Body Galvanizing in Porsche 911

[randywebb]

This is a controversial, rumor-laden topic -- here is what I was able to find from sources that should be authoritative. Note the weight tidbit found -- so the body shells didn't really add too much weight because of the rust-proof steel per se.

Thyssen steel = steel with Zinc layers on both sides; thickness of the Zinc layers varied from 10 um to 20 um, depending on exposure conditions (Frere, p. 201)

1970 – Galvanized steel (not Thyssen type) used in floor pan and wheel arches (Bob White in Pano V: 142); the “entire platform, including the floor, the longitudinal members, the wheel arches and the seat pans were galvanized.” (Boschen & Barth, p. 124)
1971 models – had galvanized steel in area particularly exposed to rust (Frere, p. 201)
1972-1973 – Thyssen steel use began (Bob White in Pano V: 142)
1973 – Thyssen steel: rocker panels, inner rocker panels, floor pans, & some other parts (Chuck Stoddard in Pano V: 142)
1975 – Thyssen steel: entire body treated (Bob White & Chuck Stoddard {began in Feb. ’75 production} in Pano V: 142, 192)
1976 models – had Thyssen steel in entire body except roof (Frere, p. 201)
1977 models – on – had Thyssen steel in entire body (Frere, p. 201); an “important step forward was the use of zinc-coated sheet steel for the manufacture of the entire body structure (except for the coupe’s roof on early production cars). Coated on both sides, this made the structure virtually immune against the formation of rust….” (Boschen & Barth, p. 143)


The Zinc steel added 22 lbs. to the weight of the body structure (Frere, p. 202)

Pano = Panorama volume: page number
Frere = Frere, Paul. 1997. PORSCHE 911 STORY. 6th ed., Patrick Stephens Ltd. Newbury Park, CA.
Boschen & Barth = Boschen, Lothar and Jurgen Barth. 1978. THE PORSCHE BOOK: A DEFINITIVE ILLUSTRATED HISTORY. Argo Books.


Note: the Panorama and Frere comments can be harmonized since most cars for one model year are constructed in the previous chronological year

[dotorg]

Here's a question for any metallurgists in the crowd...

The galvanized zinc steel is a sacrificial coating, and most people seem to say that the galvanization doesn't last more than ten years or so, so at this point essentially all air-cooled 911's are relying on their paint as their sole protection.

That said, what happens to the weight of the steel as the zinc is sacrificed? Does it get heavier, or lighter?

I know mine gets lighter as bits of it rust away!

[724doorE]

Depends on how you look at it.

The gal is only sacrificial if its the protecting layer.

The paint will protect the gal until the gal is exposed to the elements.

There are also stories of Porsche leaving unfinished, unpainted shells outside for years to study the effects, I'm sure some one here has some info on that.

So, no the gal does not just disappear after ten years.
The rate depends on the conditions.

[daka]

I seem to remember that there was an unpainted 911 body on a "pedestal" outside the Stuttgart factory. I think it was a 77 body and I saw it in 83, no rust or discoloration that I remember seeing at the time..

[Joeaksa]

Daka,

You are correct. Last time I was there (early 90's) it was still there.

Regarding the metal, what usually happens is that the car is involved in an accident. The metal is "distressed" and then repaired. Most body shop operations (torch, grinding etc) takes the coating off of the metal and then its possible for it to rust. Also, when someone drills a hole in the car, it just opened the possibility for rust.

Really love the early cars but hate rust with a passion. Thats why I backdated my 85 model car!

JoeA

[Randy W]

JoeA, did you use early front fenders that were galvanized?

[randywebb]

There were 3 of the long-life cars made. I may be confusing the galv. steel with stainless tho...

There is a Pano article on this and it was reprinted in one of the UpFixin books.

I agree re holes - whenever I do this, I use a rust inhibiting primer on it and then a top coat (since I assume that metal primers, like house paint primers won't last long w/o a top coat). Then I will put sil. seal or a rubber grommet in the hole depending on why I drilled it.

[randywebb]

- I edited the original post to update it with the info from Boschen & Barth.

[dd74]

Originally posted by randywebb
1970 – Galvanized steel (not Thyssen type) used in floor pan and wheel arches (Bob White in Pano V: 142); the “entire platform, including the floor, the longitudinal members, the wheel arches and the seat pans were galvanized.” (Boschen & Barth, p. 124)

Correct me if I'm wrong, but when I read "seat buckets" I imagine the buckets that hold the rear seats. When I stripped out my car, I found minor rust beneath the sound deadening, which I treated with an inhibitior before installing RS carpeting. Of course, I'm talking about a 31 year old car with original rear pop out and windshield seals - the pop outs of which leak, and each heavy rain or a wash, causes water to collect in these buckets. I will certainly fix the seals, however, the PO probably paid no attention to this as he probably never removed even the seat cushions. Anyway, what I'm getting at is the question of whether gal can prevent rust when water stands in one spot, such as the seat buckets.

Randy - your information doesn't cite my model year - '74 - so I'm wondering if what was used in '73 simply carried over to '74.

Also, I wonder about the statement "dotorg" wrote about gal not lasting longer than ten years. Could seem like the case with my car.

Lastly, no evidence of an accident near the buckets. I think if there was an accident that effected the seat buckets, such as distressing the gal, the car would have gone through a catastrophic accident, and not be in existence.

Any thoughts?

