Vaccuum pump fix - maybe?

[Jeremy R King <kingjer@eng.auburn.edu>]

Warning - long post.  I was going to write this just to Heidi, but I 
thought some of the rest of you may be interested.  If someone can prove 
me right or wrong (either with testimonials reguarding this "fix" or with 
hard, researched facts about the workings of the pump), please let me know.

Heidi,

Believe me, I know just how that little sound grates on the ole nerves.  
My dad spent $500 for a guy (who claimed the sound was my lifters) to 
replace all ten lifters and seal my exhaust manifold leak (I did have the 
manifold leak).  In fact, your car probably has the exhaust manifold 
leak.  Audi wasn't thinking quite hard enough and used a stud to secure 
the thing that expanded at a different rate than the head.  I think the 
head is Al and they used steel studs.  The studs snap off right between 
the head and the manifold - quite a chore to remove out of the head.  
Often you have to re-tap the holes in the heads and go to bigger studs.  
Audi has a stud kit for around $20, but labor is usually through the roof.

Anyhow, back to the task at hand.  First you must locate this ever 
elusive vaccuum pump.  You've doubtless heard us sing the praises of 
Bentley Factory Repair Manuals for our Audis (my half Audi).  They are 
wonderful and you NEED to obtain one.  However, I've searched through 
page by page three times and haven't seen even mention of the vaccuum 
pump.  I did, however, find the hole in the head that it mounts to.  So I 
can tell you that it is just beside the 4th cam lobe/2nd cylinder from 
the front.  Looking at your engine from the front bumper (facing the 
windshield), it's on the right side of the head.  It's just behind the 
power steering pump on my car, but I think Audi might have a different 
arrangement since they use that single hydraulic system thing.  Crank 
your car, pop the hood, and follow the knocking noise.  You'll end up 
staring it in the face.  

The pump attatches to the head with two nuts (13mm I think) via a flange 
on the pump.  The pump then has a neck and extends out roughly to a disc 
shape.  Take these two nuts off (you'll probably end up sacrificing one 
to the Audi Gods like I did - no worries, it's a standard 13mm 100thread 
nut).  Now, there's tension on the pump from the plunger, so you might 
want to back one nut off a couple of turns, then the other, and alternate 
until it's off.  This would minimize the risk of breaking one of the 
studs coming out of the head.  I just whip out the Makita and do one all 
the way out, then the other.  When you get the nuts loose, pull the pump 
off the head (leave all the hoses attatched to the pump).  You'll 
immediately see the cause of the aweful noise you've been hearing.  The 
rod will either come out with the removal of the pump, or (more likely) 
remain sticking out of the head.  

OK.  If you look at the pump to see where the plunger rod applies its 
force, you'll notice a huge (17 or 19mm by my recollection, maybe 15mm) 
bolt head.  The bolt goes through a big spring to the diaphram.  So what 
happens is the cam lobe pushes the rod which pushes the bolt which pumps 
the diaphram.  On the return, the spring pushes the bolt which pushes the 
rod to hold it up against the cam lobe in preparation for the next pump.
My theory (weakly founded) is that that bolt head can be adjusted out to 
keep proper pressure on the rod.  I hooked my socket wrench up to the 
bolt and unscrewed it about 10-15 or so turns (over three different 
attempts).  After doing this, reattach the pump to the head.  You may 
have to use two sets of hands - one to push the pump up against the head 
and another to screw on the nuts.  

This whole procedure takes about 15 minutes.  The first time I tried 
this, I only turned the bolt a few times.  It was quiet for a while, but 
soon reared its ugly head once more.  I think I got it right the third 
time (either that or just taking the thing off and playing with it a lot 
makes it happy and it shuts up).  It's been almost a year now and mine 
has been quiet since (it was very loud before).  

The "adjustment" may be a fluke, but for 15 minutes of your time I figure 
it's worth a shot.

Do any of the Audi Bentley Manuals show or discuss the vaccuum pump?  
Just curious.

I hope this is the cure.  If it's not, I've got a couple of other ideas.

Jeremy R. King
1986 VW Quantum GL5
Audi at Heart