904 Durability

[Beekeeper]

Will a 904 hold up to the power from a 340? The 904 was rebuilt by previous owner to stock configuration. The 340 will be similar in power to factory specs but a little lower in the power band with less top end.

I know the factory put 727s behind the 340 but that doesn’t necessarily mean the 904 can’t take it.

 

[Juan Veldez]

My rebuilt 904 internals had the space for the extra clutch pack, so I have it behind my 340. Saves rotating weight and HP compared to the 727, and I had two 904's to select the best parts from each. Not on the road yet, so I will find out soon how long it takes to grenade. I have a 727 drive shaft ready. My understanding is as long as you don't hammer it too hard, it can hang. A friend had one in a SS/KA Aspen with a 360. Ran under the index with the 904 and survived a long time.

 

[Beekeeper]

Thanks.

 

[moparleo]

Depends on how much you abuse it. Drive "normally" and no problem.
If you don't...let us know what happened...

 

[fasjac]

I had one in my first car, SE Challenger, warmed up 318. The 904 seemed to hold up for kid abuse with pro-trac 60’s.
The small rear end broke first. Normal slightly sporty driving and you’ll be ok. IMO

 

[Beekeeper]

Ok, that was kind of what I feared but that’s not so bad. I really prefer four spends anyway so I’ll do the whole conversion at once.

 

[JKCuda]

I'm currently rebuilding my 904....will be behind either my 318 or a 360 if I can find one at a decent price. Plan is for 3-400 HP depending on which setup I go with and from what I've read it shouldn't be an issue for street use.

Not to hijack...but does anyone know if the torque converter dust shield is the same for a 727 and a 904? I can't find a replacement that is marked for a 904...

 

[Rapidfire]

I think they are different.

 

[JKCuda]

I think they are different.

I figured as much but was hoping to get lucky since I can't seem to find one, lol.

 

[Juan Veldez]

I figured as much but was hoping to get lucky since I can't seem to find one, lol.

P/N MP800118 from Classic Industries - just got one!

 

[JKCuda]

P/N MP800118 from Classic Industries - just got one!

THANK YOU! I hadn't looked there...

 

[Challenger RTA]

I had a 70 dart 318 904 110k miles rear end went.changed it and everything was fine.

 

[DaveBob]

Will a 904 hold up to the power from a 340? The 904 was rebuilt by previous owner to stock configuration. The 340 will be similar in power to factory specs but a little lower in the power band with less top end.

I know the factory put 727s behind the 340 but that doesn’t necessarily mean the 904 can’t take it.

View attachment 92206

I have two friends in Colorado who raced small block cars with 904 transmissions. Both preferred the 904 over the 727, believing that it helped them to run faster. Both of them beefed up the 904's for racing, but I don't know what all they did to them. Neither of them ever grenaded a trans, but they went through the trans and freshened it up every year, between seasons. The fact that both cars were dedicated race cars and gutted for weight probably helped trans longevity. However, both cars ran consistently in the 10's, with one of them occasionally dipping into the 9's in the quarter, so the "light duty" 904 may have more strength than some think.

 

[michael bucklew]

My rebuilt 904 internals had the space for the extra clutch pack, so I have it behind my 340. Saves rotating weight and HP compared to the 727, and I had two 904's to select the best parts from each. Not on the road yet, so I will find out soon how long it takes to grenade. I have a 727 drive shaft ready. My understanding is as long as you don't hammer it too hard, it can hang. A friend had one in a SS/KA Aspen with a 360. Ran under the index with the 904 and survived a long time.

way back--a famous drag racer did a comparison of the 727 and the 904---not much difference---article was in HOT ROD magazine---i am running a 904--stock to car

 

[moparmike65]

I'm putting a TCI 904 behind my 408, they claim to be good up to 700 HP. I tore up a few stock ones behind a 318 as a kid but I also killed a few 727s. If you're running a stock transmission the 727 is far more up to the task than the 904 but if you're no hotrodding it a lot the 904 should suffice.