Transmission issues and a question

D

Dwayne Brooks

So my '67 sedan DeVille is having transmission problems. Once up to speed it feels fine, but from a stop it almost feels like it has a stall convertor in it. it feels like it's slipping and when you accelerate a little harder it'll sometimes slam and then act as if nothing's wrong. I've heard of these trannys having a sump issue where the sump slides out of the transmission enough to lay on the pan and cause a similar situation.

Anyone had similar problems? The car has only 46,000 original miles but I think this transmission is baked.

The next question is will a transmission from a 1969 472c.i. Cadillac interchange with a 1967 429c.i. Cadillac? One option is to just do a transmission swap for now is why i'm asking. I'd like to learn as much as I can before dropping the transmission pan. I do know my transmission can have one of 2 filters/sumps... 1967 was a transition year and 2 filters/sumps were used... an "early" style which looks similar to an engine oil sump and the "late" style that is the more flimsy, flat filter-type. I don't have the pan off yet to determine which I have. The fluid is full and isn't scorched, so i'm guessing the front pump or torque convertor are giving up if it isn't a sump issue.

Any suggestions/comments? Thanks!
 
I'm lost on them.but it sounds like a sticky valve body or a slipping brake ban. to me trading tyrannies is a waste of time. you usually end up trading troubles. some things you just need to bite the bullet and go get rebuilt
 
Bad vacuum modulator or vacuum line is off. Also, could be that the linkage from the transmission back up to the carburetor is out of adjustment or it has come apart somewhere. Those cars were prone to vacuum leaks, and that is all that it takes to mess up the shifting pattern of the car.
 
Sound like issues I just went through with my 67 Fleetwood Special. The 1-2 shift was delayed and felt strange and the delay kept getting worse. Finally got to where it would only shift at high rpms when you would manually go through the 1-2-3 gears with the lever.

A $19 modulator from O'Reillys later, she shift like butter and at the right points.
 
As far as the low mileage goes, mine is a 12,000 original mile car that has been hibernating since 1980 so I would definately try a modulator first.
 
I also had this problem with my 70 C/B Olds and a new modulator fixed it. As others have said its a cheap part so start there.
 
I had an issue with the TH400 behind my '67 429 last fall, and didn't have time to get it rebuilt before a parade I was scheduled to be in. I knew a guy (don't we all ;)) who had a TH400 from behind a 472 in his barn. I was going to have the mechanic swap transmissions for me, but quickly realized the bell housings were different. Luckily, it turned out to only be a governor gear (not your issue, it caused different symptoms.) Also, depending on what model car the transmission and 429 came out of, I know that my parts book shows the '65/'66/'67 commercial chassis had a different tailshaft housing versus a passenger car, so it might not even be the right length for your Deville.
 
Thank you all for your advice.

Bought a new modulator valve sunday morning. It helped a little, but not much. It's an adjustable one and following the instructions every adjustment it got worse, so I put it back to the original setting. A phone conversation with Paul pionted me towards the Sea-Foam transmission product. It said to add the treatment and drive at least 5 miles, so I took it on a 20 mile run. Time will tell if it gets any better or stays the same...
 
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