Adrian

Dear Dave,
I am afraid they are wrong they were all bonded so that is simply not true. The 993 versus 964 comes from the airbag issue. Airbags were not mandatory on the 964 in the UK but by the time of the 993 I think they were. This is a case of a little truth getting mixed with a lot of fiction. I checked the 928 manual from 1990-1995 and it says the same.
Ciao,
Adrian
964C4

PS: I do agree that poor workmanship which was rife during the period of the 964 at Porsche due to serious labour disputes is something we do not touch on anywhere near enough. A lot of people just believe Porsche is perfect and some think Porsche is a religious order not a car manufacturer. Porsches are built by people, or they were, and people make mistakes, accident and deliberate sometimes.

Christer

Of course Porsches are perfect!!!!!!!!

I don't have airbags so I am OK then.

GMS

I think we need to define "glue" or "bonded" and "sealed".
928, 944 and 993 glass is "bonded" or "glued" as there is no rubber weatherstrip and the glass is bonded straight onto the vehicle.
With materials available there is no excuse for leaks as nearly every other manufacturer uses bonded glass.

964 use a rubber weatherstrip and are sealed. The side glass of a 993, which has a rubber weatherstrip is bonded using the two-part, doesn't-quite-work-all-that-well Porsche glue. When I worked at an official Porsche dealer 964 glass was installed without glue but was sealed after installation. Unfortunately, I can't remember whether they were glued in, but bearing in mind the time we were allowed for install, don't think they were. Car with airbags have to have glued in glass. Of course, that didn't stop 968 side windows falling out when the air bag deployed.......

kris

I found out the hard way that corrosion beneath the windscreen rubber seal is usually more important than what can be seen with the glass in place; Last year I only had a few very small spots appearing beside the rubber. Last week when I removed the glass it appeared that the rust was eating its way on both lower corners. The windscreen I replaced was not bonded but there were obvious traces of sealant/glue from the original factory fitting. I'm now starting with the rust removal, I would like to apply micro sand blasting to treat the spots and follow the WSM to the letter when replacing the windscreen. Just for the sake of the newer 964 owners I copy/pasted one of Adrian's posts which contains all of the necessary advice and caveats. BTW, removing the old rubber and sealant is a major PITA, I've had a bit of success with silicone remover but it remains difficult.


When your 964 left the factory the windscreen was sealed and glued into position. Fact! Since this time it has been smashed or had to be smashed to be replaced. To remove all the glued in glass takes a lot of effort and Porsche acknowledge that this will cause damage to the metal work and the galvanisation. Once the glass is removed the glue or sealant has to be removed by scrapping it off. This also damages the metalwork. The damaged metalwork has to be repaired. IF this is not done properly and IF the new windshield is not glued into place and IF the incorrect seal is used you will get water onto bare exposed steel under and around the glass and it rusts. Seriously rusts in lower corners and under the dash.
There is an approved procedure for installing the windscreens. I cannot understand why people argue against following the laid down procedure. It is there for a reason. The only reason I can see for arguing against doing the job properly is one of cost. It costs a little more to use the right parts, use the sealant/glue, so what. Nobody said Porsche ownership is cheap.
Ciao,
Adrian
964C4

colo964

I took off my own glass after 10 yrs of ownership, fully expecting rust. There was some but not bad for a 16 yr old car (about 3 inches along the bottom center and around a rock chip that was just at the edge of the seal). Some POR 15 and their rust inhibitor, better than new.

In the lower left I had the infamous wet thigh effect, but surprisingly, no rust.

The old seal was glued on like the factory manual says (a few hours to clean that up). Safelite brought a green bad Sigla with an antenna (that actually works) then used a sealant around the outer lip, but only used a primer (over my gleaming POR coat) while installing. The factory manual says to put primer and adhesive before putting the seal in, which is impractical since the fitting takes about an hour (with sometimes remove and repositioning) and placing the adhesive afterwards allows for ensuring the outer lip overlaps the metal which I'll be glad for a few thunderstorms from now.

