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Question: 63 SWC: Advice on Suspension Changes

Jds3660

New member
Joined
Dec 15, 2014
Messages
4
Location
Waterford, MI
Corvette
1963 Split Window Coupe 327/340hp
I own a ‘63 SWC and will be going through the front and rear suspensions soon – I’m contemplating a change to the shocks and springs while I have the car apart. My dilemma is this – whether to go with the “stock” 1963 parts versus upgrading to Z06/F40/F41 type parts while I’m doing this.

Let me first say make these disclaimers/explanations:
The car will never be a track car. Nor may it ever be an NCRS-type restored car as it has a non-numbers matching engine block, and I have run into dead ends being able to get the original paperwork for the car. What I can say is everything points to it originally being a 340hp Hi-Po. While I try to put “correct” parts on the car as I replace different things, I am willing to do deviate from original to improve drivability or durability (examples I’m considering – dual master cylinder change, front disk conversion, stainless exhaust). I also am willing to do things that would move it into what I would call a “Day-2” car (examples – ET Sebring wheels that look like the Halibrand racing wheels GM used in the period, and 670-15 Coker radial reproduction tires that look like period bias-plys).

With all that said……..here finally are my questions for the group:
1) When comparing the Z06/F40/F41 spring specs to stock – they appear to be significantly stiff. The specs show the springs are roughly double stock (550# front vs. 260#, 270# rear vs. 160#). Would I regret putting a setup like this on a street driven car – does anyone have a car so equipped? I see that some packages out there go somewhere in between stock and Z06/F40/F41 (example-a “GT” kit at Eckler’s that uses a 460# front spring).
2) Was the factory able to “get away” with such stiff springs because they also were using relatively small sway bars, and were tuning with relatively soft bias-ply tires at the time? Keep in mind I intend to stay with a stock looking 15” wheel/tire, so there will be some compliance there.
3) Note I’m somewhat reticent to use a composite rear spring – not only because it is a visual tip-off the car is modified (whereas a 7-leaf Z06 spring would require a 2[SUP]nd[/SUP] look), but also because I’ve read negative things about composite springs failing catastrophically. Does anyone have real experience with a composite spring?
4) If I buy a kit or package, I see a couple different shock types offered. I’ve seen Delco performance shocks, Monroe and KYB’s recommended. Without knowing the specifics of how these are valved, I’m flying blind. Any recommendations? I see Eckler’s pairs KYBs in their suspension packages. Most other companies offer bits/pieces separately and I don’t know enough to match up shocks to springs unless I see them in a pre-matched kit.
5) I am also considering Poly bushings. First, to firm up responses, but also because I’m thinking they will be more immune to dry-rot versus a stock rubber piece. But I have also been warned they can squeak. Does anyone have any experience with these?
 

00fxd

Well-known member
Joined
Feb 14, 2003
Messages
358
Location
B.C. Canada
Corvette
'65 Convertable
I'm not sure if you have ridden in a Composite rear spring equipped car. I have ridden in a couple. Both owners expressed to me frustration at the bounciness of of the ride which I also noticed was very prevalent. NOT GOOD. The shocks that come/came with the system don't solve it. I know that some have solved it but had to work at it - special shocks etc. It's not a done deal so beware. Made me avoid it and I have the composite system on the front of my '65. I think the front system is a lot of "Bling" too. Cool Idea but not really a lot of benefit.
Regarding Urethane bushings, do your homework there too. For instance the. trailing arm bushing only are designed to rotate but in service they need to be able to move in and out as well. And there are many reports of some urethane bushings deteriorating to - "turning to dust"
after several years. Possibly alternate chinese manufacturers/suppliers.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,452
Location
CenCoast CA
Corvette
71 04 12 19
(snip)
With all that said……..here finally are my questions for the group:
1) When comparing the Z06/F40/F41 spring specs to stock – they appear to be significantly stiff. The specs show the springs are roughly double stock (550# front vs. 260#, 270# rear vs. 160#). Would I regret putting a setup like this on a street driven car – does anyone have a car so equipped? I see that some packages out there go somewhere in between stock and Z06/F40/F41 (example-a “GT” kit at Eckler’s that uses a 460# front spring).
How a car rides, as well as, it's level of noise and harshness are subjective characteristics. If your daily driver is a modern car mid-sized or larger, it's not going to matter if you have base springs or HD springs, your 63's ride quality will be awful in comparison to what you live with every day.

2) Was the factory able to “get away” with such stiff springs because they also were using relatively small sway bars, and were tuning with relatively soft bias-ply tires at the time?(snip)
Yes and no. By 50+ year old standards, an F41 car really didn't ride all that bad, considering the chassis was aimed at road racing. The stabilizer bars are a minor issue with ride in many types of driving but tire are a major issue and, yes, the high-profile tires of the day improved the situation with harshness and noise. Modern lower profile tires transmits a lot more of that.

3) Note I’m somewhat reticent to use a composite rear spring – not only because it is a visual tip-off the car is modified (whereas a 7-leaf Z06 spring would require a 2[SUP]nd[/SUP] look), but also because I’ve read negative things about composite springs failing catastrophically. Does anyone have real experience with a composite spring?
I've been using a composite rear spring on my 71 since the late 80s.. I wouldn't put anything else on it. They are more durable than steel springs. As for "failing catastrophically"–any spring can break. I've had two steel leaf springs break on C2s and C3s. The plastic spring I have on the back of my Big-Block Coupe has been there for about 25 years. The belief that composite leaf springs are prone to breakage is a myth.

4) If I buy a kit or package, I see a couple different shock types offered. I’ve seen Delco performance shocks, Monroe and KYB’s recommended.
Delco and Monroe are junk, IMO. KYBs are marginal but acceptable. If you want good shocks for a C3 try Bilstein which are quite good. Real good are QA-1s.

