We are finally at the end of the C4 replacement with an AOD transmission for our 1973 Mach 1. The last day, or half day, was largely uneventful. The majority of effort today was spent on double checking for leaks, ensuring the Throttle Valve Pressure lever at the transmission of the cable linkage had an adequate return spring, and setting the Throttle Valve pressure at the carburetor end of the T.V Pressure cable end. The old C4 vacuum modulator vacuum steel lines were also removed, and the old, no longer used, vacuum sources were capped off. No surprises.

The ride home was the "test drive," as I was confident everything would work properly. I was not disappointed, although I was concerned at how quickly the transmission upshifted into overdrive (4th gear) at only 20 MPH. Overall, the early upshifts notwithstanding, I was thrilled with the result. The upshifts from forward gear 1 through overdrive gear 4 were crisp enough to feel, but not bone jarring. Rather, they were as smooth as they were confidently crisp. I had expected a little more delay in upshift speeds as the Throttle Valve pressure was set at 36.5 - 37.5 PSI, as opposed to the 35 PSI in the various manuals. A little too much pressure is not harmful. It is the lack of adequate pressure that can cause problems.

For those folks wondering where I had the AOD transplant performed, it was performed at Horsepower Motorworks, in Victor, NY (near Rochester). These folks have done some extensive, and excellent, work for me on several of our vintage vehicles. It is not possible for me to overstate how pleased I am with the quality of their work. Anyone considering having their transmission upgraded to an AOD really ought to chat with these folks. They have a Facebook presence, as well as a web site at:
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There is another YouTube video that shows more detail on adjusting the Throttle Valve Pressure. The "action" begins just after 4:15 in the video, although it is all useful.
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Throttle Valve Return Spring video sections at: 8:35, 9:50, 10:37

To see how we spliced in the wiring harness for the AOD Neutral Safety/Backup Lamp Switch see the video at:
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