Need help on ford differential, RWD

[95SleeperAcheiva]

2000 Lincoln Town Car, 295852 miles. It's a non-stretched limo. Think of it as a really nice taxi.

there are 6 trailing arms on it. 4 regular front to back, 2 that go across the car left to right.
Bushings were shot, replaced all of them. Car no longer feels like it has rear wheel steering, this is a good thing. :P

Next, rear diff had a constant gear whine to it. Sounded like a gyro compass spooling up, or a little jet engine.

I went to junk yard (pull-a-part) and yanked the only rear end within 600 miles of me (cleveland oh).

I was going to just swap the rear ends. Started taking off brake system of replacement rear end and discovered axle bearing had failed and axle chewed through differential tube. Pulled the cover off and inspected rear. Ring and Pinion looked better then what i had in car, spider gears looked good too. So I figured to just swap the guts.

So I gutted original rear end. only thing i left in there was the pinion races, and axle bearings. Installed new axle seals, installed new outer pinion bearing on junk yard pinion gear, inner is a press fit and so are carrier bearings, they looked ok, no excessive play, so i left those alone. Installed new crush sleeve on pinion, new pinion seal, installed pinion, torqued flange and flange nut to spec, 21 inch lbs of pinion bearing pre-load.

installed junk yard carrier with junk yard bearings, races, and spacers, torqued carrier bearing caps to spec @ 77 ft lbs. Using magnetic base and dial indicator measured carrier lateral play, perfectly within spec at .004". I couldn't get gear marking compound anywhere close and was on time constraint so i packed about 6 of the ring gear teeth with white grease, spun the rear end and looked at the tooth strike pattern...as she said in, "My Cousin Vinny"...... "Dead on balls accurate!" center of tooth on front to back and depth, perfect. Filled with Valvoline Full Synthetic 90W120.

Bitch still whines. But! Only whines under load/acceleration, doesn't start whining till 30 mph, increases in pitch all the way to 85 mph then wind and road noise drowns it out.

This is the first rear end I've rebuilt. I've seen it done, but this is the first for me. What did I do wrong or miss?

[86FieroSEv6]

You did everything right . . . . . for "new" gears, that is. Those gears being used, needed to be setup on their established contact point. By setting them up to spec, you have shifted the tooth contact enough to cause a load "whine". Try a little Lucas heavy duty gear lube treatment and see if that will help with the noise . . . . . . . 'cause it ain't ever gonna go away.

[GEN II JBODY]

Just pack it full of banana's. Works every time LOL.
free bump

[95SleeperAcheiva]

so a new ring and pinion, install kit, and about $400 should fix it then?

thx for the intel, i'm going to try the lucas first.

I had a 12-bolt in '66 olds 98 fail with heavy chatter, 3rd day i drove the car, about 12 miles on it. I only paid $400 for the car, gave it a tune, rebuilt the carb, body was in good original condition. I packed the rear-end full of un-sliced chunks of bologna, saw dust, wheel bearing grease, and finally got about a quart of gear lube in there. Drove it back up to the dealer that sold it to me 3 weeks later. They gave me $750 for the car. I really would hate to be the poor tech that opened that cover back up weeks later....eeeewwwww!