Herald 1200 air distribution box refurbishment

[Morgana]

This has never worked in my ownership. In fact, on the test drive I pulled the air direction knob out of the dashboard as it wasn't hooked up to anything...

Having had the gearbox tunnel cover off I decided to do something about it, and thought putting my findings here for reference may help someone else. The flap that approximately directs the air is formed of two plates riveted together with felt seals clamped between them. The flap couldn't move as the felt seal had come partly out and was binding against the box. My box looks rather less fancy than the one in the manual, which is perhaps a later cost-cutting measure.

I drilled out the rivets, cleaned and repainted the plates and cut new seals from some 3mm felt offcuts I had around. I tacked them in place with some contact adhesive before pop-riveting the plates back together. The self-tapping screws that held the plates to the spindle that connects to the operating cable were either non-original or very worn, as the whole thing was slopping about. As the spindle has a hole all the way through, and the plates are symmetrical, I used some 4BA machine screws and nuts as a more secure option. I would have used some #8 or #10 UNFs had I got any to hand, but at least this is still a bit 'period'. After a small amount of trimming, the flap can be pushed over to each position easily by hand.

The screw that clamps the operating cable to the trunnion was patently wrong as it didn't clamp and the threads were stripped. I ascertained the correct thread was #6-32 UNC. The workshop diagram looks like it could be a slotted hex head, but as I didn't have one I used a slotted pan, which ought to be workable to adjust the cable even when upside-down under the dashboard...

I got it in, then discovered I hadn't trimmed the top of the upper felt seal enough, as it binds on something in the heater box when trying to flip the plate. However, with a trip to go on it'll do for now and I'll investigate it on getting back.

Edited October 6, 2023 by Morgana

[Colin Lindsay]

Nice job! I did that over Lockdown with one of mine, the felt had fallen out and was blocking the movement completely. It's great the way the flap just slides out once the screws are undone.

[Morgana]

I still haven't got this working satisfactorily. I've trimmed the felt down several times, as it moves freely off the car and binds as soon as it's inserted and the nuts put on to fix it.

Now I'm struggling with the air distribution control on the dashboard. It pulls out fine, but on trying to push it in the outer cable sheath just moves back with the inner wire, thus failing to push the flap back. There is no way for the outer sheath to fix to the control slider, as it's only clamped at the distribution box end.

Should there be something else to hold the cable hard against the dashboard control?

[Pete Lewis]

that end is a sort of crimped fit , i guess a dab of solder might help 

or araldite etc. 

Pete

[Morgana]

Aha, that would explain it if they're supposed to be a single entity. Funny, there's just a smooth recess on my switch housing with no hint of having been crimped or more permanently attached. Thank you.

[Colin Lindsay]

I've taken a couple of photos of spare cables to show what they're meant to look like; is yours missing a retaining ring? Can't be sure if there's another ring round those or just brazing.

 

[Peter Truman]

They look Di-cast so can't be brazed or soldered, on the daughters Mk2 Spit the heater valve push pull cable and knob was always missing why in Aus she needed one? but she insisted so I modified a choke assembly where the push/pull was brass but of similar action, I soldered the bowden cable outer into the brass assembly, and cable into the inner slider all works well and she's happy! 

[Morgana]

Well that shows very clearly that mine is not right. There's no sign of tampering, or a broken fixing or casting - yours looks very securely connected by contrast! I just have a clean recess down to the hex-reamed tube for the detented slider, and a smooth circular outer cable end. It certainly is non-ferrous, and has that greyish look of that die-cast alloy that doesn't take well to anything like solder. I guess I can try with some aggressive flux as there's nothing to be damaged by the heat, and those in your photograph do look 'wetted' by something.

There's no retaining ring marked in the exploded diagrams I've seen, but then the pictures are very small and the knob assembly is shown as one element.

Either it's something the PO got wrong as a replacement part (the grub screw it came with was a wildly wrong thread, too and this mechanism has never been connected so far in my ownership); or it's never been soldered.

[Wagger]

You may be able to Copper Plate the die cast alloy using copper sulphate solution and a battery. Connect the -ve side to the bits that you want plated dangled in the solution. You may then be able to solder the plated bits together.

The Triumph Speed Twin up to the 'Bathtub' models used this process on the front number plate and the tank badges to do Copper, Nickel then Chrome plating. It was a devil to replate these when I had it done in 1986.

