Looked over the transmission diagnostic thread because my c4 is shifting too soon at around 3000 rpms when i floor it in first or second. It says to turn a screw with a new modulator but do you NEED a new modulator?
Justin, If your C4 is shifting at 3000 at wide open throttle, then you need to; 1. adjust the kick-down linkage 2. use a longer modulator rod (up to 1 3/4" with a push-in modulator) 3. use a green stripe modulator 4. check your carb size... (manifold vacuum at WOT) 5. Never adjust a modulator unless you know it has never been adjusted or you know what adjustments have been made. The maximum amount a modulator can be adjusted is 4 turns - 2 in either direction is what I recommend.
Green stripe modulators are cheap, so just go buy one from Orielly or Autozone. They didn't have one in stock when I just bought mine, but it was a "be here at 2:30" item. Pioneer brand Green Stripe was $25 and part number 747011. Then you KNOW what you have. A good modulator set at ZERO, and you can adjust it that way. I didn't adjust mine at all, just used it at stock setting.
Which one should i try first? The linkage must be working fine because even before the headers, it was still shifting at 3000, The modualator is what i will probably try but what will the rod actually do? Just make it shift later, right?
If you have a push-in modulator then use a green stripe modulator with a 1 11/16" pin. That will give you later, firmer shifts. If you have a screw-in modulator you need a white stripe modulator and a pin that is 1 3/4" long - that will give you firmer, later shifts. Don't assume that your linkage is OK. Check it and your throttle linkage as well. The modulator only controls PART-THROTTLE shifts. The governor and kick-down linkage are what controls full throttle shifts.
