[Brad Gris]

Let's face it, a lot of us Mustang owners have modified our engines to increase horsepower. However, this usually means reving higher than the C4 tranny automatically shifts at to utilize the extra power. I have the C4 tranny and despite several attempts to adjust my vacuum modulator with my transmission mechanic, my tranny won't automatically shift higher than it's typical 4,500 rpm without hard damaging downshifts while coasting. I can manually shift to reach 7,000 rpm, but I prefer my tranny to do this automatically. I guess my only option is to purchase an electronic transmission. I prefer an AOD (4 speed automatic overdrive) electronic transmission. The overdrive would also be nice to reduce my high 2,800 rpm while driving at 60 mph. I don't prefer a manual transmission. I own a modified 1971 sportsroof Mustang. Is it my only option to replace my C4 with an electronic tranny, and if so, what transmissions do you recommend?

 

[steferg]

Let's face it, a lot of us Mustang owners have modified our engines to increase horsepower. However, this usually means reving higher than the C4 tranny automatically shifts at to utilize the extra power. I have the C4 tranny and despite several attempts to adjust my vacuum modulator with my transmission mechanic, my tranny won't automatically shift higher than it's typical 4,500 rpm without hard damaging downshifts while coasting. I can manually shift to reach 7,000 rpm, but I prefer my tranny to do this automatically. I guess my only option is to purchase an electronic transmission. I prefer an AOD (4 speed automatic overdrive) electronic transmission. The overdrive would also be nice to reduce my high 2,800 rpm while driving at 60 mph. I don't prefer a manual transmission. I own a modified 1971 sportsroof Mustang. Is it my only option to replace my C4 with an electronic tranny, and if so, what transmissions do you recommend?

I believe the vacuum modulator screw only adjusts part throttle shift points.
If you want to adjust the full throttle shift point you have to change the secondary governor spring and/or lighten the secondary governor piston (which requires taking off the C4 tail shaft).

Check the below thread and email Bill, I believe he sells lighter springs. You’d probably have to lighten the piston if you want more than 1000 rpm higher.

C4 Secondary Governor Spring for higher full throttle...

Secondary piston lightened. C4 Secondary Governor Spring for higher full throttle shifts in drive. Average 500-1000 rpms. $25.00 includes shipping. I accept paypal. [email protected]

www.vintage-mustang.com

Steve