tranny shift question

[paul cass]

Hey guys
I think I'm in the home stretch on the 73 Mach 1. All of the little problems you encounter in restoring a car have been resolved except for one. The owner wanted to put a 4 barrel carb in place of the 2 barrel. The problem is with the shifit of the transmission. I had to lengthen the kick down rod and I made it adjustable to try to match the movement it had with the 2 barrel. The problem I'm having is with the shift. I've lenghtened and shortened the rod but the problem I'm having is that when the tranny shifts from 1st to second and 2nd to 3rd the engine races before it changes gears. Some times when it warms up the shift is better but it still seems to slip as it goes into gear. The tranny is rebuilt and the vacume modulator is new. The car guys here have offered suggestions but I'm not having any luck fixing the problem. Some said to adjust the vacume modulator, but I don't know if I should screw it in or out. The vacume is coming form the base of the carb. I tried using vacume from the intake first but the symptoms seem to be the same either way. My experience is with c-4's and aod's. This tranny has me stumped. Any help would be greatly apprciated.
Thanks.
Paul

[1969jimmach]

You failed to mention what mods have been made to the car and engine.Have you checked the vac at the source you are getting it from.You should have engine vacuum.A larger cam can give you less vacuum.Hope this helps.Keep us posted.

[paul cass]

No modifications to the engine or tranny. So everything is stock. The only change is the 4 barrel carb. The vacume source orginally was at the base of the carb so that is where I plugged it in. Feedback among my car guys here alternates between adjusting the kick down rod and or adjusting the vacume modulator. Just not sure what the adjustments should be.
Thanks,
Paul

[JTS71 Mach1]

Paul you didn't mention what trans you have, c6 or fmx. My suggestion is to find an old transmission shop one thats been around for 30-40 years, and find the oldest mechanic in the place, and describe your problem to him. First he'll tell you which one you have and how to adjust them accordingly. As best as I can remember the FMX is the only one that had an adjustable modulator. But I could be wrong as it's been a lot of years since I messed with transmissions in these old cars. But going to someone who knows first hand should get you fixed. JTS 71 Mach1