The Loctite brand used to offer a product specifically for repairing rear window defrost grids.  Came in a small glass bottle with a little applicator brush built into the cap.

8 hours ago, ensys said:

Just a couple thoughts...

I think perhaps there is a good reason that all the old manuals illustrate repairs being done with an old fashion drafting pen (looks like the long bill of a bird). The advantage is that (theoretically) one doesn't have to mask (the bill or "nib" is adjustable for width, and when used properly, will produce a very clean edge. the other positive is that the bead will have a slightly rounded top that would provide more net cross section.

The other is that isn't such a grid usually coated with a thin, clear protective layer of something?

Or not.

 

the issue is I have lost prob more than 50% of the grid, so its more of a restoration process than a repair. the grid literally appears to have faded away. I don't know about any coating, but I doubt it since that would make even a repair difficult. there are kits that have stick on grids, but I really did not like the idea of that. Maybe they work but seems like that would have its own set of issues. I rarely use the defogger mode, but sometimes with high humidity and my AC on high it does fog up from the outside.

I bought a defrost fan from OReilly, replaced the cigarette lighter terminal with two spade connectors and connected it to the power circuit for the grid.  It was kind of noisy but it worked.  

The grid is better of course but if you want something to use in the meantime, the fan's only about $20.  The defrost grid is on a 20 amp circuit, so lots of juice there.

https://www.oreillyauto.com/detail/b/custom-accessories-3126/accessories-16449/winter-accessories-16523/defroster-defogger-23801/5aa88c03919b/custom-accessories-defroster/48701/5981244

Just wanted to ad.. i had 5! rear windows for my 280zx and i installed the one with the lowest ohms.. it was if i remember correctly around 2,2-2,4 ohms.. (incl. 0.2 ohms for leads)  The one i installed worked on every line! so i think the total resistance of your 240z def.grid should be around 2-2.5 ohms..

Long ago i used some bison silverglue on a grid but did'nt like it..  very difficult to put on and not make a mess  haha..

33 minutes ago, dutchzcarguy said:

Just wanted to ad.. i had 5! rear windows for my 280zx and i installed the one with the lowest ohms.. it was if i remember correctly around 2,2-2,4 ohms.. (incl. 0.2 ohms for leads)  The one i installed worked on every line! so i think the total resistance of your 240z def.grid should be around 2-2.5 ohms..

Long ago i used some bison silverglue on a grid but did'nt like it..  very difficult to put on and not make a mess  haha..

I am hoping the stencil helps, what was the process you used to apply? so far I have tried masking tape and plastic electrical tape applied free hand (masking tape had too much bleed under, electrical tape was better but very hard to get a consistent width). this was on a plain sheet of glass as a test. I also purchased a pin stripe brush hoping it loads better.

Might I suggest that given a clean surface to start, plastic Scotch tape has a good edge, and is more stable than elect. tape, making a straight line easier to obtain. Plus, it leaves less adhesive residue than moderne masking tape.

 

Just a thought...

15 minutes ago, ensys said:

Might I suggest that given a clean surface to start, plastic Scotch tape has a good edge, and is more stable than elect. tape, making a straight line easier to obtain. Plus, it leaves less adhesive residue than moderne masking tape.

 

Just a thought...

the plan is to try the purpose made stencil tape, it has provision for a constant 1/16 line once applied then the center is removed. I was not happy with any of the various tape methods as getting the constant width was an issue, esp when considering I have to do the entire grid. The stencil was designed around the idea of quick pin stripe methods not requiring great skill to apply in the automotive industry.

Edited September 5, 20204 yr by Dave WM

Have you considered replacing the entire grid by overlaying with one of these?


https://frostfighter.com/clear-view-defrosters-16.htm

19 hours ago, Dave WM said:

what was the process you used to apply?

i used a sort of pinstripe brush.. a small brush with long hairs and just a few hair..  did'nt work well.  the bison silverglue was very liquid..  never tried masking it.

Do anyone know how the process was originally done? Seems that would help come up with a replacement process

@HS30-H

Done with a stencil and a liquid-copper spray would be my guess.  Anybody have OEM automotive glass experience?

I would guess they silk screened it.