Trans shifts to 3rd by 20 mph

[luke-ao]

Just picked up a '71 with a 302 and a c4 trans. It shifts from 1st to drive by 20 mph and shifts so soft you really have to pay attention to feel it shift. Is this normal?

[fijidad]

Just picked up a '71 with a 302 and a c4 trans. It shifts from 1st to drive by 20 mph and shifts so soft you really have to pay attention to feel it shift. Is this normal?

I have a '71 with a 360 and auto trans and it does the same thing. Smooth shifting unit, but the reason for shifting through the gears by 20 is the rear axle ratio. The VIN on my truck indicates I have a 3.73 rear axle ratio. You might check the attached link to see what you've got.

http://www.fordification.com/tech/VIN71.htm

Regards, Dan

[luke-ao]

I'm 90% certain it original 3.50 rear

[cep62]

Do you have the kick down rod from the carb to the trans ?
If not thats why. it controls the shift points, along with the vacuum modulator .

[luke-ao]

Yes. That's the first thing I checked, is there an adjustment on these? I've never messed with one.

[cjarvis]

Upshifts are controlled by the vacuum modulator. Kick down rod controls downshifts. Search on C4 vacuum modulator adjustment. I believe turning the screw in will delay the shift points. I have my 71 CS with 360/C6 and 3.73 gear adjusted so 2-3 shift is at about 40 mph.

[luke-ao]

Thanks. I'll look into the VM.