73 Heater Box Cracked

[73droptop]

After reading all the great advice on how to remove my 73 heater /AC box on the forum, I got it out without a lot of surprises. I put the box on my work bench and knocked it off where it dropped to the concrete floor and cracked. The crack is very clean and if I push it together I can hardly see it.

Any idea how to repair the crack? Other than the new crack the box is in great shape.

The internet says to clamp the crack, grind a small V in the crack and fill with resin. But I am not sure if that will hold up, I have no experience with fiberglass. Any help is greatly appreciated. I would be up for buying one if anyone had one in decent shape.



Sorry about the upside down pics, they are upright in my file.

 

[72HCODE]

fiberglass repair kit, Sand the area of repair, then Clean it REALLY well, mix up the resin and cut the cloth to the area, Butter the repair area with the resin, apply the mesh, then coat with resin, push together the repair as needed, use vice etc.. then adjust the mesh smooth, let dry, sand if needed.

you can cut a V if you want also.

 

[73droptop]

Ok, that sounds like something I can do, I thought I would need a patch. Thanks for the advice.

 

[piper62j]

I have found that fiberglass tends to release from the material these heater boxes are made of.. I use JB Weld Epoxy. Clean the area very well with 90 percent denatured alcohol inside and out and let it dry. This is critical because when these parts were molded, they used a silicone mold release agent, which tended to penetrate the material.. After cleaning, lightly sand each side of the crack, inside and out, 1 to 1 1/2 inches out on either side of the crack. No v-grove needed.. Mix the JB Weld per instructions and lather into the crack and clamp it together immediately.. The epoxy only gives you a few short minutes before it cures. I use a small woodworkers slide clamp you can get from Harbor Freight.. Let it cure and keep it clamped... Now, lather JB weld out on each side of the crack and overlay the seam with more of the epoxy.. Let it cure.. Repeat lathering it on the inside.. Build it enough to achieve a solid bond and sand it back for looks..

 

[judge]

I fix these all the time. I use a product called"Plastix" available from Eastwood. The black kit allows for almost an undetectable repair. It is an Acrylic powder.

 

[Pastel Blue]

.....

 

[73droptop]

I thought about JB weld first, I have used it for many years. Its messy but with the right amount of sanding it may work. My experience with JB weld is on hard smooth surfaces it tends to release, I know the housing is much different at it may work well, again I have no expedience with fiberglass.

Piper, that is an interesting note about the silicon mold process. Do you think a fiberglass patch will release even if I sand the area real well and clean it as you and 72Hcode are saying?

Judge, I dont see that product at Eastwood, and a google search didn't return anything. Do you have a link?

This car was restored back in 1995 ish and is still in excellent shape, I would like to replace the housing first then try the repair if I cant find a bottom cover in good shape to purchase.

 

[72HCODE]

you know another option if you just don't want to deal with it as a repair; they make a reproduction heater box now

http://www.cjponyparts.com/heater-box-assembly-with-air-conditioning-1971-1973/p/HBA6/

 

[73droptop]

Thanks 72Hcode, I see the new ones but I'm trying to avoid spending those kind of dollars and if I can keep OEM I am always happier with OEM. Ebay has a real nice original one at $400, I would buy that first. I'm in no rush, the car is in storage until the end of March. Either I fix it or Ill find a used one. I cant believe the self inflicted trouble I caused.

 

[Pastel Blue]

+1 for jb weld.

 

[judge]

found it Eastwood online catalog "Plastex" . I think that's the correct spelling.

 

[73droptop]

Judge thank you, I found it, I was spelling it wrong. Interesting product. With this product though I would be worried that without additional support the crack would return because it seems there is a lot of outward "spring" pressure. The crack goes to the end of the housing so I think once I take off the metal ring the crack is going to widen and that outward pressure will always be there. If the crack was on the side of the housing or not to the end I would be good to go. Using a glass patch or spreading JB may help keep it in place over time.

 

[Stanglover]

Ok, I'm flying blind here as I've not looked at the heater box on my car, so I don't know what material it is made from. Is it fiberglass or is it ABS plastic??? JB Weld make another excellent product for gluing plastic and that is JB Weld Plastic Bonder which is an epoxy type. The down side is it takes a long time to cure, so clamping the crack repair for several hours will be needed.

If it is ABS, personally I would weld it as it is a thermoplastic and I have the knowledge and equipment to do that. There are likely how to's on YouTube. At a pinch, you could "weld" it with a clean solder iron of about 80W, using a strip of the same material cut off from an inconspicuous area.

It sucks when these thing happen and it happens to all of us at some point.

 

[judge]

It's not abs or any plastic. It's a fiberous press molded something, more like masonite and thin particle board mixed. When it cracks or you ripe a mount out of it, it leaves a fiberous cavity that accepts the material I previously mentioned. You should try it. I use it almost everyday on something. I buy quart size jars of the stuff.

 

[Stanglover]

It's not abs or any plastic. It's a fiberous press molded something, more like masonite and thin particle board mixed. When it cracks or you ripe a mount out of it, it leaves a fiberous cavity that accepts the material I previously mentioned. You should try it. I use it almost everyday on something. I buy quart size jars of the stuff.

Ah, I see!! So they are fiber material. I'll keep that in mind should I need to make a repair. The product you suggested looks very good, so I'm sure it will help others.

Thanks for the heads-up,

Geoff.

 

[Carolina_Mountain_Mustangs]

The material is probably a thermoset molded material. You take a slug of the material heat it up either in oven or microwave toss into the cylinder and plunger forces the material into a heated mold. The heat and pressure cures the material. That is how lots of the electrical blocks you seen in transformers and things are made. They use pretty much anything as filler in the material. The heater box has long strand fiberglass in it.

They probably use carnauba wax for release agent that is what we used in our thermoset parts. The silicone causes too many issues in a mfg. plant to use it very much.

I think you should always vee out the crack from back side. It is like welding if you vee it out you stand a better chance for repair that holds. The box should not be under a lot of stress unless you drop it, lol. So about any repair that seals it up should work.

If you want to clean up the entire box you can blast with walnut shells and then spray with satin clear to look original. As stated wash thoroughly with Dawn and also alcohol to get any contaminates off.

Be sure to add the screen wire where it joins to the cowl to keep the critters out it is in a thread I posted last year search for it. Pic is included.

 

[Pastorpat]

They do sell new boxes. I think for around $300.00. I used JB Weld on mine with fiberglass cloth. Worked great. Make sure you have all the bolts loose. It will come out without much force. It you are forcing it stop and look for bolts and nuts. They do like to break at the drain.

Sent from my iPad using Tapatalk

 

[73droptop]

Thanks for all the suggestions. I ended up patching it with fiberglass, I sanded it with 120 grit and cleaned it with Acetone. It seems to be sticking real well, but I guess time will only tell. I fiberglassed the inside and oustside and I made sure hardner got between the crack before clamping it. Now just need to sand it and spray it lightly with some black. It seems like it is made with "chopped" fiberglass and hard plastic. Its a strange material.

I ended up cleaning it with 409, then some soap and water, it looks brand new, except for the giant crack I put it in. I have the screen cut, that is all I need a bunch of mice move in.

Thanks again for all the suggestions.