Unusual tapping noise

[Freshup]

Don't rush into servo. replaced one vacuum pump at 100000k, started tapping again at 220000. Now done 660000k just put up with it. Noise disappears when brake pumped.

[derbydrifter]

Me neither, but someone on the forum, in an earlier reply, said that it could be the servo-valve. Personaly, I don't think it is coming from the servo, but it is strange that the noise always temporarily stops when the brake pedal is pressed.

[derbydrifter]

The tapping, which is now quite loud and a little embarrassing, definitely is not coming from the vacuum pump - which as far as we can make out is at the front of the engine. Sure it does stop when the brake pedal is pressed, but the worrying thing is that the noise is getting loulder.

[kenney]

Hi (Sure it does stop when the brake pedal is pressed) this is typical of the vacuum pump,if it had of been any thing else then the noise would not have stopped by pressing the brake pedal.The valve is plastic and there is nothing in the servo that could make such an noise.Try removing the vacuum hose from the pump,see what happens.I had one ACV engine were the cam that operates the pump was completely worn ,but this resulted in the pump not producing enough vacuum.To check this you must remove the cylinder head cover

[derbydrifter]

Hi Kenney,
I am going to have to investigate your diagnosis by suggesting that my mechanic takes of the cylinder head cover - because to me, that's where the noise appears to be coming from.
Would you believe, I took my van to the garage today to get this thing sorted once and for all, and the noise stopped. The mechanic managed to get it to do it occasionally, but not long enough to track it down. So, I'm going to take your advice and get him to take that cover off. Any idea what he's supposed to be looking for, and what new bits I had better order in preparation?
Thanks for your help,
Derbydrifter

[kenney]

To diagnose the noise,if it is the pump,when the knocking is present,pull the vacuum hose of the pump,this releases the pressure on the pump and the noise should stop immediatly.I cant understand it can be anything else,a leaking valve lifter, can make the same noise,but applying the brake pedal,would not have any influence on it.

[derbydrifter]

Kenney,

over the weekend I'll try pulling the hose off to see what happens. Thanks for the tip. Like you, I'm convinced it is the vacuum pump and its operating mechanism. I told my mechanic what you said, and he agreed also. So, we're on the case. I'll keep you posted how things go.

Thanks again...Kurt

[diggerboy]

Hi folks,

I know I'm blowing the dust off this original post, but I've got the same problem - intermittent tapping from near the top of the engine on my LT35 109 5-cylinder diesel.

I've noticed it getting slightly louder over the last 1,000 miles. Ony happens when hot, and the tapping is slightly irregular.

I'm going to have it looked at as soon as I can, but assuming it is a vac-pump problem what are the potential running problems and how long can I run before any further damage is done?

Are there any other ideas about what the problem could be?

Thanks in advance.

[rayl]

Hi Diggerboy, mine has gone on to do 400,000 plus miles and still taps now and again, first started taping around 150,000 miles or so, noise has not got any louder, engine oil and filter has been changed on or even before the 15,000 service time with out fail, hope this helps.
rayl

[Walesy]

What a great thread! I have a 2002 2.5TDI which is just about to hit 140k, this noise appeared about 6 weeks ago and has been getting me progressively worried - I just went out and gave the old brake pedal to the floor twice trick and it worked! Its great to know it's not engine related and is something I can remedy as and when I find the time/money!

Thanks for the free info guys!