VW Polo - Break pedal seized up at 50mph down a hill!!!

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Tue 18 Mar 2014 19:45
VW Polo - Break pedal seized up at 50mph down a hill!!! - Ciaran88

Hi guys,

Need some help on this. Bought a 2003 VW Polo recently and was driving it to work this morning. Going 50mph downhill towards a queue of traffic as I moved to slow the car I suddenly felt I was unable to depress the break pedal..

It went down about 15% and I could feel the car just starting to break but beyond that, not matter how much pressure I applied, I couldn't get the pedal down, it was just stuck. It didn't feel like it was hitting anything solid, just like there was a pressure I couldn't overcome.

I kept pumping the pedal and eventually it just returned to normal, since then it was fine. I took it to a garage and the guy took a look and said he couldn't see any problem, and just topped up the break fluid.

I feel extremely edgy not having a diagnosis, I have read that possible causes such as an air bubble or debris in the break fluid could cause this and that it will happen periodically, and I'm not sure if the guy that checked the car over looked for that. He just seemed happy there was no problem, but I've never ever had a car do that before and it could easily be a deadly malfunction so I would like a better understanding to be honest...

Edited by Ciaran88 on 18/03/2014 at 19:47

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Tue 18 Mar 2014 20:09
VW Polo - Break pedal seized up at 50mph down a hill!!! - craig-pd130

Could be either a small leak in the vacuum line to the brake servo (which reduces the brake assistance and will make the pedal feel very solid), or contamination in the brake fluid. If you don't know when the brake fluid was last changed, get it changed.

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Tue 18 Mar 2014 20:30
VW Polo - Break pedal seized up at 50mph down a hill!!! - Ciaran88

Thanks for the reply craig.

I had the fluid topped up today but I'm gonna have it completely replaced tomorrow.

It's this vacuum leak that worries me and I don't think that the guy really checked for anything like that.

Would the break be so stiff even if it had no boost at all? I would have thought it would be possible to deress it, just with a lot of pressure? I was using all my stregnth to try and cram it down but it would budge beyond the first few cm.

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Tue 18 Mar 2014 21:53
VW Polo - Break pedal seized up at 50mph down a hill!!! - Peter.N.

Disc brakes without power assistance are pretty useless and the effect of loosing the servo vacuum is as you described, the pedal goes pretty solid. If yours is diesel it will have a vacuum pump which can fail all though its very rare, if its petrol it will probably use manifold depression so could have a flow valve fault. They will usually stop if you are not following to close or going to fast so until the fault manifests its self again you will just have to take it steady - good for your fuel consumption.

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Tue 18 Mar 2014 22:02
VW Polo - Break pedal seized up at 50mph down a hill!!! - Ciaran88

Ok thanks, sounds like this might be the issue.

Is this the kind of thing that can be identified by a mechanic if he specifically looks for it? What I want is a proper diagnosis and solution rather than today where I was told it sounded "odd" and given no advice or whether or not I should even drive the thing.

I'm driving to Leeds this weekend, not being able to brake on the M1 sounds like a pretty effective way of ending up in a morgue.

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Tue 18 Mar 2014 22:19
VW Polo - Break pedal seized up at 50mph down a hill!!! - gordonbennet

If you run your engine for a few seconds to build a full vacuum, then switch engine off, so you can hear.

Now press the brake pedal about 4 or 5 times, each time in the quiet you should hear a slight hiss as the vacuum is used up, by about the 5th press the vacuum will have been exhausted and you should feel the rock hard pedal you experienced.

Any half decent mechanic should be able to confirm this and isolate the fault whatever it is, if he can't i'd look for another mech.

The dogs rubber ball isn't floating about in the footwell is it?...:-)

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Tue 18 Mar 2014 22:53
VW Polo - Break pedal seized up at 50mph down a hill!!! - The-Mechanic

If the polo is petrol engined, they have a common problem with the servo vacuum pipe splitting. Look at the brake servo unit under the bonnet, on the right hand side as you look at it you'll see a black plastic pipe approx 15mm in diameter on a 90 degree elbow. Follow the pipe across the bulkhead of the engine bay to your right where it connects to the inlet manifold.

