Random Brake Failure - Hard Pedal - please help - Suspension, Brakes and Chassis - uk-mkivs

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Random Brake Failure - Hard Pedal - please help


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#1 banier

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Posted 14 January 2021 - 02:17 PM

About a month ago I had my paniced girlfriend on the phone saying the brakes had failed on our 2003 Mk4 TDI.

So I cycled over to take a look and everything seemed fine and no problem evident and was able to drive the car away.

She complained that the brake pedal went really hard and could not provide any braking.

Obviously quite scary, so I took it to a mechanic friend the next day, who said it could be a servo valve but suggested it could have been a once in a lifetime event and to do nothing, but keep an eye on it.

Been using the car regularly (as you can in Lockdown!) and no problem.

Today the brakes failed again as previously described before.  Very hard brake pedal and probably only 5-10% of braking action, so very very dangerous.

Luckily I was on a quiet road, so no imminent danger (  :) )  However after eventually stopping I tried to move away and try the brakes again and they were still not working.

I then parked up, switched off engine and left it for 20 minutes.  When I restarted the car and tried the brakes again everything was fine, no problem.  All working normally.

 

What could be causing this problem?  I'm slightly scared to use the car again.

Please note that on both days of failure it was very wet, including travelling through big puddles on country roads.  Could the water in the brake system somehow causing this issue?

 

Has anyone else had something simliar?

I looked on other forum posts, (namely https://uk-mkivs.net...o-stop-the-car/ & https://uk-mkivs.net/topic/237835-braking-stiff-vacuum-line-issue-2001-19-tdi-solved/ ), but both these issues were not random events like mine and did not cure themselves.

 

Any help / suggestion much appreciated.

 

Thanks.




#2 adam-

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Posted 14 January 2021 - 02:19 PM

Check vacuum line from servo to pump.  Check all vacuum pipework too.  It'll be split somewhere.


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#3 banier

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Posted 14 January 2021 - 03:43 PM

Check vacuum line from servo to pump.  Check all vacuum pipework too.  It'll be split somewhere.

Thanks for your reply.  I'm unlcear how it could be random and possibly rain-related problem.  Can you think why this would be?
In the meantime I will check the piping...



#4 elektrikbanana

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Posted 14 January 2021 - 04:01 PM

See this pipe at the back of the tandem pump: 

 

 

This pipe that's replaced in this video then connects to another pipe running along the firewall that connects to the brake booster which should also be checked. Monkey grips or similar will help you remove the intake pipe from the airbox to get a better look behind the pump.


Edited by elektrikbanana, 14 January 2021 - 04:01 PM.


#5 adam-

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Posted 14 January 2021 - 04:22 PM

Thanks for your reply.  I'm unlcear how it could be random and possibly rain-related problem.  Can you think why this would be?
In the meantime I will check the piping...

 

It's not.  Vacuum is a mechanical system, no electrical parts.  Water cannot change it.  It's also high so won't even be close to being wet.  It's a fluke.


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#6 Bandit127

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Posted 14 January 2021 - 07:21 PM

The servo is a vacuum tank that has a capacity. A healthy system maintains the level of vacuum in it as it is used up when applying the brakes.  When you have a vacuum leak to the servo you reduce the amount of vacuum in the servo - to the point that repeated brake applications can exhaust it and you get a hard pedal. Like driving in a town centre for example. This can make it look like the problem is intermittent because the symptoms are. 

 

The answer is probably a vacuum leak, probaly in the main vacuum supply hose. My Mk5 was hose was cracked. There is a check valve in there too, you will get the same problem if that has started leaking/bypassing. The main hose looks like rubber but is actually plastic that hardens and cracks over time.



#7 Imagewerx

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Posted 14 January 2021 - 09:34 PM

Your post has been moved.Always ask technical questions in the relevant technical section,they really very easy to find.


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#8 banier

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Posted 15 January 2021 - 09:35 AM

Your post has been moved.Always ask technical questions in the relevant technical section,they really very easy to find.

Thanks, being a newbie, I didn't realise I was in the wrong section.  Cheers,



#9 banier

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Posted 15 January 2021 - 12:23 PM

Thanks for all your advice.  I lifted the bonnet this morning, as I had another brake failure last night, on my way back from Tescos.

