Vacuum Guage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GMC_Aaron · 10-10-2002, 02:36 AM

I was browsing through my new Early Classic Enterprises catalog and I saw a vacuum guage for my 1972 GMC Super Custom. Was this an option on our trucks? This is the first I've seen for vacuum guages for our truck. I know there's a spot on the instrument bezel next to the oil pressure guage that doesn't have anything in it. Was that spot intended for something such as the vacuum guage?

JJR · 10-10-2002, 07:08 AM

Not sure if they were available in C10-30 but I have seen several in C40-60. The big trucks could have a vacuum gauge or an air pressure gauge in the spot next to the oil pressure gauge.

JimKshortstep4x4 · 10-10-2002, 09:04 AM

The vacuum gages do fit in the open spot on the dash. The face and inside reveal are different. If you wanted one, usually someone on the parts board will come up with one. They are kind of cool.

Jim

MStokes · 10-10-2002, 09:06 AM

Does anyone have a photo of one they could post?

GMC_Aaron · 10-10-2002, 09:36 AM

Thanks guys!

I think I will get one to fill up that empty spot on my instrument bezel.

jmil1974 · 10-10-2002, 12:19 PM

Just a question. . .
vacuum gauges are cool but what the heck are they good for? To know if you have enough vacuum to run your power brakes?

Alex Hayley · 10-10-2002, 03:56 PM

They are great for watching your gas mileage. The more vacuum you are pulling, the better your gas mileage could be. By the way, I am quite sure that it is the air pressure guage that tells you how much air pressure you have to operate the air brakes.

GMC1967 · 10-10-2002, 04:52 PM

Air pressure gauge is if you have air breaks, however if you have standard automotive power breaks, those run off of engine vacuum. And the vacuum gauge measures just that, engine vacuum.

Rod · 10-10-2002, 11:07 PM

Here's one pic

Spoof · 10-10-2002, 11:55 PM

Vacuum gauges are great for optimum gas mileage ( or kilometerage here in Canada) but they are also great for adjusting timing, indicating blown gaskets and a whole host of other engine problems. My rebuild manual for sbc's goes into great detail on using a vacuum gauge for engine problem diagnosis, of course it's not necessary to have one in your instrument panel but I would like one.

Longhorn Man · 10-11-2002, 12:01 AM

Quote:

kilometerage

That just sounds funny...at least to this yankee.
Burned valves or sticking valves is another thing that a vac guage can reveal, along with exhaust restrictions.
Basicly it is something else to distract you from the road...kinda like your first tachometer.
How many of us had fun watching the needle jump and drop on our first tachs?
Heck, I found the gas guage distracting when i first fixed it...was trying to see if i could actually watch it drop when I hammered it.

Fred T · 10-11-2002, 12:16 AM

The aftermarket guys are now selling vacuum gauges to fit in your bezel. They were available in the pickups, but I have never seen an original in a 67-72 pickup.

C10 - C90 Bill · 10-11-2002, 07:52 PM

I pulled a vacuum gauge set up out of a C-60, but never did put it in my C-30 yet. It ain't as easy as you would think it would be like most other GM products.

MStokes · 10-12-2002, 01:52 AM

I know what you mean longhornmail about the gas gauge being distracting. I drove for a long time without one and since I got it working it only depresses me because it sure looks like you can see it moving.

MStokes · 10-12-2002, 01:54 AM

I am interested in finding out more about installing a vacuum gauge in my truck. Can anyone tell me what is involved in the install? What and where does it hook up?

**'68OrangeSunshine** · 10-12-2002, 03:02 AM

I have an aftermarket [MoonEyes] Vacuum gauge, so I can tell you how to hook that up. As far as a production GM oem hole #3 rig, I have no experience, (but it may be similiar).
There are usually fittings on the intake manifold that have plugs in them. Find one, and remove the plug. Thread a brass fitting into the hole. Attach a copper line (throw out any nylon vacuum piping that may come with the kit -- it's NG) with an inside ferrule onto the mainfold securing it with a compression fitting. Run the vac line thru the firewall, under the dash, to your Gauge. Install the same type compression fittings from the line to the back of the gauge to complete the circuit. You need to have mounted the guage already, Also run the Pos side of the inst light to the fuse junction tab marked "PNL LTS" and the Neg side to Ground. It's really easy and if you screw it up the first time, it will only whistle -- not spew hot oil all over your new nubuck Wolverines like an Oil Gauge did to me once. LOL
Run it up for test & check. Manifold pressure is expressed in Inches of Mercury. The needle should dip toward the low end when you step on the gas; when you let off of the accelerator, the needle should climb. You will get used to it, and -- say on a long cruise -- try seeing if you can let off the gas and shave down your RPMs while gaining a few "/Hg without losing any speed. That's where you find your fuel economy.
Hope this helps.

