yesterday I had a scary moment when I had to stop the car in city traffic and the brake pedal turned hard and the car would not slow down!! so I released it and pressed again, and then it was fine! New pads were installed 1 month ago, and otherwise the car brakes great! It felt like a momentary loss of vacuum assistance. Do these cars have a vacuum reservoir for the brakes and should I get my vac pump checked? btw it is a 2.5 auto. Were there any recalls on this?

That sounds a lot like a servo problem yes. You seem to understand how a vacumn servo works, so I won't insult your intelligence, just observe that the vacumn tank is limited in size, so if you were on the brakes a lot it wouldn't be impossible that you emptied it.

Now, I'm by no means that tech-savvy - so I'll just copy this text from http://www.honestjohn.co.uk/carbycar/volkswagen/passat-2001?section=bad that may or may not be of interest or relevance:

In 2007 VAG issued a dealer TSB 51B8 to check for blocked drain holes in the plenum chamber. Trouble is, they do not send recall notice letters to owners who have not used their franchised dealers for servicing. The first signs are a flooded vent well with water slopping about and emulsified oil under the oil cap. Apparently this water can be drawn into the brake servo and causes corrosion to the servo housing and brake master cylinder that can result in reduced brake force or failure altogether. Replacement of perforated brake servo, pipework and tandem pump be replaced can cost £980.

cheers

Now, I'm by no means that tech-savvy - so I'll just copy this text from http://www.honestjohn.co.uk/carbycar/volkswagen/passat-2001?section=bad that may or may not be of interest or relevance:

In 2007 VAG issued a dealer TSB 51B8 to check for blocked drain holes in the plenum chamber. Trouble is, they do not send recall notice letters to owners who have not used their franchised dealers for servicing. The first signs are a flooded vent well with water slopping about and emulsified oil under the oil cap. Apparently this water can be drawn into the brake servo and causes corrosion to the servo housing and brake master cylinder that can result in reduced brake force or failure altogether. Replacement of perforated brake servo, pipework and tandem pump be replaced can cost £980.

cheers

oh yes, I have seen this too... worried a bit!

oh yes, I have seen this too... worried a bit!

...but now I notice that the same version of report on the Superb as opposed to Passat at http://www.honestjohn.co.uk/carbycar/skoda/superb-2002/?section=bad , seems to indicate it only applies to petrol engines:

"Petrol engines can hydraulic for an extraordinary reason: water built up in the ventilation plenum chamber due to failure to clear the drains can perforate the seam of the two halves of the brake servo, rust the inside and make the brake pedal hard. That water can then get sucked into the engine if the servo diaphragm becomes perforated."

I'm confused :S As I said, I'm not that tech-savvy...

...but now I notice that the same version of report on the Superb as opposed to Passat at http://www.honestjohn.co.uk/carbycar/skoda/superb-2002/?section=bad , seems to indicate it only applies to petrol engines:

"Petrol engines can hydraulic for an extraordinary reason: water built up in the ventilation plenum chamber due to failure to clear the drains can perforate the seam of the two halves of the brake servo, rust the inside and make the brake pedal hard. That water can then get sucked into the engine if the servo diaphragm becomes perforated."

I'm confused :S As I said, I'm not that tech-savvy...

I'll have to have a look under the bonnet, currently all of this theory doesn't really make sense to me, how can a vacuum servo lead to water from the plenum chamber going into the inlet manifold???

If it only affects petrol engines, maybe I can understand it, because they always have a vacuum in the inlet manifold anyway and no separate vacuum pump (or "servo") so it would get sucked in, whatever is in there, water or otherwise.... but on a diesel running boost.... no idea :no:

Except... the servo unit will have bearings, which will be lubricated by engine oil, and similar to a turbo, the oil will have a return path to the crankcase... if the internal seal of the servo breaks down, you could have the unit (maybe) sucking oil out of the crankcase and then dumping it into the vacuum circuit, contaminating all the miles and miles of vacuum lines which affect the turbo actuation, EGR valve, brakes.... But I still don't understand how it could hydraulic. And I also don't understand how the servo could actually suck in water from the plenum.

