Big Block Died When on the Brakes Hard

[Yellowstone]

Finally got my 69 Charger running after 25 years...

It has a 440-512 stroker in it pushing 550hp and 600ft.lbs. I'm pretty happy with that.

I've only got about 20 miles on it, just easy local streets to home and work so far a few times. But on a recent road test, I had to brake a little harder than normal to make the turn into the driveway (I guess I was going faster than I thought! Don't blame me!) and the engine died.

Engine has been running very well up until that moment. I'm hearing that a leak in the brake booster could cause it symptom? I've got power brakes, but no other vacuum accessories. The headlights are now electric actuated.

How do I test the brake booster for leaks? It's a never used booster, new 25 years ago when I first started working on the car. But I never ran the car until now. I guess after 25 years of not being used the booster could go bad. Thoughts?

 

[Stroked438]

Sounds like the floats are a little to high.

 

[69Bee]

Cam doesn't produce enough vacuum, and the emergency braking used all the engine had and killed it. My '74 Charger would do this if I made a panic stop because the cam was too big for the engine.

 

[Yellowstone]

I didn't do the carburetor work personally. I'll check with the engine builder on that. But I do have a nice lumpy cam in it, so vacuum could be an issue. I don't have a vacuum canister, but I suppose some small reserve vacuum canister would solve that problem.

 

[Kern Dog]

Sounds like the floats are a little too high.

Interesting.
I have had a similar condition as the OP.
Hard braking making the idle drop to where I need throttle input to keep it from stalling. I swapped in a Tremec 5 speed from the 727 so now I have a 3rd pedal to deal with.
I suspected that the float level was too low. Maybe I was wrong?
Too high would what...flood the venturis as the fuel spilled over on a sudden stop?
Going down a hill and slowing rapidly was the worst. With the automatic, I'd just tap it up into neutral, brake with the left foot and throttle with the right. With the 5 speed, I have to shift to neutral and do pretty much the same.

 

[Mick56]

Could be fuel sloshing into the manifold. Are you running a Holley? I think Holley used to make a baffle that helped stop fuel sloshing.

 

[Yellowstone]

Kern Dog - interesting indeed...I was going down hill and braking harder when it stalled on me. So that is something similar to what you experience. I have not tried to brake hard on level ground and see if it stalls. I'll try that this afternoon.

 

[Yellowstone]

Could be fuel sloshing into the manifold. Are you running a Holley? I think Holley used to make a baffle that helped stop fuel sloshing.

Yes it's an 850 Holley. I'll ask the builder if this is something he can check.

 

[Kern Dog]

A float level too high is easy to determine. The carburetor bowls have either sight plugs or screws. The fuel level is supposed to be at the middle of the sight plug or just barely oozing out with screws removed. If the fuel pours out, the level is too high.
Mine hasn't been consistent enough to motivate me to address it yet.

 

[Dennis H]

The 440 did this on occasion when it had the 850 Demon. Became normal but infrequent. Doesn’t do it with the EFI.

 

[Cranky]

How bout giving us the combo? Hard to help when we don't know the details.....

 

[Fran Blacker]

(I guess I was going faster than I thought! Don't blame me!) and the engine died.

Who hell else was driving if your not to blame?

 

[BSB67]

Interesting responses. I don't know what the problem is or the solution. But my gut says too lean on decel, and/or timing.

So with that, simple stuff first: 1) make sure you have at least 18° initial timing, and if you have a cam with a lot of overlap, 22° or more, 2) simply open the idle mixture screws, and if it get worse, or doesnt help, close up the idle mixtures screws a little.

 

[Lefty71]

Cam doesn't produce enough vacuum, and the emergency braking used all the engine had and killed it.

On any power brake vehicle, I thought there was a check valve at the elbow leading from the vacuum line into the booster that prevents this. The brakes should never rob the engine..... Am I remembering this wrong????

 

[69Bee]

On any power brake vehicle, I thought there was a check valve at the elbow leading from the vacuum line into the booster that prevents this. The brakes should never rob the engine..... Am I remembering this wrong????

Yes, and that is how it works. With my large overlap cam, only had about two pedal presses worth of vacuum. I am only going off experience when I "Double Footed" the brake pedal, and it died, but you are correct with the operation of the check valve.

 

[BSB67]

On any power brake vehicle, I thought there was a check valve at the elbow leading from the vacuum line into the booster that prevents this. The brakes should never rob the engine..... Am I remembering this wrong????

You are correct.

 

[Mick56]

Holley 26-89 - Holley Fuel Bowl Vent Baffles
( 5 )


Part Number: HLY-26-89

 

[1 Wild R/T]

Back in the day the fix was to loop the bowl vents...

 

[Wietse]

Same had happened to me in the past when i had to brake hard and the engine stalled.
My car also has the check valve at the vacuum brake booster, but i am sure the fuel from the rear bowl spilled out in the intake as i had to crank quite a bit to get it running again as it flooded.