[PeteH]

If it`s "MAZAC" (trade name) and likley is, it has a low melting point, around 350degC. It is a composition of Zinc (96%) and Aluminium (4%) with small amounts of copper sometimes added (up to 3%). Often known as monkey metal, or by me as sh!t. It can take plating as Wagger has said. Soldering? is problematic, but ocasionally an Acid flux and a clean/new wire brush, will work, getting the heat balance right though you need a BIG solder iron and careful preheating. I have tried back in the 60`s and it is very hit and miss, producing a low strength joint at best.

Pete

Edited December 24, 2023 by PeteH

[Peter Truman]

I recently fixed a part by making like a top hat that fitted over the sleeve/barrel and had the top of the hat with a hole in it that let the rod/cable slide through, this was then indented in the sleeve to stop it coming off. I hunted thro my bits and pieces and found a suitable brass part that suited,  bit of brass tube with a brass washer soldered over one end might work.

[Morgana]

Mazac! That's it! Well remembered. I can see soldering coming a cropper - a big Magnastat will be getting on for 500C and there's a lot of heatsinking going on. Mr Truman's mechanical idea is probably less likely to go wrong, if I don't crack the casting.

I just don't understand how it's never been attached, unless the switch mechanism and cable are the wrong parts, perhaps off a different car. The cable is the right length, and the cable sheath end fits into the casting, but that's as far as usefulness goes.

[Colin Lindsay]

Nothing worse than thinking it's fixed securely, and then once you try to pull it it all comes apart again. If you need a replacement, I have a few in the garage.

[Wagger]

Araldite may just be good enough. Push-pull cables always become tight if not used often. Grease the length and even fit a pull spring at the far end. That would compress the parts together and take up the slack. Finding the correct balance might be tricky.

[Morgana]

Thank you all for the suggestions. Mechanical attachment seemed the way to go, so I have attempted a mechanical solution which I'll mount in the morning. I think I'll need it as I'm off to Scotland tomorrow where the heater's probably going to be required going by the weather forecast.

I drilled four small holes around the circumference of the knob assembly, then mounted the cable sheath and continued the holes into it. I pressed 5/32" lengths of paperclip into the holes along with some Araldite around the circumference and the mating surfaces. I filed the paperclip ends off flush and finished with some adhesive-lined heatshrink. The knob can now be pushed and pulled with the distribution flap moving successfully.

I hope the shear strength of the paperclip pins will hold the sheath against the stress of pushing the knob, and the heatshrink/Araldite will prevent the two pieces moving against each other too much and loosening the pins.

Time will tell...

[Peter Truman]

well done, looks like a (good) plan

[Pete Lewis]

there should be a manual to show how many fixes have been achieved with the humble paper clip

my dad repaired his false teeth with them and the orig araldite 

will do for a start       

i often have one opened out to press tiny reset buttons 

Pete

[Peter Truman]

Araldite when repairing large wrought iron mains under pressure tapered timber perf pegs are impailed into the hole and then when watertight a patch is welded over the area

Around 25 years ago I was called out to a century old 36in main where the patch coupon had just blown off and the water spout was going around 60 feet into the air drenching a house but there was no sign of any weld, closer inspection revealed a whitish hardened paste on the main and steel coupon we reckoned someone in the early 60’s had tried this wonder glue Araldite! Well it did last 20 plus years!

[Wagger]

12 hours ago, Morgana said:

Thank you all for the suggestions. Mechanical attachment seemed the way to go, so I have attempted a mechanical solution which I'll mount in the morning. I think I'll need it as I'm off to Scotland tomorrow where the heater's probably going to be required going by the weather forecast.

I drilled four small holes around the circumference of the knob assembly, then mounted the cable sheath and continued the holes into it. I pressed 5/32" lengths of paperclip into the holes along with some Araldite around the circumference and the mating surfaces. I filed the paperclip ends off flush and finished with some adhesive-lined heatshrink. The knob can now be pushed and pulled with the distribution flap moving successfully.

I hope the shear strength of the paperclip pins will hold the sheath against the stress of pushing the knob, and the heatshrink/Araldite will prevent the two pieces moving against each other too much and loosening the pins.

Time will tell...

I could not have done better myself. Well done. Stronger than original, I suspect.

[Colin Lindsay]

4 hours ago, Pete Lewis said:

there should be a manual to show how many fixes have been achieved with the humble paper clip

my dad repaired his false teeth with them and the orig araldite 

I once had a loose front crown (back in my folkie days it flew out in the middle of a performance....) so more than once I stuck it on with Araldite until I worked up the courage to visit the Dentist.