that is very close to steering wheel, looks like it is connected to the cabin) there is not so much suction at all. Engine works fine, and I don't see any power loss. Diesel consumption is normal.

But brakes are still acting crazy. One day you can ride without any problem, but the next day the brake pedal is tiff, and won't soften at all.
Does that mean that I need to change brake servo, or the vacuum pump(that sits on the side of the engine)?
I had 4 different mechanic to look at the problem, but we can't find a solution to that.
 
Hi folks, adding to an old thread as it has some good info above. My issue is brake fade when repeatedly braking hard, like down steep hills. The pedal is firm, but braking efficiency is lost and have to push the brakes HARD for them to work. i'm losing vacuum somewhere. So, i started having a look around under the bonnet and have decided I need a bit more knowledge of the pipe routing from the three sensors top right in engine bay, where all the little pipes congregate. Does anyone have any decent photos of these sensors with pipes in place, and where the pipes should go. Would help me alot. cheers nod.
PS my car is 2001 AMF TDI, no fault codes.
 
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@nod
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Audi Workshop Service and Repair Manuals > A2 > Power unit | 3-cylinder TDI unit injector engine (1.4 ltr. 2-valve), mechanics | Exhaust turbocharger, G-charger | Checking charge air system with turbocharger | Diagram of vacuum hose connections

A2 > Audi Workshop Service and Repair Manuals > Power unit | 3-cylinder TDI unit injector engine (1.4 ltr. 2-valve), mechanics | Exhaust turbocharger, G-charger | Checking charge air system with turbocharger | Diagram of vacuum hose connections
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@nod It is worth checking the source of the vacuum i.e. the tandem pump. If it has not already been replaced I would certainly say it is probably over due. There is a weak point on the LUK tandems, the spigot where the vacuum pipe joins onto the housing can become loose allowing a vacuum leak. It is possible in some cases to refit this spigot using a liquid metal epoxy to seal it back together.
 
audifan said:
@nod It is worth checking the source of the vacuum i.e. the tandem pump. If it has not already been replaced I would certainly say it is probably over due. There is a weak point on the LUK tandems, the spigot where the vacuum pipe joins onto the housing can become loose allowing a vacuum leak. It is possible in some cases to refit this spigot using a liquid metal epoxy to seal it back together.
Click to expand...
hi, thanks for the advice, I have a spare pump here so may as well swap it out for bosch. I had a look at this earlier and did think it looked a bit dodgey. The hose is tight on the spigot, but the spigot turns in the pump and has some play at the junction, so could be the culprit. I'll let you know once its done...cheers
 
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