I fixed the cruise control on my Superb a few weeks back after it had stopped working. The brake pedal switch had come a bit loose over time and wasn't disengaging fully so the cruise control always thought I was braking and so it would never engage.

I tightened the brake switch up so it worked again no problems.

I now have a disturbing new problem that nearly gave me a heart attack on the motorway today.

When the cruise control has been on for a long time and I brake, the brake is stiff and has to be pressed a lot harder than normal. For a split second it feels like it is stuck which is scary when you are travelling at 70mph+ I can tell you.

My problem with diagnosing this is that it is intermittent and doesn't happen all the time. When the CC is not on there are no problems and the brake moves normally.

I'll be replacing the brake switch completely tomorrow but I really want to get to the root of the problem so I don't have brake issues next time I want to use CC on the motorway!

Edited to add:

1) I've sorted the water ingress issue and there are no problems with the servo rusting up etc.

2) This problem has only ever occurred when the cruise control has been engaged, and even then it is only intermittent. This might just be coincidence though.

3) The vacuum hose that runs from the EGR valve to the secondary air pump is perishing and occasionally gives an error message on VAGCOM. Could this fault with the brake be connected to a similar vacuum issue?

4) Will scan the car with VAGCOM tomorrow to see if there are any fault stored.

Edited 22 June, 201114 yr by BDZ10

Your brake pedal going hard is unrelated to the cruise control. Loss of vacuum will mean you have no brake assistance. The Superb is a heavy car and takes a lot of muscle power to stop. You need to check all the vacuum pipes and the brake servo for leaks.

Your brake pedal going hard is unrelated to the cruise control. Loss of vacuum will mean you have no brake assistance. The Superb is a heavy car and takes a lot of muscle power to stop. You need to check all the vacuum pipes and the brake servo for leaks.

Ta for the reply. I'm going to send it off to the garage, it's too big a job for me to do. Are there any particular parts of the vacuum system that are prone to failure on the Superb, or is it just general wear and tear?

It could just be perished vacuum hoses.

If you are unlucky, it could be that the brake servo has corroded due to water in the plenum chamber. If it's the brake servo, then it's a bit of a pain to replace and it's not cheap - probably £400 all in at a dealer.

It could just be perished vacuum hoses.

If you are unlucky, it could be that the brake servo has corroded due to water in the plenum chamber. If it's the brake servo, then it's a bit of a pain to replace and it's not cheap - probably £400 all in at a dealer.

I'm crossing my fingers that it's the vacuum hoses. Won't be going anywhere near a dealership though, I've got a trusted independent who charges about half of what the dealers usually do.

If the car is off I can pump the brake pedal and when the engine comes on it sinks to the floor as it should (I don't know any other diagnostic procedures for brake vacuum issues without getting more technical). The car is off to the garage on Monday but the fault only appears to be intermittent so hopefully they can diagnose it without any issues.

I did a VAGCOM scan but it didn't throw up anything obvious. The only fault was this one, which I already knew about:

16795 - Secondary Air Injection System: Incorrect Flow Detected

P0411 - 35-00 - -

I know that one is caused by a perished vacuum hose (I can see the split, but haven't got around to fixing it yet) but this isn't linked to the brakes as far as I know.

There is a standard vacuum pump driven off the camshaft and then there is (I believe) a secondary electrical vacuum pump somwhere behind the bumper I think on the driver's side which back up the vacuum supplies if there are leaks etc.

I had the brake pedal go hard on me once (approaching traffic lights!!!) - it turned out the brake servo was sitting in a pool of water. But that was 20k miles ago and no issues since, with the original servo still, but the battery chamber obviously had to be drained.

Check all your hoses and also the hoses to and from the electric vacuum pump, it should engage to compensate.

Having said that, if your servo is shot, there is no getting away from it you will need a new one. There are pattern ones on ebay for £160 or so, though I personally would probably go OEM on this item rather than a Chinese cheap product.

There is a standard vacuum pump driven off the camshaft and then there is (I believe) a secondary electrical vacuum pump somwhere behind the bumper I think on the driver's side which back up the vacuum supplies if there are leaks etc.

I had the brake pedal go hard on me once (approaching traffic lights!!!) - it turned out the brake servo was sitting in a pool of water. But that was 20k miles ago and no issues since, with the original servo still, but the battery chamber obviously had to be drained.

Check all your hoses and also the hoses to and from the electric vacuum pump, it should engage to compensate.

Having said that, if your servo is shot, there is no getting away from it you will need a new one. There are pattern ones on ebay for £160 or so, though I personally would probably go OEM on this item rather than a Chinese cheap product.

I've had the battery tray out this afternoon and it's all dry. It's possible there has been some water in there around the servo but if there was it's gone now. I've removed the drainage bungs as a precaution, no idea why I forgot to do this last time I drained the water out 6 months ago.

Is there a way to check with VAGCOM whether there are vacuum leaks, or whether the vacuum is coming from the main servo or the backup one? Just curious,

An update...

Had the car in the garage today to get the brake system looked at and still can't diagnose the trouble. There's no damage to the brake servo and no apparent vacuum leaks.

The odd thing is that as soon as you turn the engine off, you can hear a hiss of air escaping from the brake servo and the pedal immediately goes solid when it should retain vacuum for another few presses of the pedal after turning off the engine.

