C6 DAD Port
Thread Starter
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
C6 DAD Port
My 73' 400 has a C6 bolted up to it. The vacuum hose running to the EGR valve tees off and runs to what I believe is the DAD port on the transmission. What is the DAD port, and why does EGR vacuum run to it?
Thanks
Thanks
Posting Guru
Joined: May 2003
Posts: 1,525
Likes: 3
On dual area diaphram vacumn modulators the larger port is hooked to manifold vacumn and the smaller port is hooked to spark or carb vacumn above the throttle plate. Many older C6 transmissions had the DAD modulator.
Thread Starter
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
On mine, the vacuum running to EGR is not pure ported vacuum. The ported vacuum goes through a ported vacuum switch, then through a vacuum shut-off solenoid that opens and closes vacuum based on signal from an amplifier under the dash that reads vehicle speed and ambient temperature. Then the vacuum goes to the EGR valve. The vacuum that goes to the transmission tees off right before the EGR valve, then goes through a loop connector and down to the transmission.
What does the DAD port do and why is it only in use when the EGR valve is opening?
Thanks
What does the DAD port do and why is it only in use when the EGR valve is opening?
Thanks
Senior User
Joined: Oct 2001
Posts: 258
Likes: 1
From: Central Virginia
In the early days of EGR, the intake vacuum would drop off a good bit when the EGR opened causing the tranny to shift later. The extra vacuum port from the EGR vacuum line gave a little vac. boost to the modulator valve getting the upshifts back in line. We found later that most of the time the EGR port hose can be unhooked and the tranny would shift just fine.
