The Stovebolt Site Forums The Shop Area Engine Shop Vacuum gauge install ?????

I am thinking of installing a vacuum gauge in the truck and was wondering if I tapped the vacuum line from the distributor would it affect the distributor advance?

A vacuum gauge is always great to have, and I'll probably put one in myself at some point. Putting a tee fitting for the wipers, and the gauge on the vac port below the carb would be the best spot for the line. Or you could maybe even tee the vacuum line under the dash off of the wiper hose vac circuit.

The gauge shouldn't leak vacuum. So other than odd readings on it from where you install it, it shouldn't effect anything to install it anyplace.

Thanks, 4100 and LeeP, I had not thought of the wiper hose. The line to the distributor is tapped in the back carb and I could fit a tee on it. But to keep it simple the wiper would be a better place. I might even be able to do it myself.

I use the wiper hose for my vacuum gauge. If you try and drive by the gauge, your mileage will increase, they are fun to watch. I notice my will run about 10 to 12 inches at highway speed on level ground, pulling inclines it will drop just under 10, letting off just a touch I can keep it at 10 or more. The higher you can keep it, the better the engine is working as long as you are maintaining speed.

17-18 is good/OK
I think I get at least 20 on a my 1960 261.
I see Internet posts of up the 24 inches on late-model good-condition 235s.

My father had a 1971 International Travelall that he pulled his 36-foot travel trailer and usually got 10 inches of vacuum. One time he drafted a semi from somewhere in Va. to DC and pulled 14. Very dangerous but the semi driver did not seem to mind. I looked under my dash and it is a mess wiring wise, AC installed. It is difficult to contort myself to figure out what hoses are what. This the one that I have chosen.

You are talking about at idle, right?
It would be tough to get much over 10 if you have your foot on the gas at all. That is why the vacuum wipers are such a pain, especially when under a moderate load like when accelerating or going up a hill.
Carl

Yes - at idle, or when steady cruising on flat/level road.

The distributor vacuum line does not get full manifold vacuum- - - - - -little if any at idle, and only partial vacuum during acceleration and/or cruise. Just put a tee fitting into the port directly below the carburetor and run the line through any available hole in the firewall. The closer to the carb, the more accurate and responsive the reading will be. Any load at all such as acceleration or passing that requires the throttle to be opened will kill most of the vacuum reading.
Jerry

G.M. used a hollow manifold stud as one vacuum source on later tripower setups.

Jon

I would love to use the wiper vacuum because all the holes in the firewall have been plugged and painted. I am trying to keep it as simple as possible so I can do it myself. The back carb is already tapped for the distributor. I already drive moderately but it would be nice to see proof of that. The truck will run at any speed I chose but I usually drive at 5 mph under the speed limit. Now in my new car, it is 5 mph over. I always try to leave early enough I don't have to speed.

A vacuum gauge is also an early warning device of a tight valve, worn/leaking seat, intake leak - the needle will fluctuate at idle. A constant slightly low reading at cruise may mean your vacuum advance isn't coming in on time, point setting slipped etc. - not enough spark. I used to have a favorite test road - a long slightly uphill with no traffic and mile posts. I'd check the gauge at the same air temperature, gear & MPH after every mod (including oil viscosity, tire pressure, alignment), if the vacuum was up I'm doing the right thing.

Very low vacuum at cruise speed is also an indication of a restricted exhaust system- - - - -something that most people don't even consider when performance deteriorates.
Jerry

Pulled this pic from Brad Allens web site

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I am using a Summit Racing gauge that I modified. I pulled the dial out, scanned it, changed colors and font, and added some details to match the '37 style gauges. I have more gauges then I need!

HRL, I check the exhaust because I thought I had damaged it coming back from HQ when I made a turnaround when I missed a turn in to a gas station and I dropped into a small hole. When I checked the exhaust was when I found out my rear shock bushing were gone.