904 to 727 swap

[Thalidomide]

I have a 73 duster with a tired 904 in it. Are there any modifications required to run a 727? What are the benefits? Arent the 727s alot stronger?

Thanks

[bubby440]

the 727 is stronger but also has heavier internal parts and draws more hp. a 727 will require a 4" shorter driveshaft and yoke.

[Dart]

The 727 will also require a new converter and kickdown set-up.

I am in the process of doing the same swap myself. I have asked a lot of different people about the 904 vs. the 727. Most of the racers I spoke to suggested going with the 904 using the 999/998 (RV trans.)internals. My transmission builder suggested not going with the 904 strickly from a reliability standpoint - especially for the street. Most of the racers only get about 100 passes out of a 904 before it needs to be rebuilt. I also asked about power loss and my tranny builder explained that it would only be about 1-2 tenths. A built 727 would last indefinately compared to a maxed 904. I don't want to have to take my 904 apart in a few years for another rebuild so I am going with the 727. A little bit of a hassle, but well worth it.

[MoPaul]

In, I believe, Popular Hot Rodding summer of 98, they projected that behind the same engine, a 727 would survive 300 passes compared to the 904's 100. But the 904 has a better gear ratio, typically good for 2/10's in a 14 second car.
Disclaimer: I have no personal knowledge on this subject, only what I have read. Also, THE MoPar Guru of these parts somehow swaps internals, using the 904's superior ratio with the stronger 727 housing. But he is a wizard, not recommended for just everyone. I don't know what it does for durability exactly, as I have no knowledge of one of his transmissions ever failing.
- Just a couple of thoughts.

[cuda367]

Anybody who goes to the trouble off slowing their car down 2-3 tenths needs more help than how to swap a transmission. If I could bolt a 999 to a big block I'd do it in a heart beat. 999 in a 10.5 sec. cuda six years still ok what more do you want? What do you think the pro flite is in comp eliminator.

[Dart]

Cuda367: You proved my point exactly. The rest of us slobs don't want to rebuild their transmissions every 100 passes like a racer does. 1-2 tenths is not worth having to take the trans apart every 100 passes. Half of the people I know can find more than 2 tenths in their tuning and car set up.

I think your trans has lived way longer than any others I have seen.