Along it's length, you'll find connection pieces. The pipe usually cracks/splits at these joints allowing the vacuum to escape causing the problems you describe.

If you find any breaks/splits in the pipe, don't be tempted to try and tape them up, get a new one for safety's sake. They are dead easy to replace so if you don't feel confident doing it yourself, don't get ripped off by a garage who may try to quote you a rediculous price.

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Wed 19 Mar 2014 12:53
VW Polo - Break pedal seized up at 50mph down a hill!!! - Ciaran88
Thanks for the replies guys.

As you guys described, what I felt was EXACTLY like pressing the pedal with the engine off a few times: you can press it in about a cm but beyond that no matter what you just can't get it any further. That 1cm was applying a bit of braking power, but obviously nowhere near enough to stop or significantly slow the car.

In fact with the engine off, the first pump goes in about half way but the second and onwards give that effect. I haven't listened for a hiss yet.

It's at a brake and clutch specialists now and they say they can't see any cracks and just want to change the fluid (a bit dirty) and replace the rear pads (a bit corroded).

I'm just worried that my problem felt exactly like you and others describe as a vacuum/booster fault but nobody has found a problem there, and other stories like mine suggest that this will happen sporadically every now and then until it's found and fixed.

If it happens at 70mph on the motorway I am dead man.
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Wed 19 Mar 2014 13:27
VW Polo - Break pedal seized up at 50mph down a hill!!! - skidpan

Disc brakes without power assistance are pretty useless.

My classic has discs on the front with no servo. It was designed like that and works fine. The car will stop as fast (if not faster) than most cars. When it gets the new calipers (4 pots) fitted it should be even better, for the first time that will mean it has bigger pads on the front, no need to restrict the rear bias.

Even on cars with servo's they hold enough vacuem in the system to allow a few applications before you loose assistance. Even then the car will stop but it requires a very hefty push, ever tried stopping a car that is being towed with a dead engine.

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Wed 19 Mar 2014 15:13
VW Polo - Break pedal seized up at 50mph down a hill!!! - gordonbennet

Whilst checking, and from the sounds of things its a lack of vacuum problem, don't forget to remove the vacuum flexible pipes/connections and check them carefully, i've had flexy vacuum pipes collapsing internally before now, so 1/2" bore on the outside but down to knitting needle bore inside.

Maybe the car needs new fluid and work on the rear brakes, but i don't think either of those are causing this fault, IMO you need an old school mechanic to find this fault if you can't sort it yourself.

Update, ignore my earlier suggestion of the vacuum lasting 4/5 presses, don't have my MB here though i'm sure that does have a 4/5 brake application vacuum capacity, but i've just tried emptying the Outlander servo of vacuum and that only took 2 brake applications..

Edited by gordonbennet on 19/03/2014 at 15:15

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Wed 19 Mar 2014 15:52
VW Polo - Break pedal seized up at 50mph down a hill!!! - Ciaran88
I took it to an old school mechanic and to the boss at a specialist brake and clutch service centre and both said they couldn't find anything wrong with the vacuum. I told the latter to specifically look for problems there and they seem to think it's all fine with no leak.

They drained and replaced the fluid and changed the back pads which the said were sticky, and said either could have caused the problem, but I really think that the descriptions given for boost failure for what I experienced exactly.

I still feel edgy because nobody has found a fault that concincgly would explain what I experienced.
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Sun 23 Mar 2014 21:32
VW Polo - Break pedal seized up at 50mph down a hill!!! - Big John

I would change the brake servo pipe anyway, as well rotting and leaking on the outside they can collapse internally. This happened a few years ago on my dads Volvo 740 - usually causing the pedal to go solid at the wrong moment.

Change anyway - it's a really cheap job.

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Sun 23 Mar 2014 21:39
VW Polo - Break pedal seized up at 50mph down a hill!!! - Big John

In addition as mentioned above if the brake fluid hasn't been changed in the last couple of years - change it now! Absorbed moisture plays havoc with hydraulic systems especially ABS units.

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