Brake Problem!?!?!?

[Baker21]

After some help / suggestions if possible?!?!?

Yesterday I drove the car to work as normal and left it parked in my usual spot, then at lunchtime I popped out to get something to eat and found that when I braked the pedal was stiff and although the brake's worked, slightly, I could hear air escaping from the pedal area, pumping the brake even more made the pedak braking even harder.

I managed to get the car back to work and left it until home time when the brakes returned to normal. I have now just driven in to work this morning and as soon as I came into park the same thing happened? Brake pedal sounding of air when pumped and poor breaking?

Anyone got any suggestions for this? Remedies? What is wrong with my braking system?

[Bluefox]

I think it might have something to do with the servo, perhaps a vacuum leak? On a petrol engine obviously the servo gets it's "suck" from the manifold but on a diesel there's a vacuum pump, isn't there?

Other than that I'm not 100% sure - I think the air noise is significant.

Unless you've changed to air brakes :P

[Baker21]

I think it might have something to do with the servo, perhaps a vacuum leak? On a petrol engine obviously the servo gets it's "suck" from the manifold but on a diesel there's a vacuum pump, isn't there?

Other than that I'm not 100% sure - I think the air noise is significant.

Unless you've changed to air brakes :P

Hmm.......

That is intersting mate as I have another problem at the moment that is air leak related and this could be linked........

[Tom_vRS]

But I remember on my Passat you get the whoosy noise from pushing the pedal, its just how it is, and nothing to worry about.

Likewise, pumping the brakes will build up the pressure in the system and make the pedal stiffer.

Have the brakes felt very weak at any time, pedal travelling to the floor under normal braking for example?

Also, try this test - with the ignition off, pump the brake pedal until it goes really hard. While keeping your foot on the pedal, turn the ignition on, and the pedal should travel towards the floor.

[Baker21]

But I remember on my Passat you get the whoosy noise from pushing the pedal, its just how it is, and nothing to worry about.

Likewise, pumping the brakes will build up the pressure in the system and make the pedal stiffer.

Have the brakes felt very weak at any time, pedal travelling to the floor under normal braking for example?

Also, try this test - with the ignition off, pump the brake pedal until it goes really hard. While keeping your foot on the pedal, turn the ignition on, and the pedal should travel towards the floor.

I also remember the Bora being like this but this seems strange that it does it at certain times and it really doesn't feel safe when driving, like I have no brakes almost..................:confused:

I will try that test at lunchtime mate and update the thread.......

[Bluefox]

Also, try this test - with the ignition off, pump the brake pedal until it goes really hard. While keeping your foot on the pedal, turn the ignition on, and the pedal should travel towards the floor.

I thought that only worked on petrols?

[Baker21]

I thought that only worked on petrols?

Spot on mate..............

Tried Tom's suggestion and it didn't work, went out at lunchtime to find the car was fine and then while driving I had the same stiff pedal, then it went normal....

Rang my mechanic who explained that the diesel has it's own vacuum pump and that or the servo could be at fault or a split in one of the pipes may be causing it so I am booked in for early next week and just taking it steady on the roads at the moment................:thumbdwn:

[rotodiesel]

The B5.5 is a very poor conversion to right hand drive in this area. The vac pipe from the tandem pump to the servo is too short and does not have a proper loop in it to absorb engine movement. It's also too stiff.

Look here first - VAG have only had about 10 years to sort this one out. No doubt they don't give a toss about the Brits losing their brakes. LHD cars are OK.

rotodiesel.

[Baker21]

The B5.5 is a very poor conversion to right hand drive in this area. The vac pipe from the tandem pump to the servo is too short and does not have a proper loop in it to absorb engine movement. It's also too stiff.

Look here first - VAG have only had about 10 years to sort this one out. No doubt they don't give a toss about the Brits losing their brakes. LHD cars are OK.

rotodiesel.

Thanks Roto, I will check this out and update the thread once it's resolved....

[Chris]

Mine did this today too...I was driving home tonight and I went to break and there was hardly any braking...it felt l had no brakes. Then I started again and all was fine, tried to brake hard and all was fine???

[bryanp]

I thought that only worked on petrols?

Can anyone explain why this is so? I just thought that the only difference between a diesel and a petrol was the block and fuel system, why should a deisel affect the way brakes work compared to a petrol?

Cheers.

Enquiring minds need to know!

[rotodiesel]

Assuming a car has a conventional vac servo and ABS system (some early non VAG vehicles had electric booster pumps) the difference between a petrol and a diesel is simply the way in which the vacuum is generated and the route for the waste air.

Because a petrol engine has a throttle, a vacuum is generated by the engine pistons as they move on the induction stroke. This vacuum is obtained from the inlet manifold (downstream of the throttle butterfly) and is used to operate the servo. When the servo recuperates after a brake application, some air goes into the manifold - not usually a problem unless you have a Passat/Superb.

The diesel has no throttle (one of the reasons why it's much more efficient) so there is no significant vacuum developed at the intake. Diesels therefore have an engine driven vacuum pump (half of the "tandem" pump on the PDs) to do the job. Exhaust air is usually vented into the engine crankcase.

As far as the servo is concerned, there's no real difference - as long as a sufficient vacuum is developed the servo will do most of the work. A vac failure results in no servo action and impossibly heavy brakes.

Good old VAG always has something special for its customers. The B5.5 has a serious design fault which means the plenum chamber can fill up with rain water when the (stupidly inadequate) drains get blocked. The servo vac chamber is mild steel and sits in a well where the water collects. Eventually it rusts through and water gets into the servo. If the water in the servo happens to freeze as it loses latent heat of vaporisation due to the air flow - the brakes can fail completely.

Apart from the less than ideal operation of the brakes under these conditions, the water is sucked into the system and goes out via the route of the exhausted air. This means that if you have a petrol engine, the water ends up in the inlet manifold and the engine hydraulics - bent con rods. If you have a diesel, the water ends up in the crankcase, mixes with the oil and wrecks the whole engine.

A true VAG masterstroke. Keep the plenum drains clear.

rotodiesel.

Edited 6 July, 2008 by rotodiesel

[primey]

Roto You seriously know your sh!t. Glad yer on this forum..

[Bluefox]

Roto You seriously know your sh!t. Glad yer on this forum..

You and me both.

Long live Rotodiesel!

[cjb]

A true VAG masterstroke.

rotodiesel.

Crikey. That's a good one. Of course, the other common fail if the drains block is the central convenience unit.

Keep the plenum drains clear.

Sounds like very good advice.

[bryanp]

Roto You seriously know your sh!t. Glad yer on this forum..

Cheers mate, Clear as mud!