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MG MGB Technical - Heater Parts

Hi

I have a 74.5 MGB which I have owned for many years.
I recently removed the heater to have the heater core repaired.
As I was re-assembling the assembly I noticed that the defroster hose was just inserted into the holes through the firewall, but didn't insert into the actual heater itself.
Looking at the Moss schematic http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29084
I see there are a couple of parts I don't have. The connector tube and the defrost elbows.
Is every MGB suppose to have these parts?
As I look at this set up further I see that the air is being forced over the heater core and down into an area between the firewall and the heater unit. If the heater gasket between the heater body and the shelf is not air tight (Mine isn't), then the air will not be forced through the tubes proberly.
Or am I missing something here?

Bruce
Bruce Mills

Hi Bruce - I suspect your car is similar to mine (73B) with same dash etc. I have two corrugated tubes that lead from the bottom of the heater box up to the defrosters at the base of the windshield. In my car these tubes fit into circular openings, albeit fairly loosely. I don't have the separate connector tubes, or the elbows, I have one-piece tubes. If I recall correctly, the amount of air that gets into the footwells is dependent on a decent seal around the top of the heater box, which is why there is the large foam padding around the box (which it so happens, tends to make it very hard to remove and replace the box).
When I was reinstalling my box last year, I used alittle grease on the foam pad (after 30 mins of swearing at it for not going even close to into its home) after which it slid right in. My car had the extra clearance for the cable to be attached first before trying to push the box down. Some cars don't seem to have this, even cars built after mine. If yours doesn't, enlarge one of the holes (search the archives on this, there is lots of info on this) it avoids the extremely difficult task of hooking up the cable to the flap later on.

The more work I do on my B, the more I am surprised the engineers didn't make things easier on their assemblers, by simply designing things alittle differently. The heater box is only one of those things!

Erick
Erick Vesterback

Hi Erick

Your car sound like it is the same set up.
Is the foam you are talking about the heater outlet seal? I got mine in the same way, a bunch of swearing, taking a step back and then it slid right in. Must be the swearing!!

If I remember correctly the first time I did this job I replaced the heater gasket but it wasn't a very good fit, the back of the gasket folded over and really didn't seal anything.

If my heater box was sealed better between the heater box and the engine bay shelf the defrost would work better. But I don't see how that is possible with the parts which are offered on the Moss page.

I wonder if it is possible to add the connector tube and the defrost elbows. If so, then this would be an upgrade I would think

Bruce

Bruce Mills

As long as the tubes from the defroster vents reach into the two holes at the bottom of the heater box (holes are about 1.5 inches in diameter I would guess) you should have good airflow to the windshield. In my car the flex tubes run from vent to heaterbox, could be that a PO had replaced the tubes and the elbows with this tubing. The tubes/elbows push into the heater box right behind the radio, in fact my radio actually dents into the flextubing coming out of my heater box. The seal of the box in its hole in the firewall (the hole which is so difficult to remove the heater box from) won't matter for the defrosting, that seal only matters for the footwell airflow, as far as I know. I hope I am making sense.

Erick
Erick Vesterback

After talking a closer look the heater set up last night I discovered the defrost tubes go into the recess provided by the heater outlet seal. So there is only one place for the air to go. To the windscreen.
The flapper inside the heater has three positions. The first position directs air only through the defrost tubes. When the flapper (2nd position) is vertical, the air goes through to the foot wells. It is curios because the defrost tubes are not sealed off in this position so air/heat is probably still going through the defrost tubes as well.
It is also interesting that the Chicago club http://www.chicagolandmgclub.com/photos/b_heater/
mentions a "thicker foam rubber strip to be glued to the back of the box just above the flanges to seal the fourth side of the box against the vertical bulkhead" but I am unable to find this part listed with 3 MGB parts dealers.
I cut a piece of pipe insulation cut to suite to seal this area.
And finaly it looks like converting to the elbows and tubes will not only not work, but be a step backwards.

Thanks for the help

Bruce

Bruce Mills

If you can get a seal around the heater ducts you get a huge improvement of demisting ability. I used black gaffer tape and some foam rubber at the bottom. You need to tape every join, including around the vent join.
Previous to doing this the dimister was that in name only.
You might also use some windscreen sealant around the various joins of heater to car. That black stuff that never sets completly. seals nicely, but doesn't make it too hard to get the heater out again.

I have seen people make up a flat plate with two PVC elbows glued into it. They attach this to the outside of the forward tunnel support.
Peter

This thread was discussed between 01/05/2007 and 05/05/2007

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