Effect of Leak in the Vacuum Tank on Engine Idle/Engine Vacuum Leak?

[Paul C.]

I really don't want to remove the vacuum tank again (I have power brakes)!!!!!
Two questions:
1. Would a leak in the vacuum tank cause low manifold vacuum--since it's leak in the system and effect idle, etc?
2. If I clamp off the 2 hoses on the tank and apply a Mityvac hand pump to the third hose which goes to the engine manifold---is the Mityvac large enough to get a negative pressure in th tank if there is no leak--detect a leaky vacuum tank?

This is in a 71 LT-1.

Thanks in advance for all your help. It is always appreciated!!!

[Owen L.]

Re: Effect of Leak in the Vacuum Tank on Engine Idle/Engine Vacuum Leak?

To test the entire vacuum system on the engine, note the idle rpm then disconnect and plug the single main line coming off the manifold. If the idle changes, when comparing plugged vs. connected, you have a significant leak in the system. Do your lights and wipers work as they should?

The mityvac is a very, very, (did I say very?) low volume pump and will give you Popeye arms pumping out the tank to test it. An electric vacuum pump with a one-way valve would be the best test tool. A single line to the pump with the others capped off at the nipples - not clamped off. If you can locate the leak then a vacuum tank is easier to repair than a pressure tank since the outside is trying to push its way in and makes the seal stronger. If it's leaking it's probably a seam and black caulking would work.

[Paul C.]

Re: Effect of Leak in the Vacuum Tank on Engine Idle/Engine Vacuum Leak?

Thank you. Hooked a vacuum gauge to one hose; a vacuum pump to another hose, and blocked the third hose. It held vacuum.

Engine vacuum is at 15 and idle didn't change when main hose disconnected.

I still think I might have a vacuum leak somewhere--I'll keep looking.

[Owen L.]

Re: Effect of Leak in the Vacuum Tank on Engine Idle/Engine Vacuum Leak?

That's good news; removing that tank would be a nightmare. I think not only would the power brake booster have to be pulled but the steering column as well. I gave up trying to remove my '72's tank to clean and paint it and the surrounding area when I discovered that there is no way it was going to come out without major surgery.

Do both your headlights and wiper door work as expected? Next would be a similar vacuum test on the headlight system followed by the wiper system.