Mid year rear license lens heat cracks

[Dan B.]

I was wondering if anyone has experienced cracks in the rear license lamp lens on their C2 mid year. My original lens had some small cracks and replaced it with a new reproduction and did not tighten the screws too much and the white gasket was present.
Was under the car the other day working on something else when I noticed the lens had multiple cracks and a heat dimple from the bulb which is very close to the lens and generates a lot of heat. It has the correct #67 bulb in there and it does get pretty hot after being on for a while. Notice the heat mark in the plastic where the bulb is close, it melted a small circle there.

Looking to hear from others on this subject before going ahead and installing another new lens. I was also thinking about substituting an LED as a means of lowering the heat. Thoughts?

[Bill M.]

[Leif A.]

Re: Mid year rear license lens heat cracks

Dan,
I had a similar issue and was told there were two different styles of the #67 bulb. There is a round globe bulb and a more tubular globe bulb (called a mini bulb). There is very little clearance between the lens and the round globe bulb, so the mini made sense to me. Of course, I think you'd need to be doing an awful lot of night time driving for that license plate lens to heat up like it has...especially being as you state it was brand new. See pics for the two different bulbs mentioned.

[Dan B.]

Re: Mid year rear license lens heat cracks

Leif, Yes the bulb on the right is a NAPA listed ABV67 which is a thinner taper. Of course it's still rated at 4CP, so I'm guessing it is still producing the same amount of heat. That said, I do a fair amount of night driving but would not expect the lens to melt with either bulb. I'm wondering what experience others might have that drive at night. Thanks for the reply.

Bill, I can't imagine it's bent, I restored it some years ago and it looked fine and the lens and gasket seem to fit well, but I never checked it for straightness. I'll do that, thanks for the suggestion.

[Thomas S.]

Re: Mid year rear license lens heat cracks

G6 is an old industry standard which describes the glass envelope. G = globe. 6 = 6/8”. (3/4) The number is 1/8’s of an inch

All G6 envelope (glass) are supposed to be the same dimensionally but since no sub-miniature incandescents have been made on-shore for decades, anything is possible. A deviation to a smaller “G” envelope would not be problem and no one would complain.

BA = bayonet base, S = single contact, D = Double contact

Page 5 gets into dimensional detail.

https://www.adamsaviation.com/files/ww/Catalogues/GE.pdf

I own an electronics distribution company and back in the day these designation were widely used. There were even separate Mil-Spec versions of most lamps (cockpit) where they would be run at full voltage for X hours. Anything that lasted more than X would probably last the full rated life and were were then considered usable in Military applications.

LEDs do produce heat as well although much less than a filament. You can’t go wrong with an LED except for judging of course.

The lens on my 63 looked to be original and did not have any heat damage. The plastic used by GM could have been different than what is now used for knock-offs.

probably more info than you wanted, but hopefully of use.

https://normanlamps.com/miniature/incandescent-miniature

[Joe R.]

Re: Mid year rear license lens heat cracks

Here's a pair of License plate lens. One is a GM and one is an aftermarket replacement! Can you tell the difference.

Yes, this is a trick question! I'm sure only Black Hats can identify the original GM!

JRIMG_0782[1].jpgIMG_0782[1].jpg

[Dan B.]

Re: Mid year rear license lens heat cracks

I removed the license lamp assembly for a closer inspection, not an easy task (you have to remove the rear valence to get to the nuts).

The housing is straight and with the lens in place, I notice the bottom side portion of the bulb just kisses the lens at the point where it melted a slight divot. The socket is pressed in, so I don't see any way to slightly bend it away from the lens. What about the gasket? It's compressed with indentations from the lens, I'm thinking a new gasket might help space the lens out slightly farther away from the bulb and I'm going to use the narrow taper bulb as well.

[Dan B.]

Re: Mid year rear license lens heat cracks

Here's a pair of License plate lens. One is a GM and one is an aftermarket replacement! Can you tell the difference.

Yes, this is a trick question! I'm sure only Black Hats can identify the original GM!

JR[ATTACH=CONFIG]115646[/ATTACH][ATTACH=CONFIG]115646[/ATTACH]

Both pictures look the same to me, but I think the top lens in each one one is the reproduction........beyond that dunno Joe

[Gary B.]

[Joseph S.]

Re: Mid year rear license lens heat cracks

I removed the license lamp assembly for a closer inspection, not an easy task (you have to remove the rear valence to get to the nuts).

The housing is straight and with the lens in place, I notice the bottom side portion of the bulb just kisses the lens at the point where it melted a slight divot. The socket is pressed in, so I don't see any way to slightly bend it away from the lens. What about the gasket? It's compressed with indentations from the lens, I'm thinking a new gasket might help space the lens out slightly farther away from the bulb and I'm going to use the narrow taper bulb as well.

Dan, What do your screws look like? They should have a shoulder on them preventing the lens from being over tightened into the gasket.

[Dan B.]

Re: Mid year rear license lens heat cracks

Dan, What do your screws look like? They should have a shoulder on them preventing the lens from being over tightened into the gasket.

Yes, I have the correct screws Joe. The original gasket was compressed, but as you say the screws should limit how tight the lens can be. Hopefully a new gasket with the thinner profile bulb globe will do the trick. I'm surprised no one else has experienced this. Guess I'm just lucky

[James W.]

Re: Mid year rear license lens heat cracks

Not to hijack this thread, but where do you get a decent "white" lens gasket?

James

[Leif A.]

Re: Mid year rear license lens heat cracks

Not to hijack this thread, but where do you get a decent "white" lens gasket?

James

You have a PM.

[Joe R.]

Re: Mid year rear license lens heat cracks

OK, here's the scoop on the lens. The one on the top is a reproduction BUT the number is wrong for an original installed by GM in the C2 time frame. The lower one with the correct number is a GM original sold after the C2 time frame. BUT as you notice from the picture that Leif has supplied there are reinforcements in the sides of the lens to keep it from cracking when installed. The reproduction has the reinforcements like the original but not the correct number. The GM original with the correct part number does not have the reinforcements.
Now there are no copies or GM replacements that should receive full credit as originals. Also the GM replacements were sold with a gray gasket which was probably stiffer to prevent cracking so they dropped the reinforcements along the edges.
My two cents, JR