ChevLoRay · 10-12-2002, 08:18 AM

A vacuum guage can provide peace of mind. I'll give you the scenario.

Waaaaaay back when I was younger, like only 31 years old, I had a '65 Chevy pick up with a 283/stick. I'd had duals put on it, with glass packs and it sounded goooood. Arriving at work for the 4-12 shift, I backed into a parking spot. A co-worker backed his '75 LeMans in, next to me. He revved his up really good, and gave me an earful of braaack-a-wapppa-wapppa! So, I had to one-up him. I did. However, fate struck. As the revs came down, I noticed a violent vibration. I shut the engine off. I sat for a minute, thinking about the possibilities....dropped a valve, etc. So, thinking I had nothing to lose, I fired it up and watched my vacuum guage. Even though the vibration was bad, the vacuum needle was steady as the Rock of Gibralter. No valve problems!

Oh, there was a problem though. Seems the fan/alternator belt had a little too much play, and the belt rolled and twisted. As it did, there wasn't anything to absorb the increased tension. It would have been nice if the belt had just broken, but instead the result was a bent shaft on the water pump. I cut the belt, fired it up and the vibration was gone.

That night, I had to drive it home without the water pump. I only lived two miles from work, and I didn't waste any time getting there....I didn't speed. The weather was cool, thankfully.

Next day, I pulled the water pump off and decided it was a good idea to have the radiator cleaned and checked. After plunking down another $125 of my 1978 dollars, I had a new 4-row core (my truck had factory A/C in the dash). The rebuilt water pump leaked (the back plate wasn't tight from the rebuilder). So, I bought a new water pump and finished the job.

The vacuum guage? Well, at least I new I didn't have anything else to fix!

MStokes · 10-12-2002, 11:42 PM

Thanks for the info and sharing your experiences.

Longhorn Man · 10-13-2002, 12:08 AM

Rubber hose is fine to run to the guage, after all, it is what runs every vacume controlled gizmo under the hood of a '77 Caprice, and anyone who's been under the hood of a '77 ANYTHIG knows there are a butt load of lines in there.
If they can deal with the harsh conditions of the eng compartment, they cans sure deal with the under dash conditions.

**'68OrangeSunshine** · 10-13-2002, 04:46 AM

Longhornmail,
I guess rubber hose is OK if you check periodically. It has a tendency to rot in smoggy and hi-heat environments. I prefer copper for instrument lines, because of its longevity. I was refering to that clear plastic or nylon line that comes with some of the less expensive aftermarket gauge sets. It gets brittle in the above conditions and cracks. Not good for vacuum, worse for oil gauge.

Longhorn Man · 10-13-2002, 03:58 PM

Ahh, ok, I'll agree with you then.
Heck, i have that cheap crap your talking about going to my oil guage. And I agree with you. It is getting kinda stiff.

**Tim Christian** · 10-13-2002, 04:22 PM

I think the clock looks the best. But if you had air bags I guess the air pressure guage would be cool also.

NuBomb · 10-13-2002, 10:56 PM

Here's a link to a guy who offers them

http://www.truckdash.com/index.asp

10-10-2002, 02:36 AM	#1
GMC_Aaron Registered User Join Date: Jul 2002 Location: Ventura, Ca. Posts: 87	Vacuum Guage I was browsing through my new Early Classic Enterprises catalog and I saw a vacuum guage for my 1972 GMC Super Custom. Was this an option on our trucks? This is the first I've seen for vacuum guages for our truck. I know there's a spot on the instrument bezel next to the oil pressure guage that doesn't have anything in it. Was that spot intended for something such as the vacuum guage? __________________ Aaron Ventura, Ca. 1972 GMC Super Custom SB350/TH400

