rear defroster

[cbudvet]

Its a rainy Sunday afternoon and I was thinking about the rear defroster in my 240z. It's still in the shop but I know that many of the defroster grid lines are broken/worn away. I know this topic has been discussed before on the different ways to try and fix it. Some have used the paint/epoxy to fill in the lines and restore function. Frost fighters makes a replacement system but you would potentially have to upgrade the wiring. One of the parts of the Frost Fighters system is a pre-placed system of wires that then hooks up to their bus bars. What about just using the prepared lines to fix the existing defroster without upgrading to their entire system? Unfortunately I don't have my car to go out and look at but thought it seemed like a decent idea and it would cost about $50. Any thoughts?

Carl

[5thhorsemann]

The rear window defroster on my 73 is in excellent condition, and still doesn't work worth a damn. If you are looking to upgrade, do the whole system, it's hard to immagine you would be disapointed.

[Mikes Z car]

If you wanted to use the prepared lines you would have to clean the adhesive off the side that faces the glass where they cross the bus bars at the top and bottom and I would think you would have to glue them to the bus bars with the versachem or other conductive paint. My grid lines are all bad and I am not sure the bus bars are good either. I get inconsistent test results with a volt/ ohmmeter. I want to start another thread on this, since I want to use the frostfighter repair system but need more information. Would you have to upgrade the wiring due to heavier current flow? Did they say what the current flow would be? If the current flow was too great would it be practical to put in a series resistor and if so where would one mount the resistor?

[Arne]

Carl, are you thinking of running the new lines over top of the original? Cutting it apart to adjust the spacing to match the Z's spacing? That might work. As Mike noted, you might need to use the paint/epoxy product to make the connection from the new lines to the bus-bars. But that would give you an entire new grid, rather than a grid with repaired spots. In my experience, while the repair spots work, they actually work better than the non-repaired spots. So my grid defogged in a rather spotty and irregular pattern. I had decided that if I were to try it again, I'd probably re-coat the entire grid, not just the gaps.

I think I'd want to scrape off all of the original grid right up to the bus-bars, not apply the new lines over the old material.

This might work really well. Good idea.

[cbudvet]

Arne,

Thats exactly what I had in mind. Scrape off the old ones and use their replacement grid lines. I have to get the car back from the shop first. Its something to think about at least.

Carl

[SteveJ]

Carl, did you ask Frost Fighter about the minimum width of the grid? Their FAQ lists 38 inches, and our cars have a rear window that is not that wide.

[cbudvet]

Steve,

To be honest, I was just think of using as many lines that would fit the rough space of the original grid. I say this with know knowledge as to how it works. My thoughts were just using the pre-spaced lines and not the entire setup. There is a lot more that goes into this than what I have thought of. I guess that is why I posted this originally. To see if you guys think if this would even work or if I'm way off base.

Carl

[SteveJ]

Carl, I haven't contacted Frostfighter myself, but I would speculate that the issue is too little resistance. The current flow through the grid is inversely proportional to the width, left to right (on a typical setup) and proportional to the number of elements. When I measured the rear window, I measured left to right, not thinking that with the 1970, you might want to go top to bottom. You might want to take some measurements and contact them. They can probably give you a rule of thumb about current flow through the grid.

[cbudvet]

Steve,

See, that's stuff I have no idea about. I guess I thought "it's a wire" and that's it. I don't have the money to just experiment. Did you post a while ago about seeing if Frost Fighters would make a version that would fit the z window? Somehow I have the recollection that someone was going to?

Carl

Carl