mhrrs525

hi, just finished a 1966 Mustang, dropped a 78 Fairmont's C4-A6 transmission onto the back. Only problem is the shifting is impreceptible, I don't think it is actually shifting completely. It does accelerate up to about 60 mph but, i just don't think the thing is shifting like an automatic transmission should. Everything is connected up, the fluids are checked daily and are all good, no leaks and the transmission is like new. I've heard that the problem may lie in the vacuum modulator, i would like to replace it to find out if that's the problem. However, I am not sure which modulator should go back on, the threaded type, or the push in type? hope someone has an opinion on this....

Scrubtik

If you can get hold of a Vacuum guage you should have about 17-20lb at the modulator.If you're not getting near this,the shifts will be mushy,if at all.Check the vacuum line for kinks,cracks ect,'specially where it enters the modulator.
Does it shift properly with manual shifting?
Not sure on the later C4's,but the earlier models had a screw in the modulator that allowed you to adjust the shift points.Using a long,thin blade screw driver,Clockwise will shorten the shift points & vice-versa.Could be worth a shot,try 1 complete turn at a time & road test.

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