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Old 12-14-2012, 09:40 PM
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C4 Transmission

I have had this trans into a shop a few times and they dont seem to be able to solve the problem.
When its cold it will shift fron 1st to second just fine. But will not shift from 2nd to 3rd until its been driven a few miles and the tranny get up to temp.
From there on it shifts fine, with no problems. The mod valve has been replaced and there are no vac leaks. Any help would be appreciated.
Thank you.

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Old 12-15-2012, 09:29 AM
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What's been tried that didn't fix it? Like, what did the tran shop do/try, in other words, just to give some direction. YA know?
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Old 12-15-2012, 10:00 AM
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Has the valve body been modified? Are all of the check balls, springs and spools back in correctly? Is it the correct valve body - C4/5 look much the same but aren't. Also, the 4 and 6 cylinder versions plus the Pinto version don't necessarily have the same valve body as the V8 version and that thin plate directing flow needs to be modified correctly if the tranny has a shift kit installed. Then - is the front pump(and the only one)cracked or heavily worn? Next and the easiest to check - the modulator needs to be connected to a full vacuum source (below the throttle plates) not the ported vacuum (above the throttle plates). Also, make sure the tubing to the modulator is in good shape, no leaks. There is an elbow at the modulator itself that likes to crack every few years or the steel tubing rusts.
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Old 12-15-2012, 11:03 AM
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Is this a rebuilt trans? and does it have a slow engagement or any slipping in reverse when cold?

Last edited by rick 427; 12-15-2012 at 11:27 AM.
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Old 12-15-2012, 01:45 PM
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are u getting good vacume when cold i rebuilt a c4 in a 65 mustang a few yrs ago a spent hrs chasing a simple problem until the choke opened it would not go into 3rd found a better vacume source and work great
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