I have a 1990 Ford F150 pickup 4WD with 5 liter engine.  Manual trans.
I bought it a year ago, and it's been a lemon.  I had to replace all
the 4WD U-joints, one shaft, one lockout, several front end parts and
the front brakes rotors and calipers when I got it.  This cost almost
as much as the truck cost me.  The following month I had to replace
the starter, then the exhaust system fell apart, then the ignition
switch, then the seatbelt came loose because the floor was so rusted,
then the master cylinder, then the center (driveshaft) bearing on the
rear end, then the rear brakes and parking brake cables, and this dont
include tires and a new battery. as well as the dead fuel pump and
tank leak in the rear tank which I never fixed.

I just finished changing the water pump last week when I noticed
grease running out of the rear end at one of the wheels.  On my way to
the mechanic that rear wheel started on fire.  It turned out the
bearing was completely gone, and the axel wore right thru the rear end
housing.  My mechanic told me to put in a used rear end would be at
least $600 for the rear end and installation, plus the brakes are all
burned up again, and will need a complete new brake assembly and
cylinder, and there could be more costs. Needless to say, I am not
going to repair it.  I'll sell the engine, trans, (both are good), the
new 4WD parts, and take off the tires.  The rest goes to the junk
yard.

My mechanic told me that the rear ends on the late 80's early 90's
trucks were all junk.  That's why it costs so much to replace it,
because they are hard to find in scrap yards.  I find it hard to
believe that they make such crappy rear ends, because I have never had
a single problem with the rear end in any other vehicle I have ever
owned.  (Ford, Chevy, and Mopar).  

To prove they are bad, the guy who sold me the truck said he replaced
the rear end too.

I was just out looking for a new used truck and found a 1994 F150
pickup with the same engine.  It runs good, has an automatic trans
instead of the manual, and has push button 4WD instead of the shift
lever.  The body is in much better shape than my old truck.
What bothers me is whether it has that same rear end.  If it does, I
dont want it.

I cant afford a real new vehicle, the early to mid 90s trucks are in
my price range.  However if they all have the same crappy rear ends, I
may buy a GM truck instead.  I saw one of them that was a fair price
and runs well.

Does anyone know the details about the Ford rear ends and the years
they changed to a new style?

Thanks