The best core to get is the 1975-1977 360 904 trans, which is a non-lock-up, wide 5 clutch front drum, and steel planets. You can upgrade to the 2.74 low gear set which are found in 1981-up 904's. This will allow a better launch without increasing the rear axle ratio. I would use Red lined bands that are solid backed, NOT flex bands. I have had good luck with the standard Raybestos Tan waffle clutches for high gear, with an upgrade to the Alto Red Eagles,
www.altousa.com . Use the 2 spring front servo with at least a 4.2 lever. Use the 5.0 lever if you are really pushing a high pressure valvebody or using Nitrous. The 4.2 should work with most applications. Use a bronze output shaft thrust washer between the front of the output shaft and the rear of the forward clutch retainer. Set all end plays to minimum factory specs. Set direct clutch clearances to 0.010"-0.015" per disc or to the valvebody manufacturers' specs. The forward clutch clearance to 0.020" - 0.035", and use only FLAT selective snap rings. I would use the Griner 1222G20B transbrake w/ low band apply.
You can install a shim in the low/rev servo piston to allow a better 1-2 shift. Most valvebodies have all these extras to aid the VB to better performance. I use the MP deep pan with drain plug and a good cooler. I also use Turbo Action converters with excellent results. I currently use a '73 core, 2.74 low, wide 5 clutch drum, T/A Cheetah valvebody, T/A 8" converter, deep pan, T/A Tranz Box rebuild kit. Rick Allison at A&A
www.aandtrans.com is top notch and can provide any parts you need, and John Cope at CRT sells A&A parts as well.
I would recommend 5 direct clutches no matter which drum you have. Use A&A thin direct clutches, P/N 12750A-6 if you have the standard 4 clutch drum. This will allow 5 clutches in the 4 clutch drum. If you have the wide 5 clutch drum, just use 5 Raybestos Tan waffle clutches. Also, concerning the front band, I would use the narrow center apply lug solid red band (kickdown, with grooves) on either the standard 4 clutch drum OR the wide 5 clutch drum. Normally, the wide drum gets a wider band, however, the apply lug on the band is offset from the center, and thus does not apply the band evenly, causing uneven wear, overheating, etc.
In order to use the wide 5 clutch direct drum, you need a forward drum with input shaft from a non-lock-up trans. These will have an 1-1/8" wide splined clutch hub that fits into the direct clutches. The clutch hub for the standard 4 clutch direct drum has a 1" splined clutch hub on the front end of the clutch retainer. Also, you need a beveled back front pump reaction shaft support to clear the wider 5 clutch drum. You need to keep the years separated when swapping parts, 1975-77 or 1978+ all non-lock-up. The diameter of the sealing rings on the input shaft have a 0.062" difference between the two year groups and do not interchange.
www.aandatrans.com www.coperacingtrans.com www.tcsproducts.comwww.727specialist.comThe 904 clutches have about 1/2 the surface area of a 727, so in order to live behind some serious torque, more line pressure is needed.
904 FLAT snap rings for clutch drums: (Mopar P/N's)
1942421 0.060"
1942423 0.076"
2538617 0.098"
These numbers are old, and may be superceded to newer P/Ns. Ask your local Mopar dealer to check availability and price. If they don't have a way to order them, ask Rick at A&A, as he sells a kit with them. One required for each drum (2), and of the correct thickness to set clutch clearances properly depending upon which drum you are adjusting. In some cases, the snap ring will not give you the exact clearance you need. It is better to go a little loose than too tight. Also, A&A sells different thickness steel plates that fit between the clutch discs to help in zeroing in on the correct clearance. Another option is to machine the thick outer pressure plate a little if you have to. A machine shop should be able to grind the plate like a flywheel for a good flat surface after you figure how much needs to be removed. Remember, measure as many times as needed to be sure, and cut once.
For reference, the snap rings that hold the gear train on the output shaft are selective, and are used to set gear train end play. These are the Mopar P/Ns:
06026289 0.041"
06030938 0.062"
06030404 0.084"
Remember, always set the gear train end play and the input shaft end play close to minimum factory specs. The input shaft end play is adjusted by using a selective thickness fiber washer between the front pump and the direct drum. I don't have those numbers handy, but Rick would be able to help you with those as well.
I mostly buy parts separately. I can buy a standard rebuild kit locally with Raybestos clutches, and I simply buy the performance solid red bands from A&A, CRT. They usually require a core to return as the solid bands are getting scarce. However, you can buy a complete race kit from either CRT or A&A. They can build to kit the way you want it. I have also bought from Bulk parts at a real good price,
http://www.bulkpart.com At your power level and weight, you may need 300M steel input and output shafts. I would ask Rick Allison at A&A for his recommendation. Roller thrust bearings with steel planetaries may also be needed to ensure longevity. Aluminum direct drum may not be necessary in a 904 due to the smaller diameter and lower inertia, there is less probability of explosion.
Main parts needed are a well designed high pressure transbrake to keep the small clutches and bands from slipping, good quality clutches and solid backed bands, pay attention to detail with clutch clearances and gear train & end play dimensions, and a rear roller support with oiling mods to the sprague and direct clutch oil port in the reaction shaft support. A multi-spring pack for the direct clutch to replace the single coil spring.
John
