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C4 Coupes vs C4 Convertibles - A question

OldCorvetteFan

Well-known member
Joined
Jul 3, 2005
Messages
117
Location
Northwest Illinois
Corvette
Black 95 6 spd Coupe (Sold); 2011 GS
I have a coupe. I know lots of people that have coupes. One of the things that coupe owners talk about is the way our coupes feel when we take the targa top out - the descriptions range from mild symptoms of less than stellar chassis rigidity to tales of feeling like the center of the frame was rotating about an axis (and it's right under you!).

My experience is about in the middle - when the top is removed, I can feel it in the steering column, as it picks up this very odd horizontal oscillation at low speeds, and just moves a lot when encountering rough pavement. The car also complains by generating more squeaks and rattles. Railroad crossings become a real adventure, as the car seemingly flexes through them rather than driving over them.

Here's what I want to know - do you convertible driver's contend with the same thing? Does your car flex and move around? Do you get significant cowl shake and movement of the steering column?

I know that convertibles got some additional bracings (primarily the cross brace under the car). However, there are coupe owners that have purchased not only the cross brace, but the camber brace, and the targa bar. These items usually help, but don't cure, the problem.

This is a concern of mine because a friend of mine is on a quest to obtain a convertible C4 or C5. I don't want to recommend a C4 vert if it's gonna feel like the automotive equivalent of the Straw Man.

I'd appreciate your feedback - both coupe owners that may have gotten their flexure under control, and convertible owners that can shed some light on the vehicle's characteristics compared to the targa-less coupe!

Thanks,
Steven
 

*89x2*

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Feb 18, 2002
Messages
10,357
Location
CallawayOwnersGroup.com
I have coupes and a convertible and in all hoesty, none have ever demonstrated a "dangerous" degree of shake, certainly never any unsafe feelings.

It is true that the convertible has the factory X-brace bolted at various points underneath it. I do not think the aftermarket one uses the bolts in the floor, only at each corner ;shrug they could have redesigned it by now however, I do recall the design when it was introduced almost two decades ago.

I have no regrets with my cars (c4s), but your friend should drive a few, at least, as many cars will differ in quality. I should add mine do not squeek or rattle like others have reported over the decades. Maybe I got lucky ;shrug

I hope this helps :beer
 

OldCorvetteFan

Well-known member
Joined
Jul 3, 2005
Messages
117
Location
Northwest Illinois
Corvette
Black 95 6 spd Coupe (Sold); 2011 GS
I don't regard it as dangerous - just different.

Are you saying that your convertible doesn't feel like your coupes do when their tops are out?

It could be that what I'm feeling is muscle memory - when you get used to the way car feels with the top in, and then you feel something different with the top out, it's kind of startling. That said, I drove with my top out yesterday for over sixty miles, and after I got out of town, I didn't notice it either (until I crossed those railroad tracks).

Thanks for the reply!

Steven
 
F

fatboyreyn

Guest
I have an 86 coupe and don't really notice the flexing as you say. I also have 90% of the rattles under control. Then again I avoid rough roads, and cross railroad tracks like a old man. But don't get in front of me on a smooth highway.
 
Joined
Apr 18, 2002
Messages
1,441
Location
Staten Island, NY
Corvette
1999 Torch Red Coupe
The C5 Vert and the C4 Vert are very different in ride with regard to flex. The C5 Vert is almost the same as the C5 coupe.

The C4 I owned, and the C4 Verts I have driven were much less rigid than the coupe. The coupe had noticeable flex with the rooof panel off.
 
T

tonylong

Guest
I've never noticed any flexing or cowl shake at all - with top up or down. My ride is an 89 vert w/60,000 miles. No mods - original shocks, springs, etc.
 

Ruby Fan

Well-known member
Joined
Oct 7, 2004
Messages
189
Location
NY
Corvette
1985 Black Beauty Coupe, 93 Ruby, 96 CE vert
I understand the C5 and C6 were designed as convertibles first, so they are both suppose to be more rigid than previous verts, meaning you are not suppose to notice much of a difference, that is between the coupe & vert. The C4 was set up as a coupe, then the law changed making it possible for manufacturers to produce convertibles in '86. So in effect the convertible C4 is an afterthought of sorts and could be much different than C5/6. I have both versions of the C4 and enjoy them very much. If I ever bought a C5/6 I would get a vert, the coupe would just make a better speed racer, as the Z06 is only fixed roof.
 

