john roth

I just bought a new Hand Held Vacuum Pump but I can't find what the ideal Hg is anywhere. Anybody know off the top of their head. 1969

JR

gerry72

You're not being charged by the word so feel free to elaborate on what vacuum you're referring to.

pauldana

7T1vette

Why do you need a hand-held vacuum pump? I suppose that you can hook it in the vacuum system and use its gauge to read engine vacuum level??? Every engine configuration will produce some level of vacuum when at idle. 'Base' 350 engines usually produce somewhere in the 17-20" Hg range; engines with more agressive cams might only produce 10" Hg or so. You need to do a search for info on how to check-out your vacuum system to see where you are with yours.

john roth

WELL..... stupid me, I thought once the vacuum system was charged the vacuum would equalize throughout the system, headlights, wipers etc. :o

Thaks 7T1 vette, I will be reassembling the car (finally) and I want to test everything as I go so I won't have to go back.

VictoriaVette

Are you talking about pulling a vacuum on the AC? If not I know my 77 runs at around 14 with the cam I have.

noonie

As mentioned ideal vacumn is from 17 to 20.
You can test everything as you go with the hand pump as in good or not good, parts hold a vacumn and operate or not or not. When assembled, then the only thing to change might be the advance can. I even set the vacumn advance using a hand pump and a dial back lite.

john roth

Thanks Noonie.
My mechanic has told me he doubts my crate engine will make the vacuum I need so as I put things togethwer I want to nail any leaks or bad valves or whatever as I go. If the engine in fact doesn't make the vac required I plan onfindind a 12V vac pump to mount next to the reservoir tank.
JR

7T1vette

Unless you have a very radical cam, your engine should make more than 12" Hg. If the system has no other leak paths, that should be enough to operate all of the circuits with no trouble. Just make sure the vacuum tank is in good shape, and you have a good line filter and check valve.

71coupe454

I have a vacumn hand pump and no engine in the car, how can I check the system with it? I gave it a quick try a while back but didnt get anything to move at all.

Rich's'78

What I think you want is a source of vacuum that will not be so strong as to compensate / hide any small leaks in a system. I believe the pump you have is too small to deal with the leak, ie: you can't pump it fast enough to deal with the leak you have. "Real" vacuum pumps (ones that will move a lot of air and still pull a vacuum) are expensive.
Here is a suggestion, although I can't say I have done it.
You have a vacuum pump sitting in your driveway! An engine pulls air, giving you manifold vacuum. But a V8 pulls way too much air because it is running (dynamic). Why not use it to create a static source of vacuum you can use?
So you need a vacuum resevoir - a tank that is sturdy enough that it won't collapse under partial vacuum (minus 25 inches Hg / minus 13 psi). And the right size that it will not take a long time to lose vacuum with a fairly small leak, so you can see it dropping while you check things out.
Maybe a 5 gallon compressed air tank. Take off the pressure gauge so it doesn't get wrecked and substitute a vacuum gauge. Hook it up to a running engine (stock cam at 2000 rpm should give you about -25" Hg manifold vacuum). Isolate the tank after it is pumped down. Voila - a vacuum source you can use. Dumb idea?
So how do you know what tank will hold vacuum? A tank rated for 100 psi pressure (maybe less, I don't know) will hold FULL vacuum as well.

7T1vette

FULL vacuum is "0 psi"; atmospheric pressure is around 14.7 psig. So, your tank only needs to withstand a ~15 psig...on the outside.

tarby

like the tank idea but it wont work for long if you have a good enough leak, if you know a friendly hvac guy you might borrow his vac pump or rent one

noonie

If your engine doesn't run or is missing and you want to test the whole system without pumping a hand pump 5000 times, then just get a longer length of vacumn hose and tee into another car idling beside yours. All the vacumn you'll ever need to test the whole system.

You can even test power brakes this way.