C4 transmission issue.

I have a C4 automatic in my 73 Maverick 302 and it shifts from 1st to third and completely ignores 2nd gear. 2nd gear is there because I can shift through the gears manually and there's no problem. Just when I take off in drive does it ignore 2nd gear. I recently installed a new engine and had the tranny fluid and filter replaced. Any suggestions on what could be causing this?

Thanks

 

I don't know the circuits right off hand.. but that sounds like a valve body issue to me. Also check the modulators diaphram/hose connection. Also be sure it's running to manifold vacuum.. NOT ported/timed vacuum off the carb. If the leak is big, you'll usually know when somethings up there but small leaks can add variable.

 

I would think vac also...try leaning into it kind of heavy and see if will shift to 2nd...

 

Yeah I should've replaced the modulator valve. I'll do that. The vacuum hoses are all new.

 

I copied this reply from PaulS off another forum to the exact same symptoms. He always gave solid advice and is considered an expert in C4 transmissions. The credit is all his.


Re: C4 has no 2nd gear
Start with pulling the vacuum line at the modulator with the engine off. If there is oil there then replace the modulator. Be careful when replacing it because you don't want to lose the modulator pin. Buy a "Green Stripe" modulator. How did you adjust the front band? did you torque the adjusting screw to 10 foot pounds and then back it out 1 1/2 turns? If not try that. Be sure the lock nut is loose when torquing and that it is tight when you are done. If everything in these areas is OK then check the linkage adjustment. Put the lever in Drive with a rope or bunjie cord holding it in drive toward the second gear detent at the column or floor shifter. Go under the vehicle and loosen the lock nut on the linkage and shift the transmission manual lever dolidly into the Drive position. Tighten the locknut without letting the linkage slip one way or the other. Road test it and see if that fixed it. If none of the above fixes the problem then you will have to remove the valve body and check all the valves for free travel and no scoring. (this would be a good time to install a TransGo 40-2 kit in the valve body, It will add performance and years of life to your transmission.)
While you have the valve body out you check the operation of the second gear servo with 40 psi air. If it moves and you hear a clunk as you hit it with air then it is good. If your hear hissing then the seals are bad in the servo and you should replace them.

 

Good advice. I'll check it out.

 

I had replaced the motor in the Maverick a while back and installed a new intake and Holley 4bbl. I had to extend the passing gear linkage to reach where it connects to the new carb from where it was on the old 2bbl. (about 1-1/4 inch). I'm thinking this may also be the culprit. Is there a way to set the linkage to where it is in the correct position? I can punch it a little more when taking off and it shifts into 2nd like it's supposed to. Taking off normally it shifts from 1st to 3rd and ignores 2nd gear.

 

You could toss the kick down linkage, won't make any difference in shifting... I ran my Comet for a year without it, just didn't have a kick down...