c4

[whitea62.7t]

i have c4 that wont hold 2nd gear during a burnout, shift 1-2 and it shifts to 3rd very fast on it's own, with selector in 2nd
What does the vacuum modulator do?
i changed from dual plane air gap to a funnel web , now i have this issue
shifts on it's own into 3rd going down track randomly
Than you for any help

[e philpott]

Vacuum Modulator controls pump pressure, to me it sounds like a Govenor problem assuming it does not have manual valve body

[whitea62.7t]

It worked fine , until i changed the intake

[e philpott]

Is the Kickdown lever attached to the carburetor?

[whitea62.7t]

no , it's a drag car , i got a 68 stage 4 broader valve body , worked great , switched intake and now it wont hold 2nd gear , with shifter in 2nd , it randomly shifts into 3rd
vacuum signal is close between the 2 intakes
i cant figure out why it's doing this

[Falcon67]

If its drag, you need to ditch the auto valve body, they are nothing but a PITA and will shift when they like.  A vacuum modulator has no place in a drag car and neither does the governor.  A modulator fail, or no vacuum, typically causes a failed shift to high.  Shift in the burnout would be governor IMHO.  At any rate your trans will be much better off with a reverse manual body in it.  Parts last longer and you can hold any gear in the burnout.

[e philpott]

Jay only shows 4 valve body choices now and all are Manual shift , if yours is one of these then you got problems  , might be best to give Jay a call

http://www.broaderperformance.com/25-ford-c4-

[blykins]

I'm not a reverse manual valve body fan.  If you're racing and need to clear the engine out or knock it out of gear quickly, you're going the wrong direction on your shifter pattern. 

[whitea62.7t]

It's a 66 trans with a 68 valve body
all the ones he shows are for 70 and up
i got the only 68 he had