vacuum guage purpose

[Darren MagooGardner]

I recently purchased a tach dash w vacuum guage from e-bay. I was wondering what the purpose of having one was? I was also needing to know what you hook it up to? what type of trucks did they come in?

[hugger6933]

Darren, Techs will use a vac gauge to tell the basic condition of an engine by glancing at it. Also the vaccum will tell the ecoomy of an engine as in cruise mode the vac is high as you open the throttle the vaccum decreases. You can also set the idle mixture of your carb by them by turning in the idle screws until the gauge reaches its highest point then stop and do the other side. when you move the idle screws in and out it will move the vaccum up or down so the goal is to obtain the highest reading possible. The same goes for normal driving if you try to keep the gauge reading as high as it can be your mileage will be at its best. But you should keep in mind that tuning is gonna be hard to do with the smaller size of the guage that we have in our trucks. They are quite useful and fun to boot. If Iam not mistaken the hose will need to be hooked into manifold vaccum, being that it is under the throttle plates of the carb. Jim

[jocko]

this might help: http://www.secondchancegarage.com/public/186.cfm
Have seen it passed around in a few other posts. It is often used IN the cab as a "let off the gas, you're getting horibble gas mileage" gauge, but - in these trucks, kinda unavoidable. But a handheld vac is most useful for tuning under the hood when jimmying carb settings, etc. I installed a Pontiac Vac Gauge in my 66 and went thru the "how do I hook this thing up" question as well. Must be hooked to a "full time" vac port. So, as hugger points out, past the throttle plates is correct.

[Darren MagooGardner]

Good info guys. thanks. But what trucks came stock w them?

[Livrat]

Originally Posted by Darren MagooGardner

Good info guys. thanks. But what trucks came stock w them?

They came as an option in the medium duty trucks.. (C40/50/60)

[SS Tim]

The gauge was used on medium duty trucks with Hydrovac brake boosters.

[truckster]

I had one in my old motorhome. Mostly it just scared the crap out of me any time I touched the accelerator pedal.

[Already Gone]

Originally Posted by SS Tim

The gauge was used on medium duty trucks with Hydrovac brake boosters.

Does ths mean it wasn't available as an option on C10's-20' and 30's ?
Posted via Mobile Device

[SS Tim]

Originally Posted by Already Gone

Does ths mean it wasn't available as an option on C10's-20' and 30's ?

Not as an RPO that I have been able to find. There is code Z72 Vacuum Reserve Tank, Gauge and Warning Light. But again this is a Medium Duty Truck option.

[1972RedNeck]

Originally Posted by Already Gone

Does ths mean it wasn't available as an option on C10's-20' and 30's ?

I thought there was somebody on here with a manual throttle and vac gauge (no tach) in a C10. I *thought* it said that it was factory. That was a while ago though.

[SS Tim]

Originally Posted by 1972RedNeck

I thought there was somebody on here with a manual throttle and vac gauge (no tach) in a C10. I *thought* it said that it was factory. That was a while ago though.

May have been. There are a lot of interpretations as to "factory". It is possible that a fleet order truck had a vacuum gauge for some reason, just unlikely. Not sure why though as it is really too small and poorly located to be a driving aid.
In the medium duty trucks it was an important part of the braking system to have vacuum on call and lots of it for the Hydrovacs, hence the gauge for trending and the light for a "too late dude" warning.
If there is a light duty that has it called out for on the SPID I would like to see it. The only possible C30 application I can think of might be a 14K GVW C30

[JCD]

They register the magic..

J.

[Darren MagooGardner]

thanks for all the info.I cant wait to get mine in and see how well it works.

[prostreetC-10]

Tach dashes with vacuum gauges are know for shorting out and causing a cab fire. This is why they were discontinued. I am happy to help you out of your problem though. I will give you $50 for it in working condition so I can use it for parts! ;o)

[Darren MagooGardner]

Originally Posted by prostreetC-10

Tach dashes with vacuum gauges are know for shorting out and causing a cab fire. This is why they were discontinued. I am happy to help you out of your problem though. I will give you $50 for it in working condition so I can use it for parts! ;o)

I dont think I ever heard that one before.Has any one else heard of this?

[too much stuff]

Originally Posted by Already Gone

Does ths mean it wasn't available as an option on C10's-20' and 30's ?
Posted via Mobile Device

Correct, not available on 10-30 series that i am aware of.

Originally Posted by Darren MagooGardner

I dont think I ever heard that one before.Has any one else heard of this?

I think he is yanking ya trying to get your dash for $50... All in good fun i am sure...

[Marko3002]

My 72 has a vac guage. Looks factory, on the right side of the column.

[SS Tim]

Originally Posted by Marko3002

My 72 has a vac guage. Looks factory, on the right side of the column.

It looks factory because it is factory, but only in larger trucks. The clusters are very similar and the parts can be swapped. Twenty years ago you would see a magazine article oh and ah over a "rare factory vacuum gauge" in their write-ups on some "restored" truck. Often these trucks were a combination of years and parts to get a "look". Generally this included bucket seats, shoulder harnesses, rally wheels and a "comfort grip" steering wheel. Even today people are still seeking the vacuum gauges out more for status than real usability, I feel. The heavy truck air pressure gauge is another popular cluster addition now that air suspensions have become prevalent.

But if yours is listed on the SPID I would very much like to see a picture of it.

[prostreetC-10]

My bad.....totally messing with you because the vacuum gauge is something that I think 99.738% of us would love to have. Heck, even if it didn't work it would balance out the gauge cluster!

[Darren MagooGardner]

Originally Posted by prostreetC-10

My bad.....totally messing with you because the vacuum gauge is something that I think 99.738% of us would love to have. Heck, even if it didn't work it would balance out the gauge cluster!

you aint rite for that...you had me doin research on the subject,,,I am paranoid about cab fires. I did see a truck awile back that had a tach and had a cab fire..

[prostreetC-10]

Vacuum is air....would be hard to have a cab fire due to an air leak. LOL My bad still!

Many on here will agree that I aint right for a lot of reasons.