Contributed by Neil Sharp.
Remove rear seat, remove battery cover and disconnect battery.
Remove front seats (The seat "axle" is sprung at one mounting trunnion - usually the side towards the centre of the car. Press in the end of the "axle" - use a lever if your thumbs aren't strong enough - and pull the seat upwards and free from both trunnions.)
Remove front carpets.
Remove front floorboards. These are held in by machine screws set in cup washers. (If these boards are a bit "second hand", it is a good time to replace them. Use half inch marine plywood and use the old ones as patterns. Remove seat trunnions on both boards and (the brake rod cover on the driver's side board on a Briggs car) this cover is not present on the Barker model. Cut to pattern and hold together the new and the old boards. Drill the holes in the new board using the old ones as a pattern. Countersink the securing screw holes to take the cup washers. Refit seat trunnions and brake adjuster cover.)
Remove the gearbox cover. This is held in by short bolts set in to captive nuts.
Remove the transmission cover. This is also held in by similar short bolts and captive nuts. When all bolts are removed, grab the rear end of the cover and remove by pulling back and up, enabling the front end to slide down and clear the bulkhead.
Remove the speedometer drive and tie clear of the gearbox.
Remove the gear engagement lever rod and tie clear of gearbox.
Remove the gear selector lever rod from the gearbox and AND the quadrant linkage end. (otherwise it will get bent)
Remove the earth strap (replace if it is frayed - any motorists shop will sell you one for a few pounds)
Jack up rear of car and remove the propeller shaft from both ends and push back in to the transmission tunnel sufficiently to clear the gearbox. The rear end is attached to the differential by bolts with captive nuts. If these do not hold whilst attempting to undo the bolts, pein the captive nut covers to hold the nut more securely. Lower car back on to floor.
Jack up front of car.
Remove the starter motor bolts and rest starter on the exhaust. (no need to disconnect the electrics)
Remove all the bell housing bolts (two from the rear, all the rest from the front). Some of these can be really awkward and a long ratchet extension will help immensely with this job.
Lower car back to the floor.
Support the engine under the sump by placing a piece of wood on top of a trolley jack and jacking up to the engine until it JUST rests on the wood.
Remove the four nuts and bolts which secure the rear gearbox mounting to the chassis.
Remove the two bolts which secure the rear gearbox mounting to the gearbox and remove mounting.
This is where you need an assistant. With the aid of your willing volunteer, pull the gearbox backwards off the fluid flywheel twisting it slightly to the left to clear the end of the starter motor bendix and lower it FRONT FIRST on to the ground. Have a rest, congratulate your assistant and then grab the gearbox and pull up and out through the floor of the car. Take care not to tip it too violently or you will get an oil bath!
Place the new / second hand/ reconditioned box on the ground inside the car. While your assistant lifts the box up, (front end first to twisting slightly as when removing it to clear the starter motor) offer it on to the flywheel spigot, again turning it as required to ensure the gearbox spines line up with the spigot splines. A tip here is to use an old fan belt or something similar to help your assistant hold the box up while you jiggle it around to get it on the splines.
Once you have it on the splines, push it forwards and ensure that the two holes in the bellhousing engage with the two dowels on the engine face. Push the box firmly home on to the dowels and insert the two top bell housing bolts to stop it going anywhere.
Replace the rear gearbox mounting and
replace the two bolts which attach the box to the mounting.
Lower the jack.
This is important. Do it now before you forget. CHECK THE OIL LEVEL IN THE GEARBOX AND REFILL AS REQUIRED.
The remainder of the reassembly is the opposite of dismantling. Replace all bell housing bolts, refit the starter motor, refit the propellor shaft, refit or replace the earth strap, reattach speedometer drive, reattach selector and engagement linkages.
At this point check for the operation of the gearbox.
Put the driver's seat inside the car and rest it on the chassis. Start the engine and select each gear in turn, ensuring each one engages and does not either slip or engage too harshly.
If the gears will not engage at all, remove the gear selector rod at the gearbox end, select TOP on the quadrant, push the gearbox selector lever as far back as it will go and ensure the socket on the selector rod lines up with the ball joint on the selector lever. Adjust the length if required until all gears engage properly.
If any slip or harsh selection is apparent, remove the top cover on the gearbox and adjust each gear in turn until a smooth take up with no slip is obtained for each gear. The method of adjustment is described in the section "Adjusting the Gearbox"
Refit the transmission covers, floorboards and carpets, refit the front seats.
Road test.