OK - I want to do a cool suspension/frame project on this stock 96 Coupe. Seen a lot of different aftermarket parts - roof braces, x-braces, frame tensioner, sway bar updates, heim joint bushing upgrades etc.

Assuming that fabrication skills are readily available, and access to a lift and a shop, and willingness to strip the car down to access the frame.. what would you like to see as a project? Need to keep the car roadworthy and drivable in the street, so any "cage" setup would have to be subtle/inconspicuous. I'd love to stop all the squeaking and flexing! Greenwood wrote an article that was critical of the C4 design and in their (rare) G-350 and G-383 builds they did some frame mods, would love to know what they did. Lots of debate on the viability of cross-bracing. Gordon Killibrew's frame flex solution seems kind of a band aid?

If you are aware of any good articles - post them here!

 

If you haven't done so yet, I recommend going through this thread here: https://www.corvetteforum.com/forums...ollection.html. Although it's nominally about creating a "Vette kart," there's a trove of info on frame flex with some actual empirical work done by the OP to identify the weaker areas of the car.

 

thanks!

 

I'm that guy!

I also started THIS THREAD with a mission to understand the frame weak points better. I learned some things from that thread....but not nearly as much as I learned from the 'Vette Kart. I was convinced that the problem was in the rocker rails or the in the joints where the rocker rails connect to the "front" of the car and/or the "rear" of the car. However, when I started playing with the Kart, it seems alot more like the issues is due to a lack of cross members and/or a hinging of the two frame rails, about the firewall. I'd read about the frame having a "hinge point" in "Corvette from the Inside", but didn't understand what that meant. I think that I do now, but maybe I don't. Anyway, you can see vids that illustrate the flex pretty clearly in THIS POST (#257) and then scroll down to post #283 and you can see the same thing, in a full/complete car also.

Based on that, I think a big "X" that connects the shoulder belt mounting point to the lower seat belt mounting point behind the seats, might help....but IDK. I tried to test that philosophy with a chain (post #275), but that test was not fruitful. Chain may have a poor material to try to test with.

 

The harness brace I have that connects to the upper seat belt bolts and to the frame via the targa top holder bolts ( I never take the top off, so I removed the top holders from the interior) helped a lot. So did the camber brace I installed. The car no longer creaks and moans pulling into my driveway. (It slopes down so you come in at an angle and the front then drops).

I have the convertible x-brace I am going to install and see how that works, as far as bolt ons, other than the vette-to-vette braces (Gordon K design) that is about the extent of bolt ons available (there is a x-brace that is or was available from another company).

I read and followed Tom's threads and such and I believe these cars can be fixed BUT BUT BUT it won't be cost effective unless you have a great big stack of disposable money and a point to make.

If you study the frame of the C5's, you will see that GM added a brace structure across the bottom of the cars. It was/is such a big deal, that it was patented. If you had someone cut out the floor pan in a manner it could be reinstalled, and fabricated a similar structure, it would really stiffen the cars up. Then turn it into a real fixed roof coupe via permanent modifications to attach the hoop to the windshield frame. Along with a harness brace and camber brace, I believe the result would be an ultra stiff C4 that would really surprise people.

If you wanted to go a step further, the welded frame could be reinforced at all the weld/panel joints via formed plates, that are glued and riveted, bridging the welds, similar in engineering
concept to how airplanes are constructed.

For spirited (safe) fun driving, the mods I have done are almost enough. I need to get the x-brace under the car and see what that does.

 

After jacking my car up and down a couple hundred times over the winter... they definitely need some help everywhere. The frame itself is actually pretty strong... the problem seems to be like everyone said, the angles and twisting aren't really controlled well. If you hit a speed hump square the car really is stiff, its the other uneven loading that is the problem it seems. On the few smooth roads I have around its great. You get into anything that isn't though and you do notice it. Listen to the guys above. They know their ****.

