I have posted recently that I noticed some very minor rust coming through at the rear base of the quarter window where it meets the rear spoiler. It has been on my to do list for a while to address this. I Finally pulled the rear spoiler off and noticed several rust spots under there as well so into the body shop yesterday to finally address it.

Here is a pic from the driver's side quarter window once the glass was removed.

FWIW my car is generally kept out of the rain, under carport at work, garaged at home, and has been an indoor car for at least the last 8 years.

 

Park car on level ground, pour a little water on the bottom edge of the window frame. Drill a small tapered hole in the middle of where the water pools. Sand, prime & paint. T

 

My friend doing the repair owns a hi-end body shop in town that specailizes in restoration / show cars and has a lot of experience on old school technology. He said the main issue with the design is that since the window is not urethaned in like most modern cars it is basicallly a "floating" support on the rubber seal between the glass and the body of the car.

He has hypothesized that not only can water seep in, but any little sand or grit that washes in over the years and settles gets locked in between the rubber and the channel and as the very small vibrations in the body / glass basically act like sandpaper gradually removing paint over years and years. Keep in mind this surface was coated with zinc oxide when new and once painted and primed, even left wet for 30 years should not have allowed so much of the finish to be removed down to bare metal and then lead to this level of rust.

In my field (environmental engineering) I've pulled 30 year old steel fuel tanks that were buried below the groundwater table with less rust - as long as the coating has not been damaged.

 

Sounds like your friend does good work, Mine (MY83) looked the same, original owner had a car port and the back end saw some rain over the years.
Good you're taking care of it. It seems one of the few areas of concern..

FWIW, i re installed my quarter windows last year after rust repair w/o sealant so they can easily be removed again knowing i was notdone with it's renovation.

The windows with out sealant come out fairly easily from inside with a small plastic pry tool. Just move the seal to the outside of the pinch weld and go around)

I plan to re install again w/o sealant to be able to take mine out annually to check/clean.

 

Wish I drilled the holes in the GTS when it was in for paint. Now I blow out the excess water with compressed air after washing. T

 

I'm taking your advice on this one Tony, especially since i am not using sealant. Great idea, I didn't go tiny went with 3/16" holes where the pitting took place and acid etch primed twice. With sealant some water could make it's way in and be trapped (with no way of knowing) as evident with many 928s having corrosion here..
Thanks.
-Matt

 

"Fix your Quarter Window Rust!" That's easy for you to say. It would be easy to do that if there was such a place near me like you have. What was the cost? How much time did it take?

Dan
'91 928GT S/C 475hp/460lb.ft

 

I feel like drilling a hole isn't going to make much of a difference and here's why: Water has surface tension. Water gets drawn into the seal through capillary action. Water gets stuck in between seal and body of car, with no air and just sits there.
Also, you've now exposed that spot to more road grime being thrown off the tires and wedging its way under the seal, as you'll spray out the dirt underneath but also effectively push some further under which will hold even more water.

 

What did it cost? Well let's say it costs less to fix now than if I let it sit another year. I removed the rear spoiler myself (water and rust also settle under the rear spoiler of the 83S/84S cars) brought the car to him. He said he could do just the rust repairs (including pulling and installing rear windows for $1500. I went a further step, since I want to do a good qualtiy "windows out" repaint on the whole car at some point.

So we are buying enough paint to do the entire car - it has a long shelf life and this way it will all be from the same batch. Pulling the rear bumper, light, signals, hatch, trim and glass and painting the back half of the car for $3000. This includes all rust repair and there is a natural break at the roofline and doors to do a good blend. Then I'll save up another $3000 and we will finish the rest of the car in 2014.

For the complete car, when its all said and done, total cost for a very good quality finish with all trim removed and no tape lines will be about $6000, maybe a little less depending on how much I do myself It could have been a little cheaper if I had the time to pull the rear bumper cover, lights, antenna and hatch myself, but work is hectic right now and I did not want to let the rust si any longer.

Its all in the hours that you want to invest vs. what you want to pay for. Labor rate is about $50 an hour for paint and body here in Gainesville and if its a 100 hour job you have $5K in labor. If you can pull the trim, bumpers, doors, mirrors, hood, hatch, glass, etc, you can save a good chunk of money.

 

I think a lot of water gets in there and has no place to go. If enough can escape then the rest will evaporate. I thought about road grime too but want to try this idea.

I will be able to test your theory and Tony's, i will pull mine out after it has been re installed for a few months and check back in here.

Can always caulk it closed.

 

Swapped out the GTS rear bumper cover for an S4. That pesky GTS middle reflector strip would ooze water after washing along with the tailights. This mod worked great. Note: Not necessary on the 78-86 cars. T

 

Interesting. I'm removing the rear spoiler(s) on my 86.5 for exactly the same reason, constantly oozing water after a wash or rain (plus I like the look of the original OB). That "ooze" is a huge problem for me, living on a dusty road- the rear end of my car always looks like crap because of it. Gone soon!

 

Martin,
Would you mind posting a couple of pics of your progress when you do this? Not how to, just what it looks like off before you fill the holes. Thanks.

 

Yes, post some pics Martin.

 

This thread is a little bit old, but I'm in need of some rust/paint correction since a bubble has developed at the base of the rear quarter glass window on the driver side. The size is about 1" in diameter. I'm not sure if it requires cutting and welding, but I was planning on just doing a patch behind it and building it with Bondo if required.

Also, I have seen threads about rust on OB cars, but why is my S4 rusting in the same area???