A while back i changed my rear differential from a 4:10 to a 3:55.
its been running great with no noise from the rear axle as far as i can tell.
today i had some issues on my u-joint, and while the rear axle was up on jackstands i noticed a problem with my differential:

while in gear and the brakes loose, i can not turn either wheel.. i should be able to turn one wheel in one direction and the other turns in the opposite?

with out of gear and blocking one wheel, i can not turn the axle... its like i have a locked differential.. any thoughts?

 

If I understand your situation correctly, this is normal. My assumptions from your statement:

1. Engine is off.
2. ZF is in gear.
3. Parking brake is released.

If this is the condition you're talking about, the rear wheels will not turn because they are locked in running position by the driveline. Place your ZF in neutral and try it again. The wheels should turn freely with the parking brake released and the transmission in neutral.

 

Doe your truck have a limited slip, or is it an open diff. With an open diff the tires will spin in opposite directions while in gear. With a limited slip or some kind of locker they will not move.

 

engine is off, zf is in neutral, i can turn the wheels, but both spin in the same direction.

if i put it in gear, brake off, i can not turn one wheel.. shouldn’t the other one turn in reverse?

i am not aware of a limited slip and i do not have a locker. It is a stock sterling 10.25 with 3:55 gears.

 

I'd say it has a limited slip of some kind in it. If not you would be hearing some pretty wild noises

 

Well let's hope it does has a limited slip... Don't want to have a bad diff

 

Check this out: https://www.ford-trucks.com/forums/1...xle-codes.html

 

thanks Glenn,

that makes me feel better.. this is what i have per code

D5- Ford Sterling 10.25 dual rear wheel 4.10 with limited slip diff (7400 rating)

so, when i changed the gears i guess i was just to ignorant to realize i got limited slip

 

You bet Stefan, I like the limited slip! Mine once was making a lot of noise on tight turns. I put one of those Ford little bottles of limited slip in and no problems after. Warning, that stuff stinks!!!

 

speaking of which. Always add the friction modifier to your limited slip when changing the oil.