Hi there,

Ever since I've owned Betsie, she has lost vacuum after about a minute after stopping the engine. With the engine running, I have vacuum everywhere.

All door locks work, transmission shifts OK, shut-off works perfectly, brakes are fine, air selection (feet, dash etc) work fine as well. The latter is surprising as so many things on Betsie are broken, and the vents not working correctly seems fairly common, but mine all work OK. For now.

I've honestly never attempted to chase the vacuum leak, as so many other things have been popping up, but I think I found it yesterday when I was changing the oil.

I turned the engine off as the hood was popped open and heard a very audible "ppssssjjj" coming from the brake booster. This went on for about 60 seconds. After the sound stopped, so did my working door locks.

I'm fairly certain this is where my leak is coming from. Vacuum hose is securely attached to the brake booster, I don't think that's where it's leaking vacuum.

I will go and get one of those hand-pump vacuum testers. Once I have it, where should I start? Attach it to the brake booster and pump?

Is there a common failure point on a brake booster that would be worth investigating?

I do not have a firm grasp on this vacuum stuff at all, obviously.

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)

Buy a Mityvac.

Not saying that your ears deceive you but I would not start at the brake booster. I would go to the VCV and start by checking the rubber connectors, then work outwards toward the brake booster.

Or before you do that just plug off the main big vac line from the brake booster to everything else - and hook up the Mityvac to it. You might be lucky and find that your ears did identify the leak.

But generally speaking the other procedure is a better methodical way to go.

Good luck. Not a hard process, just tedious.

It's guaranteed coming from the brake booster, I have no doubts about that. The question I need to answer is "where" exactly. Yes, I will buy a mightyvac. Should have bought one long ago anyway.

You're saying, undo the big line and plug it with a big bolt or something, then run the engine to get vacuum and see if the vacuum remains? That's a great idea! Thanks.

__________________
"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)

Yup; Mityvac comes with plugs.

There is an O-ring between the Brake Booster and the Master Cylinder if it is not sealing you will have a vacuum leak.

Also check for rust in the area that the O-ring would seal on.

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84 300D, 82 Volvo 244Gl Diesel