c4 tranny problems

[cvenom96]

OK here's the deal. The c4 in my 67 has about 8k miles on a rebuild. The car has started to slip bad on the 2-3 shift under light acceleration. Hard or moderate accel and it shifts fine. The modulator valve has been replaced and I've tried adjusting it but it still does it. Also, when I hit the gas to go into passing gear, it downshifts for a second but goes right back into high gear. It does this at varying speeds. Any ideas? It's a stock rebuild, new stock type torque convertor, no shift kit or anything.

 

[bumblebee03]

OK here's the deal. The c4 in my 67 has about 8k miles on a rebuild. The car has started to slip bad on the 2-3 shift under light acceleration. Hard or moderate accel and it shifts fine. The modulator valve has been replaced and I've tried adjusting it but it still does it. Also, when I hit the gas to go into passing gear, it downshifts for a second but goes right back into high gear. It does this at varying speeds. Any ideas? It's a stock rebuild, new stock type torque convertor, no shift kit or anything.

Do you have the kick down linkage connected? , , sounds like it may not be adjusted correctly,,, Bee

 

[cvenom96]

Yeah it's connected. I was working on it this weekend trying to figure out why it wasn't working and I noticed that when the gas pedal was fully depressed, it wasn't moving it. I adjusted the linkage to where it moves the kickdown lever on the tranny to it's fullest extent. In other words it pulls it till it won't go anymore when it at full throttle. At that point it started actually kicking down but wouldn't stay kicked down. What other adjustment can be done to it?

 

[mustangdave]

I would double check to see that you have the correct mod. valve because I don't think they were adjustable then. If that fails, I think there is an adjustment on the bands by loosening a lock nut and turning a bolt; could be the second gear band has settled in and needs a slight tweak. Again, double check the mod. valve first, it could be the wrong part number.

 

[Lswhat]

well mine does the same thing and im almost sure the valvebody is to blame but i did exploded the plantery and it went all over the tranny and piece some how ended up in the valvebody how that happened i dont know but puting out there to be considered . well since yall are looking at it i have a prob to my tranny kinda stuter shifts third like it goes to nuetral before shifting any ideas.

 

[cvenom96]

You are correct on the modulator valve. It has been replaced though with an adjustable one however this was before I bought it back. Originally the car was mine and I sold it then bought it back 3 years later. Lswhat that's exactly what mine does. It revs just like it was put in neutral between the 2-3 shift. I remember the guy I bought it back from saying they changed the filted in it so I'm wondering if they didn't screw something up when they did or get junk in it. I've adjusted the bands but according to the Haynes manual, the adjustments you can make affect either the 1-2 gear band or the 1-R band. From what I understand the 2-3 shift is vacuum controlled.

 

[GaPonyFarm]

Try replacing the intermediate servo with one coded "H". It should provide a more positive 2-3 shift. You should also check for a vacuum leak to the modulator valve, just as a precaution. At what speed is the transmission shifting back to 3rd, when using the passing gear? Adjusting the modulator will onlt slightly effect the shift points, not the firmness.

 

[cvenom96]

Well, it shifts into 3rd if I'm just putting along at around 15-20 mph, if I stomp it then it goes back to 2nd and will stay there but anything over about 30 mph it'll kick down but come right back to 3rd. I checked for a vacuum leak while I was under there but I'll check the metal line to see if maybe it's rubbed a hole in it or something.

 

[Lswhat]

dude ur tranny is doing the same exact thing mine has been doing for 3yrs and the past 6 rebuilds. im glad im not the only one having the problem but the problem does suck. i have all the race stuff in my tranny kevlar clucthes and bands upgraded servos and planatery gears the only things i havent reaplaced are the front pump and the vavle body if that helps. i also have to shift mine manually cuz if i dont it will short shift every gear so bad that it will burn the clutches and ive been manually shifting it since i last put it in in august. just fyi but if u figure it before i do let me know.

 

[cvenom96]

Definetly will let you know. I've been racking my brain trying to remember how it shifted when I first got it back from being rebuilt back in 99. I swear I don't think it shifted as quick as it does now. I'm gonna try and find out from the dude that had it for a little while after it was rebuilt what he did to it. I know he told me they changed the filter in it so I'm gonna see if maybe they've clogged something.

 

[cvenom96]

I found this while searching around. Don't know if you've read it before or not but I'll look into it.

http://www.network54.com/Hide/Forum/message?forumid=260730&messageid=1066929467

It's a ford tranny forum in case you are wondering.