Adrian

Kris,
I have a friend of mine who does a lot of Porsche body repairs. We were chatting over a beer a few weeks ago and he brought this subject up because once we were talking years ago about the 964 and he claimed they will not rust. He told me (Wilhelm Jenni is his name) that he has seen many 964s in for glass replacements in the past couple of years and when the glass was removed the lower support sections were rusted away. None of these 964s had correctly installed windscreens (not sealed) and he said you could even see the salt deposits from winter driving where they had collected after passing around the rubber seal and draining down into the lower support sections.
The problem is also occurring where the rear windows have also been replaced without being properly sealed/glued/bonded.
Since this thread was started some three years ago, rust has become an issue in many Porsche model ranges and whilst I wrote a little about this in my 964 book, if anyone is looking at the older Porsche models I recommend you learn to use a paint depth meter. I have been converted to their use and you can see a lot without seeing anything on the surface.
By the way this is why my 996 will not be driven in winter and in the salt. This crap gets everywhere and if it finds exposed steel it turns brown real quick and once the rust starts it is hard to control especially if you don't catch it until it bubbles out from underneath the paint.
Ciao,
Adrian.

Bearclaw

You mean, to look for evidence of rust repair? I have an electronic paint thinkness meter and have found it to be a valuable tool in car purchasing. In fact, the only place on my 964 that shows more than original thickness is on the cowl panel - and I suspect this is why.

There's a fellow on one of the Saab boards, a chemical engineer, who insists that once rust has started, that panel is doomed. Even if that spot is repaired it is inevitable that it will soon pop out on the same panel in another spot, due to the chemistry involved. Don't know if that's true.

911addict

Regardless of how careful, or proper procedures followed, it is reasonable to expect that these older cars will get some rust. Having paint repairs, panel resprays and replacement is all part of the total experience of owning and running a 'classic' car. Not saying you shouldn't folow best practices, but if you use your car, then make sure you budget for body repairs.

If corrosion doesn't get you, then vanadalism, accidents and fair wear and tear will!

ps: I use my car daily, all year round, all weathers, redline it frequently, and spin my tyres. My view is to use and enjoy my 911's and just maintain them regardless.

Adrian

Barry,
Yep. Paint thickness right or wrong or even lack of a reading, provides a great overview of the under the surface condition of any car.
One thing I have learned about Porsches and before using the paint meter is to check the thickness of the roof gutter. Just run your fingers along each one. If one feels thicker than the other this is usually an indication of a repair on the thicker side. You then use the paint meter to reveal the extent of the repair. Once you have learned how to use one of these babies properly you can really get quite accurate.
I would also agree with your SAAB colleague. My daughter is also a Chemical engineer and she says the same thing and my own experience supports their conclusions as well. Once the rust is inside the metal as opposed to just being on the surface, then the panel is almost certainly doomed. Yes the rust can be cut out, but rust is like a cancerous tumour. Did you get it all? Did you create the conditions for more rust when you welded in the new section? Been there done that bought that t-shirt. A lot does depend upon the environmental conditions in which you live as well. Salt and water combined are the real big fast killers.
Ciao,
Adrian.

kris

My car is now in the shop to have the final bodywork done. The rusted area's will me sandblasted and treated, the pillars, roof and the area below the windscreen will be repainted and the complete roof will receive a clearcoat. The window is a Saint Gobain Sekurit with the green sunband, exactly the same as the original except for the Porsche word. The price is still quite reasonable and it shouldn't prevent anybody from tackling the job.
Windscreen: 265 euro with VAT
Bodywork: 200 euro
Rubber seal: 121 euro with VAT
Porsche sealing kit: 21 euro with VAT
The independant carglass guy told me that he wanted to glue/seal the window even before me asking anything about it. Told me he works for the largest dealer in the country and he has seen too many casualties from unsealed windscreens. Quite a contrast with my OPC where the Service manager still denied the sealant with the WSM on 64-5 in front of him.