I think I know what I am doing this weekend! Having a good look and cleanup of the plenum and related seals, grommets, the works :p

Hopefully there is no damage. Has not re-occurred since. Will test the vacuum capacity, by repeatedly pumping brakes, when my 3 month old boy isn't on board!

The failure mode is simple - and absolutely unforgivable.

A vac servo relies on the vacuum developed either at the inlet manifold (petrol) or by an engine driven pump (diesel) to provide additional braking effort. To do this, it has a large diaphragm (hence the size of the unit) with vac on one side and, when effort is required, atmospheric air pressure on the other.

When the brakes are not required, the vacuum is applied to both sides of the diaphragm (via a non return valve) and a spring holds the brakes off. When braking is required, air is admitted to the other side of the diaphragm, which causes it to move - until the required position is reached, governed by the pedal position - whereupon the air supply is cut off, and the diaphragm maintains its position. It is the action of atmospheric air which moves the diaphragm and hence the master cylinder pushrod, applying the brakes.

It follows that any vac servo has to admit air to work. The servo used by VAG is standard, and admits air from around the pushrod - there is an air channel here. VAG of course, can do better than this...

When the plenum drains block, the bottom of the servo housing sits in a pool of water - and rusts. Eventually, the housing rusts through and water gets sucked into the servo causing lack of brake assist. A car as heavy as a Superb is unstoppable under these conditions. If the housing isn't rusted, water can still get in through the servo's normal air inlet. The result is the same - brake failure for a normal mortal.

VAG will hide behind the "loss of assist only" argument. Let them try stopping it - it's frightening.

As to where the water ends up - diesel: into the engine oil via the tandem pump. Water in the oil wrecks the engine. Petrol: into the intake, causing a hydraulic lock - engine wrecked.

Why our spineless inspectorate have not insisted that these vehicles are recalled and re-worked is beyond me. VAG clearly don't give a toss about the customer - remember this fault was well known on the Passat before the Superb clone was even made. B@stards.

rotodiesel.

Edited 30 March, 201016 yr by rotodiesel

yep, that's just what I was thinking it was

cheers Roto - good explanation as usual.

Edited 30 March, 201016 yr by sidewaze samm

The failure mode is simple - and absolutely unforgivable.

A vac servo relies on the vacuum developed either at the inlet manifold (petrol) or by an engine driven pump (diesel) to provide additional braking effort. To do this, it has a large diaphragm (hence the size of the unit) with vac on one side and, when effort is required, atmospheric air pressure on the other.

When the brakes are not required, the vacuum is applied to one side of the diaphragm (via a non return valve) which holds the brakes off. When braking is required, air is admitted to the other side of the diaphragm, which causes it to move - until the required position is reached, governed by the pedal position - whereupon the air supply is cut off, and the diaphragm maintains its position. It is the action of atmospheric air which moves the diaphragm and hence the master cylinder pushrod, applying the brakes.

It follows that any vac servo has to admit air to work. The servo used by VAG is standard, and admits air from around the pushrod - there is an air channel here. VAG of course, can do better than this...

When the plenum drains block, the bottom of the servo housing sits in a pool of water - and rusts. Eventually, the housing rusts through and water gets sucked into the servo causing lack of brake assist. A car as heavy as a Superb is unstoppable under these conditions. If the housing isn't rusted, water can still get in through the servo's normal air inlet. The result is the same - brake failure for a normal mortal.

VAG will hide behind the "loss of assist only" argument. Let them try stopping it - it's frightening.

As to where the water ends up - diesel: into the engine oil via the tandem pump. Water in the oil wrecks the engine. Petrol: into the intake, causing a hydraulic lock - engine wrecked.

