C4 Tranny Question
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Junior User
Joined: Apr 2001
Posts: 93
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From: South Africa
C4 Tranny Question
ok, this may sound very vague but i will try and explain as best I can.
i recently installed a 351C and a C4 automatic tranny in my 65 F100. Everything is running well except for some tranny problems.
I do still have the original rear diff from the 3 speed manual 240I I had previously.
The problem is that the engine revs very high before shifting into the next gear. I understand that the final drive would rev high due the the rear diff. I have been advised to set the modulator but I have no info or any advice on this.
Does anybody know what spec oil I should use in the tranny?
Any advice will be apreciated...
i recently installed a 351C and a C4 automatic tranny in my 65 F100. Everything is running well except for some tranny problems.
I do still have the original rear diff from the 3 speed manual 240I I had previously.
The problem is that the engine revs very high before shifting into the next gear. I understand that the final drive would rev high due the the rear diff. I have been advised to set the modulator but I have no info or any advice on this.
Does anybody know what spec oil I should use in the tranny?
Any advice will be apreciated...
Senior User
Joined: Apr 2003
Posts: 221
Likes: 0
From: Greater Cleveland Ohio
C4 Tranny Question
I'm not sure if the factory modulator is adjustable, but most after-market modulators are adjustable for C-4 and C-6. There is only one screw and it is turned in or out (I forgot which direction tightens or loosens the shift...but whatever direction tightens the shift is the same direction that raises the shift RPM). It is also a single vacuum modulator as opposed to the duals on some C-6's.
I have the same combination 351-C/C-4. Mine is from a 1970 Mustang. So I use the Type F fluid.
If the transmission dipstick is original, it will either have a number preceded by "F" for type F Fluid use, or "CJ" for Dexron III /Mercon
I have the same combination 351-C/C-4. Mine is from a 1970 Mustang. So I use the Type F fluid.
If the transmission dipstick is original, it will either have a number preceded by "F" for type F Fluid use, or "CJ" for Dexron III /Mercon
New User
Joined: Jul 2003
Posts: 24
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From: east coast
C4 Tranny Question
I would reccomend before you buy the modulator to check the vacuum that the tranny is seeing. Tee in at the modulator hose and expect to see somewhere around 17- 20 inches. Snap the throttle and vac. should instantly flash to zero. In other words the needle will mimick the gas pedal. Fix or quallify this first before you start spending money
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