who is wrenching today?

[[DHT]Osiris]

Weird… I'm not familiar with those older systems. Air vacuum at the master cylinder…?

So there is an air vacuum brake assist behind the cylinder, what I suspect is happening is that there's air bubbles in the cylinder itself, and while the spring and a small amount of fluid is enough to resist the brake while the engine is off, with the added force of the vacuum it just plunges straight to the floor. At least that's what makes the most sense to me right now.

 

[iRONic]

If that brake assist module is made out of metal it might have pin holes or corrosion-induced leaks that's allowing the air to bleed in. Or out, depending on the vacuum being held by engine power.

 

[[DHT]Osiris]

If that brake assist module is made out of metal it might have pin holes or corrosion-induced leaks that's allowing the air to bleed in. Or out, depending on the vacuum being held by engine power.

Well, the issue is the pedal is going to the floor under power (under vacuum), implying that the supply of the vacuum is just fine; there's just no/minimal backwards resistance from the braking system toward the atmospheric pressure/my foot.

If the brake assist had a hole in it, it wouldn't be helping me brake, not the other way around.

 

[[DHT]Osiris]

Well, the issue is the pedal is going to the floor under power (under vacuum), implying that the supply of the vacuum is just fine; there's just no/minimal backwards resistance from the braking system toward the atmospheric pressure/my foot.

If the brake assist had a hole in it, it wouldn't be helping me brake, not the other way around.

Figured it out! Had some air in the master cylinder, I thought I cleared it but it needed another round. The brakes still hit the floor with the vacuum pump running but at least it actually brakes now. Side note, once the engine warms up and the viscosity of the brake fluid lowers, I'm getting some leakage. I'm wondering if a) that'll stop once the back brakes are operational (and the pressure is spread over twice the area) or if I'm going to need to get something on the threading.