Tied of my daily driver an '05 Grand Prix with 140k miles handling better than my 72 sb/auto/roadster.
Tied of the front end shimmy when going over rough roads, average cornering and NOT having the confidence to take curves fast.

Car has unknown coils, 3/4" original sway bar, Bilstiens in the front, in the rear, an older 7 leave spring w/8 inch bolts, KYB shocks, VBP adj strut rods, no sway bar. Steering is as good as it can get for stock!

Leaning towards the VBP Grand Touring plus package with
460 lb coils, 330 lb composite monospring rear
Bilstein Sports on all corners
ADDCO 1 1/8" front and 3/4" rear, sway bars
Adj strut rods (which I have)
Also considering a spreader bar, read here on the CF this would help with the shimmies!!
Just want a decent ride and decent handling.
Concerns are the ride height with the 460 Lb GT springs, any twitchiness I read about when a rear sway bar is added
I would appreciate any and all comments. Thanks

 

Not sure what your budget is, but I have the VBP Performance Plus Suspension full kit, offset trailing arms, 17" x 9.5" wheels with 275/40 ZR17 Nitto NT555 Extreme Performance tires front and rear, VBP spreader bar, replaced steering and have a blueprinted steering box by Gary, and replaced the steering rag joint with a Flaming River SS u-joint. Drivetrain is a 383 with a T56 6 speed and 370 rear.

Just to give you some ideas.

 

Mike I like the idea of the T56 6 speed!!
How does that fit in C3?

 

"front end shimmy when going over rough roads, average cornering and NOT having the confidence to take curves fast.

The above does not translate to...

"Steering is as good as it can get for stock!"

However if you throw enough money at it the steering system can be improved.
I would start with the spreader bar.
Are you sure ALL your stock components are in good condition?

 

First, make sure all of the steering components are in good or better shape- tie rod ends, idler arm, pitman arm, center link, steering box and rag joint. Then look at ball joints and control arm bushings. Alignment can have a profound effect too. And if any of the components are sloppy, alignment won't matter too much.
I replaced the control arm bushings in my 69- just because they were very ugly looking. Had an alignmnet done- they set it up to the specs I provided them. Drives straight, and handles very well. Without any aftermarket big $$ parts. I did use poly bushings, the cost difference was not a factor, and I'll most likely never have to replace them again.

 

Some modifications, not too bad though. Here's a thread I did on my swap. Definitely an awesome upgrade to do!

http://forums.corvetteforum.com/c3-t...gs-list-7.html

 

Hi there, the best mod I did was to go with the Borgeson steering conversion. The stock vette has a needlessly complex steering setup and I never liked the control valve setup and when I saw the Borgeson set up doesn't need that then I was all ears, you replace the control valve with a manual setup as the new modified Delphi Jeep steering box has the power steering lines running straight to it, it simplifies the steering and you get a new box, go with a solid rag joint as mine fell apart within a year. also replace the idler arm with a bearing version and replace the ball joints and steering ends with new branded ones and your steering will be like a new car.

You could also go with rack and pinion, I would have done this over the Borgeson had I known the steering box slightly moves on the frame when turning the wheel, it's the way the boxes are bolted to the frame, does it with the standard box too, this doesn't matter too much on a stockish car but mines a pro tourer and I can see the rack being more rigidly located.

On top of this get offset top arms to get more caster and align it yourself. Caster is what keeps the car stable in a straight line. Our vettes have say 1 degree of caster and a C5 has up to 7 odd, there's a reason for it, My VBP arms give approx 3 degrees ( all from memory!)

Older cars don't have much caster so they could be driven with manual steering, but modern cars have much more caster for stability but you need power steering with caster as the more caster you have the harder it is to turn the wheels, modern cars all have power steering now hence they all have lots of caster

 

add - change the upper control arms (front, obviously) to tubular. Your car was designed for bias-ply tires, changing the front geometry (specifically, the caster) will make a load of difference to how it handles.


