C6 shift issues
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i ain't rite
Joined: Mar 2005
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From: Marlboro Mental Hospital.
C6 shift issues
my 88 superduty diesel 4X4 now has almost 300 miles on it since the swap from 5 speed to C6. everything is fine with it except for a late/hard shift on wot due to low vacuum. if you use up to 3/4 throttle, it shifts smooth and on time, but at wot it will not shift till you let off, and then it is hard. i have 17 lbs vacuum at idle, and 2 lbs at wot. according to the service manual, it should be 5-6 lbs at wot. the vacuum control valve on the injector pump is adjusted as far as it will go. any ideas ???
Cargo Master
Joined: Jun 2003
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From: Somewhere Saskatchewan
Originally Posted by rclarke
If you have the kickdown rod hooked up and adjusted properly, you will not get an upshift to 3rd. When the kickdown is activated (WOT) the valve body will not allow 3rd gear.
I don't know where you get your information from but that is incorrect.
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i ain't rite
Joined: Mar 2005
Posts: 65,561
Likes: 5,595
From: Marlboro Mental Hospital.
ok stuart, thanks. what way should i turn the modulator adjuster screw, clockwise, or counter?? and is it an allenscrew, or torx??
this is all new to me, everything i have ever had has had a stick in it except for my crown vic, and that is still under warrenty, but i doubt anything is gonna go wrong with it before that runs out.
this is all new to me, everything i have ever had has had a stick in it except for my crown vic, and that is still under warrenty, but i doubt anything is gonna go wrong with it before that runs out.
Last edited by tjc transport; Jun 1, 2005 at 07:08 PM.
Cargo Master
Joined: Jun 2003
Posts: 2,982
Likes: 7
From: Somewhere Saskatchewan
rclarke you are wrong with your concept.
No matter what transmission you have it will shift into 2nd, 3rd, 4th or whatever gear is the top range. No matter how far down you have the pedal.
However some vehicles don't have enough jam to turn the engine fast enough to allow centrifugal force of the governor to overcome throttle pressure.
The screw is turned counter clockwise to lower shifts. It is just a small flat bladed screw driver.
No matter what transmission you have it will shift into 2nd, 3rd, 4th or whatever gear is the top range. No matter how far down you have the pedal.
However some vehicles don't have enough jam to turn the engine fast enough to allow centrifugal force of the governor to overcome throttle pressure.
The screw is turned counter clockwise to lower shifts. It is just a small flat bladed screw driver.
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Posting Guru
Joined: Nov 2004
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From: Asheville, NC
Try turning the modulator screw a half-turn CCW and drive it. If it is still not right, give it another half-turn. The screw is in the hole where the vaccuum line connects. Be gentle.
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Posting Guru
Joined: May 2003
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C6 kickdown is not a throttle pressure valve like AOD or some other transmissions. It is a mechanical downshift valve. If you want only throttle pressure control of downshifts remove the kickdown rod and use only the vacumn modulator for kickdown.
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