10-10-2002, 07:08 AM	#2
JJR Registered User Join Date: Apr 2000 Location: Leesburg, GA Posts: 746	Not sure if they were available in C10-30 but I have seen several in C40-60. The big trucks could have a vacuum gauge or an air pressure gauge in the spot next to the oil pressure gauge. __________________ FOUNDING MEMBER OF THE DRUM BRAKE CLUB Second Owner 70 C-10 Second Owner 93 GMC C1500 Third Owner 99 C2500 Crew Cab Short Bed

10-10-2002, 09:06 AM	#4
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	Does anyone have a photo of one they could post? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

10-10-2002, 09:36 AM	#5
GMC_Aaron Registered User Join Date: Jul 2002 Location: Ventura, Ca. Posts: 87	Thanks guys! I think I will get one to fill up that empty spot on my instrument bezel. __________________ Aaron Ventura, Ca. 1972 GMC Super Custom SB350/TH400

10-10-2002, 12:19 PM	#6
jmil1974 Ain't we cute? Join Date: May 2002 Location: Friendswood, TX Posts: 700	Just a question. . . vacuum gauges are cool but what the heck are they good for? To know if you have enough vacuum to run your power brakes? __________________ 69 C10 2WD LWB Fleet 350/350 power front disc conversion (6 lug disc kit from gmcpauls) and new engine, PS, A/C, fresh fluids, SHE DRIVES! FOR SALE $3900

10-10-2002, 09:04 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	The vacuum gages do fit in the open spot on the dash. The face and inside reveal are different. If you wanted one, usually someone on the parts board will come up with one. They are kind of cool. Jim

10-10-2002, 03:56 PM	#7
Alex Hayley Registered User Join Date: Jul 2000 Location: NC Posts: 987	They are great for watching your gas mileage. The more vacuum you are pulling, the better your gas mileage could be. By the way, I am quite sure that it is the air pressure guage that tells you how much air pressure you have to operate the air brakes.

10-10-2002, 04:52 PM	#8
GMC1967 Registered User Join Date: Jan 2002 Location: South Deerfield, MA Posts: 162	Air pressure gauge is if you have air breaks, however if you have standard automotive power breaks, those run off of engine vacuum. And the vacuum gauge measures just that, engine vacuum. __________________ 1967 GMC Custom 8ft Fleetside 292 L6, 4spd. 1973 Oldsmobile Delta 88 Convertible 455, TH 400 1969 F#$% Bronco 302, 3spd 4.11's 1958 Oldsmobile Super 88 Fiesta Wagon

10-10-2002, 11:07 PM	#9
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	Here's one pic Attached Images __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

10-10-2002, 11:55 PM	#10
Spoof Registered User Join Date: Jul 2000 Location: Victoria,BC, Canada Posts: 1,300	Vacuum gauges are great for optimum gas mileage ( or kilometerage here in Canada) but they are also great for adjusting timing, indicating blown gaskets and a whole host of other engine problems. My rebuild manual for sbc's goes into great detail on using a vacuum gauge for engine problem diagnosis, of course it's not necessary to have one in your instrument panel but I would like one. __________________ 71 GMC 1500 LWB

10-11-2002, 12:16 AM	#12
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	The aftermarket guys are now selling vacuum gauges to fit in your bezel. They were available in the pickups, but I have never seen an original in a 67-72 pickup. __________________ Fred There is no such thing as too much cam...just not enough engine.

10-11-2002, 07:52 PM	#13
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,087	I pulled a vacuum gauge set up out of a C-60, but never did put it in my C-30 yet. It ain't as easy as you would think it would be like most other GM products.

10-12-2002, 01:52 AM	#14
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	I know what you mean longhornmail about the gas gauge being distracting. I drove for a long time without one and since I got it working it only depresses me because it sure looks like you can see it moving. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

10-12-2002, 01:54 AM	#15
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	I am interested in finding out more about installing a vacuum gauge in my truck. Can anyone tell me what is involved in the install? What and where does it hook up? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