5) I am also considering Poly bushings. First, to firm up responses, but also because I’m thinking they will be more immune to dry-rot versus a stock rubber piece. But I have also been warned they can squeak. Does anyone have any experience with these?
I have poly in only one place on my C3, the rear trailing arm end bushing. Otherwise I use Global West Del-A-Lum "bushings" or I have spherical bearings. That said, my 71 is a serious hot rod which does not see daily driving very often. Poly bushings are ok as long as you use the graphite-impregnated versions and, even then, are wiling to listen to squeaks and groans in cold/wet weather. You'll also find that poly suspension parts will increase noise and harshness. DO NOT use poly bushings in the rear strut rods. Use either stock rubber or spherical bearings.

As for rubber bushings being short lived due to "dry rot", if you buy crappy Chinese replacements, I suppose that can happen but if you buy top quality rubber, such as Moog chassis parts, rubber bushings last a long time.

Finally, take a look at Zip Products as far as a source for C2 suspension parts. They have a great stuff, competitive prices and great service.

P.S. OMG. I just noticed you are in Waterford MI. You guys in MI have roads worse than we do in California. Because of that, if you are going to drive the car on the street much at all, I'd think very carefully about suspension mods which increase harshness and noise. I visit the greater Detroit area about once a year and I was just there for a visit to GM Powertain in Pontiac. I noted on I-75 and I-94 potholes big enough for a Smart or a Mini to fall into.
 
Last edited:

kpic

Well-known member
Joined
Mar 29, 2014
Messages
2,292
Location
Columbus, NC/NE Georgia
Corvette
1997 boosted silver coupe
P.S. OMG. I just noticed you are in Waterford MI. You guys in MI have roads worse than we do in California. Because of that, if you are going to drive the car on the street much at all, I'd think very carefully about suspension mods which increase harshness and noise. I visit the greater Detroit area about once a year and I was just there for a visit to GM Powertain in Pontiac. I noted on I-75 and I-94 potholes big enough for a Smart or a Mini to fall into.

I worked in Detroit for two years; I lived near Clarkston up 75. The road was terrible and the neighbors got the county to attend a meeting. The county's representative said the road was in good shape. I suggested when he left he do the speed limit while holding his tongue between his teeth. ;)
 

00fxd

Well-known member
Joined
Feb 14, 2003
Messages
358
Location
B.C. Canada
Corvette
'65 Convertable
Hib, what rear shocks are you using on your car? Apparently there are some specially valved Bilstiens available but you have to hunt them down. Both cars that I have experience with received rear spring "kits" with shocks - Bilstiens. They bounced so bad that I could not believe that the manufacturer could get away with selling a product kit that produced those results.
Further, I am under the impression that the trailing arm front bushings are one of the positions that one should refrain from using urethane due to the fact that trailing arms don't just rotate on their axis but the bushings also need to flex inward in their travel. I know that you are a respected technical guy so where am I wrong here on my conclusions?
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,452
Location
CenCoast CA
Corvette
71 04 12 19
I'm using Bilsteins with "Sport" valving. I've had them on there for years. My experience is that Bilsteins have great durability. As for the Sport Valving, Bilstein used to sell two grades of C2/C3 shocks, "regular" and Sport valved. I don't know if that's the case today.

If I had it to do over again, I'd probably use QA-1s.

As for cars with composite rear springs being "bouncy" that's because, when you go to a single leaf you loose the internal damping in the spring that a multi leaf steel spring offers, so when you go to the plastic spring, you need a more aggressive shock to compensate.

With the plastic spring, if you have the proper rate and the right damper, it won't bounce.
 

00fxd

Well-known member
Joined
Feb 14, 2003
Messages
358
Location
B.C. Canada
Corvette
'65 Convertable
Bilstien used to offer "Heavy Duty" and "Sports" for c2-3 Corvette application - "Sports" being the stiffer . I see now that there is nothing in their on-line catalogs for c2/3 anymore. Vette brake still shows "Sports" available. I at one time considered replacing my sports for regular driving because I felt that they were too stiff. A conversation with Dick Guldstrand quickly changed my mind about that - he has a way of making me see the light about things.
The question is, what shocks are shipped with monoleaf/fibreglas/plastic/composite - whatever you want to call them, spring kits nowdays. Yes we agree that one needs an appropriate shock due to the nature of the mono spring. My caution was to the original poster was that the vendours, at least in the past, left customers to sort it out on their own, and when pressed it seemed that their answer was "Oh yes, you'll need to buy our special valved shocks". After receiving regular valved shocks in their kits.
In my trailing arms other than stock rubber I would only consider a spherical bearings - some companies are installing a product called johnny joints, to account for the 3 dimensional movement required by the trailing arms which the urethane aren't really designed for. The same situation appears for cars with coil spring/trailing arm suspensions. Energy susp etc offers a urethane in those positions as well but due to the nature of this suspension system urethane bushings there are not appropriate. The Urethane are more appropriate for control arms etc which only rotate on the axis - tho I wouldn't use them, see below.
Have a look at this site:
Savitske Classic & Custom
Mark there is energetic and happy to help. He's not so much into Corvette but you can see his products do not not have urethane at the business end of the trailing arms "To prevent Binding" of "non linear movement". I have his control arms [solid bushings] and other components on my car - nice stuff.
I also prefer "Hi Durometer" bushings to urethane - Del a lum and Delrin are brand names for that material I think, And spherical bearings where possible. A caution there too. Spherical rod ends are very positive but transfer bumps and vibration and wear out quickly from road grime in street applications so use these seals for sure - they really work: rod end seals from Speedway Motors, America's Oldest Speed Shop
Or just rebuild your suspension to stock specs - they're really not that bad.
 

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