I wonder if someone here could again offer guidance. I have managed (I think) to change my ring and pinion unit but somehow reinserting the 4 beveled differential gear is giving me a hard time. Or maybe it was a long day. If one of you could indicate a step by step functional approach to putting these components together I would be grateful.

Haybayian

 

I've never done a 7.5" diff before, but I've done a couple of 8.8" and 9" diffs, both open and limited-slip. I don't recall any major difficulties in re-assembling the spider and side gears. I think you first place the side gears in place, and then sort of "roll" the spider gears in between them to the correct positions. Once they're in place, slide the cross shaft through them (and the carrier), and install the lock bolt to keep the shaft in place.

By the way, I just cleaned out the 9" diff on my 69 Mach, and I am starting to wonder whether it really is easier to work on than the new 8.8". I had to pull the axle shafts, and struggled with those collapsed copper washers for about 1/2 hour before being able to try to pull out the 3rd member. I had forgotten how heavy that sucker was, and working under the car did not provide much leverage to manipulate it. For what I was doing, cleaning out the housing, the new style diffs with the rear cover plate would not have required anything other than just removing the plate. When I was installing it, I had to use a jack to help get it into position.

Maybe I'll get a better idea if I ever have to replace the gears in the 8.8" diff.

 

neither Haynes or Chiltons are any good on their coverage of rear end diff work

rent or buy Differential Rebuilding by Paul Zank, avail online

detailed coverage of backlash ring/pinion setup and diff. teardown/assemble

 

I have the factory manual on CD. I'd have to check at home if it has the instructions on this job but I'll wager it does

eBay Motors: FORD AEROSTAR 1993-1994 OEM Service Repair Manual CD (item 8060254072 end time Jul-14-08 07:01:16 PDT)

 

i just bought one of those cd's... yay!

 

Are you referring to putting the gears back into the differential carrier (which shouldn't have had to come out for ring & pinion changes). If that's the case, XLT's description is correct. The side gears go in first, then the spider gears can be rolled into place. If you have an LSD, then the Z-spring has to be inserted after, then the cross pin goes through the spiders.

However, my first impression was that your question was regarding installing the differential assembly as a whole into the axle, now that your new ring gear has been bolted to it. Is that the case? When doing that, the shims on either end are thick enough to cause about an .008" interference (typically). This puts a preload on the taper-roller bearings. But it also means that the diff doesn't just drop in, even if you get it aligned perfectly. What I normally do is this:
1) place both bearing races over their respective bearings
2) hold the left side shim against the bearing race
3) place the diff/ring gear assy into the axle
4) bolt the left side bearing journal cap on to hold the diff in
5) use a prybar/screwdriver to lever the right side bearing race against the bearing
6) tap the right side shim into place using a soft mallet (careful - they're cast iron and can fracture)
7) bolt on the right hand journal cap

Then you go through the normal c-clip install routine, etc. All of that said, if you changed the ring and pinion gear set, you will have to go through the trial and error of reshimming the differential to set lash and verify that your new gears' contact pattern is correct. That means going through the above procedure several times...