SPANISHVETTS

Well-known member
Joined
Nov 5, 2002
Messages
1,143
Location
El puerto de Santa Maria Spain
Corvette
before 60,63&82 now 90 383 Stroker & 91 ZR1-Sold
Thunder has an X-brace from an '88 vert and the beefed up torsion bar from the trany to the 3rd member. I still get a lot of flex but the 383 is throwing out in excess of 450 ftlbs of torque.

I have only removed the top one time for the wife's birthday 2 years so it is really a non issue here but with a close to stock power plant I do not think that you will experience many problems and if you are pushing a 20 year old car that hard with out the proper mods you deserve what you get.

I never removed the top from the ZR-1 but the zed's power came on so far up the torque curve that a lot of energy was already transfered into the chassis negating the un-happy feed back to the driver.

On the street the Zed was more driver friendly than Thunder because you could come off of the clutch at 2000 RPMs with out enough stupid HP to light up the tires... Thunder comes on at 2200 with more torque than a stock LT-4 at 4K and loves to cause trouble in the round-a-bouts. Let your right foot get silly and you will make a fool of yourself.

The C4 is probably the best platform that GM ever sold to the public but the bean counters made sure that the cars we bought were only a fraction of what they were designed to be.

End of story:
Build your C4 to be ¨your car¨:
If you never go to the drag strip you have no use for a rearend bigger than +/-3.50.
If Auto-Cross is your thing then the springs and shocks need to be changed and the steering is suspect as well. You will need to buy some more shims to get enough Camber into the front wheels.

If the car is a daily driver a few performance mods will keep you happy for a long - long time.

If the body flex makes you nuts then go drive the competition... you will be happy when you get home.

All of Thunder's torque comes on before 4000 RPM and I can see the body flexing... sometimes I think that the windshield may pop out but the Euro trash trying to run with me are having much worse problems...

The C4 is one f'ing great platform up to about 750 HP. After that you should be looking at a CR-6.:D
 

Radar

Well-known member
Joined
Oct 23, 2001
Messages
200
Location
Oconomowoc, WI
Corvette
1989 Medium Blue Metalic Convertible
Hi all!

I have an 89 vert. I do notice some cowl shake but it is not bad by any stretch of the imagination. My car is basically rattle free and I can even take RR crossings well. The car has a beefy factory x-brace that looks bolted to the front and rear rails. The brace also appears removable so one could get the exhaust and drive shaft out.

My Vett is faily stiff but not even close to the rigidity of the newer C5's and C6's. Those chassis are really nice. But I like my C4 convertible. It looks good and I only have a small investment in it.

Regards,
Radar :beer
 

vee93

Well-known member
Joined
Nov 15, 2002
Messages
585
Location
Mississippi
Corvette
1993 Medium Quasar Blue Metallic Coupe
What you're experiencing is flex in the body. The fact is that the C4 coupe was originally designed to be a t-top vehicle. The head guy with the say so at the time nixed the t-top design inspite of testing results indicating body flex would occur with the targa top off the car and gave the word to build the Vette with the targa top.
Uneven ripples in the road will cause the vehicle to bounce around a bit. Pot holes and dips will cause a coupe C4 to flex. Tip-top suspension can tamp this down a bit, but it'll still occur.
I've experienced it myself while taking a curve or two and found the road to be uneven. Not fun.
C4 convertibles don't have this problem. A degree of rigidness in the C4 coupe body is missing because the stiffening factor is missing when the targa top is removed.
You can counter your Vette flexing by purchasing an aftermarket brace for when the targa top is off the car. TTR Performance offers an anti-flex bar--http://www.rlenterprizesinc.com/TTRperformance/index.html
I think I remember Corvette Central offers something called the targa truss bar (basically the same design as the TTR one) for about $400 and some change. They aren't cheap.
'Course you could just be extra careful around the rip-rap in the road when the top is out and carry on. :w
 

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