I want to replace a 904 with a 727 (small block) with TTI headers, will it fit without modifications other than the driveshaft? 340 in a 72 Cuda.
TIA, Jon

I don't see why it wouldn't. The 727 doesn't take up much more room than the 904. Most small block headers don't ask which transmission you are going to run. You should be fine.

Hopefully you know that the 727 will take, eat, a little more power than the 904 will, correct? You will probably need a 1972 or 1973 only 727 340 small block externally balanced torque converter also due to being those motors were externally balanced in 1972 and 1973 only
The driveshafts are shorter on the stock 727 cars also so you will need to get the correct length and one with matching U joints ends for your rear end pinion yoke and to work on the 727 tranny output shaft also

just an FYI, back it the day I had more than one 72 340 that was internally balanced I believe the changeover took place sometime in the 72 model year

As was said the swap is pretty easy.
Driveshaft & Transmission Yoke are different.
Like CAB said the balance on the 340 is probably cast BUT If you have an external balanced engine and an internally balanced torque convertor you can get an externally balanced flex plate.
Also it is not uncommon for the lower mount for the shifter to be different if using the original slapstick shifter.

Different car but I have a 727 and TTI headers on my '89 Diplomat AHB and no fitment problems. Car was originally an A999 trans.

You'll need a balanced flex plate, shorter drive shaft and 727 slip yoke. Trans should go right in without any tunnel or header modifications.

B&M 10235

Assuming you don't have weights on the torque converter for the 727. The converter will not interchange between the two transmissions.

I do know about the power loss, but I can't seem to keep a 904 together. I have a SB 727, and know about the balance and such but just wanted to know if there would be a problem with the headers. I have been looking for a 998 or 999 non lockup, but they are pretty scarce.

You know you can build a 904 to take some serious horsepower. I know a few of them running 10's and one is running in the mid 9's
Just saying you can build what you have and keep all your other components the same.

Gus

There shouldnt be any fitment problems from a 904 to 727. The size difference is mostly in the bell are and the main body, both should not affect the exhaust clearance. You may have to modify your linkage if you have column shift (rare for an E body). If you have console shift you need to make sure you get a trans with the two tabs to mount the shift bracket on the tailshaft. Column shift linkage is where you may come into problems with the headers but im betting you have console shifter.
For a street car the 727 would be the better option. You can build a bullet proof 904 but its going to be big $$$. A stock rebuild on the 727 should be good for a mild 340. I would recommend upgrading to a bolt in sprag assembly.

What failure are you having? You shouldn't have an issue.
Doug

Converter, you need a 904 converter. I just went the other way, 727 to 904. Picked up 2/10’s+. How much power are you making?

I wouldn't use anything but a 904 on a small block, had one in a 340 that ran mid 11 seconds for years and never had a problem. I would find a new builder if yours are not holding up.

I prefer durability over speed so once a 904 dies I usually go 727 and never look back. Unless it's behind a 318.

I'm not sure yet, I was driving about 35 nice and easy, I felt what I thought was I drove over something hard and looked in the rear view mirror for something on the ground and turned around to find it. I didn't find anything but as I gave it some throttle very easy there was a very pronounced thunk thunk thunk. I would still move, so with just coasting and super light on the throttle to try and keep it moving it would thunk thunk thunk. Let up on throttle and coasts smooth, just touch throttle very slightly and thunk thunk thunk. At first I thought I had broken the snout off the Torque converter, pulled the transmission and torque converter looks fine. It was a slow thunk thunk thunk so I pulled the differential and it looks good. The driveshaft looks good and the u joints look good. Any suggestions.? Oh, and all the mounts look good. Some slight mods on the engine, just guessing 350-375 HP.

Change that to "EVEN IF" it's behind a 318!