Black phosphate underbody reinforcements

[Steve L.]

Why is it the Bairs and Caledonia produce these reinforcements in black phosphate rather than chassis black paint? JM calls for chassis black paint.

[Alan S.]

Re: Black phosphate underbody reinforcements

Hi Steve,
Which reinforcements are you referring to... seat, seat belt, battery mount?
Regards,
Alan

[Steve L.]

Re: Black phosphate underbody reinforcements

Seat and seat belts

[Terry M.]

Re: Black phosphate underbody reinforcements

There could be a couple of reasons.

Some times the phosphate coating has nothing to do with the desired end finish, but rather is a result of what it takes to get the part completed.

A phosphate surface treatment is often used in metal forming operations to give the material surface some "tooth" or microscopic openings for the lubricant to penetrate so that the metal will more easily move in the die forming operation(s). This lubricant coating also prevents material transfer to the forming die, which could necessitate taking the die out of service for refinishing.

A phosphate coating, with a good lubricant, also lowers the pressure needed to move the material in the die. This could result in using a smaller, less expensive, press for the forming operation.

I expect this improved lubricity is the reason for gray phosphate use in the Corvette hood latches from 1968-1972. Your 1973 hood latches may be similar. Whether the 1973 seat belt mounts are similar, I do not know.

Of course it is also possible the 1973-74 TIM&JG is wrong on the finish for these parts.

Or they were painted black over phosphate. Phosphate makes an excellent primary finish if the lubricant is thoroughly cleaned from the part.

[Steve L.]

Re: Black phosphate underbody reinforcements

Thanks,
I'm going to see Gary at Caledonia on Fri at Carlisle and I will ask him these questions.

[Patrick H.]

Re: Black phosphate underbody reinforcements

On my 72, some appear black phosphate and some appear that they "may" be painted black. So, it may be that the JG is wrong?

I'd do more investigating.

[Steve L.]

Re: Black phosphate underbody reinforcements

The JG is at least partially wrong since it states that all underbody reinforcements are chassis black. We already know that the lap belt bracket under the tunnel and the rear compartment door reinforcement are both natural.

[Patrick H.]

Re: Black phosphate underbody reinforcements

The JG is at least partially wrong since it states that all underbody reinforcements are chassis black. We already know that the lap belt bracket under the tunnel and the rear compartment door reinforcement are both natural.

Steve,

71 lap belt bracket (the U-shaped piece in the tunnel) was zinc on a Bowtie 71, it's black phosphate on my 72.

[Steve L.]

Re: Black phosphate underbody reinforcements

Thanks( I think) Patrick

Now I'm really confused. I've gotten back replys for every finish except gold.

I pulled my tunnel bracket out but there is a lot of rust on it. I'll have to look at it carefully through a magnifying glass to see if I can see any remanents of the finish on my '73

[John H.]

Re: Black phosphate underbody reinforcements

Steve,

71 lap belt bracket (the U-shaped piece in the tunnel) was zinc on a Bowtie 71, it's black phosphate on my 72.

It wouldn't be unusual for the same part to be treated differently (in terms of paint) from one year to the next; the Chevrolet (and later GMAD) Central Office Paint Standards Department issued the "Painted Parts List" to the plants, which identified by part number the parts that came raw from the suppliers and required in-plant paint processing.

Those parts were intercepted on the receiving dock and sent to the Small Parts Paint area where they were processed through the prime system, then sent to their point of use on the line.

The "Painted Parts List" was revised monthly based on input from Engineering and Purchasing, and was re-issued in its entirety at model change.

Plants stopped painting small parts in-house in the mid- to late 80's due to maintenance costs and EPA VOC compliance issues, and the parts were purchased already painted.

[Steve L.]

Re: Black phosphate underbody reinforcements

I closely checked my 73 tunnel reinforcement for the lap belt. RIght under the but for the cable anchor, it looks silver. It appears to be zinc but it hard to tell. It's definetly not painted or black phosphate.

Is there a test for zinc plating as opposed to bare steel? I only have the area under the nut to check.