Sorry if this isn't necessairly well thought out or coherent as I am compleately distraught and drained here...

Yesterday, I was sitting at an intersection waiting for a green light when in an instant, my brake pedal lost pressure, the engine choked, sputtered and died, and I was smoking worse than if someone put seafoam down the vaccume line! People began shouting fromt he sidewalks that the car was on fire (it wasn't).

The smoke cleared and I was pushed off to the side. I called for a tow and it is now sitting in my driveway. Based on the incident, I presumed by bake booster failed (it is almost 40 years old, so no surprise) and have all the parts on order.

Today, I disconnected the vaccume line from the booster and was expecting to see some evidence of brake fluid in the line, but found none. With the line disconnected, I started the engine, but it wouldn't stay running at idle and sounded like it was missing. I gave it a little rev, and the vibrations smoothed out, but it was still missing and I was smoking (much less than the incident) like I was burning a little oil. After about 20 seconds of that, I cut it as I was out of my comfort zone.

I thought disconnecting the booster would have cleared it all up and stopped the smoking as the engine wouldn't be ingesting brake fluid.

I'm looking for a little direction and guidance. Is my diagnosis likely correct? Is something else wrong? Remember this engine did suffer a major oil leak earlier this season (https://www.ford-trucks.com/forums/1...-proofing.html).

Drinking a cool one...

 

Hey Bmoran,
A cool one is a good idea. We've also had several total failures by the side of the road. They can be very uncomfortable. Hang in there.
Whereabouts are you in Western New York?

Ben in Austin
1950 F1

 

I forget, do you have an automatic in this truck? Because vacuum modulator failure was my first thought.

I assume you plugged the booster vac line when you pulled it off?

Have you checked the brake system to see if it was actually a brake hydraulic system failure? On a dual MC system, when one fails, you have to pump it a couple times to bring the pedal back up.

 

Shhh! I'm cheating - it's not a truck - it is a 78 Mustang II with a 302 and C4. While not a truck, the members of this forum are so friendly and there are many who operate 302s and such...

No, I didn't plug it up...

While it is a dual master, I don't think that matters in this case. My presumption is the diaphram in the power booster failed allowing the engine vaccum to suck some brake fluid into the engine causing it to burn and smoke.

To test my theory, I disconnected the vac line from the booster (not plugging it) and tried to run the engine. The engine would not smooth out, so I killed it.

And ben, I'd perfer not to get more specific with my location as it only takes one internet weirdo to make real-life more interesting in a not so good way...

 

Yeah, I've seen this. The master cylinder has been leaking fluid into the area behind the diaphragm for a while, collecting in there. The diaphragm ruptured, at 36 years, and you charged the engine induction system with a heavy dose of brake fluid. It will take some running of the engine to burn it out. Seriously doubt if it hydrolocked and did any damage.

 

Plug the vac line and try running it again , as it will not run properly with that massive vac leak .

 

When I had a 75 MII, the same thing happened and it was a failure of the master cylinder. Anytime there is a gross vacuum leak like that, the engine will idle rough or hardly at all.
Check the brake fluid levels, check the vacuum check valve that plugs into the brake booster if that does not lead to anything, have another cool one.

 

A new master cylinder and power booster are going to be installed once they get here and I find some time - apparently the booster is a bear to mount/dismount...

 

Can't imagine why except a space issue?
Did you check the vacuum hose for a crack or split? A split or cracked hose could cause the symptoms you described.
Have you tried running the engine with the vacuum line plugged yet? If you sucked brake fluid into the engine the vacuum hose would smell strongly of brake fluid inside and possibly have brake fluid in it. The line should not have any odor except possibly a slight rubber odor.
If it does smell of brake fluid you might want to pull the spark plugs and clean or replace them if fouled and change the oil and filter. Replace the hose when you replace the booster (make sure you use vacuum hose)