The Model T service book basically sais to throw the pieces together, but the Macs catalog has a note that sais the back lash between the pinion and the ring gear should be .005". How is the back lash set when assembling the drive shaft to the diff? Is there a way to set it with the differential together?
I rebuilding my first rear axle and there is many items to be checked and/or adjusted. I think that you should purchase a copy of "The Model T Ford Front and Rear Axles". It is a fine publication that the MTFCA club provides for about $10.
This will help you with most any question you may have. Then when a more specific question comes up this forum is a wealth of knowledge.
The book that Mike talked about is a good investment. Also the Model T Ford Service Manual, available from the parts suppliers, is good as it tells you how Ford said it should have been done.
Just looking at it, there is side to side clearance inside the rear axle housings, which is pretty much set. If you feel too much clearance or it is bound up, something isn't right. What probably has happened, is something has too much wear (rare) or a thrust washer has gotten off of its pin to cause binding. I don't use a gasket in between the axle housings, just Blue Permatex on final assembly.
The driveshaft assembly, by itself, has allowable end play. If I remember right it is like 0.005". If you put a new bushing in the front of the driveshaft housing, you may need to "face" it to bring the clearance in. (Make sure the back end of the u-joint is smooth as it is a thrust surface.) At the same time you need to work this in concert with the position of the pinion gear in relation to the ring gear. Various thickness of gaskets can be used move the pinion gear either in or out of the ring gear but you need to keep the end play of the driveshaft within tolerance. It may be you won't use a gasket in either the front or rear of the driveshaft spool. Gaskets in various thicknesses are available from industrial supply houses. You can get like 0.003", 0.004", 0.005", etc...just about any thickness you want. They might give you some drop offs of various sizes up to 0.015". I assemble the driveshaft to the rear end with some Prussian Blue on the gears. The bluing will tell you where the gear is running...too far in, too far out, etc. Make a complete revolution. You want the pattern to run in the center of the tooth with an even mark along the entire tooth length. When it is right, there is very little play and no binding as you rotate the u-joint on the assembled rear end. I use Blue Permatex between the driveshaft spool and the driveshaft housing on final assembly. It takes a while to set one up right. I assemble/disassemble, at the very least, 2 dozen times on a normal rebuild. The alternative might be to look into one of the driveshaft bearing set-ups that John Regan sells.
Here's my experience. Re side to side differential clearance, you usually have to mill the face of replacement thrust washers to get acceptible clearance, .005-.010". Re ring and pinion mesh, Ford originally set them at .020" lash, but most folks want them closer, .010-.015" is about right, although I have asembled good parts without shims and they work just as well. The parts houses sell a spring steel shim you place behind the ring gear. It usually takes one .010" shim.
I used to play with the depth of the pinion but found its not necessary if you have good parts. If you wish to do that you can increase the distance by adding a shim between the lower lip of the spool and the RE housings or a smaller diameter shim just ahead of the DS thrust washer to close the distance.
The rule is don't get things too tight. If you have any tight spots when turning the ring gear by hand before installing the DS, eliminate it.
It might be the side to side clearance is too close (remember the differential cage and RE housings are not perfectly square after 80 plus years) the axels are bent, the axel roller bearings are binding, etc.
One thing hardly mentioned is bent tubes in the axel housings. According to one knowledgeable source, most all are bent to one degree or another. That's pretty much been my experience. I recall one set of housings that were sprung. Before I knew about checking for straightness, I tried shims everywhere you could think to eliminate the whine, (either at acceleration or braking or both) including tapered shims, but after a couple dozen attempts, just gave up and found another set. Now I have a jig I use with a lathe to measure run out and straighten them.
Like a lot of things with a Model T, you can get an acceptible job easy, but to get a truely quiet rear end, its tough.