Why our spineless inspectorate have not insisted that these vehicles are recalled and re-worked is beyond me. VAG clearly don't give a toss about the customer - remember this fault was well known on the Passat before the Superb clone was even made. B@stards.

rotodiesel.

Thank you very much rotodiesel!

I tell you I am not a small bloke but I pressed the pedal pretty damn hard and the car just rolled on! I would have smashed into the car in front of me guaranteed had I not released the brake pedal and pressed again!

But I did grab the handbrake already, ready to use it in case the footbrake refused to work on 2nd attempt!

I will have to do the plenum clean/inspection on Saturday.

MY concern is: do I need a new vac pump, or is it a matter of it "just" having ingested some water, or... god knows what.

Currently I do not have any water in the cabin.

Might write a threatening letter to Skoda. Depends what I find really.

I am an engineer by profession, so could put a case together, but I have to see where we are at the moment, as it seems that there are a few plausible scenarios here, albeit all down to poor engineering.

You will have to inspect and act on what you find. As an Engineer, your judgement is worth far more than any BS you may get from VAG.

I would be interested to know the age of your vehicle and what you find when you've had a good look at it. The condition of the lower part of the servo housing would be of particular interest.

Vac pumps don't usually mind a bit of water - but engines don't like it in the oil at all. If you think water has been through via this route, I would recommend an engine oil and filter change ASAP, additional to the work required to prevent further brake failure.

rotodiesel.

You will have to inspect and act on what you find. As an Engineer, your judgement is worth far more than any BS you may get from VAG.

I would be interested to know the age of your vehicle and what you find when you've had a good look at it. The condition of the lower part of the servo housing would be of particular interest.

Vac pumps don't usually mind a bit of water - but engines don't like it in the oil at all. If you think water has been through via this route, I would recommend an engine oil and filter change ASAP, additional to the work required to prevent further brake failure.

rotodiesel.

I agree mate. Will give this my top attention in the coming days. I hope it doesn't rain on Saturday, as I will be spending quite a bit of time outdoors it seems.

BTW my car is a 2002 model with full dealer service history and one dilligent owner. The brakes (pads) were changed 2 weeks before I bought the car all round at a cost of £200. I wonder if he has had this symptom and thought he just needed new pads....

Will check the oil for emulsified water pronto.

Surely presence of water in the oil could be quickly checked by seeing if there's any emulsification around the underside of the filler cap? Thick, creamy, gunky pale brown liquid stuff.

edit: Ignore the above comment, I just spotted your last post.

Not an engineer, but judging by the comments about the PDs need for specific oil I guess if water has gotten into oil circulation then a full change of filters and oil is needed pronto. The plenum chamber blockage removal thing is easy enough to do, just time consuming and awkward to remove battery from experience. Good luck fella.

Edited 30 March, 201016 yr by allclownsareevi

His car is not a PD, it's a V6. A 2002 car will have plenty of rotting biomass in the plenum drains unless they have been kept clear. Remove the bungs.

Small amounts of water in the oil will not show as an emulsion - try making salad dressing with 95% oil. Such small amounts seriously degrade the oil's lubricity - if in any doubt, change the oil.

rotodiesel.

Well people, I have finally had some time to look into this "issue" I had. With hard brakes (just once).

I have removed the battery cover and I have had a shocking revelation, I probably had about 3-4 gallons of water sitting in there, the battery was half submerged in fresh rainwater!!!!

So the servo must have sucked in some water. My concern now is whether corrosion has set into the servo, or whether it just sucked in a bit of water through the breather or shaft filter. A new servo from Skoda is £300. Not sure if I can fit myself. If anyone can suggest a way of testing its integrity and functionality, I'm listening

Is there a back-up electric vacuum pump serving as backup in case of loss of vacuum from the main vacuum pump or the servo housing, and if so, where is it, can I somehow monitor its deployment. If it works full time that may be an indication of a constant loss of vacuum from the servo??

