I have a '71 Satellite with an 8 1/4 rear and the 904 it has will not shift to 3rd at all anymore.
But I have a 727 in my garage and im going to get it checked out/maybe rebuilt. I was wondering if anybody knew the length of the driveshaft I need. and the yoke too.

 

Why not rebuild the 904 ? High gear Clutches are probably fried. About 3.5"???? difference in the drive shaft You need to measure it AFTER you have everything installed. Install the Yoke and pull it out of the trans about 1 " then measure from the U joint center to center. There are two U joint sizes. small one is most common and what you need.

 

Unless you have "a lot of power" under the hood, I'd either find a good 904 or rebuild the one you have. There's a good book out.....

http://www.amazon.com/Torqueflite-72...f=pd_rhf_p_t_1

It specifically covers the 727, but much of it applies to the 904. I also recommend you buy an "ATSG" book. I think, you can find 'em cheaper on ebay than at their own site:

http://www.txchange.com/atsg.htm

Also, someone came across some EXCELLENT videos on Youtube I think there's 17? of them:

http://www.youtube.com/watch?v=xzJhCBZ1wMY

(I hate this new BS the way videos imbed---what I intended was to take you actually to the youtube page)

http://www.youtube.com/user/Autotransmissions