 

I do know that the frames flex bad. Everyone says no, BUT, my buddy's '90, well now his daughter's '90 (he just completed a high dollar '69 restomod build) would flex if you jacked the side up bad. He jacked it up with the hood closed. The nose drooped, the hood hinge on that side was drug backwards due to the attaching mechanism. When the car was put back down, the hood didn't want to open and close. He took a 2/4, put it on the hinge and smacked it with a sledge to knock the hinge back forward to where is should have been to allow all components to align. Happened 2 times, subsequently he popped the hood as I told him to.

There is significant twisting and droop in the frames. There was a lot of compromise with the targa top after the fact decision.

 

Thanks guys - awesome set of opinions and resources. My plan is to try and get some meaningful measures so I can track progress, but I haven’t figured out what that looks like yet. Also want to be a little more specific than “it creaks and groans on my driveway”.. lol. Easy enough for me to fab up a couple initial solutions to test.

This will take a while.. first I have to fix a few “drivability” issues.. slight initial vibration while braking plus soft brake pedal on hot days (new master, fluid, stainless lines, pads, rotors going in), alarmingly loose throttle pedal, window travel limiters not working, loose drivers door card, losing coolant (I suspect Water pump). The joy of C4 ownership!

 

That's not normal. That sounds like a damaged frame to me. When was his car hit?

 

Never. His friend bought it new. We know the entire history of the car.

The only way to document (and prove) how much these cars flex is with a a rigid dial indicator setup (a 2" travel dial would work). We would need to rigidly attach a bar at say the midpoint of the door with the indicators out on the end of the frame (as far out as possible) then jack the car up and see the deflection. I bet it would alarm you.

Another way that might work is with a leveling laser. Open the hood up (this will allow the frame to flex, use the laser to run a line down the car. Use blue tape and strike a line across the
middle of the door, out on the hood and back on the rear of the rear quarter. Then jack up the car, raise the level to run with the tape line on the door and see if the front or rear or both has drooped.

I have a leveling laser and if anyone local wants to try this I will. Accuse me of wearing a tinfoil hat, but I use 2 jacks when lifting my car for the front, and a Gadgetman device for lifting the rear. I crack the doors and pop the hood.

I had a 1980 Z28 that I bought new. It had the GM T-tops (GM started putting their own t-tops in the Camaros in 1979). Before then, the t-tops were sourced and the structure across the top was quite wide. Anyway, that car would open both doors up and they would swing open when jacked up at its factory point. It flexed so much it actually popped the windshield.

I was advised to dump it and I used it as a trade in on the 1965 ragtop that started me into the world of Corvettes.

I can surmise that if the hood bolts were not as torqued down as much as they should have been that it allowed the hinge to slide.

My driveway angles down. There is enough of an angle up at the top, that I can put ramps and drive the vehicles on them and the car(s)/truck will be level. That is what I do when I change the oil. Lets me slide under the car.

Before I put the braces I have in my '96, it would really creak and moan when pulling into the drive at an angle (which unless I pulled into the neighbors drive across the street first) there is no way to hit it straight on. My car was owned by lady who took car of it and it only had 11,800 when I bought it in 2016. So it was actually pretty new.

 

How about the dash and components squeaked and rattled. The targa top seals squeaked. You know what a car sounds like when components are moving against each other and shifting.

 

After the other bolt ons, I would try making something like the Targa Truss, but with an X instead of the H. I think the top is the biggest weakness, that can easily be improved.

 

That targa truss is pretty substantial. I would suspect it is actually stronger than the windshield frame is.

 

The windshield frame is disappointingly flimsy.

 

Here is the Killebrew-designed frame after I installed it on my 91. I got down in a ditch to take the picture. One of the best mods I ever made to the car. Even with the targa top off it handled like a new car instead of one with 113,000 miles.

 

I did the R/D racing S/T frame thingy.. Its a 4 point roll bar, that bolts in.. I can lift the car up and balance it on one tire.. It made that much of a difference.
I have the roof connector and r/d racing camber brace
Lots of band-aids for a car that was never designed to be a targa or convertible.. They knew it too.
I have never been in a quick squeak free C4. Even sound dampening throughout interior. Stereo or windows down is the easiest way to fix the interior noises