i have a 66 c-4 automatic i rebuilt about 3000 miles ago, and last week i dropped 3rd gear or so it felt. It will shift fine 1-2 but as soon as it should go into third theres a vibration from the transmission or when i reach 60 mph. i pulled the driveshaft and ran the car and it still only does it at 60 or when it should go into third so it is not the rear end or the u-joints and it has a brand new driveshaft and rear end also. i have just replaced the valve body, the governor, vac module, and readjusted the bands, but i still have a vibration. has anyone else had this problem thanks.

 

I'd look at the tires. Maybe they kicked some wieght. But just because the driveshaft is new, do not ignore it. You could chase your tail a very long time that way.Look at everything that it could be, and verify they are good.

 

if i read him right he said pulled driveshaft and still had the vibration so that would take the tires out of the problem.
so theres no 3rd gear do you have a tach to see if the motor changes rpms when it should shift?did it do it all at once or just get worse?try running the motor up to were it vibrates in park if it does it in park onlything turing then is motor converter pump and i think 1 drum in tranny.really nothing in a trans should have vibration unless bushings are really bad or maybe tryin to be in 2nd and 3rd at the same time but that would make it lock up like a trans brake will do
good luck.

 

Yes i took the drive shaft out to eliminate wheels, axle bearings, bent driveshaft or u-loints as the culprit and it still vibrated violently at 60. I have a tach and it will shift into second just fine and when i'm driving it i'll be around 55-59 mph at 1800-1900 rpms but as soon as i hit 2000 rpms and 60 mph thats when the violent shaking is felt from the trans tunnel but if i bring it up to 2500 and 65 or faster it goes away. It just stated last week on my way to a car show in nh i waas doing about 70 and the car felt like it was gonna come apart on me, so i babied ait at 55 all the way home.

 

I might be missing something. How are you taking the drive shaft out and testing it at 60mph? I don't follow.

 

OK you have a problem. I had this happen years ago with a C4 in the Cougar. It would shake so violently the dash looked like it would come lose and fly in the back seat. At that time I couldnt rebuild transmissions, since I was 16 and hadnt learned yet. A wisened old tech my dad was friends with said it was probably a broken band, since it was a common thing in C4s back then. If its under warranty from whoever rebuilt it, take it back. If it isnt, then you will still need another one or yours fixed. Its internal for sure.

Just so you know, if you pull the driveshaft, fluid will leak out where the yoke goes. You probably already discovered that.

CPR you can do what he is saying if you put another slipyoke in with no U joint or shaft attached, the speedo will still register since its driven by the output shaft. I really wouldnt recommend doing it that way, but I suppose you could.

 

So he means the MPH is registering, but the car is not going 60. But if a band was broken, he woulda lost R, or 3rd gear. The internals of the tranny are very little rotating weight. If it does it sitting still like you describe, I would suspect the pump bushing, or converter snout.

 

That could be too, the third gear only part, and no vibration in second is the part that says possibly not. Maybe a planetary is losing a pinion, that would do it for high gear only. Maybe I will look in the book tonight.

I havent really done much with the C4 lately other than kit one for the Cougar. I cant even remember the power flow for them without consulting the book. I didnt tear mine down that had the same problem 20 years ago, it didnt lose any gears, but one thing is for certain, ihis needs to come out of there and get opened up a bit for a look.

Now ask about a TH400 or Th350 and I have been doing quite a bit with them lately, as well as 700R4/4L60s.

 

i'm definitely going to tear into this tranny this winter, it's begining to get worse now if i put it in gear with my foot on the brake it will start vibrating a bit till i start rolling then it will go away and then come back when i start start slowing down to a stop.

 

Ok, quick question, how's reverse? C4 transmissions have two bands and two clutches. Front clutch is reverse/3rd, rear clutch (inside the shell) is forward. Front band is 2nd gear, rear band is manual low/reverse. If 3rd clutch is totally hosed, reverse will chatter too. If for some reason the 2nd band is not releasing, then you might get what you describe. The 67 C4 information is on my website http://www.oldschoolhotrodder.com just go to files and links then downloads.