[zimmej51]

Why Remove Original Seam Sealer

A friend asked me why I was removing the original seam sealer from the "dogleg" area just below the lower windshield corner, just inside the door jamb area. It was smooth and looked to be intact. It looked a lot better than the "before" picture below implies, I had already stripped some of the paint from it. And it did look totally usable. But in my experience I've learned that looks can be deceiving, especially in any windshield pinch weld area.

Our old "friend" Mr. Rust found a good hiding place...

Cleaned and awaiting fresh application of seam sealer.

Jamb area thoroughly cleaned, ready for fresh seam sealer and joint sealer.

So that's why, as a rule, I try and expose certain areas even though they look fine on the surface. Especially pinch weld joints around windshields and back glass on regular cars. I realize that you can't completely clean out the pinchweld, but you can get it as clean as possible and ensure that any additional water infiltration is prevented. It will make a big difference in the life span of the vehicle. In this case I had already repaired the other side of the pinchweld followed by careful inspection to be sure all potential leak areas have been corked up.


It's also interesting to note that this particular 81 has lived a remarkably sheltered life. In it's 48K mile life (confirmed by the way) it slept in a garage most of it's life with minimal exposure to the elements. Surprisingly, I actually could reuse all of the body mount bolts, notorious for rusting away. The point is, even with this pampered life, there was still significant corrosion caused by tiny leaks that developed most likely in the seam sealer. So I recommend taking no chances. If you are this deep into it you might as well do a little preventive maintenance. It WILL make a difference.

 

[77blue]

Your spot-on zimmej51, these are still 40 year old cars and even those low mileage, slightly used C3's can bear surprises. Mine had 9K miles on the odometer when it was parked but the owner obviously had no clue regarding storing a car. Parts of the car were pristine and others, well, not so much. Keep these informative posts coming !

 

[zimmej51]

Here are two WTF's for you....

Ok, maybe I've been breathing too many stripper fumes, but I thought I'd share a couple of those "WTF" moments with you.


Here is the first one.



"READ AND FOLLOW DIRECTIONS!" Ok, I'm cool with that. Let's see.... I have this can of "Aircraft Stripper" in front of me. It shows a picture of an airplane on the front. Check it out...

Ok, got it. Now let's look at the back side of the same can...

Well, that's just great... And I was thinking of refinishing that Airbus I have parked out back. Would probably be cheaper than painting this Corvette....WTF!!

Here's number two...
Holy crap, that HURT!!!..... WTF!!!


You have these..... these..... THINGS! See Below

If you look these things up in the assembly manual it says they are part of the front fender skirt or something like that. Don't fall for it. It's a trick.


After extensive research and shop experience I have discovered what these things really are. They are secretly known to GM insiders as "Model C3 Longitudinal Skull Splitters".


I have also discovered that these diabolical devices were designed with 3 primary objectives:


Objective 1: To cause you to stumble around in your shop cradling your head in both hands while quietly sobbing in a manner that only dedicated C3 owners are capable of.


Objective 2: To expose your brain so that your significant other can poke around and determine what is causing all this Corvette nonsense.


Objective 3: To give first year interns at the ER an opportunity to brush up on their suture skills after your wife has thoroughly whisked your brain with a salad fork.


These things I have determined to be facts.




Ok, back to work now. After my last year I find it beneficial to visit the lighter side of life from time to time! Cheers to all my new friends here!!

 

[lsejlowe]

Objective 1: To cause you to stumble around in your shop cradling your head in both hands while quietly sobbing in a manner that only dedicated C3 owners are capable of.

Objective 2: To expose your brain so that your significant other can poke around and determine what is causing all this Corvette nonsense.

Objective 3: To give first year interns at the ER an opportunity to brush up on their suture skills after your wife has thoroughly whisked your brain with a salad fork.

:rolling:

 

[lsejlowe]

Jamb area thoroughly cleaned, ready for fresh seam sealer and joint sealer.

Was this cleaned using the stripper you mention above or with an abrasive method like a wire wheel? Looks really clean!

 

[zimmej51]

Prepping door jambs for paint

Was this cleaned using the stripper you mention above or with an abrasive method like a wire wheel? Looks really clean!

I used the Klean Strip Aircraft stripper mentioned and grade 1 steel wool for the most part. The first step is to remove as much of the whitish seam sealer as possible using small scrapers. One of the best scraper tools I have for this purpose is a modified screwdriver. I took an old standard screwdriver, blade width about 1/4", and reground the tip so looked like a chisel. Flat on one side, tapered on the other. Since it isn't as hardened as a purpose built scraper it has to be resharpened frequently but also won't damage the surface as easily.