10-12-2002, 03:02 AM	#16
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,504	I have an aftermarket [MoonEyes] Vacuum gauge, so I can tell you how to hook that up. As far as a production GM oem hole #3 rig, I have no experience, (but it may be similiar). There are usually fittings on the intake manifold that have plugs in them. Find one, and remove the plug. Thread a brass fitting into the hole. Attach a copper line (throw out any nylon vacuum piping that may come with the kit -- it's NG) with an inside ferrule onto the mainfold securing it with a compression fitting. Run the vac line thru the firewall, under the dash, to your Gauge. Install the same type compression fittings from the line to the back of the gauge to complete the circuit. You need to have mounted the guage already, Also run the Pos side of the inst light to the fuse junction tab marked "PNL LTS" and the Neg side to Ground. It's really easy and if you screw it up the first time, it will only whistle -- not spew hot oil all over your new nubuck Wolverines like an Oil Gauge did to me once. LOL Run it up for test & check. Manifold pressure is expressed in Inches of Mercury. The needle should dip toward the low end when you step on the gas; when you let off of the accelerator, the needle should climb. You will get used to it, and -- say on a long cruise -- try seeing if you can let off the gas and shave down your RPMs while gaining a few "/Hg without losing any speed. That's where you find your fuel economy. Hope this helps.



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10-12-2002, 08:18 AM	#17
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	A vacuum guage can provide peace of mind. I'll give you the scenario. Waaaaaay back when I was younger, like only 31 years old, I had a '65 Chevy pick up with a 283/stick. I'd had duals put on it, with glass packs and it sounded goooood. Arriving at work for the 4-12 shift, I backed into a parking spot. A co-worker backed his '75 LeMans in, next to me. He revved his up really good, and gave me an earful of braaack-a-wapppa-wapppa! So, I had to one-up him. I did. However, fate struck. As the revs came down, I noticed a violent vibration. I shut the engine off. I sat for a minute, thinking about the possibilities....dropped a valve, etc. So, thinking I had nothing to lose, I fired it up and watched my vacuum guage. Even though the vibration was bad, the vacuum needle was steady as the Rock of Gibralter. No valve problems! Oh, there was a problem though. Seems the fan/alternator belt had a little too much play, and the belt rolled and twisted. As it did, there wasn't anything to absorb the increased tension. It would have been nice if the belt had just broken, but instead the result was a bent shaft on the water pump. I cut the belt, fired it up and the vibration was gone. That night, I had to drive it home without the water pump. I only lived two miles from work, and I didn't waste any time getting there....I didn't speed. The weather was cool, thankfully. Next day, I pulled the water pump off and decided it was a good idea to have the radiator cleaned and checked. After plunking down another $125 of my 1978 dollars, I had a new 4-row core (my truck had factory A/C in the dash). The rebuilt water pump leaked (the back plate wasn't tight from the rebuilder). So, I bought a new water pump and finished the job. The vacuum guage? Well, at least I new I didn't have anything else to fix! __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

10-12-2002, 11:42 PM	#18
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	Thanks for the info and sharing your experiences. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

10-13-2002, 12:08 AM	#19
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Rubber hose is fine to run to the guage, after all, it is what runs every vacume controlled gizmo under the hood of a '77 Caprice, and anyone who's been under the hood of a '77 ANYTHIG knows there are a butt load of lines in there. If they can deal with the harsh conditions of the eng compartment, they cans sure deal with the under dash conditions.

10-13-2002, 04:46 AM	#20
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,504	Longhornmail, I guess rubber hose is OK if you check periodically. It has a tendency to rot in smoggy and hi-heat environments. I prefer copper for instrument lines, because of its longevity. I was refering to that clear plastic or nylon line that comes with some of the less expensive aftermarket gauge sets. It gets brittle in the above conditions and cracks. Not good for vacuum, worse for oil gauge.

10-13-2002, 03:58 PM	#21
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Ahh, ok, I'll agree with you then. Heck, i have that cheap crap your talking about going to my oil guage. And I agree with you. It is getting kinda stiff.

10-13-2002, 04:22 PM	#22
Tim Christian Senior Member Join Date: Dec 1999 Location: TN/VA Posts: 6,388	I think the clock looks the best. But if you had air bags I guess the air pressure guage would be cool also. Attached Images

10-13-2002, 10:56 PM	#23
NuBomb Registered User Join Date: Jan 2002 Location: Canton, Georgia, USA Posts: 1,119	Dash Link Here's a link to a guy who offers them http://www.truckdash.com/index.asp __________________ Jeremy (NUBOMB) 72K5 CST 350/350/205 1951 Chevy 1/2 ton North Georgia Group "... And the first rule to being a man is you gotta spend your life doing crap you don't wanna do." Red Forman.

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