I removed the power steering altogether. I may go with a rack and pinion at some point, but it handles well-enough now that it's not really even on the to-do list

 

Thanks for all the replies, I need to clarify what I mean by "shimmies". Its not the steering.
On rough or bumpy roads the front of the car seems to bounce or maybe oscilate. Believe some call it "cowl shake" ?? Steering is tight, ball joints are good. Car tracks straight and is stable at higher speeds, it's just this bad behavior on rough roads. Maybe thats just the character of C3 roadsters

 

I have completely redone my front and rear suspension piece by piece over the last 30 years so that i could access each change made and I wanted to keep the stock suspension design. The key to improving the stock suspension design is to eliminate any and all play in the stock components. As others have noted, make sure that all stock components such as tie rods, idler arm, ball joints, Trailing arm bushings are perfect first, then:

Front suspension:

1. upper and lower poly control arm bushings
2. Stock 1 1/8 inch sway bar with poly mounting and endlink bushings
3. Speedirect spreader bar-this is a must to stop chassis flex-all C3's need a spreader bar.
4. 550 springs 1 inch shorter than stock
5. Bilstein HD shocks with poly bushings
6. GTR 1999 Custom blue printed/rebuilt OEM steering box-This step is a must to eliminate all play in the steering-A borgeson/R&P Steering will not "improve" handling but handling feel along with a quicker steering ratio. This change has transformed the steering using the stock components-Could not be happier! Not as good as my 10 Z06 but pretty darn good for a C3!
7. 255/45/17 ZR tires and rims-This is a must! You will never achieve optimal steering response, handling and feel with 255/60/15 S/T rated tires. Ask me how I know?

Rear Suspension:

1. VBP 360 Composite spring with poly mounting bushings-Ditch the steel spring for better rear reaction time and ride-installed in 1986-AND it will save 40 lbs off the rear end. Considering a 420 spring since I would prefer a slightly stiffer ride-believe it or not.
2. Competition Adjustable struts with heim joints-NO Bushings-this is a must.
3. I replaced the 7/16 rear oem sway bar with a 3/4 inch OEM type bar, NOT an aftermarket bar with the endlinks like the front bar-Allows more movement of the rear trailing arms.
4. Bilstein Sports (30% stiffer than the front HD's)
5. Modified Shark bar behind the rear seats that ties the bird cage to the floor.
6. 255/45/17 ZR tires.

The car rides, steers, and handles better than most C3's I have ever been in or seen! It's not harsh at all.

BTW-I have a 2001 Grand Prix SE as a train/airport car and it too motivated me to make some of the recent changes to the 78. The GP has strut tower braces front and rear, Oldsmobile Intrigue variable rate Moog rear springs, GM performance (AKA police sways bars-front and rear) and 225/55/16 ZR tires.

Hope that helps!

 

420#.... the only way to fly - especially if your car is lowered

 

mine.... and i have a C4, a C5 and a C5 guldstrand... and my C3 kicks all there butts out at Willow Springs Raceway!!!

Lowered about 2-3" over stock
18" custom Centerline 2 piece rims
BFG tires

Front:
550# springs cut 1/2 coil
Bilstein sports shocks
poly bushings
spreader bar
Rack and pinion steering
1 1/4" sway bar


rear:
3/4" sway bar
360# composite spring
Bilstein sport shocks
poly bushings everywhere
10" bolts


and alignment per VBP chart for road racing

 

I assume you did not convert it and you are using power steering components to run manual, whats involved in that process?

 

I converted it to manual. I bought the manual conversion joint from (IIRC) eckler's (maybe Mid America).

I drove the car after I took the control valve internals off, but before I swapped the manual conversion joint - it was kind of scary.



