Gearbox Removal

  1. Remove front box joint (see elsewhere)
  2. Remove final propshaft (see elsewhere)
  3. Remove transmission brake (see elsewhere)
  4. Support the gearbox using the tool labeled “gearbox lowering thingumyjig” by bolting it onto the EBCO jack and jacking it up under the gearbox.
  5. Remove the eight bolts securing the gearbox to the sub chassis.
  6. Lower the gearbox. Ensure the selector rods clear the linkage, once they are clear slide the jack forward so the output shaft clears the transmission brake assembly. Ensure the gearbox does not catch on the speedo cable.
  7. Carefully draw the jack out from under the appliance.

Since the new transmission brake was fitted it has been decided it SHOULD NOT be removed from the gearbox output shaft.

To do this the transmission brake shoes must be removed, then with the aid of some wiggling it is possible to remove the gearbox with the brake still attatched.

Gearbox Disassembly

  1. Remove the four bolts securing each of the four plates on the ends of the gearbox.
  2. Pull these plates away from the gearbox.
  3. Remove the 14 bolts holding the two gearbox halves together.
  4. Separate the gearbox halves.
  5. Remove the end-float spacers from either end of the layshaft.

Removing the shafts

  1. Remove the layshaft, by lifting it out of the lower gearbox half.
  2. Remove the Gearbox input and output shafts together, being careful they do not separate in the middle, and they do not catch on the selector forks.
  3. To separate the input from the output shaft simply slide them apart, but be careful not to loose the large ball bearing nesting between the two shafts.

Gearbox Detent Mechanism

In order to keep the fire engine in gear and to prevent the possibility of two gears being selected simultaneously the selector rods have notches cut into then into which a sprung loaded wedge is forced by a spring. In order to prevent possible catastrophic failure it must be ensured that these are operating correctly.

Loose movement of the lever is an indication of a failing detent mechanism; a stiff change can also be an indication of a problem that may lead to later failure.

The failure can either be a flattening of the selector rod or a problem with the sprung wedge assembly. The sprung wedge has a mechanism to release the hydraulic pressure resulting from the build up of oil under the wedge.

Dismantling the detent mechanism.

Either drain the oil from the gearbox or be prepared to plug the hole immediately after removal of the assembly.

To access the middle assembly one of the side assemblies must first be removed to allow access.

From the underside of the gearbox the first stage is to remove the brass dome nuts from the assembly. These have slots cut in their mating surface to allow oil flow to prevent hydraulic locking.

The lower end of the detent wedge can now be seen, it is prevented from moving by a pin through the assembly, this must first be removed to prevent shearing it when unscrewing the assembly.

The assembly can now be removed for investigation.

Lift out the wedge examining it for excessive wear.

The spring can now be examined to see if it is still intact.

Reassembly is the reversal of removal. The alignment must be checked however to ensure the detent wedge is not locked up by the anti-rotation pin.