C4 won't downshift
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Senior User
Joined: Nov 2001
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From: Calgary Canada
C4 won't downshift
My C4 upshifts just fine and will downshift from 2nd to 1st at low speeds and from 3rd to 2nd up to about 30 or 35 mph. Above that though, it will not downshift. My manual says that up to 35 mph it will downshift from 3-2 "to detent (torque demand)" which it does but for speed above that it will downshift from 3-2 "through detent (W.O.T.)". Does this mean that at the lower speeds it's the vaccum signal that determines the downshift and at high speed the downshift rod causes the downshift? If that's the case may vaccum diaphram is OK but the adjustment on the downshift rod is wrong. I've adjusted it according to the manual...any other suggestions?
Posting Guru
Joined: Mar 2001
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C4 won't downshift
I'm no tranny expert, but my C4 always downshifts on demand depending on torque load or the downshift lever. I believe the downshift lever dominates the downshift mechanism...vacuum is more for upshifting?
Senior User
Joined: Mar 2001
Posts: 112
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From: South St. Paul, MN
C4 won't downshift
Sounds like a kickdown rod problem to me. My tranny never used to drop out of high gear even floored until I put in a kickdown rod. Now when floored the tranny will downshift. I just wish the vacuum modulator would allow the tranny to drop out of the higher gear sooner than full throttle.
1979 F150 Custom 2wd C4 302 painted ford blue, bored .040 over, flat top pistons with valve reliefs, Edelbrock Performer cam, carb, and intake, stock heads til next spring, MSD Ready-To-Run distributor, MSD Blaster 2 coil, Edelbrock air cleaner and valve covers, Dynomax headers, dual exhaust with Flowmaster 40 Series mufflers, 38 gallon fuel tank(how i can drive it further than around the block) 9" rear end with 2.75 gears and open diff to change to 3.50s and locker next spring.
"Your only as fast as me until the light turns green"
1979 F150 Custom 2wd C4 302 painted ford blue, bored .040 over, flat top pistons with valve reliefs, Edelbrock Performer cam, carb, and intake, stock heads til next spring, MSD Ready-To-Run distributor, MSD Blaster 2 coil, Edelbrock air cleaner and valve covers, Dynomax headers, dual exhaust with Flowmaster 40 Series mufflers, 38 gallon fuel tank(how i can drive it further than around the block) 9" rear end with 2.75 gears and open diff to change to 3.50s and locker next spring.
"Your only as fast as me until the light turns green"
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
C4 won't downshift
Sedric, this may sound dumb but when you floor it, is the throttle really wide open? I have seen quite a few trucks that the pedal bottoms out at about ¾ throttle on the carb (and they wondered why their truck had no power). Have someone in the cab floor it while you watch the linkage. It should open the carb. all the way and push on the kickdown. With the throttle all the way open, you should be able to push the kickdown just a little more. If I remember correctly, the gap is .060" between the lever and adjusting screw.
Barry
Barry
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Joined: Nov 2001
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From: Calgary Canada
C4 won't downshift
You're a genius BBB. I crawled into the engine compartment and watched the throttle plates as I held the gas peddle to the floor by pushing the end of the gas peddle lever toward the fire wall. Sure enough the plates only went to about 3/4 open.
There is an intermediate lever assembly mounted on the manifold that links the peddle rod and the throttle rod. There is another rod that moves the whole lever assembly back and forth and is connected to the fire wall. This is the rod that I adjusted...I moved the whole lever assembly closer to the carb which also brought my peddle out more giving me a greater range of movement.
Now with the throttle openning fully the trans. kicks down to 2nd, no problem, plus I notice a big improvement in acceleration because now I'm getting more throttle openning.
Thanks
There is an intermediate lever assembly mounted on the manifold that links the peddle rod and the throttle rod. There is another rod that moves the whole lever assembly back and forth and is connected to the fire wall. This is the rod that I adjusted...I moved the whole lever assembly closer to the carb which also brought my peddle out more giving me a greater range of movement.
Now with the throttle openning fully the trans. kicks down to 2nd, no problem, plus I notice a big improvement in acceleration because now I'm getting more throttle openning.
Thanks
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