Hissing from drivers footwell

[tjb]

Picked up a Skoda Fabia 2004 1.4 16v last week and I've been really impressed with the car except for a few little things which I can probably sort out myself.

 

However I'm stumped by a hissing sound that's coming from the drivers foot well. It's there at idle and for a few seconds after pulling away, once the revs climb either I can't hear it or it goes away.

 

Pressing the brake pedal seems to quieten it down somewhat but it never goes away completely. Sort of sounds like static from an untuned radio.

 

Anyone had experience with this sort of issue before? I only paid £1050 for the car but it comes with a 28 day warranty, really don't want to return it but if it needs fixing I'll chase them for garage fee's which I think would be fair considering a car sold as good condition with a years MOT should really have fully functioning brakes!

 

I've tried brake tests recommended in the Haynes manual. With the engine off the peddle build up pressure then dips when the engine is started. With the engine running and the brake depressed turning the engine off forces the brake peddle up immediately; from what I understand that's suspicious?

 

Thanks for any help in advance  

 

Edited 28 June, 2017 by tjb

[sepulchrave]

Yes, you have a vacuum leak, very common I'm afraid, the crappy pipe between the manifold and servo has a non-return valve inline and the ends of the pipe generally split where it is pushed onto the barbs of the valve, check the entire pipe for splits anyway. You can cut the split bits off, warm the pipe with a hot air gun and push it back on to the barbs, whereupon it will harden again.

[tjb]

Thanks for the reply, I'll have a look at the pipe this evening.

 

When I checked it yesterday I couldn't hear any leaking noises from the engine bay only from inside the car 

 

If all the vacuum hoses are fine what's the next step, brake servo itself? What sort of garage costs would I expect for replacing a brake servo?

[Breezy_Pete]

Could be the valve in the servo that lets atmospheric pressure air in from the cabin as you push the brake pedal, leaking slightly.  Try hooking a toe under the brake pedal and lifting it to see if that makes it stop, just in case it's a mechanical/pedal issue only.

 

I'm not sure that your servo testing was really suspicious, that sounds normal, I think? Link me to where it describes the tests you did and the expected results.

 

Is there anything functionally wrong with regards to stopping power? If not I would either ignore, or swap for a car without this issue.  Servo change is a PITA from what I've heard.

[tjb]

I've now checked the vacuum line from the engine and it's in order, can't see any visual degradation or hear any leaks.

 

@Wino I ran the test under the heading "Test if the Brake Booster Can Maintain a Vacuum" from here: http://www.ebay.co.uk/gds/How-to-Diagnose-a-Faulty-Brake-Booster-/10000000178571669/g.html

 

The pedal pushed back as soon as the engine was switched off. According to the article this means my servo can't hold a vacuum. Actually, I found out the brake loses it's efficiency as soon as the engine is switched off, I tested this (possibly not the smartest idea) by rolling along and switching the engine off, immediately I had virtually no brakes. Trying this on my other car and it slowly loses brake efficiency as the brake is pumped multiple times. The reason this bothers me is if for some random reason the engine cuts out I wont have any buffer with the residual vacuum to slow the car down.

 

Car booked in tomorrow with a garage who will hopefully diagnose the issue and give me a quote for the work. If that's the case I'll be asking the dealer to cough up on grounds of the braking system not being fit for purpose.

[sepulchrave]

Remember the non-return valve I mentioned earlier? It's gooched.

[tjb]

@sepulchrave you were bang on the first time. When to check the value operation this morning and in trying to remove the pipe I noticed the vacuum pipe had split around the bottom. Didn't remove it when I first inspected it and missed the small split! I've patched it up and ordering a new pipe. Thank you both for your help

[Breezy_Pete]

Excellent news. Not sure I was any help though!