Disco I - failing differential?
 

Out for a drive on Saturday and then just about 3-4 miles from the house doing about 50 mph... I hear something hit the underside of the hood and I 'think' the sound of something hitting the road. Immediately, A/C goes from cold to hot. Battery Light comes on. Temp Gauge starts to rise. Immediately suspect serpentine belt failure; turn off radio and a/c. Roll down windows and kick heater on high, finish the drive home.

Problem really starts once I pull to a stop in my drive and shift to reverse to back into parking spot. Nothing. Shift back to drive. Nothing. Car won't move. Try it twice more... then shut engine off due to heat. Pop the hood to help things cool down in the breeze, as suspected serpentine belt is off. Not shredded as suspected, but off the pulleys. Culprit? Tensioner pulley center cracked and belt slipped off. Replaced pulley, waiting on new belt (felt it best to just replace though not torn) but for now put old belt on.

Start Disco up, put in drive... won't move. Reverse... won't move. Check fluid level... just fine. Have someone shift car thru gear range while I check out transmission linkage for slippage... no problems. When started and shifting to drive or reverse, it sounds like something spinning but not catching. Double check that differential is in 'unlocked' high, won't move. Try 'unlocked' lock... wont move.

However, when I LOCK the differential: differential lock indicator lights up on console panel as expected and Disco will move in both drive and reverse. Great. Why isn't it moving when differential is unlocked in high or low?

Any ideas on what the issue could be or what simple solution (hopefully) is evading me?

Mileage just over 138K.

Hey there.

If your truck moves when the diff is locked, but not when it is unlocked, it means that either your front or rear drive shaft (or the thing leading to/from it) is messed up in some way.

When the center diff is unlocked, power will go the wheel (front OR rear) with the least resistance. If you had a broken axle or CV joint power would find its way there and the truck would not move when the center diff was unlocked.

With the diff locked, power is split evenly between front and rear drive shafts.

So first thing to do is visually inspect your front and rear drive shaft for damage (and to make sure they are both still there!).

Then I'd try to determine if they are both spinning when the center diff is locked. Get a helper and drive the car a few yards withe the diff lock engaged. You want to be sure both front and rear drive shafts are spinning. If one is not spinning when diff lock is engaged you have a center diff problem (not likely but need to rule it out).

If they look OK and spin, I'd take one off and see if the truck moves with the diff locked. If it does the one you took off is where the problem is. If it doesn't move, the other side is where the problem lies.

I STRONGLY suggest you post in the "Discover I" section of this forum. You'll get more views and better answers.

Welcome to the board!