405 Heater Box Removal

[peterf]

Hi and thank you to all those who took an interest in the 405 heater box removal.

Gerald (Brigham G), I think you may also find this useful, once I had the heater box out I decided to remove another 4-5mm off each demister tube so a good 10mm in total, so as to make the replacing of the heater box even a little easier by providing a bit more room for manoeuvring, without ripping or damaging the original felt insulating material that is attached to the bulkhead and firewall.

I then acquired some aluminum tube that would slip inside the existing demister tube, once the heater box was located back into position this length of tube, was, from inside the cabin then passed through the hole in the bulkhead into the demister tube. The rubber elbows were then attached as per normal to the new tube extensions. I am sure someone in another 60 odd years’ time will appreciate the ease at which they can now service the heater unit!!

My heater water valve which only has one arm (standard) was in pretty good shape with minimal corrosion, it was however seized. After separating the housing and then removing the diaphragm and after a week of soaking in CRC/WD40 etc. I then tried to gently heat the specific area behind were the diaphragm is located with some flame, careful not to end up with a blob of die cast aluminum at my feet. In the end the heat source that did the trick was one of those hot air heat guns that are used to plastic weld bumpers on modern cars; the type you can dial in the heat up to 900 degrees.

I sourced a rubber diaphragm from the local MG shop that happened to have a valve in pieces. A reassembly of the valve and attaching to the heater box on the work bench to test the operation and for any leaks before removing the valve and refitting the heater box to the car and then attaching the water valve again.

One point on the water valve removal, you will find that two 3/16 BSF single screw headed bolts are used.
One is located on top and the other below the valve body which is quite difficult to get undone, I replaced them with a normal bolt headed unit and cut two slots in the head (north- south and east west) now I was able to turn the head in quarter turns with a blade screw driver I also modified a spanner to allow it to get some purchase on it as well.

I am sure that you could use one of the later type water valves as described by others who have contributed to this thread but I was keen to see if I could continue with the original unit.
Job done, heater works a treat.

It was Stuart who said "Bristol made the 405 by first hanging the heater box from the work's ceiling" I tend to disagree, I think they liked the idea of starting with a ridiculous 3/16 screw head and seeing what they could add !!

Cheers

Peter

[BRIGHAM G]

Thank you again Peter.
I am making a careful note of all these good points.My car does not seem to have any felt in the heater/tool box area and wonder what type you use.
My immediate concern is to re wire the car completely.I have a wiring diagram but lack a layout for the looms to the tag strips on the right hand side and wonder if you have such a thing or indeed a good clear picture of yours which I could follow.
Best wishes, Gerald.

[peterf]

Hi Gerald,

The felt that lines the heater/tool box area on our 405 is still the original material, it is the same as what is used to line the boot. It is dyed black and quite fibrous, I have included a general photo of it on our 405.

Concerning the placement of the wiring loom, I am including a photo taken of another 405 that underwent an extensive rebuild that shows the loom attached to the frame with the front of the car removed - what a handy way to work on a 405 !! The same person also had easy access to his heater box as the firewall had been removed as part of the restoration of the car. Photo also attached.

If need be I could send you a small sample of the felt should you need it.

Cheers

Pete

[BRIGHAM G]

Dear Peter,
Thank you again for your most helpful reply.They say "a picture is worth a thousand words" which was the case for me. The picture of the wiring looms was spot on,it shows clearly that the fore and aft looms go in first followed by the midships one and lastly the one from inside.The felt should be easy to find now I know what I am looking for.
Best wishes,Gerald.