Another tool I used is a wire brush (bristles appear to be stainless) from the paint section at Home Depot. The handle is plastic, on one side it looks like a toothbrush while the other side has a round cluster of bristles at an angle. Works great for all the crevices, nooks and crannies. I would brush on the stripper, let it work for 10 minutes or so, then re-wet with more stripper. Then work the surfaces with the steel wool in areas you can reach and use the wire brush for the hard to get areas. The trick is to keep it wet with stripper while working, don't let it get dry.


I tried the Lincoln wooden handled brushes for cleaning welds but found them to be a little too stiff, too easy to damage the composite surfaces.



When done, neutralize by wiping with rags saturated with lacquer thinner, when that dries wipe it all down again with mineral spirits, then let it dry. Good idea to blow out all the crevices with air.



While the seam sealer comes off fairly easily, don't mess with the bonding adhesive unless you have a reason to do so. It is not sensitive to the stripper so paint and crap will come right off of it.


On reassembly, apply fresh seam sealer to the seams and any other area that needs it. Use care to apply only to the areas that need it. The factory used WAY too much IMHO. Most of these cars look like the sealers were applied in the dark with a 4" brush! Unnecessary and ugly.


Cleaning up the jambs was actually pretty easy, went far faster than I thought it would. If you have a car apart to this level, I recommend cleaning up everything you can touch. And, as I mentioned, be VERY suspicious of ANY pinchweld. These cars are old, and that is a very common place to encounter hidden rust.


One last thing, if you haven't read it yet be sure to check out the "sticky" by 7TRoadster. A treasure trove of good info.

 

[zimmej51]

Weld through primer failure

Sometimes I think it's important to share failures as well as successes. I read somewhere that you should always learn from the mistakes of others; you won't live long enough to make them all yourself!


So here's a bonehead move that I made when reinstalling the floor pan. I butt welded the new pan on the side of the tunnel and the rocker panel side (even though it doesn't look like it in the pic). The front is riveted to the fiberglass firewall. On the rear I decided to use a lap joint. As a rule, I don't like lap joints, especially in the floor, but in this case it looked like the best option.



The main reason I don't like lap joints is that no matter how careful you are there always seems to be a pin hole somewhere that lets moisture get in. To combat this a pinch weld, a common technique is to coat both inside surfaces with "weld through primer", then spot weld the flanges together. So, without thinking this through, I created a monster.


I don't have a spot welder, and even if I did it wouldn't work here because I wouldn't be able to get to both sides. In the past I have emulated a spot weld by using a sheet metal hole punch to poke holes in one side of the lap joint and welding through the hole to the other panel. So I poked the holes, then decided to paint both sides of the lap joint with Weld Through Primer to help prevent rust. That's when things went way south.


When I would attempt a mig weld in the hole, the primer was exposed and the weld just went bat-stupid in about 9 different ways. It actually seemed to repel the bead. Luckily I had only tacked the pan in so I was able to remove it and start over. It was an absolute disaster! I'm not an expert welder, but I'm a long way from being a novice. I've never had anything screw up that bad with welding. In the end, after removing all the Weld Through Primer, I got it welded up with no problems.


I don't have a pic of the actual screwup, but the attached pic shows the lap joint on the left side where the problem was. This was taken during fitting.

 

[zimmej51]

Driveline Angles

Had a discussion today with our oldest son regarding drive line angles. He's into trucks and getting his feet wet installing lift kits and so forth.



So the subject of correct drive line angles came up. Everybody knows that ideally the longitudinal center line of the rear differential should be parallel to the longitudinal center line of the engine/transmission. Otherwise the speedup and slowdown on each revolution of the drive shaft can create some nasty vibrations.


But wait, have you ever looked closely at the drive line angles on the C3 with the body off and the drive line in place? You will see that the center lines of the differential and transmission are anything but parallel. What's up with that?


The method of making the diff center line and transmission center line parallel to each other is often called "Type Z" because if you look at the angles from the side, the center lines and the driveshaft make kind of a "Z".


There is another method, not commonly used, called "Type W". In this case, the drive shaft center line becomes the reference point. If the differential is rotated so that the pinion points down towards the ground with respect to the drive shaft center line, AND the transmission main shaft ALSO points down towards the ground with respect to the drive shaft center line, then you have a "Type W" drive line angle. And that's exactly what the C3 uses.


On a "Type Z" setup, the task is to make the center lines PARALLEL to each other.


On a "Type W" setup, the task is to make the angle between the differential center line and the drive shaft center line EQUAL to the angle between the transmission center line and the drive shaft center line.


I was able to get mine pretty close. The differential center line points down about 3.8° and the transmission center line points down about 4.3°.



The pics show the measurements before I started the alignment. For simplicity you can subtract the reading you get from 90°, but you don't have to. The goal is for both measurements to be equal. It is important to jack up one end of your frame so the installed drive shaft is level (0°) OR measure the drive shaft center line angle and use that reading as the reference point. Either way works, but's it's easier if you position the drive shaft level.