[darkbeer]

My '75 Targa, mfg date "3/75", has original Granprix Weiss (sp?) -Grand Prix White, no accidents or repaints...I remember reading in "Excellence was Expected" that the Galv started with the 1975's & the above post backs that up. My Targa is rust free but I know that its original front & rear valances were not Galv'd....I have swapped them out with later galv'd ones form Parts Heaven.

Greg
22 lbs. of zink ??? that's a good thing !

[randywebb]

'74 - dd - maybe - I haven't seen any documented info on this tho. We really need to get the factory archivists and historians to post on Pelican...

re '75 - note that the Thyssen process is more than just galvanizing... not sure exactly what tho.

22 lbs. - Note the post of ad copy (on one of my body work/paint threads) - it cites 30 lbs. for an SC. Maybe they added more over time...?

[Porsche]

Just doublechecking - does this mean that '75 and '77 911's are totally galavanized, but '76 are only partially galavanized?

Thanks!

[Bill Verburg]

They started using the Thyssen steel for floor pans and inner body panels in the early '70s, the % was increased untill some time in late '76 the whole car was made of Thyssen galvanized steel, at the start of the '76 model run the only part not Thyseen was the roof of the coupes.

Thyssen steel is a double sided zinc coating. The thickness of the zinc varies according to application from10 microns to 50 microns on the torsion-bar tube.

at the time the Thyssen steel added ~$100 and ~20#s to the cost of the car.

In '75 all the floor and innerpanals were galvanized but most of the rest of the body was not.

[Porsche]

Hi Bill, what you say is what I've always assumed and read about, but that's not what the first post says:

1975 – Thyssen steel: entire body treated (Bob White & Chuck Stoddard {began in Feb. ’75 production} in Pano V: 142, 192)
1976 models – had Thyssen steel in entire body except roof (Frere, p. 201)
1977 models – on – had Thyssen steel in entire body

Hence my request for clarification.

According to randy's source, 1975 had full body galvanization.

[jmshepard]

Has anyone investigated the possibility of re-galvanizing a bare body shell? I found a company (http://www.metalplate.com/ ) that hot dips steel building materials. I called and asked if they do cars, thinking I could have the rust protection on my 80 SC renewed. The engineer said that they get many calls from car hobbyists asking this question. The company declines this business because the process is too hot and would warp the thin sheet metal. Clearly there is a market for this type of service. There may be a company out there that will do cars; I just haven't found it yet. It would be nice to prepare the car for my son and the next 25 years on the road.
Jim S.

[Dan in Pasadena]

Originally posted by Porsche
Hi Bill, what you say is what I've always assumed and read about, but that's not what the first post says:



Hence my request for clarification.

According to randy's source, 1975 had full body galvanization.

The interesting discontinuity in these facts is that '75 was "completely galvanized" but in '76 the roof wasn't and then they were completely galvanized in '77 again? I highly doubt this was the case. Either they were fully galv'd in '75 and the tidbit about the roof is a mistake, or all the roofs were not galv'd till '77. I suspect the latter.

I have a '76 that was just fully painted and there was not a spot of rust on it anywhere...and believe me I looked and I had the painter on high alert - no rust. None on the roof either. Of course this has always been a California car...but there has been a 30 year opportunity for it to rust.

As a side question: Why do galvanized cars that live at the beach, rust? If the paint film isn't breached, the presence of salt in the air shouldn't matter....for at least 10 years or so, probably longer? But even if it is breached, the zinc film has to be completley sacrificed too before the parent metal begins to rust, right? Seems like cars rust faster than it sounds like that process would take.

[Bill Verburg]

Originally posted by Porsche
Hi Bill, what you say is what I've always assumed and read about, but that's not what the first post says:



Hence my request for clarification.

According to randy's source, 1975 had full body galvanization.

Randy's source, Bob White and Chuck Stoddard are both knowledgable and respected sources, but factory literature says that '76 is the first year where all of the major exterior panels are Thyssen

What Chuck Stoddard said at the '80 Warbonnet was that some of the ROW cars in '75 had the Thyssen exterior.

The hall mark of the all Thyssen body was the introduction in '76 of the 6yr rust warranty on ROW cars, but not Nort American models becaue the early ones didn't necessarily have the good steel. theydid by the end of the body run.

Another hallmark was the display for the first time of the unpainted, zinc protected components on a cut away '76 targa

[Dan in Pasadena]

Bill, Is there any definitive answer (or even a strongly held rumor!) of what month in '76 the "good steel" began to be used? Since my car has no rust I'll assume I have the good stuff but I think my car was built in November if memory serves.

[Bill Verburg]

Stoddard mentioned Feb '75 but I know that the '76 model run started w/ regular steel roof panels in the coupes and ended w/ full galvanization. When I bought my car in '76 in Germany that was a big selling point. The inner panels on my '72 were heavily rusted when I took it apart for the RS updates, it was pretty ugly for such a relatively new (at the time) car.

Why do galvanized cars that live at the beach, rust? If the paint film isn't breached, the presence of salt in the air shouldn't matter

Paint and the zinc coat are permeable, they breath, and salt laden air is transported across the barrier coats.

[randywebb]

re "discontinuity'

re-read the top post: "Note: the Panorama and Frere comments can be harmonized since most cars for one model year are constructed in the previous chronological year"

"factory literature says that '76 is the first year where all of the major exterior panels are Thyssen"

Bill - do you recall what factory literature it was? Dealer education booklet? Customer brochure?

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It looks like you can be pretty certain your '77 is protected... even if we can't quite pin down specifically what parts got what protection on the exact time before that.