So far I have thought of the following tests:

1. engine running, then off. Pump the brake a few times, until it goes hard. It should be 3-4 pumps until it gets hard. Any less I think is probably and indication of a rapid vacuum loss.

2. press brake, start engine, brake should drop down quickly as vacuum grows. If it doesn't, there is too much leakage.

3. engine running, press brake in rapid succession 2 dozen times, if the brake goes hard, this will be an indication that the vacuum cannot be replenished quickly enough

Is my train of thought correct?

Removing the battery was a bit of a bugger, and those two bungs were completely filled solid with earth! Even as I started undoing the battery bracket bolt, my car started weeping... and when the bungs were removed, it positively opened its flood gates. It was almost embarrassing to have it do that on our drive!

Should I do anything to sort out the pollen filter housing, I have seen some posts on this?

BTW, I have checked the passenger footwell, no dampness there, so I suppose I was a bit "lucky" in that respect, and all my convenience lights and facilities are, as far as I can see, still fully functional.

Well people, I have finally had some time to look into this "issue" I had. With hard brakes (just once).

I have removed the battery cover and I have had a shocking revelation, I probably had about 3-4 gallons of water sitting in there, the battery was half submerged in fresh rainwater!!!!

So the servo must have sucked in some water. My concern now is whether corrosion has set into the servo, or whether it just sucked in a bit of water through the breather or shaft filter. A new servo from Skoda is £300. Not sure if I can fit myself. If anyone can suggest a way of testing its integrity and functionality, I'm listening

Is there a back-up electric vacuum pump serving as backup in case of loss of vacuum from the main vacuum pump or the servo housing, and if so, where is it, can I somehow monitor its deployment. If it works full time that may be an indication of a constant loss of vacuum from the servo??

So far I have thought of the following tests:

1. engine running, then off. Pump the brake a few times, until it goes hard. It should be 3-4 pumps until it gets hard. Any less I think is probably and indication of a rapid vacuum loss.

2. press brake, start engine, brake should drop down quickly as vacuum grows. If it doesn't, there is too much leakage.

3. engine running, press brake in rapid succession 2 dozen times, if the brake goes hard, this will be an indication that the vacuum cannot be replenished quickly enough

Is my train of thought correct?

Removing the battery was a bit of a bugger, and those two bungs were completely filled solid with earth! Even as I started undoing the battery bracket bolt, my car started weeping... and when the bungs were removed, it positively opened its flood gates. It was almost embarrassing to have it do that on our drive!

Should I do anything to sort out the pollen filter housing, I have seen some posts on this?

BTW, I have checked the passenger footwell, no dampness there, so I suppose I was a bit "lucky" in that respect, and all my convenience lights and facilities are, as far as I can see, still fully functional.

See blogs and posts on Audi / VW equivalents. There is a modification to the drainage from the servo. It is a known design fault and has caused many problems on A4s with sudden or intermittent failure of the servo. You may be able to get Skoda to replace the servo/master cylinder as some VAG garages have done this free of charge. Best of luck.

Unless you get the bung out from under the servo, these cars are basically very dangerous.

Changing a servo is an awkward job and involves removing the co-axial bolts which secure the master cylinder to the servo housing and the servo to the bulkhead. The lower ones are sods to get out unless you have a crowsfoot spanner. The pedal connection is an adjustable ball joint and is also hard to get to.

The best way to check a servo is to find a very long downhill spiral car park ramp. Start at the top in neutral with the engine at tickover and go down very slowly with your foot on the brakes all the time, slowing the car on the brakes. You should not run out of vacuum.

Some B5.5 variants do have an electric vac assist pump - it sits in the bracket by the ABS controller under the plastic cover. I've never seen one - but I don't have any applications for automatics - which I think used them.

