The 904 Trans

[Bruceynz]

Hi Guys,

Ok sorry if this has been asked before, I had a look and didn't see a posting on this, I am going from a stock 318 to a warm 360, not to radical but with some help of other forum members I have bought a cam that will work nicely in a 360 to go with J heads with 2.02 valves. I think with the set up we will be between 300 - 350hp. I currently have an 7.25" rear end but will upgraded that to a 8.25" 3.21:1 ratio. My concern is my 904 A998 trans going to cope, I am not going drag racing, maybe the odd spirited take off at the lights If it won't last will the 904 be ok if an extra clutch pack is added to make it into a A999 trans or should I go 727?

Or is there a rebuild kit or parts readily available that will strengthen the 904 to what I want?

The reason I like the 904 is I have it already, light, lots of parts on ebay for it - I see rebuild kits for $150.

Also will my drive shaft need to change length when I go from a 7.25" to an 8.25"?

Thanks
Bruce

 

[jasperjacko]

904 is fine. I run one in man that's been built up, manual valve body, etc. My 360 is similar to yours, probably made 60-70 trips down the drag strip, no problems.

 

[80mirada]

Your driveshaft will probably need to be shortened. The 904 can easily be beefed up to handle a mild 360. The torque convertor will be the week link. I will look up my listings for 904 mods and parts

 

[Bruceynz]

Is there an aftermarket Torque Converter to look at?

 

[80mirada]

Yes, there are a few good ones available for the lock up converters. I have a list at home, so I will post (hopefully with links). If you run a B&M weighted flexplate it opens the choices up, but you can get most converters weighted for the external balance.

 

[Bruceynz]

yes I have on the way from the USA to NZ a B&M neutral balance flex plate.

This is what I bought here http://www.ebay.com/itm/121190284109?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

 

[Mcfly68]

There is absolutely nothing wrong with a 904, and can easily be built to handle way more power than your 360 will put out with out the expensive exotic bits needed in a 727. There is a lot less rotating mass..904 will always be faster than a 727 behind the same motor...no need for billet drums...904 drums are smaller and unless you are buzzing your engine over 9000 rpm ( drum speed will be just a hair over 24000 rpm) will never explode unlike a 727, even if the sprag breaks ( break a ujoint on launch, especially if not manually selected 1st, or with a valvebody that doesnt do band apply in manual first, you have just broken the sprag and free rev'ed the trans and exploded a 727 drum..not fun having shrapnel flying through your floor boards)...speaking of sprags the 904 is already bolted in..just change rollers and springs to new ones...if starting with a 999..you already have the low gear set and 5 and 4 clutch packs...easily upgraded to 6 and 5 with the right clutches and steels. Replace the apply spring with a reverse wound belleville spring, or the 12 spring apply pack...with the regular spring it "winds tighter" as rpm increases, reducing apply pressure, replace the piston with the sonnex problem solver to stop it from flipping in the bore ( common problem in all older torqueflights), new pump gears, a decent shift kit ( i like fairbanks) and a good grooved solid band ( the grooves help to get the oil out from between the drum and band faster for better engagement) as wide as your drum will accept, and the other one a good double wrap. I have less than 600 bucks into parts in mine ( not including the overdrive section, it is an a500/44rh) going behind a 500hp 5.7 hemi. 904's stay together behind 9 sec drag cars, even RB powered ones ( there is an adapter kit to bolt it behind a 440 because it is easier to spin, and will stay together easily and cheaper to build than a 727)

 

[80mirada]

http://www.makcotransmissionparts.com/A904.html Good source of parts.

http://www.summitracing.com/parts/tci-141350/overview/ good converter

http://aandatrans.com/Products/904-Aluminum-Multi-Spring-Retainer-Kit__K12985BA.aspx

http://aandatrans.com/Products/904-...-5-Thin-Frictions-(1972-Up)__MK12000BK-5.aspx rebuild kit with 5 pack clutch.

The front drum could be modified to accept an extra clutch by a competent machine shop. I like to add a large aux. cooler inline with the stock cooler, and a deaper trans pan like off of a A-500 or an aftermarket one. Transgo and fairbanks make excellent shift kits, and Sonnax makes a bunch of improved parts.

Rockauto.com is a good source for transmission parts as well.

 

[Locomotion]

A firm shifting transmission will help it live. As an extra measure of insurance, you can add an extra transmission cooler. Heat is the biggest problem. I like synthetic fluids, like Amsoil, because the stand up better to heat, lubricate better and reduce friction.