I think I found an issue as described above by @adam-, @elektrikbanana and @Bandit127.  I have 2x small cracks in the pipe that runs along the firewall, as mentioned by @elektrikbanana.  The location of the small cracks are where the long pipe is about to join the pipe that is replaced in @elektrikbanana 's video.
See pic below:

Crack_location.jpg?width=450&height=278&

 

with the cracks are on the underside, so were not easily evident from looking down into the engine areas.

See pic below, taken with camera facing up from below crack area.

The_Crack(1).jpg?width=450&height=278&fi

 

[slightly hard to see with the photobucket watermark in the way!]

 

So could anyone let me know the exact name and possibly part number for this hose and I'll look to replace.

 

Many Thanks Guys.



#10 adam-

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Posted 15 January 2021 - 01:38 PM

Can just use braided/hard hose.  Just remember to put the valve (little UFO shaped thing) and make sure it goes in the right way(!).


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#11 elektrikbanana

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Posted 15 January 2021 - 02:36 PM

Parts catalogue: http://www.oemepc.co...69/lang/e#sec_8

 

1J2612041K, double check but I believe this is correct.

 

Aftermarket part source: https://www.onlineca...co-8007541.html



#12 elektrikbanana

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Posted 15 January 2021 - 02:37 PM

Parts catalogue: http://www.oemepc.co...69/lang/e#sec_8

 

1J2612041K, double check but I believe this is correct.

 

Aftermarket part source: https://www.onlineca...co-8007541.html

 

I've just checked mine and found it's also perished  :rolleyes:



#13 banier

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Posted 15 January 2021 - 03:50 PM

Can just use braided/hard hose.  Just remember to put the valve (little UFO shaped thing) and make sure it goes in the right way(!).

Thanks.  Do you happen to know what size?



#14 ttg4l

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Posted 15 January 2021 - 07:20 PM

FWIW, the OEM hose is about £35 each section, I paid £70 and some pennies for the two halves of the pipe for my Golf. So that might make you more inclined to go for an aftermarket offering.

I was just paranoid about an aftermarket pipe collapsing under hard braking, so I went OEM.

#15 banier

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Posted 18 January 2021 - 11:16 AM

Thanks everybody.  I think I've identified the hose parts required.  Going to replace both the long hose that runs along the firewall and the short curve piece as replaced in @elektrikbanana 's video.  However I've not been allowed to change it myself, as my girlfriend is too scared for a car brakes issue to be carried out by anyone other than a professional mechanic.  Must keep the peace!  So messaged my friendly mechanic, who will hopefully agree with the way forward in the hose replacements.

 

Just wanted to say thanks for all your help guys.  Much Appreciated.

Will move onto my broken rear wiper, non-functioning driver's electric window switch and poor battery next.......  these items are less safety critical so hopefully will have the allowance to fix these...!


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#16 adam-

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Posted 18 January 2021 - 06:19 PM

The pipes can be heated to the point they go liquid and then slide over and then it'll seal.  Hopefully he doesn't charge you a fortune.

 

I've got a motor if you need, just take it.  Or others should offer the same.  Check the harness between the boot/body in the conduit, it breaks in here.  Also check for leaks in behind the boot trim, it'll kill your lock.


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#17 banier

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Posted 19 January 2021 - 05:41 PM

Thanks @adam-, would love to take you up on the offer of the pipe, but thinking Galsgow to Suffolk is a tad to far to collect/post.

 

Do you mean the harness holding the vacuum pipe?   

 

"Also check for leaks in behind the boot trim, it'll kill your lock."  - I'm not sure what this means or pointing towards?

 

Cheers,



#18 adam-

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Posted 20 January 2021 - 04:49 PM

Nah I mean the vacuum pipe itself.  Can be heated until its seen to go soft and then push it over the nipples needed.

 

The boot stuff, I mean because you said your rear wiper is dead.  Check the harness between the boot/shell and behind the cover.  It's known to split the washer hose here and the fluid just sprays all over the lock.


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#19 NooNoo

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Posted 20 January 2021 - 08:08 PM

We got diddled with RHD. The pipe traversing the bulkhead is only for us. Notorious.

 

:wacko:


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