Laurence Gibbs

I had a non glued screen in my RS. I had a very annoying squeal at about 75-80mph that i just could not trace. It was'nt there when i purchased the car but seemed to come on after several months of ownership. Guess what was squealing! When i had the screen replaced for a cracked screen I informed the fitter of the correct proceedure and gave him a copy of the factory manual to peruse. Needless to say screen was glued in placed and squeal has been banished forever. So if you go the non bonded/glued route and get a squeal you can't place, at least you'll know why.
As a side issue it should be perfectly possible to remove both screens without damage by cutting the seal away from the screen, care has to be taken and mistakes happen but i have had two 911 screens fitted on two different cars and both came out in one piece.

kris

I had no problems either to remove the screen, I installed my two boys, in their pyjama's btw, in both seats and had them slightly push against the screen with their feet, I had cut the rubber already. No problem at all.

springer3

Urban legend. I am not a corrosion engineer, but I know a few and I work in a lab that tests paint and does corrosion research. I have restored several rusty cars that did not have problems later. One was an early 911 - full of lap joints, spot welds, and hollow sections. Before 1973, the 911 is probably the worst body design for corrosion ever. The 964 is better, but still has some of the design problems from the early cars. The 911/964 windshield seal is a problem because it traps water and salt. Modern designs are much better, but we need to deal with what we have.

The "rust causes rust" statement is difficult to argue with because in a practical sense that is what happens. A rust spot in a panel is a good predictor of future problems, but it is not the cause.

Steel sheet is first rolled, and then stamped into the body panel. A foundry is a dirty place. The rolling dies and stamping dies press scale, slag and rust into the metal surface, leaving hundreds of microscopic defects on every panel. If the defects are painted over at the factory or after a repair, the paint will soon blister. Rust hides at the bottom of pits and cracks, and is difficult to remove. It is not impossible. Any panel that is still reasonably solid is salvageable. It needs to be stripped to bare metal, acid-etched to remove rust and passivate the surface, and then primed with corrosion-inhibiting primer. If the rust is coming from the back, both sides need to be treated.

Many shops cut corners, but the problems come only years later. The extra steps take time and cost money. Therefore there is litte incentive to do the job properly. Most cars last only a decade or so, and a repair that lasts 2 or 3 years is considered good enough. If you intend to keep the car and preserve its value, you need to insist on competent rust repair.

Bearclaw

I believe what you're saying is basically true. My old man used to say that the reason 60's and 70's- vintage Fords would sometimes rust through when they were 3 or 4 years old is because of the inferior quality steel they used - and that no amount of surface coating would have saved them. Fiat's were notorious rusters, the supposed cause was that they got a long-term sweetheart deal on inferior Russian steel.

But this also suggests that when doing a correct rust repair, you would need to strip and treat the entire panel to address the problem - and if the whole car is made of the same batch of steel, wouldn't the whole car have the same problem?
Although in practical terms, it might not ever show up in most areas of the car, like a cancer that lies dormant for 20 or 30 years...

springer3

It depends on the environment and how well the rust proofing is implemented and maintained. A garaged 964 driven only on blue-sky days in a desert will never rust. An early 911 kept outdoors near the seacoast is a rust bucket in three years. A 964 left outdoors at the seacoast has spots of rust in 10 years.

The 964 has one-side galvanizing for most body panels, and everything steel was passivated and dipped at the factory. Rust problems are infrequent and isolated - like the windshield case were scratches are not repaired, and the new gasket is not sealed.

Niel Young was right. Rust never sleeps. Even the 964 will eventually rust away if we don't fight it. Fortunately it was an expensive car and they used the best rust-protection technology available at the time it was manufactured. The fact that most of us have never seen rust blisters on our cars is testament to that.