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C4 trouble

5K views 15 replies 6 participants last post by  automatics of marion 
#1 ·
Hi, i just finished a 1966 Ford Mustang project car... dropped a C4 automatic transmission out of a 78 Ford Fairmont onto the back of a 289. fluids are good everything is new and tranny has been checked out and given clean bill of health. However, I cannot hear the thing shift, it is not noticeable at all. Bearing in mind that this car was put together from many parts but is mostly brand new anyone have any recommendations or thoughts on the shifting?

Thanks
 
#3 ·
first of all is it shifting at all ? or just staying in 1st gear, if it is changing but shifts r soft it may have the modulator pin misssing or low on fluid r u checking oil while engine running, it should have 18 inches of mercury at modulator at idle 15 is ok, r u running a high stall because that will soften shifts at low speed as well hope thats some help
 
#4 ·
yes, the vaccuum modulator is connected but, no guarantee that is is functioning. To be honest my feeling is that it must be shifting because the car can get up around 65mph with ease. It can be "manually" shifted from low to second but then nothing after that. To be honest the problem perplexes me quite a bit, perhaps it's not shifting completely. I have been considering replacing the modulator and seeing if that changes things. Yes all the vitals are checked every day and definitely while running. It's also not leaking. If the car is simply stuck in drive you won't hear the shift at all. Any other thoughts before i go and replace the modulator?
 
#7 ·
XPC66, sure mate the damn things were meant for eachother. the only tricky thing about the C4 transmission is in attaching the torque converter; when your putting it on and rotating the crankshaft you'll here it lock in once and it'll go a little ways on then you have to continue turning til the thing sort of "thumps" again and she'll go on the rest of the way, then just attach your nuts to the studs and its ready to go! lol, it's a piece of cake, now i just need to find out how to make it shift firmly instead of just sort of float through all the gears, lol! :) cheers

hope this gives you some help
 
#9 ·
I've had a similar issue with my 4th C4. It never changed hard (yet has a stage 3 shift). The problem was the shifter linkage @ the box wasn't quite lined up correctly. Well thats what the auto reconditioner suspected but I am not sure? Due to it not lining up correctly. I got weird soft shifts, low line pressure and a dead auto within 199k's.

I went back to a stock shifter and the box was replaced under warranty. Problem solved. The B&M shifter I had for some reason I couldn't line up the shift positioning @ the box properly.

Brenden
 
#10 ·
Brenx

that is interesting and perhaps helpful and extremly applicable. The transmission is from a Ford Fairmont, which had three on the column, not on the floor like in my stang. I paid to have the linkages changed inside the transmission and had assumed it would just bolt up like the man said. The box and linkages are all original 66 mustang, perhaps they're not lining up. However, I'm still not sure what i should do about it. Thanks for that thought though.
 
#12 ·
I never bothered to measure mine up. But, you should be able to measure up the back of your block and get some idea of what you need, those two "studs" sticking out of the block are like locator pins and the bell housing pushes right into them. Sorry can't be more help there.
 
#13 ·
These boxes ( like the C10 ) change gears on vaccum
If you've got a stally in it, the box will "stagger " its changes.

This means that it will change up really quick, almost imperceptibly when you are just driving normally. The stally makes the engine rev higher at the same shift point which means that there is less vaccum at that point. Less vacuum means that the box can't hold the gear so it changes up real quick, sometimes you can't even tell. When you change manually it's OK , if you leave it to its own devices, you may find that you're in 3rd gear by the time you hit 40Klmh. It's almost like you're missing a gear.

If you wind the screw in the modulator in a turn or so it will increase the pressure slightly and give you a more drawn out shift and harder shift to compensate. This may or may not work depending on what other issues you've got. ( To do this, you pull the hose from the modulator, check to see if there is a screw in there and use a small flat head screwdriver to turn the screw in approx half to one turn , if there is no screw, it means that the pressure is NOT adjustable...... :fraz: )

Drive it and see if it makes a difference.
Otherwise, listen to the other guys about the linkage alignment problem.
 
#14 ·
XPC66
It doesn't really matter what version you get,whether it is the pan fill type which has the big bell attached to the case or the case fill type that the bell bolts to the pump.
What does matter is you must get the bell/flexplate/convertor setup that matches.The pan fill type is normally the big 164 tooth flexplate/12"convertor .
The case fill type has the 157 T flex/smaller bell + convertor.
If it doesn't all match you will have starter issues where it wont line up.
 
#16 ·
getting back to your problem with it shifting, the mod pin sits inside the modulator & pushes on the modulator valve u may have pin missing or mod valve is sticky causing low line pressure, if u have no vaccum at modulator u will have no upshifts or very late shifts what happens if u drive it manually does it upshift with a firm shift or is still soft, u may have a sticky governor valve, witch is very common on C4's or pull mod hose off & check that adjustment screw hasnt wound it self out it should not protrude past outside thread. good luck
 
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