I think global west is a sponsor.... if not, I don't care - this was the easiest illustration to find. Support the site sponsors (and schmidt)...

http://www.globalwestperformance.com...-steering.html

 

the replacement moog idler arm is a big improvement over my original delco arm.ball joints and idler arm can be a bit harder to troubleshoot play in.

 

It should go without saying that there's a lot more to improved handling than simply changing springs or installing larger bars. But, it seems much advice on the subject misses some important fundamentals regarding such...

Regardless of your intended purposes, understeer/oversteer balance is always affected by spring and/or bar changes which alter the front/rear percentage of anti-roll resistance. Get too much of that resistance on the rear axle relative to the front (~80% front is where most C3's ought to be) and your car will have oversteer, period. Thing is, many a car which would oversteer at or near its limits (where balance ultimately counts) will often feel great when driven at only 7 to 8/10ths of those limits or less. My advice is to tread cautiously if you choose to run a lot of rear spring and/or rear bar.

Unfortunately, comfort and performance are pretty much at opposite ends of the scale; the more of the one you wish to have, the more you'll have to compromise the other. Soft springs require more bar to control roll, while firmer springs require less to do so. The catch is that larger bars don't do anything to reduce dive or squat, but they do increase lateral weight transfer (read, "reduce available grip"). The extent to which you can improve handling depends a lot on how firm a ride your backside is willing to tolerate.

The reason I went thru all of that is so you'll better understand when I suggest you start out on true F41 or FE7 spec bars and springs and see where you are relative to where you want to be. Honestly, 550# front coils aren't all that stiff (I'm on 860's), given that C3 front wheel rates are only ~1/2 of the spring rate. Also, few C3's really need more than an F41 rear spring, and that's the one you virtually sit on.

In any event, whatever are your purposes, don't overlook any worn components which can affect handling and response, use only quality bits (Moog, et al), definitely install a spreader bar, and precisely align to specs which most closely match your purposes (VBP's are as good as any baseline from which to work). If practical, lower your ride heights to as near 1" to 1.25" front "Z" and 1.25" rear "D" (with your approx. weight in the driver's seat and a full tank) as the roads you most often drive will allow. And, lest it go unmentioned, no single mod will do more than installing the best tires you can afford. Hope that's worth $.02


TSW

 

If you have a problem on rough roads,as you state,perhaps the shocks are not correct for the spring rate you are running.
You state that you have an older 7 leaf spring. It may be worn. And you also state you don't know what the rate of the front springs are.
With a properly tuned stock system you should have none of the oscillation you describe.
I would recommend new springs with shocks that will compliment those springs. You may be surprised with the stock set-up when tuned properly.
I personally like the composite rear spring over the steel leaf style.

 

The frame on our old lovely cars is, basically, ridiculously flexible. Especially compared to modern cars. The first thing Chevrolet (or any manufacturer) always does when they upgrade any car, through each generational redesign, is to stiffen the frame. This dramatically improves the ride, handling, and the occupants chances of surviving a crash.
Everybody has their own opinion. Here's mine.
Putting very stiff springs and sway bars on an old Corvette will twist the frame as much as it loads the tires.
Put the brace across the front spring towers. Install toe steer blocks on the steering arms. They lower the outside tie rod ends and improve the bump steer. VB&P and Guldstrand both sell them. Don't use a front sway bar any bigger than 1". Use a 9/16 or 5/8" rear bar. Stay away from the higher than stock spring rates unless you are racing/autocrossing. Keep the Bilsteins.
Have fun.

 

I agree! The spreader bar should be mandatory on every C3 and a shark bar behind the seats certainly will help dramatically .

However, i do think that a 1 inch bar is the minimal thickness for a front bar and highly recommend a 1 1/8 inch bar that came with my gymkhana suspended 78 from the factory. Balance the front bar with a rear bar of 7-9/16 inch sway bar and don't use rear bars with non factory end links. Hope that helps!

 

how does a shark bar help handling?


granted, I did a bit more than was suggested - but I'd never say it helped handling