A common fault on the early R380 gearboxes was the 4th gear baulk ring. The slot locating the synchro slipper wears and allows the baulk ring to rotate too far. This blocks the synchro assembly. It will be necessary to rebuild the gearbox, and replacing the baulk ring with a later type will eliminate this fault.

The most common cause is worn mainshaft spline but other things to check the A frame ball joint and the halfshaft drive flanges, especially if you have a 300 tdi Defender. To check mainshaft spline wear remove the PTO cover and with the main box in first gear rock the car backwards and forwards whilst looking into the end of the input gear. If the spline is worn you will see movement of the shaft in relation to the gear. Replace the gearbox and transfer box input gear (use a cross drilled gear to prevent recurrence of the problem).

There are three possible problems. 1) The mainshaft spline has worn away and is not engaging in the transfer case input gear, (most common) 2) the centre has torn out the clutch friction plate or 3) the mainshaft has sheared just inside the rear of the gearbox. 1) and 3) will require a rebuilt unit.

The layshaft extension has sheared off effectively disconnecting these two gears. You require a rebuilt or new gearbox.

We recommend MTF94 in your R380 box.