Gear change up and down

73 mach 1 2 barrel 351c with c6 auto transmission

Car goes into 3rd before 30 mph and do not change down until about 10 mph is this normal.

Nige

Factory spec shift points are in the Ford shop manual. If you don't have a copy, I can post the info later.

Factory spec shift points are in the Ford shop manual. If you don't have a copy, I can post the info later.

Click to expand...

That will be great thanks

There is a small screw head in the transmission vacuum modulator that can be turned to adjust shift points. Pull off the hose and it's located inside the modulator hose housing.

Do a search on this forum since it has been addressed several times in the past.

Here you go Nige. Hope its legible enough for you

Here you go Nige. Hope its legible enough for you

Click to expand...

Pegleg beat me to it...

Being a '73, you probably have a dual area vacuum modulator, which are not adjustable. You could swap it for an adjustable one to tweak your shift points up or down a couple MPH, but if yours are way off spec, you probably have junk in the governor, or more serious problems.

Here you go Nige. Hope its legible enough for you

Click to expand...

Thank Steve for the info Nige

Here you go Nige. Hope its legible enough for you

Click to expand...

Pegleg beat me to it...

Being a '73, you probably have a dual area vacuum modulator, which are not adjustable. You could swap it for an adjustable one to tweak your shift points up or down a couple MPH, but if yours are way off spec, you probably have junk in the governor, or more serious problems.

Click to expand...

Yes it has the dual modulator is it ok to swap for an adjustable modulator and what would be the best colour . Nige

Looking at the charts, your trans seems to be operating within the ranges spec'd by Ford. You could replace the modulator with a single, but it appears yours might be adjustable. If it looks like the unit in the pic with the nipple along the axis of the modulator, then you can adjust it. You could also increase the length of the pin to increase shift mph and firmness.

https://www.ford-trucks.com/forums/971599-auto-trans-vacuum-modulator-color-coding.html

73 mach 1 2 barrel 351c with c6 auto transmission

Car goes into 3rd before 30 mph and do not change down until about 10 mph is this normal.

Nige

Click to expand...

That sounds similar to how my c4 shifts, during NORMAL acceleration. Standing on it changes the shift points dramatically, although I do have a shift kit installed.