If you want to study up on all this Google "Drive Line Basics Machine Service Inc" and look for the booklet "Drive Line Basics". I extracted a couple of pages and posted them here as jpegs, couldn't figure out how to post a pdf.

Hope this helps if you are working a drive line vibration problem.... Cheers!

 

[77blue]

Thanks zimmej51 - I don't believe I have ever heard of, or at least recognized the "W" configuration. Even searching for it after I read your post I didn't find much - lots on the "Z" but short on C2/C3 specific info.

 

[zimmej51]

Thanks zimmej51 - I don't believe I have ever heard of, or at least recognized the "W" configuration. Even searching for it after I read your post I didn't find much - lots on the "Z" but short on C2/C3 specific info.

Yep, not much out there. It's not commonly used. I actually don't remember where I first learned of it, but I think it had to do with some accessory drives on aircraft. Decades ago I worked for an avionics company that did a lot of contract work for all kinds of aviation stuff.

 

[zimmej51]

Driveline Angles

One thing I neglected to mention regarding the alignment of the Type W driveline. Since the driveshaft centerline is the reference point, anytime you change the angle of the differential and/or the transmission, the drive shaft angle will change too.



So, after an adjustment, you must re-level the driveshaft by raising or lowering the frame from either end. Then take your measurements again. It's a little tedious, but not all that hard.


Also, you don't have to re-level the driveshaft, you can just do the math and calculate the angles as a displacement from the drive shaft centerline. But you gotta do one or the other!


Point is, you have to recheck everything after an adjustment and keep tweaking it until it's right.

 

[zimmej51]

Weatherstrip Recommendations

I will soon be at the point of ordering all new weatherstripping, everything on the car. In searching this forum as well as other forums I keep seeing CRC getting mostly good reviews. Anyone here had experience with them? Any other recommendations?

 

[zimmej51]

Door Hinge Slop

I have the doors off of my 81 and I'm wondering what the wear limits on the hinge pin and bushings are. I haven't measured it but I'd estimate the slop to be around 0.004 inch. Does this indicate that "re-pinning" the hinges is necessary?


Actually, now that I think about it, I guess what I'm really asking is how much slop does a freshly overhauled hinge have? I'd hate to go to all that work only to find out that new ones have slop close to what I have now!

 

[zimmej51]

Door Hinge Slop

I have the doors off of my 81 and I'm wondering what the wear limits on the hinge pin and bushings are. I haven't measured it but I'd estimate the slop to be around 0.004 inch. Does this indicate that "re-pinning" the hinges is necessary?


Actually, now that I think about it, I guess what I'm really asking is how much slop does a freshly overhauled hinge have? I'd hate to go to all that work only to find out that new ones have slop close to what I have now!

Never mind, I'm gonna change them out. No time like the present while everything is all apart.

 

[zimmej51]

Stripping almost done

Almost finished with the paint stripping. All I lack is the other side of this hood. Here's some before and after.

 

[zimmej51]

What is this on my hood??

I had the entire car stripped with no surprises and the last panel was the top of the hood. I immediately discovered that the first layer of hard, black primer was noticeably thicker than anywhere else on the car. Then I discovered why.



Many areas on the surface of the hood panel were peppered with hundreds of small "dimples". Several months ago during my experiments with vacuum forming ABS I overheated several sheets of the plastic and the result looked identical to what I'm seeing on the hood. Whatever it is, I'm certain it was there when it left the factory. There is no evidence anywhere on the car of any previous body work.



Has anyone ever seen this before? I guess I'll just do what GM did and lay on a little extra primer. I don't know if this is something unusual or if it is typical of GM quality back in the Roger Smith days.


The dimples are mostly concentrated in the circled areas.

The next 2 pics are zoomed in on the area in the large red circle on the left in the above pic

The next 2 pics are from the nose area of the hood.

 

[zimmej51]

What is this on my hood??

Just a follow up here, a reliable source (7TRoadster) identified this anomaly as most likely being excess release agent in the molds when this sheet was formed. I didn't think this would be a serious problem but it's good to get a second opinion.


Guess I'll just make a few more passes with the spray gun when I get to this area!



Meanwhile, pressing forward....

 

[7TRoadster]

Meanwhile, pressing forward....

How is progress, haven't seen you post in a bit.

 

[zimmej51]

How is progress, haven't seen you post in a bit.

Just getting started again, almost ready to spray the Featherfill. My leukemia relapsed a month or so ago, been spending time at MD Anderson in Houston. Back on track now, should be making more posts very soon. By the way, thanks for asking!

 

[lsejlowe]

Just getting started again, almost ready to spray the Featherfill. My leukemia relapsed a month or so ago, been spending time at MD Anderson in Houston. Back on track now, should be making more posts very soon. By the way, thanks for asking!

:thumbsup: