Date: Sat, 12 Oct 1996 13:35:25 -0700
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: ddes@anet-dfw.com (David Schwarze)
Subject: Vacuum gauge install
Volks,
I installed (well, sort of) a vacuum gauge on my bus this past week, and
thought some of you might be interested in the results.
I started by removing the oneway valve that is just in front of the front
engine tin. I replaced the valve with a piece of straight pipe so I could
use the original hoses which I had just replaced a couple of months ago.
Moving up to the area of the master cylinder, I removed the short hose that
connects the vacuum pipe (which runs the length of the bus) to the brake
booster. In place of this hose, I installed an assembly that includes
three short pieces of hose connected together by the oneway valve and a
tee. So, starting at the brake booster, there is now a short piece of hose
(about 2"0, then the oneway valve, then another short piece of hose, then
the tee, then a slightly longer piece of hose going back to the vacuum
pipe.
The reason I moved the oneway valve up next to the master cylinder is
because in order to get the engine vacuum, I had to tap into the line
behind the oneway valve, and it seemed stupid to run a second vacuum line
all the way up to the front parallel to the vacuum pipe. This seems to
have worked fine, and hasn't affected the operation of the brakes.
>From the tee, I hooked up a long hose to a vacuum gauge and fed it through
the wheelwell and in through the door for the time being. Didn't want to
install the hose under the chassis and up through the floor till I was sure
it was going to work as planned.
I started it up and drove around a while. I have two vacuum gauges at the
moment, one is a 2-1/16 no-name gauge that reads 0-30 psi in less than a 90
degree sweep. The other is a 4" Sears vacuum gauge that reads in
increments of 1 psi over about 270 degrees. MUCH more accurate. The Sears
gauge showed a max vacuum of about 20 psi (engine warm, trailing throttle)
with a low of about 2 psi (full throttle - does this mean my throttle plate
isn't opening all the way?). Normal idle is around 14 psi. The smaller
gauge didn't give much useful information because of it's small sweep.
On the freeway, I was happy to see that very slight changes in throttle
position produced a noticable change in vacuum. Cruising at 55 mph, I saw
around 10 psi on average. 62 mph saw closer to 5 psi, and was getting close
to floored. This is going to make a really good MPG indicator. I'm very
pleased with this and am going to complete the installation by ordering a
30 psi vacuum gauge from Summit (new style with fibre optic lit needle,
$27.95, ) and mounting it in the dash by running the vacuum hose up under
the floor at the front of the bus. Despite the great distance in the hose
(the hose from the tee to the gauge alone was over 20 ft) gauge response
was pretty much instantaneous.
One big problem with the whole setup - the needle of the vacuum gauge
vibrates wildly at part throttle. Enough that it was hard to read and even
made some noise. I don't think it's a problem with the engine or gauge - I
think it's just the result of the engine only producing vacuum during the
intake stroke(s). I managed to reduce the vibration by pinching the hose
- I was able to pinch it enough so that the gauge still responded quickly
but didn't vibrate. My plan is to insert a spare fuel jet into the vacuum
line to restrict the air flow down to a very small amount. I figure with
all of the different sizes of jets available I should be able to find one
that will be just about right.
That's it, have a good weekend everyone.
-David
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David Schwarze '73 VW Safare Custom Camper (Da Boat)
Dallas, Texas, USA '73 Capri GT 2800 (Da Beast)
e-mail: ddes@anet-dfw.com '87 Mustang Lx 5.0 (13.986@100.81)
or: des@eskimo.com '93 Weber WG-50 (Da Piano)
http://www.anet-dfw.com/~ddes '95, '96, '96 cats (Aackkk! Phhttt!)
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