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PostPosted: Sat Mar 28, 2020 1:31 pm 
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Need some help with this from you knowledgable guys.

My VW Camper has just failed the MOT one of the fails was for a leaking servo.

It is fitted with a BMW E30 servo (common upgrade for these vans), when the brake pedal is operated for the first time from start up there is a hissing sound of air escaping after that is doesn't do it again until the next time you start up after a period of rest. The servo works fine during normal driving.

I am sure this servo has always made this noise since I fitted it 5 years ago, I just assumed this was normal air entering the non vacuum side of the diaphragm on the first pedal press. On these vans the servo in inside the cab not in the engine bay, so it is easy to hear this hissing whereas if it was on the engine bay I don't think you would hear it. So the tester has decided this year to fail it on this.

My question is, is this normal, do all servos make this initial hiss but we don't usually hear it?

As I say the servo functions fine and it's a pig of a job to change so any advice would be appreciated. Obviously if it's a sign of a fault I will change it.

Thanks

Tony

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PostPosted: Sat Mar 28, 2020 2:50 pm 
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Whats the actual wording that hes failed it on?
As a tester, it sounds odd.


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PostPosted: Sat Mar 28, 2020 2:56 pm 
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See photo. I've not had a chance to speak to him yet as he wasn't there when I picked the van up, normally he's pretty fair and classic friendly.
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PostPosted: Sun Mar 29, 2020 9:50 am 
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I have just been out and started my Touran and that gives a quick hiss on start up. Personally i would take it elsewhere. If the hiss was there all the time? I would have failed it, but to me it is just filling the servo after being stood with the engine off. Is there a non return vale in the system Tony? If so that could be the cause.

Tony.

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PostPosted: Sun Mar 29, 2020 11:07 am 
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Hi Tony

Yes there is a non return valve, I will check it is working.
I'm going to speak to the tester once all this virus has calmed down. For now the mot has been extended by 6 months, not that I am going anywhere.

Thanks

Tony

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PostPosted: Sun Mar 29, 2020 12:45 pm 
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Tony

I have a BMW servo that i fitted to the Stag, also have a spare you could try

Dave


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PostPosted: Sun Mar 29, 2020 12:53 pm 
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Thanks for the offer Dave, I'm hoping I won't have to change it though.

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PostPosted: Sun Mar 29, 2020 1:09 pm 
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Is it possible to test its function? We have just checked an MGF for a potential servo leak and the way we were told to test it was to pump the pedal repeatedly with the engine off, then hold the pedal down. Turn the engine on and if it is working, the pedal should be pulled down by the servo.

However I don't know if that tests works for any servo or it is just a quirk of the MGF.


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PostPosted: Sun Mar 29, 2020 1:31 pm 
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Quote:
Is it possible to test its function? We have just checked an MGF for a potential servo leak and the way we were told to test it was to pump the pedal repeatedly with the engine off, then hold the pedal down. Turn the engine on and if it is working, the pedal should be pulled down by the servo.

However I don't know if that tests works for any servo or it is just a quirk of the MGF.
Part of the MOT includes this exact test. It's probably doing this that has generated the fail!

I don't know what to make of this at all, if you get your head under the dash of a Dolomite, any Dolomite, it will make a very slight pssshhh noise EVERY time you press the pedal with the engine running, you just have to be close enough to hear it above other noises! AFAIK it isn't just Dolomites, just mine are easier due to no parcel tray and precious little soundproofng! And it doesn't affect brake performance obviously!

If this so called fault doesn't affect brake performance, I can't see it's a legitimate reason for failure anyway, but the only REAL test is to take it out on the road and check brake down a long hill that will test if you are "running out of vacuum" which you would if there WAS a fault. This is certainly WAY beyond any MOT tester's remit! So I can't see any way round it other than a) fit another servo and see if it behaves the same way, or b) try a different tester, the problem with that, is that, these days, the second garage will have access to the first garage's fail, so will be alerted to the alleged "fault".

Steve

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PostPosted: Sun Mar 29, 2020 1:52 pm 
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I'll try the test you did on your MGF, I have read elsewhere about this.

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PostPosted: Sun Mar 29, 2020 1:54 pm 
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Tony as its already a fail on an immediate repair will the extension apply. I thought that under the new rules if its a fail even in the month before expiry date, then its not allowed to be used at all.

I was advised once its recorded on the system as failed its illegal to use until fixed. Someone may be able to clarify better.


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PostPosted: Sun Mar 29, 2020 3:41 pm 
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Right just done the test, pumped the pedal a few times without the engine running, nice firm pedal, held it down, started up, the servo pulled the pedal down as expected whilst hissing for about 2 seconds then hissing stops, I would say that is OK.
I'll speak to the tester next week if he is in work, get his take on it.
Not sure where I stand with the MOT as I doubt I can take it for a retest, I'm not going to be driving it anyway.

Thanks for all the advice.

Cheers

Tony

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PostPosted: Sun Mar 29, 2020 3:49 pm 
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Quote:
Right just done the test, pumped the pedal a few times without the engine running, nice firm pedal, held it down, started up, the servo pulled the pedal down as expected whilst hissing for about 2 seconds then hissing stops, I would say that is OK.
I'll speak to the tester next week if he is in work, get his take on it.
Not sure where I stand with the MOT as I doubt I can take it for a retest, I'm not going to be driving it anyway.

Thanks for all the advice.

Cheers

Tony
You can get the ministry of transport involved Tony... They will give an honest answer as they have nothing to gain, but talk to tester first if you know him?

Tony.

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