If I had a car which had any suggestion of water in the servo, I would not be happy to use it until the servo had been replaced and all possibilities of water ingress and poor drainage fixed. An unreliable servo is a danger to all road users.

A Superb can be a money pit if you don't keep on top of the stupidities - so use the Internet to find them. The dealers know nothing.

You really must change the pollen filter seal - it's about the crappiest piece of engineering I've seen in recent years. Here's the VW branded TSB - the (really honest Teutonic car Company) knew all about this problem before the Superb was made:

http://www.ukpassats...6c517aa0c3492f3

rotodiesel.

Edited 26 May, 201016 yr by rotodiesel

What annoys me is that if you want to DIY the recommended VAG fix, not sure about all dealers, but my VW dealer in Wrexham (no names) wants to sell me a whole roll of the seal and won't sell it by the length - I think I was quoted over £30 (Just enquiring about price when picking up other parts).

Morally if nothing else VAG should be handing this stuff out FOC, though they would then be admitting liability I guess.

I was lucky to blag some from an independant VAG technician (thanks Dave Beaver) when he serviced my car last year.

When I did mine, I was lucky with no leakage into the car, but like most people I found the original was saturated with water and split so I was on borrowed time.

Annoyingly I broke the rain channel when trying ot get it out but it's shared with the Passat thank goodness as I have a VW dealer local but my Skoda dealer is 20 miles away.

What annoys me is that if you want to DIY the recommended VAG fix, not sure about all dealers, but my VW dealer in Wrexham (no names) wants to sell me a whole roll of the seal and won't sell it by the length - I think I was quoted over £30 (Just enquiring about price when picking up other parts).

Morally if nothing else VAG should be handing this stuff out FOC, though they would then be admitting liability I guess.

I was lucky to blag some from an independant VAG technician (thanks Dave Beaver) when he serviced my car last year.

When I did mine, I was lucky with no leakage into the car, but like most people I found the original was saturated with water and split so I was on borrowed time.

Annoyingly I broke the rain channel when trying ot get it out but it's shared with the Passat thank goodness as I have a VW dealer local but my Skoda dealer is 20 miles away.

My local dealer gave me a length of seal for free. try another dealer!

Edited 26 May, 201016 yr by berr0010

Lads had the same problem as some of ye on 1.9 TDI hard pedal just sometimes normally on freewhelling or in busy traffic followed all the advice had the water problem so bit the bullet and changed the servo no improvment so went hunting yesterday and hey presto found the problem the god dammed pump on the back of the engine wiggle the pipe going from the pump to the servo through the body the little steel pipe leaving the pump was loose just tightened the joint by tapping the surround around it then applied apoxt glue around the joint and hey presto jobs a good one perfect brakes so lads check this before you go changing servos as this is a big job

Just to add to this I have been having brake problems for a while now, intermittent working of the brakes especially if your braking frequently, mainly in traffic.

Few days ago I lost my turbo and my brakes in one foul swoop, after a quick tip or should I say slow trip to my local mechanic, he diagnosed a cracked housing on my Vacuum Pump..............

Had this replaced yesterday and this can be seen in the pictures below:

New shiny Pump:

And the little connecting pipes that can also cause a problem and come loose:

Not a cheap part as it also acts along side the Fuel Pump I believe and cost em circa £250+VAT, problem is however now solved..........

Looks like your egr valve hose is wearing Simon, cuts itself on the engine cover, and it will send the eml on when it gets a full hole in it.

Should it perforate the car will still run fine, but it will take a few miles of driving before the eml goes out after replacing the hose, unless you V-Com it off.

hth, in future

Looks like your egr valve hose is wearing Simon, cuts itself on the engine cover, and it will send the eml on when it gets a full hole in it.

Should it perforate the car will still run fine, but it will take a few miles of driving before the eml goes out after replacing the hose, unless you V-Com it off.

hth, in future

Yeah thanks mate, I have ordered a load of new hose for that area as with the mileage they are all looking a little tired........