Sorry if this is the wrong area. Need help about possible vacuum leak

[Andrew Reda]

I had recently did a disc brake swap on my duster that has a heavy cam for starters. never an issue running the car before but was very local. so did the swap and vacuum tested at the booster bouncing at like 11 at rough idle. when I hook it up to the right stuff booster the car dies. can anyone point me in the right direction to diagnose this. I sprayed and checked for leaks and can't seem to find anything and everything seems plugged up even though there isn't any spare vacuum openings. any help id really appreciate.

 

[Dfr360cuda]

Wave an unlit propane torch around where you suspect a leak may be. When the engine revs you're in the right area.

 

[RustyRatRod]

While the propane trick will work, I don't recommend using anything flammable, whether gas or liquid. A lot of people use carburetor cleaner or other flammable aerosols like starting fluid. Think about that. You're spraying gas literally on an engine that runs on FIRE. Use a squirt bottle of water. It is very safe and will find a vacuum leak. Now, to ME, this sounds like a bad vacuum booster diaphragm. If all else is well and the engine dies when you plug the booster in, the booster is somehow at fault is my thinking.

 

[Bewy]

Bad booster or check valve.

 

[67Dart273]

Can you restate what you "did?"

You said " when I hook it up to the right stuff booster the car dies"

That sounds like a leak in the booster

 

[AJ/FormS]

In a good booster with a centered control valve, at rest; both sides of the diaphragm are evacuated.
During pedal operation the control valve isolates the front most portion, and allows atmospheric air into the back chamber, proportional to how far the pedal is and has traveled.
If the pushrod from the diaphragm to the M/C is too long, this may unseal the internal valve and allow the two chambers to be connected without the pedal being pushed, and the engine can then suck air from the atmospheric side. The solution to this situation is to just back off the nuts that attach the M/C from the booster, and pull it away from the booster about 1/8th inch. If the booster now seals up then you can know that the pushrod is too long. Shorten it up and try again.
If the pushrod is much too long, you may have damaged the control valve , during the marriage, and it will need a new valve.
If everything is perfect, and the engine is still able to suck air thru the booster, check out the large diameter seal that seals the control valve assembly to the booster housing; it may be bad.
Atmospheric air should only be able to enter thru the control valve and only whilst the pedal is being depressed

 

[RustyRatRod]

View attachment 1715909814
View attachment 1715909815
In a good booster with a centered control valve, at rest; both sides of the diaphragm are evacuated.
During pedal operation the control valve isolates the front most portion, and allows atmospheric air into the back chamber, proportional to how far the pedal is and has traveled.
If the pushrod from the diaphragm to the M/C is too long, this may unseal the internal valve and allow the two chambers to be connected without the pedal being pushed, and the engine can then suck air from the atmospheric side. The solution to this situation is to just back off the nuts that attach the M/C from the booster, and pull it away from the booster about 1/8th inch. If the booster now seals up then you can know that the pushrod is too long. Shorten it up and try again.
If the pushrod is much too long, you may have damaged the control valve , during the marriage, and it will need a new valve.
If everything is perfect, and the engine is still able to suck air thru the booster, check out the large diameter seal that seals the control valve assembly to the booster housing; it may be bad.
Atmospheric air should only be able to enter thru the control valve and only whilst the pedal is being depressed

Great idea!

 

[AJ/FormS]

Thank you RRR!
Happy Easter.