904 Trans for 500 HP?

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360duster

360duster

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Hi Guys,

i´m thinking about switching the TF727 in my Valiant to a TF904. The 727 does need a rebuild in the near future, as far as i read the 904 is lighter and does have less internal loss - means more power to the wheels and better ET´s....that´s what i´m after.

I run a 408ci SB with around 450 hp / 450 torque (no dyno numbers, could be little more in reality). best ET 12.2 with 109 mph now, still tuning.

So i´d like to rebuild a 904. What internal mods beside quality overhauling parts should i consider to beef it up? The car will see 20 - 30 dragstrip runs a year, maybe 2000 street miles a year.

Please share your knowledge, thanks!

Michael
 
To answer your question about how to build it up my suggestions are use a good quality COMPLETE re-build kit. Shim up the clutch packs properly (approx. .040" in the rear pack and .055~.075" in the front pack), shim up the total end play to .015" or as close as possible. Upgraded clutch discs and steels are a plus IMO but some say there not needed at your level. Install either a Trans-go TF-2 shift kit or good manual valve body. Check the front servo apply lever. Some are pretty wimpy at 2.9, if so replace it with a 3.8~4.2 ratio lever. Some will say use a 5.0 lever but I haven't had good luck with them in 727's (they overlap on the 2-3 shift) so I usually shy away from them for what little gain you see. Replace the front clutch carrier single wound spring pack with a multi spring pack. Install a deep pan and good cooler. That should make it plenty strong.

Performance gains are not absolute. No way anyone can say you'll gain 2 tenths going from a 727 to a 904 and be right because every car reacts differently and you might build the 904 with a better or worse converter which affects performance a lot. It could even be more then 2 tenths (if your 727 is tired and you build the 904 with a better converter) but most likely performance will be a little less. Even if it's only 1 to 1-1/2 tenths it's that much and if fuel mileage is also a concern it could help that some also.
 
i switch from a 727 to 904 back in 1993....picked up 15 hundreds... that is .15..
 
Dose anyone have the part number for the 0.061 thick grooved Alto Red Eagle frictions that can be put in the direct clutch?
Thanks
 
360duster said:
Hi Guys,

i´m thinking about switching the TF727 in my Valiant to a TF904. The 727 does need a rebuild in the near future, as far as i read the 904 is lighter and does have less internal loss - means more power to the wheels and better ET´s....that´s what i´m after.

I run a 408ci SB with around 450 hp / 450 torque (no dyno numbers, could be little more in reality). best ET 12.2 with 109 mph now, still tuning.

So i´d like to rebuild a 904. What internal mods beside quality overhauling parts should i consider to beef it up? The car will see 20 - 30 dragstrip runs a year, maybe 2000 street miles a year.

Please share your knowledge, thanks!

Michael
Click to expand...

With the right parts it's not a problem for the 904. The owner of the company I used to work for ran in the BA/A NHRA class. He ran a Steve Schmidt 500 inch Chev with about 1300 HP and a 904. The 904 had a lot of trick hard parts in it to make it live but it worked great. As others have said do it right on the rebuild with good parts and you should be OK at 500HP. If you want to consider the HD 904 hard parts go to www.tcsproducts.com
Lots of trick stuff there for the 904 and 727 for the hard core racer.
 
My neighbor runs one he built behind 600HP , launches at 3600 off the trans brake and it holds up fine.
 
I,ve been running a race prepped 904 behind 500plus HP SB for 4 yrs.My biggest expense was a good torque convertor.Still running 10,s weekly.:burnout:
 
70aarcuda said:
i switch from a 727 to 904 back in 1993....picked up 15 hundreds... that is .15..
Click to expand...

I'll back that up. Chrysler did some testing in the mid-'70's and that's what they came up with. Car weight was adjusted as needed and transmissions were built the same with the respective converters as close as possible.

I doubt I have 500hp, but I've been footbraking my 3,540+ lb car to as fast as high 11-teens @ 116mph + with 1.47 60' times with a 904. (Has a little more in it ;) ) Weight is a factor, but it's been working fine. For me the sprag has been the rare weak link in any Torqueflite. JW Transmissions in Rockledge, FL has been doing my transmissions for decades!

.15 in ET isn't anything to blow off!

While others as well as myself have done it, I've been told that a full manual valve body may not be a good idea on the street because of the constant hard shifts.
 
jimjimjimmy said:
that is not a huge gain if im reading it right. thanks for the first hand info.
Click to expand...

It's actually pretty close to what you mentioned earlier and a decent gain. .15 = 1-1/2 tenths. For a racer it's certainly worth the effort. For a street car and your having to do a trans rebuild anyway I'd say it's worth it but not just to do to try to make your car a little faster, but that's just my opinion.
 
I bought the full race kit from TCS Products out of Langley BC and built mine with the help and knowledge of Fishy68 , Trailbeast and OldKimmer . My 904 has been cross country and back and is about to go again with my 410 Stroker in front of it making more power and torque than you have ,the key is keep everything surgical clean and follow what these guys tell you and you will have a trans that you will be happy with for many miles to come.
 
So no one knows the part numbers for the thin frictions to put in the direct clutch????
 
Thanks Tony, Alto don't give too much info on the disc surface in the catalog they have. Hard to tell if they are smooth or waffle.
 
wow, i did not expect this much positive feedback about using the 904, seems the way to go for me.

Is there any good literature to read before i tear into one? On the other hand, how much is a stout street / strip 904 from a builder in U.S.? If not too much dough i´ll consider this, too. Maybe some of you can tell me some shops that know their stuff.

Does a quality rebuild kit, maybe from A&A transmission, contain all the parts i´ll need if i do it myself?

i know, a lot of questions...with your help i´m getting there!

Michael
 
JW Transmissions has been doing mine. But like some engine builders, there are trans builders who have their own little tricks to help durability and longevity......improve oiling here, use a better bushing/bearing there, certain clutches/bands, valve body mods, etc.
I regret to say that personally I've never gotten into a trans that far to know many more details.
 
Michael most rebuild kits, no matter who markets them, don't contain everything. Some get close but it seems you always have to add something. I generally buy from www.bulkpart.com or www.wittrans.com getting a kit closest to my needs and adding whatever other parts I need to finish it. As for a US shop that can build you one 3 places I have personally dealt with come to mind, Andrews Racing, Cope Racing Trans. and A&A Transmissions. Not sure on prices as I haven't had a need to check. Shipping might be the big killer with your location. If you'd like a list of what I'd buy if I were rebuilding a 904 PM me and I'll set you up.
 
thank you sir, i´ll do that!

Great input here as always on FABO, i enjoy to participate here!

Michael
 
fishy68 said:
If you'd like a list of what I'd buy if I were rebuilding a 904 PM me and I'll set you up.
Click to expand...
Why not just post it for the whole forum? Isn't that why we are here? to share?
 
Bakerlite said:
Why not just post it for the whole forum? Isn't that why we are here? to share?
Click to expand...

I can post it all but since there's different levels the parts can vary according to that plus they had some changes down through the yrs. so in the end I might as well just do a copy and past from the website because of so many options. It's a lot easier and less time consuming (and believe me, looking up parts can be time consuming) for me to answer in accordance to the specific need.
 
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