405 Series II Heater Cores

Heater core failure is a common problem in the 405 Series II and a rare occurrence in 405 Series I and the 406, which use almost the same components. I have heard many theories as to the cause but I have not come across a convincing explanation so far.

The worst case struck a reputable repairer around town where they replaced the core and had to repeat the repair three times in the following 12 months, under warranty. The painful thing about this failure is the time required to change the core using the factory workshop manual/Haynes manual instructions. It is a long and tedious job that involves the removal of the complete fascia, steering column and a multitude of electrical connectors (thankfully all colour coded and uniquely shaped so it is hard to make a mistake at re-assembly).

When dismantled, the front part of the cabin looks so bare that you could imagine you were at the beginning of the production line somewhere in England.  The first time you do the job you also have to deal with the vagaries and slight errors in some of the instructions in the manual. The job seemed to take me forever (more than 12 hours).

The second time was better; but even so it still took me about 10 working hours.  I have heard about taking a shortcut when changing the core by doing a little loosening here, bending there and cutting the odd structural piece of the fascia. This sort of bodgie stuff normally horrifies me - but this is an extraordinary problem and a well considered bodge is appropriate.

I recently had the opportunity to spend some time with a 405 Series II working out a bodge which will not drive subsequent owners and repairers to despair when discovering half-baked and careless vandalism waiting for them under the fascia.  My instructions are designed to be read in conjunction with the Haynes manual instructions for the job and are as follows:

  1. Remove the glove box from where it hinges at the bottom and the hinges from the metal support structure.
  2. Drill out the pop rivets holding the glove box surround in place, 3 at the top, 2 at the side, and 2 at the bottom. Drill out the 2 pop rivets that connect the front and rear halves of the surround, detach electrical connectors and remove the front half.
  3. Remove the gear stick surround.
  4. Remove the driver and front passenger foot well side panels covering the transmission tunnel.
  5. Remove 4 attachment screws for the centre console and move it rearwards.
  6. Remove the unit containing the radio and ashtray.
  7. Remove the panel containing the middle air ducts from the fascia. The ventilation control unit stays in place.
  8. Remove the bonnet release lever.
  9. Remove the fascia attachment screws from behind the air ducts (1 screw), at the front of the gear shift housing (2 screws), the right and left sides of the heater unit (2 screws) and the one behind the bonnet release lever.
  10. Locate the plastic structure connecting the right and left halves of the fascia just below the radio (when it is in situ) that has a tubular metal support behind it and has 2 pop rivets attaching the plastic to the tubular metal.
  11. Using a hacksaw, cut down through the plastic and tubular metal until the tubular metal is parted. Do not cut any further because you will damage the wiring loom.
  12. Drill out the left hand pop rivet and remove the metal support which extends from the cut you have made to the left hand fascia mount to the heater unit, below the glove box and all the way to fascia mount at the bonnet release lever.
  13. Cut the span of plastic which sits below the glove box in the middle.
  14. With some tolerable fiddling and flexing of the fascia you can now remove the pipes from the heater core and remove the heater core.

Reassembly is the reverse of the above with the following notes:

  1. (12) Rejoin the tubular metal support by fixing a sleeve inside the section you removed and locating it inside the section remaining on the fascia. Replace the left hand pop rivet with a self tapping screw.
  2. (2) Replace other pop rivets with general purpose screws and nuts except for the 3 upper glove box attachments where self tapping screws and those little devices that slide onto sheet metal and accept self tapping screws work well.

Bill McNamee