I have another mystery that I am hoping you can help, especially my friends and colleagues in Europe.

The story:

My son is the glass manager for a large dealership group here in Madison, Wis. He and his crew do all the glass for his dealership and, like most dealerships, they use only OEM glass and follow OEM recommendations.

He was given an installation in a 1995 Porsche 911 Carrera two-door coupe to do and ordered the glass with the use of the VIN number from the vehicle. The glass in the vehicle is the original Sigla brand glass. The glass that arrived for replacement is a Pilkington Germany product with the Porsche logo that the dealership received directly from the OEM distribution center (Porsche part #99354111106). The original glass did not have a small third visor but the new glass did. This threw up a red flag so he checked with Porsche and found that the new glass was the interchange for the old one.

The FW791, which is the NAGS number for this particular vehicle, has a four-sided wrap-around frame with a rubber insert that attaches to it which overlaps the pinchweld. It fits into an “L” shaped pinchweld on all four sides. It comes with a built-in antenna and a VIN window. This is not a very difficult installation. You just need to remove the inserted moulding and cut out the glass. The problem with this vehicle is that the pinchweld floor is very narrow so the bead application must be perfect or the urethane will ooze into the vehicle.

Once the glass was cut out, the new glass was dry set and my son found that the glass was short side to side by almost a half inch on each side. My son called Porsche and confirmed that the right glass was sent and that the problem was in the installation. Thinking that the bead of urethane would change the fit slightly and that the moulding insert would cover the gap, he installed the glass in the opening and carefully applied the urethane bead to make sure the bead would touch the glass rather than the moulding. When he centered it in the opening he noticed the bead oozed into the vehicle and made a terrible mess. We also noticed that VIN window partially covered the VIN plate. Everything he did could not get the glass to fit properly. He ordered another glass thinking that there was a defect in manufacturing but that glass fit the same way as the previous one.

Then he called me. He asked me if I knew anything that could help in finishing this installation for his customer. I compared the old Sigla windshield with the new Pilkington and there is no doubt that the glass is not the same. So I began some research. Here is what I discovered.

Supposedly, Pilkington acquired Sigla and all of its data and equipment. I tried to find out the details of the sale but could not.

This particular vehicle had a windshield change mid-model year at the VIN number … 300000 and above. The Porsche windshield part number for vehicles with VIN under … 300000 is 99354191100. The windshield part number for vehicles with above … 300000 is 99354111106.

The 1995 model, according to NAGS, has a FW791 windshield and has an interchange of a FW2032.
Model years 1996-98 use a FW2032 without any interchange.

It seems that the only vehicle that uses a FW791 is the 1995 Carrera. Is there a difference in fit between a FW791 and the FW2032? Could it be that it is not a true interchange?

My son went to Chicago to find a FW791 to compare with the Porsche part. The FW791 XYG is the same as the Porsche Pilkington part, and both were short side to side by an inch from the original Sigla windshield.

The new Pilkington windshield has a third visor as mentioned above but we also discovered that the VIN plate was partially covered by the frit paint.

What does this all mean?

I don’t know but here is my opinion and take it for what it is worth.

If the 99354111106 is the FW2032 and the 99354191100 is the FW791, was there an assumption made that the FW2032 is the same as the 791 and there was no need to make them both?

My opinion is that when Pilkington purchased Sigla and the equipment and data, an executive decision was made to reduce slow moving parts and reduce inventory which any smart business would do. They assumed that the Sigla 791 was the same as the 2032, thus defaulting to the 2032 and eliminating the FW791 production and data. The problem is that they didn’t realize or didn’t notice that there was a slight difference between the two, namely the measurements side to side and the VIN window placement.

When we quizzed Porsche and Pilkington on this theory and with the fact that the glass did not fit, their response was the same. We have not had any complaints about this before. Which on the surface is a very good question, why haven’t we heard of this problem before 2015? In fact, we have. I personally dealt with a moulding fit problem on one several years ago and I read recently on glassBYTEs.com™ forum of another tech having a similar problem. There has been problems but they have been few in number and the techs in the field have found ways to fix it.

Why are there so few? First of all, there were probably a few older produced 791s that had the correct measurements and were sold with no problems. However, as the older stock was depleted, the new defaulted 2032s took the place. The second half of 1995, ’96, ’97 and `98 models had a perfect fit because they used the 2032 as an OE part, again no reported problems. The only vehicle that needed the older 791 part was the earlier ’95 model. These were getting older and fewer in number. The vehicle is now 20 years old and I would guess that there are very few with a VIN under 300000 left. Of those, I doubt that there will be a lot of miles driven and windshields’ broke. This is why we haven’t heard too many reports of this particular problem before today.

As I am here writing this blog, my son called and said that he found a fix for the problem. He found a FW791 without a moulding. It is an aftermarket brand but by using a universal “J” moulding instead of the OE frame/moulding combination, he could achieve a proper bond and make the moulding look good. Now his only problem is to explain to the customer why an OE glass part does not fit better than an aftermarket one. This should be interesting.