1956-57 Underdash Questions

[Louis C.]

1)What type of rivits hold in the metal lower dash support? This is the long piece of metal that is mounted under the gauges from left to right.

2) Does the metal bezel that holds the gauges in go in before or after the lower metal dash reinforcement?

[Rod K.]

Re: 1956-57 Underdash Questions

Louis,

1) Believe they were 3/16 dia X 3/8 long aluminum round head

2) AIM looks like the gauge panel goes under the lower support. My car is off site or I'd check for sure.

[Dan D.]

Re: 1956-57 Underdash Questions

3/16x3/8 sounds right. Gauge panel goes in first and is captured by the lower support.

Lower support apparently came from the factory as raw steel - no plating or paint. I took mine out to clean it up - very rusty. I rattle caned it with a zinc coating, but you could clear coat it. Keep in mind it is carrying ground current and must be conductive to the gauges, the cowl vent bracket, and for the ground wires below the headlight switch. Cowl vent bracket carries the ground current from the windshield wiper motor. Dan-

[Louis C.]

Re: 1956-57 Underdash Questions

Somone took the pleasure of removing mine for me so I'm trying to put it together correctly. Rivits are inserted bottom to top?

[Rod K.]

Re: 1956-57 Underdash Questions

Heads on the bottom. Makes setting them fun.

[Dan D.]

Re: 1956-57 Underdash Questions

Setting them is not fun, but like anything else, it can be done. Bucking them is easy of course, but trying to get a hammer on top with enough force to peen them over is tough, especially the end ones. If I remember correctly there are only 5 rivets. Just remember that whatever finish you use, if any, must be electrically conductive at all places that carry ground current. That is most important. -Dan-

[Louis C.]

Re: 1956-57 Underdash Questions

Actually, bucking them will be real easy. The top of the dash is off too so I have a clear view. Mine is currently screwed in and has quite a few #10 screws. While I will try to identify the original holes and fill the rest,

Can you confirm just 5 rivits, bucked with the round head down?

[Dan D.]

Re: 1956-57 Underdash Questions

Hi Lou, I can look at mine today. You may owe me a coffee though - it is 18* out right now - garage not a lot warmer. I believe there was one in each corner and one on each side of center where it dips down. You may be able to tell from the size of the holes in the support. There are other holes, but I don't think they are 3/16. I have my extended family staying with us yesterday and part of today (daughter, son-in-law, 3 small kids and dog. So I will have to break free (which is desirable)). Rivet heads are definitively bucked from the bottom. -Dan-

[Louis C.]

Re: 1956-57 Underdash Questions

Thank you Dan for looking into this for me. So I am clear, they drop in from the top? And there are just 4 rivits? Two on the ends and two more inboard where it dips..

[Dan D.]

Re: 1956-57 Underdash Questions

No Lou, they push up from the bottom. They are supported on the bottom, and peened on the top. And there are at least 5. I will have more info for you this afternoon. Weekend was "occupied". -Dan-

[Dan D.]

Re: 1956-57 Underdash Questions

Hi Lou,

I show one in each far corner at the end of the brace near the door posts.

One between the ignition switch and fuel gauge.

One under the battery gauge

One on each side of the speaker.

Total of 6. Hope this helps. -Dan-

[Louis C.]

Re: 1956-57 Underdash Questions

Thank you Dan. I will be working on it this weekend and appreciate you crawling under that cold dash..

[Dan D.]

Re: 1956-57 Underdash Questions

No problem Lou. The factory finish on this support was raw steel, so they will, and do rust. Like I said, I sprayed mine with a zinc coating which provides rust protection and is electrically conductive. This would not pass judging, but mine is a driver and I was most concerned with rust protection and maintaining electrical continuity. Not sure what you are planning to do, but a matte clear coat over raw, well cleaned steel would probably judge fairly well, but you would have to selectively coat it in order to maintain electrical continuity. If you bought a repro, I'm not sure what finish is on it.

There should be some info on this subject in the archives, as I posted 2 or 3 years ago when I was trying to determine what the correct finish was.

As a side note, the grounding on these cars is terrible. Being fiberglass, grounding becomes a real issue, and I don't think GM addressed it well on these early cars. For one thing, there should be a ground strap between the motor and the chassis (frame). There is none. Even newer steel cars have the chassis bonded to the motor.

There are several ground wires connected together in the harnesses, but having a primary ground wire screwed to a valve cover bolt is just plain stupid. Some day I will write an article on the grounding in these cars, but not today. -Dan-