Do you mean the differential, as in the rear end? Before you go spending loads of money on these problems try this out first, it may not cure your problems but it did mine!!! The servotronic steering became very heavy all of a sudden and shortly afterwards no speedo or mileometer. After a lot of fishing the problem turned out to be the speedo sender unit on the diff housing, and all it needed was cleaning (and best of all cost not cash) On the back end of the diff remove 2x19mm housing bolts (the diff will only drop a little to give you a bit more room) then remove 2x10mm bolts that hold speedo sender in place, simply slide out and clean plastic end of sender with WD40 and replace, and hopefully like mine all will work again, and again you will be able to turn your steering with your little finger! (also check yellow connector plug attached to sender unit) good luck!