I could see my clutch packs from the same angle as picture. I say it's an open. Really just guessing. Spin the wheels.

 

Ok, First : reason i pulled dif in first place was because of grinding roaring in reverse just after i got truck.

Second: i have the truck parked in my driveway which is on incline, so to test by jacking up rear to turn wheels would mean putting in neutral... then truck would run over me as i lie underneath .. doh ..ouch.

Will try and get better pics Or just fill and with oil and additive no matter what ? I'm Trying to assess drive gear whilst its open, so sealing it back up voids that chance..

 

It's about grip, not power. If there is equal grip with both drive wheels, both are likely to spin. If you were to have one wheel on grass/dirt and the other on pavement/concrete and hit the gas, then you'll know if there's an LSD or not. Open will spin only the wheel on grass/dirt (less grip). LSD will leave a mark on the pavement/concrete also. Providing the LSD is operational.

 

Put cover back on and fill diff with all but a few ounces. Drive to safe place to block front wheels, and raise rear tires of pavement. From side of truck by hand spin one tire, and look under truck to see if other tire spins the same direction. If you can bring someone along, have them try to hold the other tire while you spin the one by hand. Both tires spin together equals LSD. Add as needed additive or/and gear lube to top off.

 

However, if clutch pack is shot, as my truck's was at 140,000 miles, the LSD action was almost totally gone when checking by hand. On the road, the diff was only as good as an open diff.

 

Ok, got in there again, and i DO see clutch plates behind both gear wheels, tucked in there mind, so IT is a LSD right ?

It was a elderly gent 2 owner truck, sat for 6 months, 150K on motor, have not yet got to all other fluid changes yet (trans, oil, steering) Or brakes, u joints etc.

Appeared to go through all gears ok, visual and smell test check on oil and trans fluid seemed fine, brakes are nearly gone and then 2nd day getting it back from previous owner, after i'd been driving about 20 mins stopped to pick son up with truck idling and then backing out from driveway was when i heard grinding. Got it home and immediately pulled dif cover and drained and here we are ....

So,
a) if clutch plates are shot would that explain grinding in reverse ?
b) Would old *** oil maybe without additive explain grinding ?
c) Other ?... Anyway to truly determine if dif/clutch is good ?

 

I think there is a test procedure in the service manual for the LSD..... the clutch retaining clips like to break as well. Didn't find anything odd in the bottom of the diff did you? lack of friction modifier will generate some interesting sounds, but, only when turning. (direction doesn't matter.)

 

You don't get any grinding in forward motion at any speed? How about very slow like 1-3 mph?

Since you've done visual check and nothing was blatantly obvious, I was thinking the clips that hold the clutch pack together is what is grinding. They have a tendency to break and can either get meat gratered up in there or actually stay in the pack and just smooth out the clutch face that it's in contact with.

Here are pics of mine back at just over 100K miles or so.

The fluid does need an additive to be added to the gear oil. It also has to be the proper amount, which is all stated in the Haynes manual (iirc) and for sure in the FSM (free download file in the FAQ/DIY section).

Your grinding could be something totally different too.

 

Check the brakes.

 

There is a torque wrench test to check the torque needed to get the clutch pack to slip between the right and left sides.