Front Differential

I've owned a 1998 Ford Expo. for the last 2 years. Since day one, I get a grinding noise from the front end, while accelerating through a turn, either right or left, from a stopped position, such as a stop sign or a traffic light. If I go straight, there's no noise. Or if I'm at speed and turn, there's no noise. Only while accelerating, and turning the wheels.
Over the past 2 years, I've replaced both front drive axles twice, thinking the first set were poorly reconditioned. When that didn't work, I replaced both front bearing and hub assemblies. That also didn't work. I tried changing the front differential lube, with a high quality synthetic lube and an additive for posi drive diffs. none of these things made any difference. The only things left are the forward drive shaft, and the front differential itself. Has anyone had this problem? Did you ever figure it out?

what hub setup does that have? the full auto or auto/manual override?

I'm not sure which is which. The hub and bearing is non serviceable, and must be replaced as a unit. (which I did.) Then a drive axle with a splinned shaft on the wheel side, inner and outer CV joints, and a flange on the differential side (pumpkin). The pumpkin has a vacumm diaphram w/2 lines, that lock and un-lock the diff. depending on where your electronic selecter is set. 2WD, 4WD, 4WDlow, auto4WD. When you switch to 4Wd, your engaging the transfer case, and locking the front diff. When in 2WD, as long as the front wheels are spinning, your turning the drive axles,CV joints, flanges, and I imagine also the front ring and pinion, and spiders. But it's not locked up by the diaphram, so each front wheel can spin independantley.
My old Bronco had the manual locking hubs. When you shifted the lever to 4wd, to engage the transfer case, you still had to get out and turn the lockers on the hubs. I changed them to auto lockers just before I traded it in.
This Vehicle has a completely different setup. No locking hubs.

Hey man I had the same problem but for the rear. Tripple check the specs on the fluid. I had put a GL5 80w90 (non syn) in the rear 10 miles prior to your description.
I checked the tag in the diff and i was mistaken. (Specs -Specs- Specs) It called for a 75w140 syntec no additives. Problem gone.

Thanks for the reply. The front calls for 70w 90, which I thought was kinda light for a gear oil. But I changed it, later I added an additive for posi rears which made no differance. And recently, I changed it again, with a LUCAS product, which wasn't cheep, and that didn't help.
I've noticed that in the winter, it takes about 10-15 minutes of driving before this problem occurs. In the summer, it happens more quickly, on a hot day it happens as soon as I start driving. As if the temp. affects the viscocity of the lube. So you may have something there. The only things I haven't changed are the front Drive shaft and the front differential itself. Trying a thicker lube is definitly much easier, and less expensive. I'll keep you posted.
Thanks