That still wouldn't explain why my brake pedal would become stiff in the middle of a high speed journey when there should be no loss of vacuum with the engine running at full tilt.

Me and my mechanic are both stumped. Anyone got any ideas?

Get another mechanic!

It sounds like the brake servo to me - you can hear it leaking. It is not unusual for a brake servo problem to be intermittant. Any good mechanic should be able to isolate the leak very quickly with a vacuum tester.

Hi, the same thing happened to me with my Skoda Yeti this week. No other brake problems and it has only occured one time, but it´s not nice when you think the brake is stuck :-)

"I now have a disturbing new problem that nearly gave me a heart attack on the motorway today.

When the cruise control has been on for a long time and I brake, the brake is stiff and has to be pressed a lot harder than normal. For a split second it feels like it is stuck which is scary when you are travelling at 70mph+ I can tell you."

I've driven over 1000 miles since this happened and it has not happened again until yesterday. On the motorway, cruise control on, and then stiff brakes.

I cannot for the life of me figure out why this only happens when cruise control is engaged.

I've driven over 1000 miles since this happened and it has not happened again until yesterday. On the motorway, cruise control on, and then stiff brakes.

I cannot for the life of me figure out why this only happens when cruise control is engaged.

It isn't anything to do with the cruise control as such. It is likely that there are times when you are generating less vacuum than you are leaking, due to where the leak is in the servo. At times when you engage the CC, you use the brakes less so you are in that leaky condition for longer periods of time. You are also at constant revs, so you will be generating constant vacuum. This may affect things too.

You need to find a better mechanic - one who doesn't let you drive away with faulty brakes.

It isn't anything to do with the cruise control as such. It is likely that there are times when you are generating less vacuum than you are leaking, due to where the leak is in the servo. At times when you engage the CC, you use the brakes less so you are in that leaky condition for longer periods of time. You are also at constant revs, so you will be generating constant vacuum. This may affect things too.

You need to find a better mechanic - one who doesn't let you drive away with faulty brakes.

Could it simply be that you simply have a faulty brake light switch that isn't dropping the cruise control at times when you hit the brakes - i.e. when you brake the engine will fight you to try to get back up to speed.

Bit of an update on this which might be of use to others who have the same problem:

I did 3500 miles this July/August and the brake seizure problem occurred again on about 4-5 occasions. There was a hissing noise of leaking vacuum coming from the master servo for about 10 seconds after I turned the engine off but by the end of last month the hissing was constant as long as the engine was running.

I bit the bullet and decided to get out the Haynes manual and replace the brake servo and master cylinder this last weekend. It took about 8 hours (with plenty of tea/rain breaks) but on looking inside the brake servo it was full of rusty water and most worrying of all the metal pin that runs through the middle had rusted up altogether and fell apart in my hand. I dread to think what would have happened if it had snapped while I was trying to brake on the motorway.

I have had the dreaded water ingress in the past and had to repair the electrics in about March this year and it seems clear that water had got into the brake servo as well and had caused it to rust from the inside out.

The good news is it's now fixed. A new master cylinder and servo cost £301 in total from Eurocarparts and took about 8 hours to replace. It could easily be done in less time than that but by far the biggest pain in the a*se was trying to release the old servo from the back of brake pedal. 3 hours of backbreaking work in the footwell was no use but managed to release the clip with a good old-fashioned upward yank in the end.

Word of warning though: I was quite tired after working on the car all day and should have stopped earlier. I rushed to put the car back together again and when replacing the wipers accidentally smashed the bottom of my windscreen. Fortunately I can replace it on my insurance but definitely a lesson about stopping working when you're too tired!

A few useful links for anyone else who has had a similar problem:

http://www.ukpassats.co.uk/phpbb/viewtopic.php?f=8&t=10572&start=0&st=0&sk=t&sd=a

http://www.passatworld.com/forums/68-b5-garage/272075-how-do-you-remove-brake-booster.html

http://www.passatworld.com/forums/68-b5-garage/307884-brake-booster-master-cylinder-writeup-w-pics.html

http://www.myturbodiesel.com/1000q/b5/brake-master-cylinder-removal-passat.htm

Despite this unbelievably shoddy bit of design from VAG that has caused me no end of problems, I'm still a huge fan of the Superb and I've learned a lot about home mechanics! I reckon replacing damaged electrics and the brake system has cost me about £500 in parts and tools and about 16-20 hours of my own time but would easily have cost treble or quadruple that from a VAG dealer!

It beats me how anyone can be "a fan" of a Company which knowingly - having done it before on the Passat/A4 - sells a car with a defect as serious as this one.

The sods must have known from day 1 production of the Superb that this would happen and that some cars would end up with no brakes as a result. Putting "check plenum drains" in the service schedule is a cop out - and they know it.

If the brakes don't fail, there's a ruined electrical system to deal with, which will never be reliable once it has been wet. Trim is not cheap either.

VAG have of course moved on - Teves Mk 60 brake controllers, 2.0PD oil pump drives and Siemens piezo unit injectors for instance. They had to be pushed into a recall for the injectors.

How can anyone who has had one of these time bombs contemplate giving more money to VAG? The worst of it is, they could have sold me a safe Superb for the sake of 10ps worth of mastic strip and the removal of a couple of bungs. They didn't and obviously don't give a damn. I'm fed up of doing corrective re-design work on this vehicle - I've never had a vehicle as badly designed as this before.

Toyota next time.

rotodiesel.