68 C4 downshift when stepping off the gas

Cougar Community Classic Cougar Maintenance Restoration and Repair
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I bought a 68 a couple of years ago that had not been driven in about 30 years. I rebuilt / replaced all the basics like, carb, tank, brakes, tune up etc to make it safe and reliable. I got tired of the transmission leaks so decided to tackle that recently, in the car btw.

So after my under car escapades, I encountered really high MPH shift points at part throttle. They would shift at 19 and 40 MPH respectively. The service manual said 9 to 10 for the 1-2 shift and I don’t remember for the 2-3 but it didn’t matter since obviously something was off because it was fine before I fixed things.

I first went after the vacuum modulator and decided to bypass the check valve and plug into the manifold directly on the vacuum line and replace the vacuum line at both ends with new hoses. Improved 1-2 shift to 13 mph. And I tried to adjust the modulator but could seem to turn it with a screwdriver.

I give you this background info because I think there is more than one adjustment needed and maybe they are interrelated. The biggest problem is that when releasing the accelerator completely, it immediately downshifts from 3-2. I’ve been through the shop manual and don’t have an ability to do a control pressure check so not sure where to go with this. Any ideas?

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I’ve never had that problem before. The only other adjustment is the intermediate band. It requires that you buy a new nut and then install the band to a specific torque and then tighten the nut. I would make sure the modulator adjustment and the intermediate band adjustment are both within specs for the factory shop manual.

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I did remove tat nut and reuse it. What is the reason for getting a new one ? Prevent leaks?

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No apparently the nut has a thread locking compound that is gone if the nut is reused.

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5

The band nuts have a seal on the face. Ford considers them a one time use item.

Are you positive that you have the modulator on manifold vacuum? I bought a 69 Mustang once that supposedly had a blown transmission. The owner had done some work and accidentally put the modulator on ported vacuum, which goes to zero with the throttle closed. Made for some interesting shift patterns. At 40mph it would try to downshift to first gear. Figured out the issue and put many miles on it afterwards.

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